GEOLOGY AND STRUCTURE OF THE PINE RIVER, FLORIDA RIVER, … · 2005-02-07 · Fruitland Formation coal beds in the Pine River, Florida River, Carbon Junction, and Basin Creek gas-seep

U.S. DEPARTMENT OF THE INTERIORU.S. GEOLOGICAL SURVEY

Open-File Report 97-59

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorialstandards (or with the North America Stratigraphic Code). Any use of trade, product, or firm names is fordescriptive purposes only and does not imply endorsement by the U.S. Government.

1997

GEOLOGY AND STRUCTURE

OF THE

PINE RIVER, FLORIDA RIVER, CARBON JUNCTION,

AND

BASIN CREEK GAS SEEPS,

LA PLATA COUNTY, COLORADO

by

James E. Fassett, Steven M. Condon, A. Curtis Huffman, and David J. Taylor

U.S. Geological SurveyP.O. Box 25046, MS 939, Denver Federal Center

Denver, Colorado 80225

CONTENTSSubsurface correlation of Late Cretaceous Fruitland Formation coal beds in thePine River, Florida River, Carbon Junction, and Basin Creek gas-seep areas,LaPlata County, ColoradoBy James E. Fassett ......................................................................................................... 1

INTRODUCTION .........................................................................................................1PINE RIVER AREA .....................................................................................................2

Coal-bed correlation ..............................................................................................2Gas flow through coal beds...................................................................................6

FLORIDA RIVER, CARBON JUNCTION, BASIN CREEK AREAS ............................9Cross Section A-A’ ................................................................................................9Florida River Area ...............................................................................................11Carbon Junction Area .........................................................................................11Basin Creek Area ................................................................................................13

REFERENCES CITED ..............................................................................................13APPENDIX 1-1—GEOPHYSICAL-LOG DATA ..........................................................15

Seismic Structure Studies of the Pine River Gas Seep Area, La Plata County,ColoradoBy A. Curtis Huffman and David J. Taylor .....................................................................115

INTRODUCTION .....................................................................................................115SEISMIC AND BOREHOLE DATA ......................................................................... 115SYNTHETIC SEISMOGRAMS ...............................................................................117SEISMIC DATA—PROCESSING ............................................................................117SEISMIC DATA—INTERPRETATION .....................................................................119CONCLUSIONS ......................................................................................................122ACKNOWLEDGMENTS......................................................................................... 125REFERENCES CITED ............................................................................................125

Geologic mapping and fracture studies of the Upper CretaceousPictured Cliffs Sandstone and Fruitland Formationin selected parts of La Plata County, ColoradoBy Steven M. Condon ..................................................................................................... 23

INTRODUCTION .......................................................................................................23PART 1—GEOLOGIC FRAMEWORK ......................................................................25

Basin Creek .........................................................................................................25Carbon Junction ..................................................................................................29Florida River ........................................................................................................32South Fork of Texas Creek to the Pine River ......................................................37Synthesis .............................................................................................................43

PART 2—FRACTURE STUDIES ..............................................................................45Basin Creek .........................................................................................................48Carbon Junction ..................................................................................................50Florida River ........................................................................................................52South Fork of Texas Creek ..................................................................................54Pine River ............................................................................................................56Discussion of fractures ........................................................................................58Summary .............................................................................................................61

REFERENCES CITED ..............................................................................................62APPENDIX 2-1—DESCRIPTION OF MAP UNITS ...................................................66APPENDIX 2-2—ROSE DIAGRAMS AT FRACTURE STATIONS............................68

PLATES (IN POCKET)1. Geologic map of the Basin Creek area2. Geologic map of the Carbon Junction area3. Geologic map of the Florida River area4. Joint and cleat stations in the Florida River area5. Geologic map of the South Fork of Texas Creek to the Pine River area6. Joint and cleat stations in the South Fork of Texas Creek to the Pine River area7. Measured sections of the Fruitland Formation

CONTENTS—CONTINUED

INTRODUCTION

This study was commissioned by a consortium consisting of the Bureau of Land Management,Durango Office; the Colorado Oil and Gas Conservation Commission; La Plata County; and all of themajor gas-producing companies operating in La Plata County, Colorado. The gas-seep study projectconsisted of four parts; 1) detailed surface mapping of Fruitland Formation coal outcrops in the abovelisted seep areas, 2) detailed measurement of joint and fracture patterns in the seep areas, 3) detailedcoal-bed correlation of Fruitland coals in the subsurface adjacent to the seep areas, and 4) studies ofdeep-seated seismic patterns in those seep areas where seismic data was available. This report is dividedinto three chapters labeled 1, 2, and 3. Chapter 1 contains the results of the subsurface coal-bed correla-tion study, chapter 2 contains the results of the surface geologic mapping and joint measurement study,and chapter 3, contains the results of the deep-seismic study.

A preliminary draft of this report was submitted to the La Plata County Group in September 1996.All of the members of the La Plata Group were given an opportunity to critically review the draft reportand their comments were the basis for revising the first draft to create this final version of a geologicreport on the major La Plata County gas seeps located north of the Southern Ute Indian Reservation.

1 U.S. Geological Survey Open File Report 97-59

Subsurface correlation of Late CretaceousFruitland Formation coal beds in the Pine River,Florida River, Carbon Junction, and Basin Creekgas-seep areas, La Plata County, Colorado

By James E. Fassett

0 25 50 Km.

0 10 20 30 Mi.

Durango

Farmington

Cuba

37

36

COLORADO

NEW MEXICO

UT

AH

AR

IZO

NA

Pagosa SpringsChimney

Rock

Kkf

Kkf

Kkf

Pine River gas seep

Florida River gas seep

Carbon Junction gas seep

Basin Creek gas seep

108 107109INTRODUCTION

The Pine River, Florida River, Carbon Junc-tion, and Basin Creek areas are located in thenorthern part of the San Juan Basin in La PlataCounty, Colorado (figure 1-1). These areas arethe sites of the major known natural-gas seepsalong the Cretaceous Fruitland Formation outcropin La Plata County (not including the SouthernUte Indian Reservation). Each of the gas seepareas is located in a place where the steeplydipping Hogback Monocline has been breachedby a stream cut, therefore, the seeps are in areasthat are topographically, relatively low.

The Fruitland Formation is the major coal-bearing rock unit in the San Juan Basin of NewMexico and Colorado. The Fruitland contains inexcess of 200 billion tons of coal throughout thebasin (Fassett and Hinds, 1971) and crops outaround most of the margin of the basin. Fruitlandcoal is strip mined in three large mines in north-western New Mexico. Fruitland coal has beenmined , mostly underground, in many smallworkings around the north and northwest rim ofthe basin; nearly all of those mines are nowabandoned. A relatively small Fruitland strip-mining operation in the northeast part of the basin,the Chimney Rock mine, is also now abandoned.

The geology and distribution of Fruitland coalin the San Juan Basin is described in detail in aU.S. Geological Survey Professional Paper(Fassett and Hinds, 1971). That study shows thatFruitland coals are present throughout the subsur-face of the basin to a maximum depth of slightlymore than 4,000 feet and that the deposition of thecoals was closely related to the regression of theWestern Interior Seaway as it retreated from the

San Juan Basin area in Late Cretaceous time. Thestudy also showed that Fruitland coals formed in atime-transgressive manner; radiometric age dates(Fassett and Steiner, in press) indicate thatFruitland coals in the southwest part of the basinare 3 million years older than coals in the north-east part of the basin. Fruitland coals occur in acomplicated, stratigraphically rising, en-echelongeometry across the basin, however it is possibleto correlate Fruitland coals using guidelines in theFassett and Hinds (1971) report.

During the past ten years, the northern SanJuan Basin has experienced a gas-drilling boomtargeting coal-bed methane in the FruitlandFormation. As a result, thousands of Fruitland

Figure 1-1. Index map showing the locationsof the Pine River, Florida River, CarbonJunction, and Basin Creek gas seeps. Kkf isthe outcrop of the Fruitland Formation andKirtland Shale, undivided (from Fassett andHinds, 1971).

2U.S. Geological Survey Open File Report 97-59

coal-bed wells now produce large volumes ofnatural gas in this part of the basin. Many wellsare located within a mile or two of the margin ofthe basin where the Fruitland coals crop out. Thegeophysical logs from these gas wells providemost of the basic data for subsurface correlationof Fruitland coal beds in the La Plata County gasseep areas.

PINE RIVER AREA

Coal-bed correlation

The Pine River gas seep area is located wherethe Los Pinos river (Pine River) has cut throughthe Hogback Monocline at the northern margin ofthe San Juan Basin (figure 1-2). The steeplydipping Hogback Monocline, is formed by themassive, cliff-forming, Pictured Cliffs Sandstone(see chapters 2 and 3 for details of the geologicstructure in this area). All of the Fruitland Forma-tion coal-gas wells in the vicinity of the PineRiver seeps are shown on figure 1-2. Monitorholes were drilled near the gas seeps in an effort todetermine the source of the escaping gas (figures1-2 and 1-4 through 1-6). Geophysical logs fromfive of these holes were used to correlate Fruitlandcoal beds in the Pine River seep area; three ofthese holes were cored. Examination of core fromthese holes by the author provided detailed corrobo-ration of the lithologies penetrated in these holes asinterpreted from geophysical logs. Two sets ofstructural and stratigraphic cross sections wereconstructed to illustrate the correlation of Fruitlandcoals in the subsurface adjacent to the gas seeps(figures 1-3 and 1-4). The location of the crosssections (A-A’ and B-B’) are shown on figure 1-2.

Figure 1-3a, a stratigraphic cross sectionalong line A-A’ shows the detailed correlation ofFruitland coal beds and major sandstone beds inthis area. The line of section is about 4.5 mileslong and roughly parallels the outcrop of the rocksshown. This cross section ranges from less than amile to about 1.5 miles downdip (south) from theoutcrop of the Pictured Cliffs in the Pine Riverarea (figure 1-2). The depth from the surface to thebase of the Fruitland ranges from 1,260 to nearly1,700 feet along the line of section. The datum forthis section is the top of the lower part of the PicturedCliffs. Coal beds and non-coal partings within coalbeds more than one foot thick are shown on this

figure, and on all subsequent cross sections. Inorder to illustrate these relatively thin beds, it wasnecessary to construct coal-correlation crosssections with a large element of vertical exaggera-tion. The geophysical log depths of all of thelithologic units shown on this and the othercorrelation diagrams in this report are listed inappendix 1-1. Geophysical log depths are shownin 100-foot increments for each drill hole shownon these cross sections as are the total depths ofeach drill hole. Surface elevations for each drillhole are listed in appendix 1-1.

Three large channel sandstones are present onsection A-A’. Sandstone no. 2 is the most continu-ous and was mapped at this same stratigraphiclevel at the surface (see geologic map in chapter2). Sandstone no. 3 was also mapped at thesurface. An unnamed sandstone bed is present atthe east end of the cross section; this bed appar-ently does not crop out at the surface west of thePine River. This cross section shows that the largechannel sandstones constrained the geometry ofsome of the coal beds shown on this cross sectionby differential compaction of the rocks in thisinterval. The sandstones clearly compacted lessthan the coals and other finer-grained lithologiesas burial and lithification of these rocks pro-gressed. For example, coals C and D (formed asan essentially horizontal deposit as peat built up inLate Cretaceous coal swamps), owes its present,somewhat twisted form, to differential compactionof it and associated underlying and overlyingsedimentary rock layers.

A significant stratigraphic rise in the top ofthe Pictured Cliffs Sandstone is seen on the eastend of the cross section in the Wommer and theMagoon wells (figure 1-3a). Coal bed A splits andthins at the base of the large Pictured CliffsSandstone tongue and coal beds of zone B termi-nate opposite this large sandstone bed. Coals Cand D were mapped separately at the surface, westof the Pine River seeps (see chapter 2), but asshown in this cross section, these coals mergeeastward in the subsurface. Coal bed E, shown atthe west end of the cross section (also mapped atthe surface) is discontinuous in the subsurface, butanother coal bed is present at about the same levelon the eastern end of the section. Two thin coalsare present in the uppermost Fruitland in theMagoon well on the east end of the cross section.


Figure 1-3b is a structural cross section alongline A-A’. This section was contructed usingmean sea level as the datum and has no verticalexaggeration. This cross section shows that theFruitland Formation is relatively flat in thesubsurface along line A-A’ .

Stratigraphic cross section B-B’ (figure 1-4a),is oriented at right angles to the Fruitland outcrop

in the Pine River area (figure 1-2). The Fruitlandis about 2,000 feet below the surface at thesouthwest end of this section. This cross sectionis approximately 3 miles long and shows thecorrelation of Fruitland coal beds from deep in thesubsurface to near the surface in the vicinity of thePine River gas seeps (figure 1-2). Vertical exaggera-tion on this cross section is 34:1. The four deepest

Colorado AX GURR Fed

GU 1

Pole Barn (Morgan Mtr.)

Salmon No. 1

Lewis GU 1

Reinsch GU 1

Hunt. GU A-1

Goeg. GU 1

Conrad GU A-1

Wommer GU A-1 Magoon

Fed 1

Dulin C-1

Parry Land Co. B-1

Dulin B-1

Dulin A-1

Bowers GU 1

Dulin D-1

Conrad Ranch B

Streeter GU B-1

Montg. Fed 1

Streeter GU-1

B

A'

A

7

18

12

13

11

14

109

16

21 22 2423

25

19

30

31

2627

36353433

28

R. 6

W.

R. 7

W.

T. 35 N.

Pictured Cliffs Sandstone

Gas Seep Areas

Lewis

Miller Fed 1

Humiston GU 1

Sower Fed GU 1

Wolter GU 1

Dulin GUR-1

Isaac Trust

Colorado AW 1

Colorado AW 2

Payne C-2

Payne C-1

Payne D-1

Fruitland Formation

and o lde r rocks

Shale

15

R i ve r Va l l ey A l l u v i um

Los P i nos R i ve r

Detailed map area (fig.5) B'Killian Deep

Figure 1-2. Index map of the Pine River gas seep area. Gas seeps are in the river-valley alluviumoverlying the Fruitland Formation subcrop in section 14. Producing Fruitland Formation coal-bedmethane wells and lines of geologic cross sections A-A’ and B-B’ are also shown. Figure 1-5 is alarge-scale map of the gas seep area. Geology west of Los Pinos river is from plate 5, chapter 2of this report. Geology east of the river is from Barnes (1953).


holes were drilled as Fruitland coal-bed methanewells and the three near-surface holes, Pole Barn,Salmon No. 1, and Killian Deep, were drilled toprovide subsurface information regarding the PineRiver gas seeps. Cores from these three shallowholes were examined and described as part of thisstudy.

Coal A, the lowermost Fruitland coal bed,directly overlies the Pictured Cliffs across the

entire line of section B-B’ (figure 1-4a). At thesouthwest end of the section in the Streeter well,coal A is 25 feet thick but less than a mile to thenortheast, it splits into two thinner coal beds. Theupper coal bed pinches out between the Hunting-ton and the GURR wells. The lower part of bed Asplits in the Gurr well but maintains its thicknessto very near the outcrop in the Salmon No. 1 hole.This basal-Fruitland coal bed thins and becomes

WEST

Colorado AX

Huntington GU A-1

Conrad GU A-1

Wommer GU A-1

Magoon Fed 1

EAST

1.2 mi. 0.65 mi. 1.4 mi. 1.15 mi.A A'

0

50

100

150

200

FEET



Coal B

Coal E

Channel Ss No. 3

Channel Sandstone No. 2

T.D. 1484' T.D. 1798' T.D. 1720' T.D. 1942' T.D. 1917'

Coals C & D

Coal A

ChannelSs (undesignated)

1100'

1200'

1600'

1500'

1500'

1400'

1600'

1700'

1500'

1600'

DATUM

Coal E ?

Fruitland Formation

Figure 1-3a. Stratigraphic cross section A-A’ showing subsurface coal-bed correlations in thePine River gas seep area. Coal beds and non-coal partings more than one foot thick are shown.The line of this cross sections is on figure 1-2. Log depths were measured from the Kellybushing. Vertical exaggeration is 57:1. Tops and bottoms of lithologic units are listed in table 1-1of appendix 1-1.

1.2 mi. .65 mi. 1.4 mi. 1.15 mi.A A'

WEST

Colorado AX

Huntington GU A-1

Conrad GU A-1

Wommer GU A-1

Magoon Fed 1

EAST

Fruitland Formation

8,000

6,000

5,500

7,500

7,000

6,500

FEET ABOVE SEA LEVEL

Pictured Cliffs Sandstone tongue

Figure 1-3b. Structural cross section A-A’ showing the Fruitland Formation in the subsurfacedown-dip from the Pine River gas seep area. Line of section is on figure 1-2. There is no verticalexaggeration. Thickness of Pictured Cliffs Sandstone tongue and underlying Fruitland Formationtongue on east end of section is exaggerated about 2.5:1.


extremely high ash (density of 1.9 gm/cc) in theKillian Deep hole. Coal bed B generally thinsnortheastward but maintains its continuity acrossthe entire line of section. This coal bed, however,

also becomes very high ash in the Killian Deepdrill hole. Coal C and D maintains a thickness ofmore than 20 feet through the Streeter, ConradRanch, and the Huntington wells, but thins to 12 feet

250

200

150

100

50

0

300

FEET

DATUM Pictured Cliffs Sandstone

Streeter GU 1

Conrad Ranch GU B

Huntington GU A-1

GURR Fed GU 1

Pole Barn

Killian Deep

Salmon No. 1

0.14 mi. 0.21 mi.

0.42 mi.0.68 mi.0.85 mi.0.75 mi.

SOUTHWEST NORTHEAST

B'

T.D. 980'

T.D. 270'

T.D. 634'

Carbonaceous shale with brackish water molluscs


G.L.

?Qal

Channel

Ss

Channel

Ss No. 3


Coals C & D

Coal B

Coal A

100'

200'

400'

500

600'

T.D. 1318'T.D. 1798'T.D. 2050'

700'

800'

900'

1000'

1100'

1200'

1400'

1500'

1600'

1600'

1700'

1800'

1700'

1800'

1900'

Cored

Cored

T.D. 2176'

B

Distributary-Estuary Sandstone Complex

Channel Ss No. 2

900'

Coal E

Coal S1

Coal S2

Coal S3

Undesignated

Coals C&D

Coal B

Coal A

Fruitland Formation

Figure 1-4a. Stratigraphic cross section B-B’ showing subsurface coal-bed correlations in thePine River gas seep area. Vertical exaggeration is 34:1. Coal beds and non-coal partings morethan one foot thick are shown. The line of this cross section is on figure 1-2. High-ash coals(density of 1.9 gm/cc) are shown in gray, coals shown in black have a density of 1.75 gm/cc orless). Cores from the GURR Federal, Pole Barn, and Killian Deep drill holes were examined anddescribed to confirm lithologic interpretations based on geophysical logs. Depths to tops andbottoms of lithologic units are listed in table 1-2 of appendix 1-1. Log depths were measuredfrom Kelly bushing.

7,000

6,000

Streeter GU 1

Conrad Ranch GU B

Huntington GU A-1 GURR Fed

GU 1

Pole Barn

Killian Deep

FEET ABOVE SEA LEVEL

Pine

RiverSalmon No. 1

.14 mi. .21 mi.

.42 mi..68 mi..85 mi..75 mi.

5,500

6,500

7,500

5,000

Fruitland

Formation Qal

B B'

Figure 1-4b. Structural cross section B-B’ showing the Fruitland Formation in the subsurfaceadjacent to the Pine River gas seeps area, no vertical exaggeration. The line of section B-B’ isshown on figure 1-2. Thickness of Pine River alluvium (Qal) is exaggerated about 2.5:1.


in the GURR well. Northeastward, this bed isthinner and is very high ash in the Salmon hole,pinches out into a sandstone bed, and is absent in theKillian Deep hole. Coal E is a thin, continuous bedin the GURR, Pole Barn, and Killian holes andprobably crops out beneath the Pine River alluviumbetween the Salmon and the Killian holes. Thin,discontinuous coal beds are present above the C andD coal bed in the Streeter, Conrad Ranch, andHuntington wells but none of these coals are continu-ous into the Pine River gas seep area.

Several discontinuous coal beds in holesadjacent to the seep area (apparently present onlyin the subsurface) are labeled coal S1 through coalS3 on figure 1-4a. Coal bed S1 might be inter-preted as three separate pods of coal in the GURR,Pole Barn, and Killian holes, but it is here por-trayed as a continuous coal bed that was drapedover the undesignated fluvial sandstone bed in thePole Barn hole because of differential compaction.This coal bed is apparently not present in theKillian hole but it may have been eroded prior todeposition of the Pine River alluvium (Qal onfigure 1-4a). Coal S2 is 13 feet thick in theSalmon No. 1 hole and 11 feet thick in the Killianhole, but abuts against the thick fluvial sandstonebed in the Pole Barn hole. Coal S3 is relativelythick in the Pole Barn and Salmon No. 1 holes,but thins and splits at the Killian hole.

Figure 1-4b is a structural cross sectionoriented at right angles to the Fruitland outcropterminating at its northeast end near the Pine Rivergas seeps. This cross section has no verticalexaggeration. The Pine River gas seeps arecoming out of the alluvium (here labeled Qal)between the Killian and the Salmon No. 1 holes(Oldaker, 1996).

Figure 1-5, a larger scale map of the gas seeparea, shows the outcrop pattern of the PicturedCliffs Sandstone and the Fruitland Formation westof the Pine River (from plate 5, chapter 2 of thisreport) and the alluvium that fills the river’s floodplain. The northeast end of cross section B-B’ isshown plus the locations of the James No. 1 andSalmon No. 3 drill holes and the line of crosssection C-C’. Line of cross section C-B’ of figure1-6 is shown. The subcrop of the FruitlandFormation is shown bounded by dotted lines anda hachure pattern. The upper and lower contactsof the Fruitland subcrop in this area were pro-

jected from the four drill holes shown in thealluvium area. The gas seep area (drawn on thebasis of data in Oldaker, 1996) is shown as thedark area overlying the upper part of the Fruitlandsubcrop. Gas seeps have been reported east of thegas-seep area shown here, but those seeps havenot been evaluated and no attempt was made toproject the gas seep area beyond the documentedarea.

The trace of the larger scale cross section C-C’is shown through the Salmon No. 1, Salmon No. 3and the James No. 1 holes. This cross section(upper panel, figure 1-6) is about 0.21 miles long.Cross section C-B’ (lower panel, figure 1-6)) is anexpanded version of the northeast end of crosssection B-B’ and is also about 0.21 miles long.These cross sections show the geometry andcontinuity of the Fruitland coal beds in the seeparea itself. The Salmon No. 1 drill hole is com-mon to both cross sections. Down-hole videoswere made in the Salmon No. 3, James No. 1, andthe Killian Deep holes. These videos were viewedto determine the points at which gas bubbles wereentering the drill holes; gas-entry points (as notedby the author) are shown on figure 1-6 with heavyarrows and the capital letter G.

On cross section C-C’ (figure 1-6) coals S2and S3 pinch out short of the Pine River alluviumFruitland subcrop. Coal S4 is present only in theSalmon No. 3 hole, and coal S5 extends throughthe Salmon No. 3 and James No. 1 drill holes, andpresumably to the subcrop. Coal A is presentacross the line of section but becomes very highash in its upper part in the Salmon No. 3 drillhole. The extent of coal S1 updip (north) from theSalmon No. 3 hole is not known. It is interestingto note that coal S2 which is apparently continu-ous across section C-B’ has thinned to a featheredge only about 0.1 mile to the south in theSalmon No. 3 hole. It is also interesting to notethat coal B on cross section C-C’ is not continuousacross this line of section but is missing in theSalmon No. 3 drill hole. Cross section C-B’shows in more detail that coals A and B are veryhigh ash in the Killian Deep hole.

Gas flow through coal beds

The key question regarding the Pine River gasseeps and other gas seeps from Fruitland coal beds


in the northern San Juan Basin is whether or notthe production of water from nearby (down dip,generally southwest) producing coal-bed methanegas wells has liberated adsorbed coal-bed gas andallowed some of this gas to migrate to the surfaceto emerge as seeps. Figure 1-4a shows that the

thicker coals that produce Fruitland gas in thesubsurface, notably coal C and D, pinch outbefore reaching the subcrop in the seep area.Coals A and B do seem to be continuous from thesubsurface to the outcrop, however, both of thesecoals become extremely high ash in the Killian

Salmon No. 1

Sec. 14Sec. 15

GU-1

Pole Barn (Morgan Monitor)

C

C

Fruitland Formation

Pictured Cliffs

Sandstone

Alluvium

Los Pinos River

GURR Fed Line of cross section B-B' (see figures 2 and 4)

C'

CGas Seep Area

Lewis Shale

and older rocks

Kirtland Shale and

younger rocks

0 0.1 0.2 0.3 0.4 0.5 miles

25 o

James No. 1

Killian Deep

CSalmon No. 3

B'

Figure 1-5. Detailed index map of Pine River gas seep area. Geology west of Pine River fromplate 5, chapter 2 of this report. Subcrop of Fruitland Formation (hachured area bounded bydotted lines) projected from monitor wells in alluvium area. Gas seep area outline drawn fromdata in Oldaker (1996). Stratigraphic cross sections C-C’ and C-B’ are shown on figure 1-6(section C-B’ is the northeast end of section B-B’ of figures 1-2 and 1-4). Monitor wellscontaining the letter C were cored through the Fruitland Formation coal beds and the upper partof the Pictured Cliffs Sandstone.




Salmon No. 1

Salmon No. 3

James No. 1

G.L.

Qal

T.D. 300'

T.D. 400'T.D. 634'



?

??

600' Distributary-Estuary Sandstone Complex

100'

200'

300'

400'

500'

?

?

Coal A

Coal B ?

?

Coal B

0.1 Mi.

Coals C & D ?

0

50

100

150

200

250

300

350FEET

Cored

Down Hole Video

100'

Down Hole Video

C'

NORTHEAST

SOUTHWEST



Salmon No. 1

T.D. 634'


Carbonaceous shale with brackish water molluscs?600' Distributary-Estuary Sandstone Complex

400'

Coal A

0.21Mi.

Cored ?

?

Killian Deep

200'

Cored and down hole video

Coal B

Coal A

Coal B

Coal E

Coal E

Coal S1

Coal S2

Coal S3

Coal S4

Coal S5

Coals S6

0.11 Mi.

0

50

100

150

200

250

300

FEET

SOUTH

NORTH

Pictured Cliffs Sandstone DATUM

Pictured Cliffs Sandstone DATUM

Coal S1

Coal S2

Coal S3

C

C B'

T.D. 270'

Fruitland Formation

Fruitland Formation

GG

G

GG

G

G

Carbonaceous shale with brackish water molluscs PC Ss tongue?

G

G.L.

Qal

Coals C & D ?

500'

GGGG

100'


hole near where they may subcrop beneath the PineRiver alluvium. High-ash coals usually have poorlydeveloped cleat and thus are normally less perme-able than low-ash coals. Figure 1-5 shows that thePine River seeps overlie the upper Fruitland coalbeds (coals E, S1, S2, and S3 on figure 1-4a andfigure 1-6). Figure 1-4a shows that these uppercoal beds are discontinuous and do not extend farinto the subsurface and thus have not been majorproducers of water or gas from commercial gaswells.

Gas-bubble entry points detected on the down-hole videos are shown by heavy arrows and theletter G on cross section C-B’ of figure 1-6. Gasemanating from the Killian-hole is entering thehole from noncoal rocks (siltstone beds) abovecoal S2 and from coals S2 and S3 (cross sectionC-B’, figure 6. No gas whatsoever was enteringthis drill hole from the lower Fruitland coal bedsB or A. It has been argued that the greater waterpressure on these deeper coal beds may be pre-venting the desorption of gas from these coals.However, if these lowermost Fruitland coal bedswere serving as conduits for gas moving up fromthe subsurface, gas liberated by production ofcoal-bed methane at depth, this gas would bemoving through the fractures in these coal beds asfree gas (not adsorbed gas) and would be seen

bubbling into the Killian hole in the down-holevideos, which is not the case.

Down hole video data from wells on crosssection C-C’ confirms this interpretation. In theSalmon No. 3 hole, gas is entering the hole onlyfrom the higher less continuous coal beds E, S1,and S2 and no gas bubbles are entering the holefrom the lower coals S4, S5, S6, and coal A. Inthe James No. 1 hole, gas bubbles are entering thedrill hole from lower Fruitland coal beds A and B;this gas was probably desorbed from these coalsdue to the presence of the Killian hole which haslowered the pressure on these coal beds. If coalbed A were a conduit for gas from the subsurface,gas would be entering the Salmon No. 3 drill holefrom this coal bed and it clearly is not.

FLORIDA RIVER,CARBON JUNCTION,BASIN CREEK AREAS

Cross Section A-A’

Figure 1-7 is a map showing the location ofthe Florida River, Carbon Junction, and BasinCreek seep areas. The outcrop of the PicturedCliffs Sandstone is shown as are all of the gas-producing wells within two miles of the PicturedCliffs outcrop. Lines of cross section A-A’, B-B’,C-C’, and D-D’ are shown on figure 1-7. SectionA-A’ (figure 1-8) is nearly 7 miles long, trendsnortheast, and parallels the steeply-dippingPictured Cliffs outcrop on the Hogback Mono-cline. Depths from the surface to the base of theFruitland range from less than 2,000 to 2,350 feetalong this line of section. The datum for thissection is the top of the lower Pictured CliffsSandstone (at two levels on this cross section).Section A-A’ shows the occurrence and correlationof Fruitland coal beds and the stratigraphicchanges in the Pictured Cliffs Sandstone along theline of section. The most striking feature shown onsection A-A’ is the large stratigraphic rise in theposition of the top of the Pictured Cliffs Sandstone inthe Federal 4-1 well. The top of the Pictured Cliffs isnearly 100 feet higher in this well than it is at theUniversity 9-2 well less than a mile to the southwest.The large stratigraphic rise in the top of the PicturedCliffs Sandstone was mapped at the surface inCarbon Junction Canyon (chapter 2 of this report).

Figure 6. Geologic cross sections C-C’ and C-B’ (northeast end of B-B’ of figure 1-4a). Linesof sections are on figure 1-5. Verticalexaggeration is 26:1. Lithologic units morethan 1 ft thick are shown. Coals shown inblack have densities of less than 1.75 gm/cc,coals shown in gray have densities to 1.9 gm/cc.The Salmon No. 1 drill hole is common to bothsections. Tops and bottoms of lithologic unitsand levels of gas bubbles entering hole ondown-hole videos are listed in table 1-3 ofappendix 1-1. Log depths measured fromKelly bushing. Cores of the Salmon No. 1 andKillian Deep holes were examined to confirmgeophysical-log interpretation. Down-holevideos of the Salmon No. 3, Killian Deep, andthe James No. 1 holes were viewed to confirmgeophysical log interpretations in those holes.These videos also showed gas bubblesentering the drill holes as shown by the arrowsand letter G.<


The lack of continuity of the coal beds shownon section A-A’ is striking. None of the more thanfifty coal beds shown on this cross section arecontinuous across the entire line of section. Themost continuous coal bed on this section is therelatively thin bed lying directly on top of thePictured Cliffs on the northeast part; this bedextends across most of the line of section but isabsent in the Indian Creek and West AnimasWheeler wells at the southwest end. The thickbasal Fruitland coal bed present at the southwestend of the section terminates northeastwardagainst the Pictured Cliffs between the West

Animas University and the Federal 4-1 wells. Thevery thick build up of coal in the West AnimasUniversity well (a total of 102 feet of coal) is seento be localized in the vicinity of this well and theWest Animas Wheeler well. A very thick coal ispresent in the Federal 4-1, and Federal 34.5 34-1wells just above the Pictured Cliffs Sandstone, butthis bed thins and pinches out northeastward andis gone at the Truman-Baird well. A slightlyhigher thick coal is present in the Truman-Bairdwell, but that bed is not present in the Day-V-Ranch well to the southwest. The only otherrelatively thick coal is at a depth of about 2,000

T. 35 N. T. 34 N.

T. 34.5 N.

T. 34 N.

23 24 19 20

30 29

T. 34 N. T. 34 N.

R. 9

W.

R. 9

W.

R. 1

0 W

. D U R A N G O

T. 35 N.

R.1

0 W

.R

.9 W

.

R.9

W.

R.8

W.

19 20 21 2213

24

25

3631 32 33 34 35 36

31 32

18 17 16 15

252627282930

31 32 33 3435 36

56

7 8

1718

123456

7 8 9 1011 12

1

12

1U2U3U4U5U6U1U2U

11U 12U

1314

7U 8U 9U 10U 11U 12U 7U

131415161718

Indian Creek SU 12U-2

SOUTHERN UTE INDIAN RESERVATION - NORTH BOUNDARY LINE

A

D'D

C

B'

C'

B

A'

Basin Creek gas seep area

Carbon Junction gas seep area

Florida River gas seep area

Indian Creek Wheeler 12U-1

Isgar GU 1

Wheeler 7U-2

Wheeler 7U-1

Koshak GU B-1

Jones GU A-1

West Animas- Wheeler 8-1

West Animas University 9-2

West Amimas University 9-1

South Florida Creek Burnett 2-1

South Florida Creek Crader 2-2

South Florida Creek Crader 3-2

Southeast Durango Fed. 3-1

Southeast Durango Fed. 4-1

Southeast Durango Fed. 34.5 34-1

Southeast Durango Fed. Day-V-Ranch 34.5 35-1

Southeast Durango Royce State 36-1

Huber Federal 2-29

Huber-Culhane 1-29

Huber Federal 1-30

Huber- Dobbins 1-31

Huber- Nelson 2-31

Southeast Durango 34-1

Day-V-Ranch 35-1

Day-V-Ranch 35-2

Truman-Baird 1-25

State 1-36

State 36-3

A n i m

a sR

i v e r

F l o r i d a

R i v e r

Pictured Cliffs Ss.

R. 8

W.

R. 8

W.

R. 9

W.

Figure 1-7. Index map of the Florida River, Carbon Junction, and Basin Creek gas seep areas.Gas wells within two miles of the outcropping Pictured Cliffs Sandstone are shown. Lines ofcross sections A-A’, B-B’, C-C’, and D-D’ show the traces of coal correlation diagrams on figures1-8, 1-9, 1-10, and 1-11, respectively.


feet in the Day-V-Ranch well; this bed thins in theTruman-Baird well and is not present to thesouthwest. A large number of thinner and morediscontinuous coal beds are present throughout theupper part of the Fruitland Formation along thisline of section.

Florida River Area

Stratigraphic cross section B-B’ (figure 1-9)shows the correlation of Fruitland coals at rightangles to the outcrop in the vicinity of the FloridaRiver seep area, the top of the Pictured CliffsSandstone is the datum for this section. (Thiscross section, as well as sections C-C’ and D-D’,was constructed at the same vertical scale as crosssection A-A’ to allow for easy comparison of these

intersecting cross sections.) This line of sectionshows relatively good correlation of Fruitlandcoals; the basal Fruitland coal bed, the twomiddle coals, and an upper thin coal bed can becorrelated across the entire line of section.Coals in the area are relatively thin, with theexception of the thick coal bed in the Truman-Baird well and the thick coal in the Huber-Dobbins well. Surface mapping of Fruitlandcoals in the vicinity of the Florida River sug-gests that the coals present in the Truman-Bairdwell probably extend to the outcrop. However,because the nearest subsurface control point(Truman-Baird well) is a mile away from theFlorida gas seep area, continuity of subsurfacecoals to the outcrop in this area can only beconsidered speculative, at best.

A 1.04 mi.

0.5 mi.

0.88 mi. 1.52 mi.

0.48 mi.

1.07 mi. 1.3 mi. A'

SE Durango Fed. 34.5 34-1


W. Animas Wheeler 8-1

W. Animas University 9-2

SE Durango Fed. 4-1

SE Durango 34-1

Day-V-Ranch 35-1

Truman-Baird 1-25

NORTHEASTSOUTHWEST

250

200

150

100

50

0

300

450

400

350

500

FEET

T.D. 7309'

T.D. 2189'

T.D. 2400'T.D. 2347'

T.D. 2399'

T.D. 2311'

1800'

1700'

1600'

1900'

2000'

2100'

2000'

1900'

1800'

2200'

2300'

2100'

2000'

1900'

1800'

1900'

2000'

2100'

2200'

T.D. 2263'

T.D. 2305'

1800'

1900'

1700'

2000'

2200'

2000'

1900'

1800'

2100'

2200'2300'

2200'

2100'

2000'

1900'

2100'

2000'

1900'

1800'

1700'

2100'

2300'2100'

Fruitland Formation

Cliffs SandstonePictured

SandstoneCliffsPictured

DATUM

DATUM

Figure 1-8. Stratigraphic cross section A-A’ showing subsurface coal-bed correlations acrossthe Florida River, Carbon Junction, and Basin Creek gas seep areas. Vertical exaggeration is48:1. Coal beds and non-coal partings more than one foot thick are shown. Trace of crosssection on figure 1-7. Tops and bottoms of lithologic units are listed in table 1-4 of appendix 1-1.Log depths measured from Kelly bushing.


0

50

100

150

200

250

300

350

400

FEET

1.2 mi. 0.5 mi.


Truman-Baird 1-25

Huber-Nelson 2-31

Huber-Dobbins 1-31

SOUTHEASTNORTHWEST

B B'

1700'

1600'

1800'

1900'

2000'

1900'

1800'

1700'

1700'

1800'

1900'

2000'

T.D. 2405' T.D. 2281'T.D. 7309'

DATUM

Fruitland Formation

Figure 1-9. Stratigraphic cross section B-B’ showing subsurface coal-bed correlations near theFlorida River gas seep area. Vertical exaggeration is 17:1. Coal beds and non-coal partings morethan one foot thick are shown. Trace of cross section on figure 1-7. Tops and bottoms oflithologic units are listed in table 1-5 of appendix 1-1. Log depths are measured from Kellybushing.

1.28 mi.

SE Durango Fed. 4-1

Everett Jones GU A-1

SOUTHEASTNORTHWEST

c c'


Top of PC in SE Durango well

Top of PC in Everett Jones well

T.D. 2733'T.D. 2250'

2500'

2400'

2600'

2300'

2200'

250

200

150

100

50

0

300

450

400

350

FEET

2100'

1700'

1800'

1900'

2000'

Fruitland Formation

Tongue of Pictured Cliffs Sandstone

Figure 1-10. Stratigraphic cross section C-C’ showing subsurface coal-bed correlations in theCarbon Junction gas seep area. Vertical exaggeration is 13:1. Coal beds and non-coal partingsmore than one foot thick are shown. The trace of this cross section is shown on figure 1-7. Topsand bottoms of lithologic units are listed in table 1-5 of appendix 1-1. Log depths measured fromKelly bushing. Datum is top of uppermost tongue of Pictured Cliffs Sandstone.


Carbon Junction Area

Stratigraphic cross section C-C’ (figure 1-10) showsFruitland coal beds at right angles to the outcrop near theCarbon Junction gas seep area. This two-wellcross section shows fairly good continuity ofthe thick coal bed just above the top of thePictured Cliffs Sandstone across the line ofsection, however, this coal bed splits to thesoutheast. The thinner coal bed lying directly ontop of the Pictured Cliffs is also continuousacross the line of section. Two thin Fruitlandcoals extend across both wells in this line ofsection higher in the Fruitland. The Fruitlandcoal tongue within the Pictured Cliffs thins to 2-feet thick in the Everett Jones well. At themouth of Carbon Junction canyon, the thickcoal buildup seen at the University 9-2 well oncross section A-A’ (figure 1-8) was measuredand mapped (see chapter 2), but section C-C’shows that this thick coal zone is not presentdirectly down dip from the Carbon Junctionseep area. Because the Federal 4-1 well is onlyabout 0.5 miles from the Carbon Junction gasseep area, and because the thick coals at theoutcrop in the gas seep area appear to have the

same thickness and geometry in the Federal 4-1well, there is a high probability that the thickbasal Fruitland coal bed is continuous from thesubsurface to the outcrop in this area.

Basin Creek AreaStratigraphic cross section D-D’ (figure 1-11)

shows the correlation of Fruitland coals in a lineof section oriented at right angles to the out-crop. There is excellent correlation of all of thecoal zones and most of the coal beds across thisline of cross section. Surface mapping at theoutcrop near the Basin Creek seep showsthinner and fewer coals than are present in thesubsurface, although some of the coal bedsshown in the subsurface appear to be present atthe outcrop.

REFERENCES CITEDBarnes, Harley, 1953, Geology of the Ignacio area,

Ignacio and Pagosa Springs quadrangles, La Plataand Archuleta Counties, Colorado: U.S. GeologicalSurvey Oil and Gas Investigations Map OM-138.

Fassett, J.E., and Hinds, J.S., 1971, Geology andfuel resources of the Fruitland Formation and

0.52 mi.


1.0 mi.

250

200

150

100

50

0

300

400

350

FEET

Indian Creek Wheeler 12U-1

Isgar 12U-1

SOUTHEAST

NORTHWEST

D D'

1900'

2000'

2100'

2200'

1800'

T.D. 2600'T.D. 2675'T.D. 2310'

2300'

2400'

2200'

2100'

2000'

2400'

2300'

2200'

2100'

2000'

Fruitland Formation

Pictured Cliffs SandstoneDATUM

Figure 1-11. Stratigraphic cross section D-D’ showing subsurface coal-bed correlations in theBasin Creek gas seep area. Vertical exaggeration is 14:1. Coal beds and non-coal partings morethan one foot thick are shown. Line of cross section is on figure 1-7. Tops and bottoms oflithologic units are listed in table 1-6 of appendix 1-1. Log depths measured from Kelly bushing.


Kirtland Shale of the San Juan Basin, NewMexico and Colorado: U.S. GeologicalSurvey Professional Paper 676, 76 p.

Fassett, J.E., and Steiner, M.B., in press, Preciseage of C33n-C32r magnetic-polarity reversal,San Juan Basin, New Mexico and Colorado:New Mexico Geological Society 1997 FieldTrip Guidebook.

Oldaker, P., 1996, Pilot mitigation program PineRiver Ranches, presentation to Colorado Oiland Gas Commission, 3 September, 1996;unpublished report, 20p.


APPENDIX 1-1Tables 1-1 through 1-6 listing geophysical log depths for lithologic contacts for all drill holes shownon geologic cross sections in this report.


Colorado Coal Ss Above Hunt. Coal Ss. Above Conrad Coal Ss Ab

AX Th. Th. PC Notes GU A-1 Th. Th. PC Notes GU A-1 Th. Th.

0 GL=7467 0 GL=7376 0

1053 204 KB=14 ft 1500 131 KB=12 ft 1437

1058 5 199 Coal 1507 7 124 Coal 1443 6

1101 156 1513 118 1445

1102 1 155 Coal 1536 23 95 Coal 1448 3

1103 154 1548 83 1454

1110 7 147 Coal 1553 5 78 Sandstone 1477 23

1117 140 1560 71 1483

1118 1 139 Coal 1595 35 36 1508 25

1131 126 1595 36 1510

1133 2 124 Coal 1600 5 31 Coal 1519 9

1149 108 1602 29 1521

1203 54 54 Sandstone 1608 6 23 Coal 1526 5

1207 50 1622 9 1544

1211 4 46 Coal 1631 9 0 Coal 1554 10

1212 45 1631 0 Top PC 1554

1219 7 38 Coal 1798 -167 T.D. 1720

1242 15 Total Coal 50 Total Coal 56

1252 10 5 Coal Magoon Coal Ss. Above

1257 0 Top PC Fed 1 Th. Th. PC Notes

1484 -227 T.D. 0 GL=7382

Total Coal 37 1508 179 KB=12 ft

Wommer Coal Ss Above 1510 2 177 Coal

GU A-1 Th. Th. PC Notes 1518 169

0 GL=7404 1519 1 168 Coal

1539 195 1529 158

1557 18 177 Sandstone 1556 27 131 Sandstone

1567 167 KB=12 ft 1561 126

1577 10 157 Coal 1569 8 118 Coal

1594 140 1571 116

1609 15 125 Sandstone 1573 2 114 Coal

1616 118 1609 78

1641 25 93 Coal 1627 18 60 Coal

1646 88 1628 59

1669 23 65 Sandstone 1637 9 50 Coal

1691 43 1641 46

1703 12 31 Sandstone 1642 1 45 Coal

1725 9 1648 39

1729 4 5 Coal 1680 32 7 Sandstone

1731 3 1681 1 6 Coal

1734 3 0 Coal 1685 2

1734 0 Top PC 1687 2 0 Coal

1942 -208 T.D. 1687 0 Top PC

Total Coal 42 1917 -230 T.D.

Total Coal 44

NOTES: All measurements shown are in feet. Log depths in first column for each drill hole are measured from Kelly bu

PC = Pictured Cliffs Sandstone, T.D. = total depth, GL = ground level.

Table 1-1. Geophysical log depths for coal beds in drill holes on Pine River cross section A-A’.


Tabl

e 1-

2. G

eoph

ysic

al lo

g de

pths

for

coal

bed

s in

drill

hol

es o

n P

ine

Riv

er c

ross

sec

tion

B-B

'

Killian

Co

al

Ss.

Ab

ove

Salm

on

Co

al

Ss.

Ab

ove

Po

leC

oal

Ss.

Ab

ove

GU

RR

Co

al

Ss.

A

Deep

Th

.T

h.

Kp

cN

otes

No

. 1

Th

.T

h.

PC

No

tes

Barn

Th

.T

h.

PC

No

tes

Fed

T

h.

Th

.P

0221

GL=7150

0624

GL=7155

0962

GL=7244

0

31

190

Top bedrk.

342

282

KB

=5 ft

679

283

KB

=4 ft

822

73

148

344

2280

Coal

682

3280

Coal

824

2

84

11

137

Coal

389

235

737

225

858

98

123

428

39

196

Sandsto

ne

753

16

209

Sandsto

ne

894

36

101

3120

Coal

437

9187

Coal

759

6203

Coal

901

7

102

119

471

153

776

186

906

103

1118

Hi-ash C

oal

484

13

140

Coal

779

3183

Sandsto

ne

918

12

121

100

496

128

794

168

968

162

41

59

Sandsto

ne

505

9119

Coal

843

49

119

Sandsto

ne

992

24

165

56

525

20

99

Sandsto

ne

850

7112

Coal

1004

12

166

155

Hi-ash C

oal

527

297

Hi-ash C

oal

873

89

1013

173

48

529

95

881

881

Coal

1024

11

176

345

Sandsto

ne

535

689

Hi-ash C

oal

883

79

1025

177

144

Hi-ash C

oal

574

39

50

Sandsto

ne

885

277

Hi-ash C

oal

1026

1

179

42

575

149

Hi-ash C

oal

903

18

59

Sandsto

ne

1033

187

834

Hi-ash C

oal

581

43

907

55

1035

2

197

24

CS

h, shells

584

340

Coal

910

352

Coal

1037

206

915

Tongue P

C598

26

CS

h, shells

911

51

1042

5

214

7C

Sh, shells

607

917

Tongue P

.C.

912

150

Hi-ash C

oal

1043

216

25

H-ash C

oal

614

10

CS

h, shells

914

48

1045

2

217

4624

10

0C

oal

917

345

Coal

1046

221

40

Hi-ash C

oal

624

0T

op P

.C

.918

44

1050

4

221

0T

op P

.C

.634

45

-10

T.D

.920

242

Coal

1073

226

5-5

Tongue P

.C.

Total C

.53

921

41

1079

6

228

-7

Tongue F

ruit.

Co

nrad

Co

al

Ab

ove

926

536

Coal

1080

270

-49

T.D

.R

an

ch

B

T

h.

Kp

cN

otes

933

29

1084

4

Total C

.31

01839

GL=7341

943

19

CS

h, shells

1084

Gas b

ub

bles en

terin

g h

ole

1704

135

KB

=12ft

951

811

Tongue P

C1318

on

vid

eo

in

K

illian

D

eep

h

ole

1706

2133

Coal

957

5C

Sh, shells

Total C

.56

Vid

eo

Log

Above P

C1719

120

958

4

63-65

61-63

158-160

1721

2118

Coal

962

40

Coal

76-87

73-84

137-148

1725

114

962

0T

op P

.C

.

101-106

98-103

118-123

1728

3111

Coal

980

-18

T.D

.

Hu

nt.

Co

al

Ss.

Ab

ove

1737

102

Total C

.44

GU

A

-1

Th

.T

h.

PC

No

tes

1758

21

81

Coal

Streeter

Co

al

Ss.

Ab

ove

01631

GL=7376

1759

80

Fed

. G

U 1

T

h.

Th

.P

CN

otes

1500

131

KB

=12 ft

1761

278

Coal

01968

GL=7330

1507

7124

Coal

1804

35

1794

174

KB

=13

1513

118

1813

926

Coal

1795

1173

Coal

1536

23

95

Coal

1814

25

1813

155

1548

83

1822

817

Coal

1814

1154

Coal

1553

578

Sandsto

ne

1827

12

1820

148

1560

71

1839

12

0C

oal

1823

3145

Coal

1595

35

36

Sandsto

ne

1839

0T

op P

C1866

102

1600

531

Coal

2050

-211

T.D

.1887

21

81

Coal

1602

29

Total C

.59

1928

40

1608

623

Coal

1934

634

Coal

1622

91943

25

1631

90

Coal

1968

25

0C

oal

1631

0T

op P

.C

.1968

0T

op P

C

1798

-167

T.D

.2150

-182

T.D

.

Total C

.50

Total C

.57

NO

TE

S:

A

ll m

easu

rem

ents

sho

wn

are

in f

eet.

Log

dep

ths

in f

irst

colu

mn

for

each

dril

l hol

e ar

e m

easu

red

from

Kel

ly b

ushi

ng (

KB

).

P

C =

Pic

ture

d C

liffs

San

dsto

ne,

T.D

. =

tot

al d

epth

, G

L =

gro

und

leve

l, C

Sh,

she

lls =

car

bona

ceou

s sh

ale

with

bra

ckis

h-w

ater

mol

lusc

s.

H

i-ash

Coa

l is

coal

with

a d

ensi

ty o

f 1.

9 gm

/cc

on d

ensi

ty lo

gs


Table 1-3. Geophysical log depths for coal beds in drill holes on Pine River cross section C-C'

Salmon Coal Ss. Above Salmon Coal Ss. Above James Coal Ss. Above

No. 1 Th. Th. Kpc Notes No. 3 Th. Th. Kpc Notes No. 1 Th. Th. Kpc

0 624 GL=7155 0 384 GL= 0 12

342 282 KB=5 ft 64 320 29 9

344 2 280 Coal 65 1 319 Hi-ash Coal 40 11 8

389 235 125 259 41 8

428 39 196 Sandstone 127 2 257 Coal 42 1 8

437 9 187 Coal 174 210 49 7

471 153 192 18 192 Sandstone 59 10 6

484 13 140 Coal 211 173 62 6

496 128 217 6 167 Coal 64 2 6

505 9 119 Coal 240 144 73 5

525 20 99 Sandstone 241 1 143 Hi-ash Coal 83 10 4

527 2 97 Hi-ash Coal 277 107 98 2

529 95 294 17 90 Sandstone 102 4 2

535 6 89 Hi-ash Coal 304 10 80 Coal 113 1

574 39 50 Sandstone 315 69 125 12

575 1 49 Hi-ash Coal 321 6 63 Coal 125

581 43 352 32 300 -17

584 3 40 Coal 353 1 31 Hi-ash Coal Total C. 25

598 26 CSh, shells 354 30 Gas bubbles entering hole

607 9 17 Tongue P.C. 356 2 28 Hi-ash Coal on down-hole video

614 10 CSh, shells 358 26 Video Log

624 10 0 Coal 359 1 25 Hi-ash Coal 79 77 4

624 0 Top P.C. 377 7 115 113 1

634 45 -10 T.D. 381 4 3 Hi-ash Coal 120 118

Total C. 53 381 3 172 170 -4

384 3 0 Coal

384 0 Top P.C.

400 -16 T.D.

Total C. 37

Gas bubbles entering hole

on down-hole video

Video Log

129 127 257

132 130 254

139-140 137-139 245

216 214 170

218 216 168

230 228 156

243 241 143

NOTES: All measurements shown are in feet. Log depths in first column for each drill hole are measured from Kelly bushing (KB). PC = Pictured Cliffs Sandstone, T.D. = total depth, GL = ground level, CSh, shells = carbonaceous shale with brackish-water molluscs. Hi-ash Coal is coal with a density of 1.9 gm/cc on density logs


Tabl

e 1-

4. G

eoph

ysic

al lo

g de

pths

for

coal

beds

in d

rill h

oles

in F

lorid

a R

iver

, Car

bon

Junc

tion,

and

Bas

in C

reek

are

as; c

ross

sect

ion

A-A

'

In

dian

C

rk.

Co

al

Ab

ove

W. A

nim

as

Co

al

Ab

ove

W. A

nim

as

Co

al

Ab

ove

SE

D

uran

go

Co

al

Ab

ove

SE

D

uran

go

Co

al

Ab

ove

SU

-12U

-2

Th

.P

.C

.N

otes

Wh

eeler 8-1

Th

.P

.C

.N

otes

Un

iv. 9-2

Th

.P

.C

.N

otes

Fed

. 4-1

Th

.P

.C

.N

otes

Fed

34.5

34-1

Th

.P

.C

.

02165

GL=6700

02259

GL=6821

02351

GL=6720

02127

GL=

02

1875

290

KB

=6

1892

367

KB

=15

1968

383

KB

=16

1712

415

KB

=14ft

1909

1877

2288

Coal

1893

1366

Coal

1969

1382

Coal

1713

1414

Coal

1910

1

1882

283

1905

354

1990

361

1714

413

1928

1887

5278

Coal

1907

2352

Coal

1992

2359

Coal

1715

1412

Coal

1929

1

1943

222

1908

351

1995

356

1814

313

1946

1950

7215

Coal

1910

2349

Coal

1996

1355

Coal

1815

1312

Coal

1948

2

1953

212

1911

348

2004

347

1819

308

2024

1955

2210

Coal

1912

1347

Coal

2006

2345

Coal

1824

5303

Coal

2029

5

2039

126

1921

338

2014

337

1961

166

2038

2045

6120

Coal

1923

2336

Coal

2015

1336

Coal

1967

6160

Coal

2042

4

2049

116

1929

330

2079

272

1968

159

2125

2053

4112

Coal

1930

1329

Coal

2080

1271

Coal

2004

36

123

Coal

2130

5

2130

35

1998

261

2130

221

2010

117

2132

2136

629

Coal

2000

2259

Coal

2132

2219

Coal

2015

5112

Coal

2166

34

2138

27

2017

242

2138

213

2016

111

2171

2147

918

Coal

2019

2240

Coal

2141

3210

Coal

2018

2109

Coal

2177

6

2149

16

2025

234

2143

208

2018

109

2177

2151

214

Coal

2026

1233

Coal

2146

3205

Coal

2108

19

2347

-1

2156

92028

231

2148

203

2127

19

0C

oal

Total C

oal

58

2165

90

Coal

2031

3228

Coal

2151

3200

Coal

2127

0T

op P

CT

ru

ma

n-

Co

al

Ab

ove

2165

0T

op P

C2033

226

2239

112

2263

-136

T.D

.B

aird

1-25

Th

.P

.C

.

2311

-146

TD

2036

3223

Coal

2242

3109

Coal

Total C

oal

76

01

Total C

oal

52

2039

220

2243

108

Day-V

-R

an

ch

Co

al

Ab

ove

1550

SE

D

uran

go

Co

al

Ab

ove

2043

4216

Coal

2248

5103

Coal

35-1

Th

.P

.C

.N

otes

1551

1

34-1

Th

.P

.C

.N

otes

2044

215

2249

102

02118

GL=7139

1656

02226

GL=7205

2046

2213

Coal

2254

597

Coal

1819

299

KB

=13ft

1658

2

1921

305

KB

=14ft

2072

187

2256

95

1820

1298

Coal

1688

1923

2303

Coal

2073

1186

Coal

2257

194

Coal

1845

273

1690

2

1946

280

2074

185

2267

84

1846

1272

Coal

1799

1947

1279

Coal

2078

4181

Coal

2276

975

Coal

1880

238

1800

1

2045

181

2116

143

2277

74

1881

1237

Coal

1804

2049

4177

Coal

2118

2141

Coal

2292

15

59

Coal

1897

221

1807

3

2067

159

2132

127

2293

58

1899

2219

Coal

1830

2070

3156

Coal

2134

2125

Coal

2305

12

46

Coal

1936

182

1837

7

2168

58

2156

103

2313

38

1937

1181

Coal

1870

2182

14

44

Coal

2162

697

Coal

2319

632

Coal

1969

149

1872

2

2195

31

2164

95

2321

30

1974

5144

Coal

1874

2212

17

14

Coal

2175

11

84

Coal

2341

20

10

Coal

1976

142

1901

27

2223

32178

81

2342

91979

3139

Coal

1938

2226

30

Coal

2182

477

Coal

2347

54

Coal

1983

135

1940

2

2226

0T

op P

C2213

46

2349

21986

3132

Coal

1940

2400

-174

T.D

.2215

244

Coal

2351

20

Coal

1991

127

7309

-53

Total C

oal

44

2225

34

2351

0T

op P

C2006

15

112

Coal

Total C

oal

47

2227

232

Coal

2399

-48

T.D

.2036

82

2228

31

Total C

oal

102

2038

280

Coal

2233

526

Coal

2104

14

2234

25

2105

113

Coal

2239

520

Coal

2115

3

2240

19

2118

30

Coal

2259

19

0C

oal

2118

0T

op P

C

2259

0T

op P

C2189

-71

T.D

.

2305

-46

T.D

.T

otal C

oal

38

Total C

oal

89

NO

TE

S:

A

ll m

easu

rem

ents

sho

wn

are

in f

eet.

Log

dep

ths

in f

irst

colu

mn

for

each

dril

l hol

e ar

e m

easu

red

from

Kel

ly B

ushi

ng (

KB

).

PC

= P

ictu

red

Clif

fs S

ands

tone

, T

.D.

= t

otal

dep

th,

GL

= g

roun

d le

vel


Table 1-5. Geophysical log depths for coal beds in drill holes on Florida River cross section B-B'and Carbon Junction cross section C-C'.

CROSS SECTION B-B' - - FLORIDA RIVER GAS SEEP AREA

Truman- Coal Above Huber- Coal Above Huber- Coal Above

Baird 1-25 Th. P.C. Notes Nelson 2-31 Th. P.C. Notes Dobbins 1-31 Th. P.C. Notes

0 1940 GL=7323 0 2003 GL=7077 0 2031 GL=7052

1550 390 KB=13ft 1831 172 KB=13.5ft 1897 134 Kb=13ft

1551 1 389 Coal 1832 1 171 Coal 1900 3 131 Coal

1656 284 1844 159 1921 110

1658 2 282 Coal 1846 2 157 Coal 1926 5 105 Coal

1688 252 1847 156 1928 103

1690 2 250 Coal 1848 1 155 Coal 1929 1 102 Coal

1799 141 1861 142 1938 93

1800 1 140 Coal 1865 4 138 Coal 1943 5 88 Coal

1804 136 1908 95 1947 84

1807 3 133 Coal 1909 1 94 Coal 1948 1 83 Coal

1830 110 1911 92 1978 53

1837 7 103 Coal 1913 2 90 Coal 1979 1 52 Coal

1870 70 1945 58 1981 50

1872 2 68 Coal 1958 13 45 Coal 1984 3 47 Coal

1874 66 1960 43 1996 35

1901 27 39 Coal 1961 1 42 Coal 2008 12 23 Coal

1938 2 1987 16 2010 21

1940 2 0 Coal 1994 7 9 Coal 2024 14 7 Coal

1940 0 Top Kpc 2003 0 Top PC 2031 0 Top PC

7309 -5369 T.D. 2102 -99 2134 -103

Total coal 47 2104 2 -101 Coal 2136 2 -105 Coal

2405 -402 T.D. 2140 -109

Total coal 34 2143 3 -112 Coal

CROSS SECTION C-C' - - CARBON JUNCTION GAS SEEP AREA 2281 -250 T.D.

SE Durango Coal Above Everett Jones Coal Above Total coal 50

Fed. 4-1 Th. P.C. Notes GU A-1 Th. P.C. Notes

0 2127 GL= 0 2492 GL=6876

1712 415 KB=14ft 2250 242 KB=13ft

1713 1 414 Coal 2254 4 238 Coal

1714 413 2268 224

1715 1 412 Coal 2271 3 221 Coal

1814 313 2324 168

1815 1 312 Coal 2329 5 163 Coal

1819 308 2334 158

1824 5 303 Coal 2336 2 156 Coal

1961 166 2429 63

1967 6 160 Coal 2435 6 57 Coal

1968 159 2437 55

2004 36 123 Coal 2445 8 47 Coal

2010 117 2447 45

2015 5 112 Coal 2480 33 12 Coal

2016 111 2485 7

2018 2 109 Coal 2492 7 0 Coal

2108 19 2492 Top PC

2127 19 0 Coal 2606 -114

2127 0 Top PC 2608 2 -116 Coal

2250 -123 T.D. 2733 -241 T.D.

Total coal 76 Total Coal 70

NOTES: All measurements shown are in feet. Log depths in first column for each drill hole are measured from the Kelly bushing (KB).



Table 1-6. Geophysical log depths for coal beds in drill holes on Basin Creek cross section D-D'.

Indian Crk. Coal Above Indian Crk. Coal Above Isgar Coal Above

SU-12U-2 Th. P.C. Notes SU-12U-1 Th. P.C. Notes GU 1 Th. P.C. Notes

0 2165 GL 0 2425 GL 0 2384 Gl

1736 429 KB=6ft 1874 551 KB=6ft 2031 353 KB=12ft

1738 2 427 Coal 1875 1 550 Coal 2032 1 352 Coal

1821 344 2007 418 2034 350

1822 1 343 Coal 2009 2 416 Coal 2035 1 349 Coal

1875 290 2097 328 2100 284

1878 3 287 Coal 2098 1 327 Coal 2102 2 282 Coal

1881 284 2158 267 2141 243

1888 7 277 Coal 2162 4 263 Coal 2144 3 240 Coal

1941 224 2168 257 2159 225

1951 10 214 Coal 2171 3 254 Coal 2161 2 223 Coal

1952 213 2179 246 2162 222

1956 4 209 Coal 2182 3 243 Coal 2171 9 213 Coal

2038 127 2184 241 2200 184

2046 8 119 Coal 2194 10 231 Coal 2203 3 181 Coal

2048 117 2211 214 2284 100

2053 5 112 Coal 2213 2 212 Coal 2288 4 96 Coal

2129 36 2313 112 2292 92

2136 7 29 Coal 2324 11 101 Coal 2297 5 87 Coal

2137 28 2326 99 2311 73

2148 11 17 Coal 2330 4 95 Coal 2316 5 68 Coal

2149 16 2332 93 2317 67

2151 2 14 Coal 2334 2 91 Coal 2321 4 63 Coal

2152 13 2348 77 2343 41

2165 13 0 Coal 2357 9 68 Coal 2345 2 39 Coal

2165 0 Top PC 2396 29 2363 21

2310 -145 T.D. 2398 2 27 Coal 2370 7 14 Coal

Total Coal 73 2401 24 2374 10

2404 3 21 Coal 2384 10 0 Coal

2406 19 2384 0 Top PC

2412 6 13 Coal 2600 -216 T.D.

2415 10 Total Coal 58

2425 10 0 Coal

2425 0 Top PC

2675 -250 T.D.

Total Coal 73

NOTES: All measurements shown are in feet. Log depths in first column for each drill hole are measured from the Kelly bushin



This page is blank.

U.S. Geological Survey Open-File Report 97-5923

INTRODUCTION

In early 1995 a proposal was submitted bythe U.S. Geological Survey to the Colorado Oiland Gas Commission to conduct a geologic studyaddressing the problem of coalbed methane gasseepage in La Plata County. Part of the originalproposal was to map the entire outcrop ofFruitland Formation in the county, exclusive ofland on the Southern Ute Indian Reservation, andto measure fractures in these same rocks. Thisproposal did not meet the budget requirements ofthe funding group, so a scaled-down proposalwas submitted, and accepted, to study onlyselected parts of the county. Beginning in July,1995, the USGS conducted studies at selectedplaces in La Plata County that had beenpreviously identified in a geochemical survey ashaving a potential for above-average amounts ofmethane and/or hydrogen sulfide gas seepagefrom coal beds in the Upper Cretaceous FruitlandFormation. These areas were at Basin Creek,southwest of Durango; Carbon Junction, at thesouth edge of Durango; Florida River, where thecoal outcrops cross the river; the South Fork ofTexas Creek, west of Columbus in northeasternLa Plata County; and an extension of that areasoutheast to the Pine River, north of Bayfield(fig. 2-1).

The objective of this study was to providedetailed geologic maps of the various sites toestablish the stratigraphic position of coal beds atthe outcrop in the Fruitland Formation. Thisstratigraphic information could then be tied tosubsurface stratigraphic studies on the samestratigraphic interval being conducted by J.E.Fassett (this report). Because methane is beingextracted from Fruitland coal beds a shortdistance south of the outcrop, and because coalbeds are known to be good conduits of gas andwater (Gayer and Harris, 1996; Law and Rice,1993; Schwochow, 1991), it is important toknow the extent of coal beds in the subsurfaceand at surface exposures. An additional part ofthis study was to measure orientations of joints insandstone and cleats in coal of the FruitlandFormation and Pictured Cliffs Sandstone atsurface exposures. These data can be used toshow the type of fracturing present and theregional trends of possible migration pathwaysfor methane and/or hydrogen sulfide from thesubsurface to surface outcrops.

Initial reconnaissance of the area was done inJuly, 1995 by S.M. Condon and E.A. Johnson;subsequent mapping and fracture studies wereconducted by Condon and R.C. Milici inSeptember and October, 1995; by Condon andJ.E. Fassett in April, 1996; and by Condon inMay, 1996. Techniques used were (1) to

Geologic mapping and fracture studies of theUpper Cretaceous Pictured Cliffs Sandstone andFruitland Formation in selected parts of La PlataCounty, Colorado

By Steven M. Condon

With Contributions From E.A. Johnson, R.C. Milici, And J.E.

Fassett

U.S. Geological Survey Open-File Report 97-59 24

measure sections of the Fruitland to gain anunderstanding of the rock types and thedistribution of rock types in the formation, (2) touse topographic maps and aerial photographs tocreate geologic maps; and (3) to measure theorientations and characteristics of fractures insandstone and coal in the Fruitland Formationand Pictured Cliffs Sandstone.

This report is divided into two parts. Part 1describes the geologic framework of the FruitlandFormation as determined from geologic mappingand from measuring stratigraphic sectionsthrough all or part of the Fruitland in variousplaces. Each of the five areas is first discussedseparately, and then a synthesis follows that tiestogether the information gathered in all of theareas. Plates 1, 2, 3, and 5 are geologic maps ofthe separate areas. Plate 7 shows correlations ofmeasured stratigraphic sections in each of theareas. Part 2 is a discussion of the fractures thatwere measured and described in each of the sub-areas. Plates 1, 2, 4, and 6 show the locations of

where fractures were measured, plotted on ageologic base map. Note that the maps on plates1 and 2 are at a scale of 1:6,000 and that theother maps are at a scale of 1:12,000. The smallsize of the mapped areas at Basin Creek (plate 1)and Carbon Junction (plate 2) allowed the use ofthe larger scale in those areas.

Thanks are extended to Jeff Olson, Bureau ofLand Management in Durango, for his help withthis project. Jeff had done preliminary geologicand geochemical studies and had contacted mostof the landowners in the study areas prior to theinvolvement of the USGS in this project. He alsoprovided valuable assistance in the field incollecting some of the data for this report. Themanuscript benefited from the comments ofLaura N.R. Roberts, Vito Nuccio, Tom AnnCasey, Debbie Baldwin, and Reed Scott.

Bayfield

Gem Village

Basin Creekarea

Carbon Junctionarea

Florida River area

Durango

Texas Creek-Pine River area

Anim

as R

iver

Florida RiverPi

ne R

iver

Columbus

240

550 172

225228

160

245

502

502 501

234FruitlandFormation

1 MILE

Figure 2-1. Map showing the location of the project area and individual sub-areas. Numbersindicate county and state roads and highways. (Modified from digital data provided by theBureau of Land Management, Durango, Colo.)


PART 1—GEOLOGIC

FRAMEWORK

Basin Creek

Mapping in the Basin Creek area was mainlyin the southwest and northeast quarters of section7 and a small part of the SE¼ of section 6, T. 34N., R. 9 W. (plate 1). This area is characterizedby fairly steep topography, with the FruitlandFormation outcrop ranging in elevation from lessthan 6700 ft along the creek to nearly 7500 ft inthe northern part of the study area. The UpperCretaceous Pictured Cliffs Sandstone andFruitland Formation strike northeasterly in thisarea and dip to the southeast, forming part of thenorthwest side of the San Juan Basin. Dipsrange from 20 degrees to 42 degrees (Table 2-1),but average about 28 degrees.

A major obstacle to geologic mapping in thepart of the area south of the creek is the presenceof dense stands of brush that completely obscuremuch of the hillsides. In that area only scatteredoutcrops are exposed, mainly along ridge lines.The area north of the creek is covered by apiñon-juniper forest, typical for this area, with

somewhat better exposures of the mapped rocks.A road is present along the north side of thecreek, and several road cuts allow forexamination of the Pictured Cliffs Sandstone,Fruitland Formation, and Kirtland Shale. Themeasured section in this area, shown on figure 2-

2 and plate 7, was measured along the road.Plate 1 shows the geology of this area. Theoldest geologic unit shown on the map is theUpper Cretaceous Lewis Shale, a gray marineshale unit. The contact of the Lewis with theoverlying Pictured Cliffs Sandstone is notexposed south of the creek, but is visible high onthe west and northwest-facing cliffs north of thecreek. This contact was interpreted from aerialphotographs, and was placed at the base of themassive sandstone beds of the Pictured Cliffs.The contact is gradational, with sandstone bedsin the upper Lewis becoming thicker up-section.The Pictured Cliffs is light brown to light gray,very fine grained, well-sorted sandstone. Someintervals in the Pictured Cliffs are firmlycemented with calcite; other intervals are non-calcareous. Black accessory minerals andreddish-orange oxidized iron minerals areabundant in this area. Also abundant areburrows of the trace fossil Ophiomorpha, whichcan be observed on the large exposed dip slopejust north of the road at station BC011. Thethickness of the Pictured Cliffs depends on wherethe contact is placed with the underlying LewisShale. Based on nearby drill holes, the thicknessin this area is estimated to be between 125 and200 ft.

1 The numbering system for fracture stations is as follows: Basin

Creek = BC__, Carbon Junction = CJ__, Florida River = FR__, PineRiver = PR__. In these areas the prefix is not shown on the maps inorder to make the maps easier to read. In the Texas Creek area aseries of flatirons was lettered A through J and stations are designatedTA__ through TJ__.

Table 2-1. Strike and dip measurements in the Basin Creek area.[Locations are shown on plate 1.]

Station No. Strike and dip Station No. Strike and dipBC01 N45ºE/29ºSE BC14 N48ºE/28ºSEBC03 N45ºE/32ºSE BC16 N45ºE/25ºSEBC04 N52ºE/24ºSE BC17 N45ºE/37ºSEBC05 N44ºE/24ºSE BC18 N60ºE/42ºSEBC07 N48ºE/26ºSE BC21 N45ºE/26ºSEBC08 N53ºE/20ºSE BC26 N62ºE/31ºSEBC09 N50ºE/20ºSE BC28 N45ºE/31ºSEBC13 N52ºE/24ºSE BC44 N53ºE/23ºSE


In the northern part of the area a tongue ofPictured Cliffs overlies the main body. From justnorth of the road to just west of station BC07 thetongue is separated from the main body by a thincoal bed. This coal bed pinches out to the north,but the tongue can still be differentiated on thebasis of weathering characteristics. It forms anupper, more massive-weathering ledge that canbe followed updip past the mapped area. Thetongue is light gray, very fine grained, well sortedsandstone that has abundant dark accessoryminerals that highlight crossbedding laminae insome places. No Ophiomorpha burrows werenoted in the Pictured Cliffs tongue, but it doesappear to be bioturbated in places. A rootedsandstone is at the top of the tongue, which isoverlain by a coal bed of the FruitlandFormation. The tongue appears to thin and pinchout southward at about the position of the roadthrough the area; it was not seen in the poorexposures south of the creek. In the northernpart of the area, at station BC08, the tongue isabout 50 ft thick, with the lower 35 ft being amixture of sandstone and shale and the upper 15ft a massive sandstone.

The Fruitland Formation is a heterogeneousunit consisting of interbedded sandstone,mudstone, carbonaceous shale, and coal beds(fig. 2-2). As mentioned above, in the centralpart of the mapped area a coal bed, which is atongue of Fruitland, separates the main body anda tongue of the Pictured Cliffs Sandstone. Thiscoal bed is only about 1 ft thick and is poorlyexposed over most of its extent, so it was notmapped separately. The Fruitland measuredalong the road is just less than 400 ft thick (fig.2-2, plate 7), which is slightly less than thethickness of the Fruitland in nearby wells. Thisdiscrepancy may be due to conservativelyestimating a thick covered interval in the upperpart of the formation along the road.

Sandstone beds of the Fruitland are very fineto fine grained, well sorted, and firmly cementedwith calcite. Accessory minerals are abundantand are of a greater variety compared to PicturedCliffs sandstones. Reddish-orange oxidized ironminerals are especially abundant in Fruitlandsandstone beds. Clay rip-up clasts are abundantin one sandstone bed near the base of theformation. Sandstone beds in the Fruitland cangenerally be grouped into two types: channelsandstones and crevasse splay sandstones. Thechannel sandstones typically fine upward, have alenticular geometry, and are crossbedded.Thicknesses of the channel sandstones in thisarea are as much as 25 ft. Crevasse splaysandstones are commonly thinner, on the order of1-3 ft thick, and maintain a more constantthickness along strike than the channelsandstones. They are commonly bioturbated anddon’t display crossbedding. These thinner, morebrittle sandstone beds fracture more readily andregularly than the channel sandstones though,and were used more than channels in measuringjoints for this study.

Mudrock is a generic term for the clay- andsilt-sized fraction of rocks in the FruitlandFormation. Two types of mudrock arerecognized: mudstone and carbonaceous shale.Mudstone ranges from light to medium gray togreenish-gray. It commonly has a hackly, orblocky fracture pattern, but is fissile in someexposures. Carbonaceous shale is dark gray toblack, moderately to highly carbonaceous, andcommonly has a fissile or platy fracture. Thetwo types of mudrock are normally interbeddedand gradational into one another. Ironstoneconcretions are common in Fruitland mudrock ofboth lithologies. These concretions are a rustyorange color, and are very dense and hard.


Coal in the Fruitland Formation in this areagenerally occurs in thin beds, except at the baseof the formation, where thick beds are present.The occurrence of coal determined the division of

the Fruitland into the units shown on the geologicmap (plate 1) and the measured section (fig. 2-2,plate 7). Although at any given outcrop in thisarea several coal beds can be distinguished, these

Explanation

Figure 2-2. Stratigraphic section at Basin Creek. See plate 7 for correlation to other sections.


beds cannot be traced very far laterally becauseof the poor exposures, especially south of thecreek. Instead of tracing individual beds, theFruitland was divided into lower, middle, andupper parts. The lower part consists of thickcoal beds, with or without mudstone or sandstonepartings. The middle part consists largely ofsandstone and mudstone beds, with relativelyminor amounts of carbonaceous shale and coal.The upper part consists of repeating cycles ofcarbonaceous shale, thin coal beds, andsandstone. South of the creek the lower andmiddle parts of the Fruitland could not beseparated, due to cover, and so are mappedtogether.

The thickest coal beds in the Fruitland lie atthe base of the formation, directly over thetongue of Pictured Cliffs, or over the main bodywhere the tongue is not present. At station BC0725 ft of coal was measured, overlain by anadditional 5-10 ft of ash from burned coal. Thisbasal coal thickens to the south of the creekwhere 38 ft was measured at station BC22. Anadditional 21 ft of coal above the basal coal wasmeasured at station BC24. A small adit was duginto the basal coal just west of station BC07,north of the creek, and a collapsed mine entranceis at station BC18 on the south side of the creek.Kaolinite beds are present in the lower coalinterval, but outcrops are so discontinuous thatthe clay beds couldn’t be traced from one area toanother.

One feature of the Basin Creek area that wasnot seen in any of the other studied areas is thepresence of thick intervals of ash from burnedcoal beds in the lower part of the Fruitland. Asmuch as 10 ft of ash is present above the coal atstation BC07, and ash is common in the narrowgully north of station BC31. An associatedfeature is the presence of abundant amounts ofreddish-orange, burned sandstone that has beenshattered into small pieces by heat. This burnedsandstone is known by the general term “clinker”,and a large area of it was mapped in the north-central part of the area. Although this is thelargest area of clinker, the whole area north of

the road has scattered occurrences of it. Thethick beds of coal at the base of the Fruitlandburned, but the thin beds higher in the section didnot.

The middle part of the Fruitland in this areais dominated by channel sandstone beds, but alsoincludes mudrock and coal. In general, themiddle part coarsens upward, with mudstone andcarbonaceous shale being more abundant low inthe middle part and sandstone being moreabundant high in the middle part. The top of themiddle part is marked by a thick sequence ofstacked fluvial channels that can be seen bothsouth and north of the creek. Coal is present inthin beds in the middle part of the Fruitland, butis not abundant.

The upper part of the Fruitland consists ofthin coal beds interbedded with mudstone,carbonaceous shale, and sandstone. In this areathere are three complete sequences of mudrock,coal, and sandstone and a partial fourthsequence. The sandstone beds are relatively thin,about 10 ft being a maximum thickness, but theycan be traced laterally throughout the area northof the road. The sandstone beds serve as markerbeds because they always overlie 1-3 ft thick coalbeds in this area. Similar sequences of mudrock,coal, and sandstone are also present south of thecreek, but the poor exposures make it impossibleto trace the units laterally.

The uppermost part of the Fruitland is well-exposed at station BC17. This unit consists ofinterbedded mudstone, carbonaceous shale, thinstreaks of coal, minor sandstone, and greensiltstone. Characteristic features are light-orangeseptarian nodules that formed in siltstoneintervals. A 1.5 inch pelecypod was found ingray mudstone in this upper unit. This unitappears to be transitional with the overlyingUpper Cretaceous Kirtland Shale; the maindifference being the presence of the carbonaceousbeds in the Fruitland and their absence in theKirtland. The lower part of the Kirtland also hasrelatively more sandstone than the upper part ofthe Fruitland, in this area and in the other areasstudied.


A small fault is well-exposed in the outcropdescribed above at station BC17. Viewed fromthe south side of the road, the trace of the fault isU-shaped, with a broad, nearly horizontal tracealong most of the outcrop. There is only about1-2 ft of offset on the fault and it is down to thenorthwest. Since this fault is only seen in avertical outcrop face, it couldn’t be shown on thegeologic map (plate 1). A second possible faultwas noted just north of station BC34. This faultappears to cut the top sandstone in the middlepart of the Fruitland. It trends N30ºW and dipssteeply to the northeast. It is down to thesouthwest and there may be as much as 10 ft ofoffset. A third area of possible faulting orslumping is near station BC15 in a roadcut.

Although somewhat covered, it appears that theremay have been faulting or slumping alongbedding planes in carbonaceous shale low in theupper part of the Fruitland.

Carbon Junction

Mapping in the Carbon Junction area was insections 4 and 5, T. 34 N., R. 9 W., east of theAnimas River (plate 2). Reconnaissance wasalso done on the west side of the river above theshooting range. Two sections were measured inthis area; one at the lower end of CarbonJunction Canyon, extending southward along thehighway roadcut, and the other on the northeast

side of the gravel pit on Ewing Mesa, outside themapped area (fig. 2-3). Both of these sectionsare shown on plate 7. The topography of CarbonJunction Canyon is steep, but the elevation isonly between about 6500 and 6700 ft. The ridgeline above the shooting range extends higher, upto about 6900 ft at the western end of the mappedarea. As in the Basin Creek area, the PicturedCliffs Sandstone and Fruitland Formation strikenortheasterly and dip to the southeast. Dipsrange from 24 to 35 degrees and average 31degrees (Table 2-2).

Table 2-2. Strike and dip measurements in the Carbon Junction area.[Locations are shown on plate 2.]

Station No. Strike and dip Station No. Strike and dipCJ01 N50ºE/33ºSE CJ11 N53ºE/35ºSECJ02 N46ºE/24ºSE CJ12 N53ºE/35ºSECJ04 N50ºE/33ºSE CJ13 N45ºE/32ºSECJ06 N57ºE/31ºSE CJ18 N48ºE/35ºSECJ07 N64ºE/29ºSE CJ20 N58ºE/27ºSECJ08 N64ºE/29ºSE CJ23 N47ºE/34ºSECJ09 N58ºE/34ºSE CJ24 N50ºE/30ºSECJ10 N64ºE/24ºSE


The vegetation in the Carbon Junction area issimilar to that at Basin Creek—piñon-juniperforest. The underbrush is not quite as dense atCarbon Junction as at Basin Creek, but the steepsoutheast canyon wall made it somewhat difficultto accurately locate outcrops on the aerialphotographs to make the geologic map. The best

exposures of the Fruitland are at two placesalong the creek, in eroded gullies that cut thesoutheast canyon wall, and also along the oldhighway road cuts south of the canyon.

Plate 2 shows the geology of the CarbonJunction area. The oldest unit shown is theLewis Shale, which underlies the Pictured CliffsSandstone. The contact of the Lewis with the

Explanation

Figure 2-3. Stratigraphic section at Ewing Mesa. See plate 7 for correlation to other sections.


Pictured Cliffs was interpreted from aerialphotographs in this area. The lithology of thePictured Cliffs is the same here as at BasinCreek—light brown to light gray, very finegrained, well sorted sandstone. A dark gray toblack sandstone is at the top of the PicturedCliffs in some exposures. This sandstone isrooted, similar to the one found at the top of thetongue of Pictured Cliffs at Basin Creek. ThePictured Cliffs forms a narrow ridge line held upby massive sandstone beds in the upper part ofthe formation.

A tongue of Pictured Cliffs is present inCarbon Junction Canyon, but it is only well-exposed at the northeastern end of the mappedarea (plate 2). At this outcrop the unit is about30 ft thick, is light yellowish-gray, fine grained,and well sorted. It displays minor amounts ofsmall-scale crossbedding, but mainly hashorizontal, wavy bedding. The upper part of thesandstone contains abundant carbonaceousmaterial. This bed thins abruptly southwestwardand is replaced by thick coal at the base of theFruitland Formation (plate 7).

Lithologies of the Fruitland Formation atCarbon Junction are the same as those in theBasin Creek area, which are sandstone, mudrock,and coal (fig. 2-3). The Fruitland was dividedinto the same lower, middle, and upper units thatwere mapped at Basin Creek. The section ofFruitland measured in and near Carbon JunctionCanyon is only about 280 ft thick; the upper partof the unit is covered by terrace gravels. Acomplete section was measured at the EwingMesa gravel pit. There, the Fruitland is about355 ft thick, not including a tongue of coal andmudstone 25 ft thick below the tongue ofPictured Cliffs Sandstone (fig 2-3, plate 7).

The lower part of the Fruitland is composedmainly of coal, with minor mudrock and siltstonepartings. There are two good exposures of thisunit at stations CJ01 and CJ25, and partialexposures at station CJ02. At station CJ25 atotal of 80 ft of coal was measured, consisting ofa lower bed 37 ft thick and an upper bed 43 ftthick, separated by 4 ft of mudrock and siltstone.At station CJ01 the lower contact of the coal isnot exposed; 20 ft of coal is exposed above thestream bed and is overlain by 3-4 ft of partings

that correlate with the same interval at stationCJ25. An upper bed of coal 45 ft thick overliesthe partings. At station CJ02 about 12 ft of coalis exposed above the stream and it is overlain bythe tongue of Pictured Cliffs Sandstone. Akaolinite bed, 6”-7” thick, that occursapproximately 1 ft below the parting is present atboth stations CJ01 and CJ02. The thick coalbeds in the lower part of the Fruitland arepartially replaced northeastward by the tongue ofPictured Cliffs, and partially overlie the tongue.A strong odor of hydrogen sulfide was noted inseveral places in Carbon Junction Canyon at thetop of the basal coal of the Fruitland.

The middle part of the Fruitland is composedof interbedded carbonaceous shale and sandstonewith relatively minor amounts of coal. Northeastof about station CJ15 a channel sandstone bed isat the base of the middle part; southwest of thatlocality carbonaceous shale is at the base.Otherwise, the amount of sandstone in the middlepart increases upward in the section, similar tothe middle part at Basin Creek. Sandstone bedsare of channel and crevasse splay origin andreach a thickness of as much as 25 ft at the top ofthe middle part of the Fruitland. One or two 1 ftthick coal beds are present just below this uppersandstone; only carbonaceous shale was notedlower in the middle part.

The best exposures of the upper part of theFruitland are at stations CJ7-10. As at BasinCreek, the upper part here consists of sequencesof carbonaceous shale and coal intervalsseparated by sandstone beds. The carbonaceousshale beds are as thick as 40 ft; the coal beds areas thick as about 3 ft; the sandstone beds averageabout 6-10 ft thick. The contact with theKirtland Shale occurs in the gravel-coveredslopes just west of the water tank at the southeastcorner of the mapped area (marked WT on thebase map, plate 2). The contact was placed at azone of septarian nodules that weathers out of thegravel-covered slope. I believe that this zone isat the same stratigraphic position as that noted atthe top of the Fruitland at Basin Creek.

Exposures of the Fruitland Formationadjacent to the shooting range (plate 2) wereexamined and found to be essentially the samelithologies as those at Basin Creek and in Carbon


Junction Canyon. There is a thick coal sequenceat the base of the Fruitland overlain by asequence of carbonaceous shale, coal, andsandstone beds. Much of the Fruitland just westof the shooting range is obscured by landslidedeposits, shown on the map as the Qls unit. I didclimb up the rim of the Pictured Cliffs west ofthe range to examine what appeared to be a thickcoal bed, but what is actually tailings frommining activity. The “coal” bed is a mixture offinely ground carbonaceous shale, mudstone, andcoal that has been dumped on top of the PicturedCliffs Sandstone.

No definite faulting was seen in CarbonJunction Canyon, but an area of disruptedbedding just northeast of station CJ15 was noted.It appears that there is some offset of a channelsandstone at the base of the middle part of theFruitland Formation at that locality, but poorexposures made it difficult to determine if therewas offset on a fault or just slumping of theoutcrop.

Florida River

Mapping in the Florida River area was

mainly in sec. 24, T. 35 N., R. 9 W., butextended southwestward into the SE¼ of section23 and northeastward into sections 18 and 19, T.35 N., R. 8 W. The area ranges in elevationfrom about 7100 ft along the Florida River toover 8100 ft where the Pictured Cliffs Sandstoneforms the ridge in the southwest part of the studyarea. This outcrop area is a continuation of theexposures at Carbon Junction and the strike ofthe Pictured Cliffs Sandstone and FruitlandFormation remain northeasterly. Dip is southeastinto the San Juan Basin. Dips in this area are thehighest of any of the areas mapped, ranging from27 degrees (which seems anomalously low) to 59degrees, averaging 48 degrees (Table 2-3).

Much of this area is covered by piñon-juniper forest, but the increase in elevation isenough for Ponderosa pine and other largerconifer trees to grow in places. In the lowerelevations, especially on the southwest side of theriver and on slopes adjacent to the east side of theriver, dense underbrush again obscures much ofthe surface geology. An old road traverses partof the area southwest of the river, providinglimited access to some of the area. The bestexposures in the area are along the Florida canal,

Table 2-3. Strike and dip measurements in the Florida River area.[Locations are shown on plate 4.]

Station No. Strike and dip Station No. Strike and dipFR01 N63ºE/54ºSE FR23 N62ºE/45ºSEFR02 N50ºE/45ºSE FR24 N51ºE/55ºSEFR03 N58ºE/53ºSE FR26 N64ºE/54ºSEFR04 N58ºE/53ºSE FR27 N66ºE/45ºSEFR05 N62ºE/42ºSE FR28 N60ºE/45ºSEFR08 N57ºE/27ºSE FR30 N74ºE/56ºSEFR11 N65ºE/39ºSE FR31 N54ºE/51ºSEFR12 N59ºE/44ºSE FR32 N65ºE/52ºSEFR15 N60ºE/38ºSE FR35 N65ºE/40ºSEFR16 N64ºE/46ºSE FR36 N55ºE/59ºSEFR17 N68ºE/48ºSE FR38 N70ºE/50ºSEFR19 N68ºE/58ºSE FR39 N66ºE/51ºSEFR20 N64ºE55`SE FR40 N61ºE/54ºSE


adjacent to the north-south paved road. Astratigraphic section was measured in the cutsalong the canal (fig. 2-4, plate 7).

Plate 3 shows the geology of the FloridaRiver area. The contact of the Lewis Shale withthe Pictured Cliffs shown on the maps wasinterpreted by aerial photo analysis. ThePictured Cliffs Sandstone—Fruitland Formationcontact is conformable and intertonging in thisarea. A tongue of Fruitland Formation is presentbelow a tongue of Pictured Cliffs Sandstone atthe Florida River area, but pinches out a shortdistance northeast of the river. The contactbetween the Fruitland Formation and KirtlandShale is also conformable and gradational in thisentire area.

In the mapped area the Pictured CliffsSandstone occurs as a lower main body and anupper tongue. The main body transitionallyoverlies the Lewis Shale and is composed of alower and an upper part. The lower part consistsof interbedded very fine-grained, argillaceous,thin, rippled sandstone and gray shale;sandstones in this interval become thicker-beddedhigher in the section, and the percentage of grayshale decreases upward. Ophiomorpha burrowswere noted at one outcrop in this interval. Thetop of this lower part is composed of massive,yellowish sandstones that form the dip slopes atstations FR02 and FR07 (plate 4). This lowerpart of the main body is not continuouslyexposed, but is estimated to be about 150-200 ftthick, depending on the placement of the lowercontact with the Lewis Shale. The upper part ofthe main body is composed of a light-gray, fine-grained sandstone that forms a distinctive ridgealong the outcrop. It is much less argillaceousthan sandstones of the lower part of the mainbody of the Pictured Cliffs. This upper part isrelatively thin, on the order of 15-25 ft thick. Adark gray to black rooted zone is present at thetop of this unit. The main body, mapped as Kpc,is poorly exposed northeast of Florida River, butregional stratigraphic relations suggest that itpinches out depositionally into the Lewis Shale ashort distance northeast of the river.

The tongue of Pictured Cliffs Sandstone islight gray to yellowish gray, very fine to fine-

grained, well sorted sandstone. It is well-exposednear the highest point in the mapped area,downslope from station FR08. There it consistsof a series of thick sandstone beds that have acombined thickness of at least 100 ft. Along theFlorida canal, near County Road 225 (plate 3),the tongue was measured at 123 ft thick. Thetongue forms a prominent outcropping ridgealong the north side of Horse Gulch Road(County Road 237) and along the irrigationcanal, but is poorly exposed northeast of FloridaRiver. Northeast of the river it is hidden in thetrees on the north-facing slope of the hogback. Itgradually rises topographically northeastwardand eventually forms the ridge line northeastwardfrom section 17.

As shown on figure 2-4 and plate 3, theFruitland Formation is divided into severalmapped intervals on the basis of lithology. Asmeasured along the Florida canal, the Fruitland isabout 460 ft thick. Where the FruitlandFormation is well exposed it can be broadlydivided into as many as three coal-bearingintervals, separated by sandstone and mudstone.Extensive cover in the Florida River area made itdifficult to accurately trace out these intervalsand some units were combined in some areas. Inthe Florida River area the tongue of FruitlandFormation (Kft), a lower coal-bearing interval(Kfab), and an upper coal-bearing interval (Kfu)are highlighted on the geologic map. The tongueof Fruitland contains a thin (1-3 ft thick) bed ofcoal at the base and another about 20 ft abovethe base, but otherwise is composed of mudstone,carbonaceous shale, and thin sandstone beds. Atstation FR09 a bed of carbonaceous shaleunderlies the tongue of Pictured Cliffs Sandstone.It is quite possible that this carbonaceous shale isreplaced by coal in other areas nearby. In theEwing Mesa area, southwest of Florida River(plate 7), a coal bed is present just below thetongue of Pictured Cliffs Sandstone. The tongueof Fruitland Formation was estimated to beapproximately 30 ft thick at station FR09; itthins northeastward and pinches out in thealluvium-covered, north-facing slope northeast ofFlorida River.


Explanation

Figure 2-4. Stratigraphic section at Florida River. See plate 7 for correlation to other sections.


The unit labeled Kfab on the geologic mapcontains the thickest beds of coal in this area.The coal immediately overlying the upper tongueof Pictured Cliffs Sandstone is poorly exposed inmost of the area, and is quite thin in comparisonwith coals in similar stratigraphic positions in theCarbon Junction and Texas Creek areas. TheKfab unit contains a thin sandstone above thelowest coal, and is overlain by anothercarbonaceous shale and coal interval. The lowestcoal is 3 ft thick along the Florida canal (plate 7)and is overlain by about 20 ft of carbonaceousshale and brown mudstone. The first sandstonein the Fruitland, which was not mappedseparately due to poor exposures, is a compositeof about 3 ft of sandstone interbedded with 7 ft ofmudstone along the canal. The interval betweenthe first and second sandstones is about 125 ftthick along the canal (possibly overestimated inthis covered interval). Coal just below Kf2 is thethickest in the area; a unit of interbedded coaland carbonaceous shale about 15 ft thickimmediately underlies Kf2. A kaolinite bed wasnoted in this coal sequence at station FR18. Anadit was discovered just off the old road in theSW¼ of section 24 within the Kfab interval (seeplates 3 or 4 for the location of the adit).Northeast of the river a small area of the upperKfab unit is covered with reddish-orange chips ofsandstone typical of burned coal intervals.Heavy brush in this area made it difficult to tracethe clinker very far to the northeast.

Kf2 is a sandstone that forms a steephogback on the southwestern end of the studyarea and forms the low ridge that much of the oldroad in section 24 was built on. The upper partof Kf2 forms the ridgeline northeast of FloridaRiver. Kf2 is very thick (50-75 ft) in thesouthwest part of the area, where it appears to bea fining-upward stacked channel complex. Theunit thins somewhat to the northeast.

At the southwest end of the mapped areaanother sandstone, Kf3, overlies the Kf2sandstone. In that part of the area no coal wasseen separating the two sandstones; however, atthe Florida canal (plate 7) and east of the river,coal is present below this third sandstoneinterval. Two to three feet of coal is present

along the irrigation canal, and a similar amountis present east of the river.

The upper part of the Fruitland, mapped asKfu, is a unit transitional with the Kirtland Shale.It consists of thin sandstone beds, greenish-graymudstone, carbonaceous shale, and thin coalbeds. Kfu generally weathers to a poorlyexposed slope, but is well-exposed along theFlorida canal. The top contact was mapped atthe base of a greenish, argillaceous sandstonethat forms a low ridge in many places. Thisupper unit of the Fruitland contains characteristicyellowish-orange septarian concretions that werealso seen in the Basin Creek and Carbon Junctionareas. A coal bed 1-2 ft thick was measured atstations FR21 and FR22 at the top of the Kfuunit (plate 4). Carbonaceous shale with thinstreaks of coal are present lower in Kfu, but noother continuous coal beds were seen.

The Fruitland Formation is gradationallyoverlain by the Kirtland Shale throughout thisarea. As noted previously in other areas alongthe Fruitland outcrop, the basal Kirtland beds aresimilar to the upper beds of the Fruitland, butlack the carbonaceous shale and coal. One otherdifference in this area is that sandstone beds ofthe Kirtland have a greenish color or are iron-richand are dark brown as opposed to the yellowish-brown sandstone beds characteristic of theFruitland. The contact between the Fruitland andKirtland could thus change laterally if coal bedsoccur higher or lower in the section.

Fairly large areas just southwest andnortheast of Horse Gulch (plate 3), are obscuredby terrace gravel and were mapped as Qg. Theseunits, and a smaller, similar unit just east of theFlorida River are composed of pebbles andcobbles of igneous and metamorphic rocks.Quaternary alluvium (Qal) is present in thevalley of Florida River and in a drainage adjacentto the largest terrace gravel deposit. Exposures inHorse Gulch, especially on the south side of thestream, are quite poor. Contacts were drawn asdashes across the drainage to show the inferreddistribution of units.

No faulting or other structural complicationswere noted in this mapped area. The mainstructural feature is the extreme dip of the beds;


however, the dip moderates abruptly just a shortdistance basinward from the Fruitland outcrop.

South Fork of Texas Creek tothe Pine River

An extensive area was mapped along part ofthe South Fork of Texas Creek andsoutheastward to the Pine River in northeastern

La Plata County. This area includes parts ofsections 6, 7, 8, 9, 10, 14, and 15, T. 35 N., R. 7W. and a small bit of sec. 12, T. 35 N., R. 8 W.(plate 5). The character of this area changessignificantly from west to east. In the west thePictured Cliffs Sandstone and FruitlandFormation form a series of isolated peaks(flatirons) separated by deep drainages. Thistopography produces a zig-zag pattern of units inthe Fruitland as the units cross the gullies and

hills. In contrast, in the eastern part of the areathe Pictured Cliffs and units of the Fruitlandform a long, linear outcrop. The elevations of thearea gradually decrease from west to east, fromnearly 8900 ft at Vosburg Pike in the west toabout 7200 ft in the east at the Pine River. Thisarea of outcrops lies at the northern rim of theSan Juan Basin; this particular segment of therim has a northwestward strike and the rocks dipsouthwestward. In the Texas Creek part of the

area dips range from 12 to 35 degrees andaverage 22 degrees (table 2-4). In the Pine Riverpart of the area the dips range from 23 to 52degrees and average 35 degrees (table 2-5).

While mapping from Texas Creek to the PineRiver it became apparent that significant errorsexist on the topographic map in some places,especially at the boundary between the Rules Hilland Ludwig Mountain quadrangles along theFruitland—Kirtland contact (plates 5 and 6).

Table 2-4. Strike and dip measurements in the South Fork of Texas Creek area.[Locations are shown on plate 6.]

Station No. Strike and dip Station No. Strike and dipTA01 N85ºW/13ºSW TD03 N76ºW/28ºSWTA03 N85ºW/25ºSW TD04 N72ºW/25ºSWTA04 N80ºW/19ºSW TD05 N85ºW/25ºSWTA05 N85ºW/16ºSW TD06 N77ºW/23ºSWTA08 N80ºE/34ºSE TD07 N90ºE/28ºSTA10 N88ºE/19ºSE TE02 N81ºW/31ºSWTA11 N90ºE/20ºS TE03 N85ºW/23ºSWTB01 N80ºE/35ºSE TE04 N52ºW/15ºSETB02 N88ºW/17ºSW TE05 N79ºW/31ºSWTB03 N80ºE/21ºSE TE06 N40ºW/20ºSWTB04 N90ºE/17ºS TE07 N75ºW/25ºSETB07 N89ºE/26ºSE TF01 N80ºW/24ºSWTC02 N80ºE/20ºSW TF03 N80ºE/21ºSWTC04 N84ºW/22ºSE TF04 N44ºW/25ºSWTC05 N84ºW/12ºSW TG01 N70ºW/12ºSWTC06 N77ºW/25ºSW TG02 N67ºW/25ºSWTC08 N85ºW/18ºSW TH01 N44ºW/15ºSWTD01 N79ºE/24ºSW TI01 N50ºW/15ºSWTD02 N73ºW/22ºSW TJ01 N50ºW/24ºSW


For example, the wide, flat-topped hill just to thewest of the Hoier property is not really as flat asthe map shows. Also, the hills shown north andeast of the unit shown as Qal, just east of Hoier’sproperty, do not agree with the aerialphotographs. The geologic contacts wereadjusted to the topographic map, but be advised

of the problems with the base map.A wide range in vegetation corresponds to

the change in elevation across the area. In thewest, vegetation consists of Ponderosa pine forestwith other mixed conifers. There is some brushin the western area, but in general the forest isopen. The eastern part of the area has mixedvegetation of both tall conifer and piñon-juniperforest mixed with some stands of denseunderbrush. The most covered area is in thecentral part of the eastern half of the area, justwest of the Hoier property. A critical area in theNW¼ of sec. 14 is also very poorly exposed,which makes interpretation of faulting in thatarea difficult. A completely exposed section ofFruitland was not found anywhere in the mappedarea, so the measured section for this area, shownin fig. 2-5 and on plate 7, is a composite ofobservations made at several places. Most of thedescriptions were made in the western half of themapped area; however, stratigraphic units can betraced through most of the mapped area. See

appendix 2-1 for a composite stratigraphicsection that was compiled for the western sectionalong Texas Creek.

Plate 5 shows the geology from Texas Creekto the Pine River. The oldest unit shown is theLewis Shale, which is overlain by the PicturedCliffs Sandstone. In this area there is one main

body of Pictured Cliffs overlain by one intervalof Fruitland. The Pictured Cliffs Sandstone inthis area is the same lithologic unit as the tongueof Pictured Cliffs Sandstone in the Florida Riverarea (plate 7). A northeastward stratigraphic riseresulted in the lower part of the Pictured Cliffs atthe Florida River pinching out depositionally intothe Lewis Shale in a northeastward directionwhile the stratigraphically higher tongue extendsinto this area. The Pictured Cliffs here can alsobe generally divided into a lower, yellowish,argillaceous part that is transitional with theLewis Shale and an upper part that is composedof clean, well sorted sandstone. A thin coal ispresent within the Pictured Cliffs in part of thenorthern San Juan Basin, such as in the AMOCOGurr Federal Gas Unit No. 1 well. Although thecoal was not seen at the outcrop in this study, thebreak between the lower and upper PicturedCliffs would be a likely place for the coal tooccur. The difference in lithology causes the twoparts of the Pictured Cliffs to weather differently

Table 2-5. Strike and dip measurements in the Pine River area.[Locations are shown on plate 6.]

Station No. Strike and dip Station No. Strike and dipPR01 N43ºE/23ºSE PR20 N57ºW/35ºSWPR02 N80ºW/36ºSW PR22 N61ºW/28ºSWPR04 N70ºW/30ºSW PR23 N85ºW/35ºSWPR05 N44ºW/32ºSW PR27 N84ºW/39ºSWPR08 N52ºW/31ºSW PR28 N84ºW/39ºSWPR10 N66ºW/39ºSW PR29 N70ºW/45ºSWPR11 N69ºW/35ºSW PR31 N70ºW/40ºSWPR12 N70ºW/31ºSW PR33 N65ºW/52ºSWPR13 N85ºW/31ºSW PR36 N68ºW/25ºSWPR16 N85ºW/32ºSW PR38 N80ºW/34ºSW


and to form a double outcrop in places. On lobeH (plate 6), north of the Ragsdale property, itappears that the upper part of the Pictured Cliffshas been eroded, producing a stripped surfacethat is at a lower elevation than the top of thePictured Cliffs on lobe G. This difference inelevation of the two outcrops could be mistakenfor offset on a fault, but we checked this area forevidence of a fault and didn’t see one.

The Fruitland in this area was again dividedinto several units of sandstone and coal-bearingintervals. The basal interval (Kfab) consists ofmudstone, carbonaceous shale, and coal, withone, thin sandstone near the middle of the unit.This coal interval has the best exposure of any inthis mapped area, particularly at the crests of theflatirons where the coal is being eroded.Reddish-orange burned sandstone chips, orclinker, are found in some areas in the basalinterval, but are not abundant in this area.Altered volcanic ash beds (kaolinite) were alsoseen in some of the better-exposed outcrops, butare not abundant in the lower coal. The coalimmediately on top of the Pictured CliffsSandstone thins irregularly to the southeast alongthis outcrop. The thickest coal was found at thebase of the Fruitland at the western end of themapped area (station TA04, plate 6). Thesection described below is of that outcrop.

Several small mines, with collapsedentrances, were found in the lower coal interval,at stations TB06, TJ02, and PR20 (plate 6).Poor exposures made it difficult to measure athickness of the coal at TJ02, but about 3 to 5 ftis estimated. In contrast, the lowest coal thins to1 foot or less in some areas toward the PineRiver and thickens to 2-4 ft at the southeast endof the outcrop. A thicker interval of coal ispresent near the top of the Kfab unit, but it isalso poorly exposed. The whole Kfab unitmaintains a thickness of 40-50 ft from west toeast across the whole area. I believe that thisKfab unit corresponds with the Ignacio coalseams as identified by AMOCO (1994) in thesubsurface nearby.

An odor of hydrogen sulfide (H2S) was notedin three places in the lower coal interval. Amoderate odor was noted at station TI01, justeast of the Ragsdale property on one occasion inMay. Another was just down-slope to the westof station PR01, the third was on the crest of thehill east of station PR20. An extensive area ofdead vegetation is associated with the H2S area atPR20. A fourth area with H2S is just downslopefrom station PR35, in the Kfcd coal interval.

Overlying Kfab is sandstone mapped as Kf2.This sandstone forms many of the long dip slopesat Texas Creek and toward the Pine River. It is a

FT Description

~1 Soil; top of exposure2.3 Coal, black, dull, poorly developed cleat and bedding. Breaks into blocky to irregular fragments

up to 1" across; fractured2.6 Claystone, weathered, yellowish orange to moderate yellowish brown with carbonaceous laminae in

upper part6.0 Coal, dark gray to black, generally dull, cleat poorly developed, poorly bedded. Includes 6" of impure

(silty?) coal about 1.9' from top of bed0.3 Claystone, yellowish gray to pale yellowish brown; kaolinitic(?)1.0 Coal, black, dull, blocky, well cleated0.3 Claystone, brownish gray1.4 Coal, bright, black, weathered, well bedded, good cleat0.9 Seat-earth, sandstone, medium gray, carbonaceous; very thin, irregular beds; rooted. Base of coal-- Pictured Cliffs Sandstone. Sandstone, quartzose, very fine grained, very light gray, thickly bedded,

wavy bedded with finely disseminated dark minerals.


composite channel sandstone that thickens to asmuch as 100 ft or more in some places. Thelower part of this sandstone is silica-cemented insome areas and has a distinctive rose color.

A unit mapped as Kfcd overlies the secondsandstone of the Fruitland Formation in this area.This unit consists of a coal bed at the base, aconcretionary limestone interval in the middle,and another coal bed at the top. The coal bedsare fairly thin, averaging about 2-4 ft thick. Thezone of concretions between the coals is theinformally named “skeleton bed” (appendix 2-1).This bed served as a marker in the west part ofthe study area because of the resistant nature ofthe concretions and their distinctive color. Thiscoal zone was mined at the east end of theoutcrop at the Pine River. According to Barnes

(1953) this was the Schutz Mine. Based onthickness and stratigraphic position, I believe thatthis coal interval corresponds to that identified asthe Lemon coal seams by AMOCO (1994). Twosandstone intervals overlie Kfcd, the Kf3 andKf4 units. The Kf3 sandstone is continuousacross the whole mapped area, but the Kf4sandstone could not be traced all the way to thePine River. Kf3 is as thick as 50 ft on the westend of the study area, but thins to about 15 ftnear the Pine River. Kf4 appears to thinsoutheastward from about 35 ft and disappearednear the area just west of section 14 that isobscured by vegetation. Kf4 was not found inthe better exposures of this part of the sectionjust west of the Pine River.


As in the other areas discussed in this report,the top unit of the Fruitland Formation wasmapped as Kfu. The lithology is similar to thatat Basin Creek and at Florida River and consistsof greenish mudstone, thin sandstone,

carbonaceous shale, and thin coal beds. Thethickness of this unit is approximately 80 ft.Here too, it has a lithology similar to the KirtlandShale, except that the Kirtland lacks the coals.Fairly good exposures are present at stations

Figure 2-5. Stratigraphic section at Texas Creek-Pine River. See plate 7 for correlation to other areas.

ExplanationExplanation


PR15, PR18, and PR36 (plate 6). There is not agood marker bed that can be used to separate theFruitland Formation from the Kirtland Shale; thepresence or absence of coal beds andcarbonaceous shale was used to place the contactin an interval that was otherwise very similarlithologically. Based on stratigraphic position,this upper interval of the Fruitland most likelycorresponds with the Pargin coal zone ofAMOCO (1994).

Quaternary alluvium (Qal) is presentprimarily in the valley of Pine River, but wasalso mapped east of the Hoier property. Anattempt was made to show the inferred positionof Fruitland units under the alluvium in the valleyof the South Fork of Texas Creek (plate 5).

One of the more interesting features of thePictured Cliffs—Fruitland outcrop in this area isa fault at the extreme east end of the outcrop, justwest of the Pine River (fig. 2-6). This fault waspreviously mapped by Barnes (1953) as a normalfault, down to the north. Some features lead meto speculate that it could be a moderate- to high-angle thrust fault, with thrusting directed

northward. The fault trace is along a steep-walled gully that cuts the outcrop just behind theField property adjacent to the outcrop. On thenorth side of the gully Pictured Cliffs Sandstoneand the Kfab and Kf2 units of the Fruitland rollsteeply into the gully at about 45 degrees.Boulders of Pictured Cliffs that were used to

construct a retaining wall on the north side of thegully display slickenside striations, which is clearevidence that the Pictured Cliffs is faulted at thislocality.

On the south side of the gully it appears thatthere is a complete repeated section of PicturedCliffs Sandstone that is between 100 and 130 ftthick. Below the lowest identified Pictured Cliffsare a few feet of fissile, fossiliferous, gray shale,underlain by Fruitland coal, probably from theKfab unit. Initially I speculated that the grayshale might be a sliver of Lewis Shale, but D.Baldwin (written commun., 1996) indicated thatthere is a similar gray shale associated with thebasal coal in several monitoring wells in the PineRiver Ranches area adjacent to the outcrop. Itstill appears that a repeated section of PicturedCliffs overlies the Kfab unit of the Fruitland inthe gully, however, suggesting that the PicturedCliffs was pushed northward over the coal,causing the abrupt increase in dip of theunderlying wedge of Pictured Cliffs—Fruitlandon the north side of the fault. D. Baldwin(written commun., 1996) noted that no fault wasencountered in the James No. 1 monitor well,which was drilled approximately .2 mi east of thegully in which the fault occurs. Unfortunatelythe well was not drilled all the way through thePictured Cliffs Sandstone to test whether there isa repeated section of Pictured Cliffs in that area.The only way to know if there is a fault therewould be to drill completely through the PicturedCliffs into underlying rocks to see if there iseither Lewis Shale or a repeated section ofPictured Cliffs. The fault in the gully could notbe traced confidently very far west due to coverby vegetation, but perhaps the poor exposurescan be explained, in part, by disruption ofbedding due to the faulting. No other significantfaulting was noted in this mapped area, althougha few inches of offset was seen on sandstone bedsat station TI02.

FruitlandFormation

Lewis Shale

LewisShale

Fruitla

nd Formati

on

Picture

d Cliff

s San

dstone


Figure 2-6. Schematic diagram of reverse fault just west of the Pine River.


Synthesis

Following is a description of regionalchanges and correlations of stratigraphic unitsfrom Basin Creek to the Pine River, based on myoutcrop studies. Fassett and Hinds (1971),Fassett (1988), Ambrose and Ayers (1991),Ayers and others (1991), and Roberts andMcCabe (1992) have previously summarized thePictured Cliffs, Fruitland, Kirtland, andassociated strata, and their depositionalenvironments.

The study area is located on what was thewestern shore of the Upper Cretaceous seawaythat bisected North America (Fassett and Hinds,1971; Fassett, 1988). Sedimentation rate and sealevel rise and fall had marked effects ondeposition of sediments that comprise thePictured Cliffs Sandstone and FruitlandFormation in the study area. Seawardprogradations and landward transgressions of theshoreline are part of a complex interplay betweensea level, sediment influx, tectonic events, andother variables.

The effects of sea level changes are clearlyexpressed in the Pictured Cliffs Sandstone in LaPlata County. The stratigraphic intertonguing ofnearshore marine and coastal plain depositsindicates that there were a series of seawardprogradations of the shoreline followed byshoreline buildups and transgressions back to thesouthwest across nearshore peat swamps. In thefar southwestern end of the study area, on thesouth side of Basin Creek, there is only one mainbody of Pictured Cliffs, overlain by Fruitlandcoal. However, in the northern part of the BasinCreek area a tongue of Pictured Cliffs overliesthe main body and is separated from the mainbody by a thin coal in places. This represents aprogradation of the Pictured Cliffs shorelinesandstone to the northeast in a seaward direction,followed by a transgression back to the southwestover the swamp deposits of the FruitlandFormation. This was a relatively short-livedtransgression, and the tongue merges with themain body of the Pictured Cliffs northeastwardinto the Carbon Junction area about 2 mi to thenortheast.

At Carbon Junction there is another doubletof a main body of Pictured Cliffs and anoverlying tongue. Near the landward extent ofthe tongue is a thick buildup of coal in the basalFruitland Formation, indicating a period ofshoreline stability just seaward of the coal. Thedoublet of Pictured Cliffs sandstones continues tothe northeast slightly past the Florida River(Zapp, 1949), at which point the lower PicturedCliffs sandstone grades out into the Lewis Shaleand the tongue becomes the only Pictured Cliffsunit present. This represents a stratigraphic riseof the prograding shoreline sandstone to thenortheast. In the Texas Creek to Pine River areathere is only the one Pictured Cliffs sandstoneunit.

The thickness of coal in the basal part of theFruitland Formation is closely tied to the rate atwhich the shoreline changed. In the Basin Creekarea there is a combined thickness of 50-60 ft ofcoal at the base of the formation; at CarbonJunction there is approximately 80 ft of coal atthe base. This indicates a relatively long periodof stability in which coal swamps developed. Incontrast, in the Florida River area the coal at thebase of the main body of Fruitland is only a fewfeet thick and much of the rest of the lower partof the Fruitland is carbonaceous shale ormudstone. This indicates a relatively quickseaward progradation of the shoreline; anenvironment in which the peat in swamps did nothave time to accumulate. At the west end of theTexas Creek area the basal coal is fairly thick,but it thins toward the Pine River, indicatinganother period of stability, followed by morerapid progradation. This sequence ofprogradation and aggradation of the shorelinewas shown diagrammatically by Fassett andHinds (1971, p. 11) and is documented in thesubsurface by Ayers and others (1991, p. 11) andRoberts and McCabe (1992, p. 121).

In the Basin Creek and Carbon Junctionareas the rock interval just above the basal coalsconsists of mudstone and carbonaceous shale thatgradually becomes more sandstone-dominatedupward in the section and culminates in astacked-channel complex that is approximately25 ft thick. This sandstone complex is very welldeveloped at the southwest end of the Florida


River area, where it approaches 75 ft of nearlyall sandstone (mapped as the number 2 sandstone[Kf2]) and comprises most of the middle part ofthe Fruitland. The sandstone complex is alsopresent in the Texas Creek to Pine River area,where it and associated mudrocks are as thick as100 ft. This interval in the Fruitland isinterpreted to represent a major influx ofsediment from the source area to the southwest ofthe La Plata County area.

Strata in the upper part of the Fruitland inthe Basin Creek and Carbon Junction areasconsist of a series of interbedded mudrock, coal,and sandstone beds that repeat in several cycles.A similar series of rocks is present in the FloridaRiver and Texas Creek—Pine River areas in theupper part of the Fruitland. Coal beds in thisinterval are relatively thin, usually only 3-4 ftthick maximum, and the sandstone channels arealso relatively thin, commonly about 10 ft, but asmuch as 30 ft thick in places. Where coal bedsare present they are commonly directly overlainby sandstone beds. This upper part of theFruitland section is interpreted as representingmeandering streams on a surface of low relief,such as a delta plain. Some of the sandstonebeds are thin and tabular, and probably are ofcrevasse splay origin. The coal developed inswampy areas adjacent to the fluvial channelsand this accounts for their relative thinness andlenticularity. Coal-bearing horizons do appear tobe fairly persistent laterally, but the coal bedspinch and swell within those intervals.

The uppermost unit of the Fruitland istransitional with the overlying Kirtland Shale andis present in all the mapped areas. This unit hascertain features characteristic of the Fruitland,such as carbonaceous shale and thin coal beds,but has other features characteristic of theKirtland, such as dense, green siltstone andabundant yellowish-orange concretions. As awhole, the unit has very little sandstone and iscommonly weathered and poorly exposed. Thetransitional unit is recognizable in all of theareas, however, and makes a good marker bed forthe contact between the Fruitland and Kirtland.It was deposited farther up the depositional slopethan the lower and middle parts of the Fruitland,

and thus does not have a good development ofcoal beds.


PART 2--FRACTURE STUDIES

Joints in sandstone and cleats in coal weremeasured at 209 localities in the project area. Byarea, the totals are 47 localities, or stations, atBasin Creek, 27 stations at Carbon Junction, 40stations at the Florida River, 57 stations alongthe south fork of Texas Creek, and 38 stationsbetween Texas Creek and the Pine River. Eachof the areas is summarized separately below; rosediagrams of the individual stations are shown inappendix 2-2. Tables 2-6 through 2-10 show inwhich geologic unit the stations were recorded;

plates 1, 2, 4, and 6 show the locations of eachstation. The rose diagrams were constructedusing a Macintosh program called Rosy. Rosediagrams in figures 2-8 through 2-12 and inappendix 2-2 show statistics for each area orstation.

In each of the rose diagrams, N is the numberof readings in each data set used to construct thediagram. The class interval indicates the numberof degrees each wedge of the diagram shows. Aclass interval of 10 degrees was used for all thediagrams. The size of the wedge is a relativemeasure of the number of readings within eachwedge. The statistics are intended to providemeasures of central values and dispersion of thedata. All the tests, such as maximum percentage,mean percentage, and standard deviation, aremade on cells having values greater than 0.Other calculations are as follows. The vectormean is the combined azimuth of all the readings

used to construct the diagram. The R magnitudeis the magnitude of the vector mean. Data setsthat exhibit large dispersion about the mean willhave small resultants, and those sets that aretightly grouped have large resultants. R isstandardized to range between 0 and 1; tightlyclustered data sets have R values near 1. Theconfidence angle is another test of the reliabilityof the vector mean. The confidence angle formsan arc plus or minus either side of the calculatedvector mean. A small confidence angle indicatestightly clustered data, a large angle indicatesdispersed data. There is a 95% probability that

the arc formed by the confidence angle containsthe true population mean direction. TheRayleigh number is a test for uniformity in a dataset. Values less than 0.05 (95% confidence level)indicate that the data are non-uniform and show apreferential orientation. These tests ofuniformity only apply to figures 2-7 through 2-12in this report, because these figures show singlesets of joints or cleats.

In general, in each area there is one mainjoint set in each geologic unit, and a second setthat is oriented at about right angles to the first.These joint sets were named the J1 and J2 sets.In some areas a third set, and even a fourth set,are also present. This discussion focuses on theJ1 and J2 sets because they are the most commonand pervasive in all the areas; individuallocalities where the other sets are important arepointed out below. All the joint sets are orientedperpendicular to bedding, even in areas of steep

Table 2-6. Average orientations of joints in sandstone and cleats in coal in the project area

Kpc-J1 Kpc-J2 Face Butt Kf-J1 Kf-J2Basin Creek N. 28º W. N. 59º E. N. 2º W. N. 88º E. N. 2º W. East-WestCarbon Junction N. 77º E. N. 50º W. N. 20º W. N. 69º E. N. 9º W. N. 85º E.Florida River N. 23º W. N. 64º E. N. 31º W. N. 58º E. N. 20º W. N. 67º E.Texas Creek N. 9º W. N. 79º E. N. 22º W. N. 68º E. N. 1º E. N. 89º W.Pine River N. 5º E. N. 75º W. N. 35º W. N. 54º E. N. 7º E. N. 81º W.Totals N. 14º W. N. 74º E. N. 21º W. N. 69º E. N. 3º W. East-WestKpc - Pictured Cliffs Sandstone; Kf - Fruitland Formation


dip. In coal beds, fractures are known as‘cleats’, and in coal too, there are two main sets,a face cleat and a butt cleat. The face cleat is themain fracture set in coal beds; butt cleats areoriented at about 90º to the face cleats.

For this study, four main characteristics ofjoints and cleats were emphasized—length,spacing, sinuosity, and mineral fillings. Inaddition, basic parameters of joints, such asterminations of one joint set against another (todetermine relative age) and surface features (todetermine mode of origin) were also noted. Ingeneral, joint surfaces in this area are weathered,obscuring surface ornamentation. Some joints ofeach set do display features such as plumosestructures, arrest lines, and twist hackle, featurescharacteristic of opening mode (mode I) fractures(Kulander and others, 1979). No evidence ofshear movement, such as slickenside striations,was noted on any of the joint sets.

Figure 2-7 shows rose diagrams thatsummarize over 1850 readings taken of all J1and J2 joints and of all face and butt cleats incoal in the entire study area. Figure 2-7 alsoshows that in a regional sense there is a goodclustering of joint and cleat directions. For thePictured Cliffs Sandstone the regional average ofJ1 joints is 346º, or N. 14º W., and the averageof J2 joints is 74º, or N. 74º E. The regionalaverage of all face cleats in all coal beds is 339º,or N. 21º W., and the average of all butt cleats is69º, or N. 69º E. The average J1 orientation forall sandstone beds in the Fruitland Formation is357º, or N. 3º W., and for J2 joints is 90º, orEast-West. Table 2-6 tabulates the averageorientations of each of the mapped areas inaddition to the totals for the whole area.

.


StatisticsAll J1 joints in project area in Pictured Cliffs

N = 315

Class Interval = 10 degrees

Maximum Percentage = 19.4

Mean Percentage = 5.56 Standard Deviation = 6.32

Vector Mean = 346.1

Conf. Angle = 6.95

R Magnitude = 0.577

Rayleigh = 0.0000

StatisticsAll J2 joints in project area in Pictured Cliffs

N = 177




Vector Mean = 74.2

Conf. Angle = 9.22

R Magnitude = 0.584

Rayleigh = 0.0000

StatisticsAll face cleats in project area, all coals

N = 342




Vector Mean = 338.8

Conf. Angle = 4.65

R Magnitude = 0.745

Rayleigh = 0.0000

StatisticsAll butt cleats in project area, all coals

N = 313




Vector Mean = 68.8

Conf. Angle = 5.36

R Magnitude = 0.696

Rayleigh = 0.0000

StatisticsAll J1 joints in project area, Fruitland sands

N = 434




Vector Mean = 357.2

Conf. Angle = 2.47

R Magnitude = 0.897

Rayleigh = 0.0000

StatisticsAll J2 joints in project area, Fruitland sands

N = 273




Vector Mean = 90.0

Conf. Angle = 3.84

R Magnitude = 0.852

Rayleigh = 0.0000

Figure 2-7. Summary rose diagrams of all J1 and J2 joints in Pictured Cliffs and Fruitland sandstones and all

face and butt cleats of coal in the project area.


Basin Creek

Figure 2-8 shows summary rose diagrams ofjoint and cleat orientations in the Pictured CliffsSandstone, Fruitland Formation coals, andFruitland sandstone beds. In the Pictured Cliffs(including both the main body and tongue) theaverage orientation of the J1 joint set is 332º, orN. 28º W. The average orientation of the J2 setis 59º, or N. 59º E. There were only scatteredoccurrences of J3 or J4 sets in the Pictured Cliffsin this area. In general, the main body of thePictured Cliffs has few joints at Basin Creek.However, the outcrop just north of the road, atstation BC01, has some of the largest J1 joints inthe area. The J1 joints there exceed 100 ft inlength and are irregularly spaced, from as closeas 6 inches to as wide as about 20 ft. The lengthof the J2 set also varies from 6 inches to 20 ft,depending on the spacing of the J1 set. J2 jointsare spaced 6-10 ft apart here. The joints aresomewhat sinuous, but extend across the entireoutcrop. No mineralization of either set wasnoted. This locality is good for examining jointsbecause it is a large, stripped dip slope at the topof the Pictured Cliffs.

In the entire Basin Creek area, the exposedlengths of J1 joints in the Pictured Cliffs varyfrom 1 ft to over 100 ft; spacing between joints isfrom 6 inches to 20 ft, and there is a wide rangeof sinuous to linear traces of joints across theoutcrops. No calcite fillings were seen in thePictured Cliffs, but iron-rich bands, or halos, arepresent along some joints. Exposed lengths of J2joints range from 6 inches to 20 ft, spacing varies

from 2-10 ft, and the joints are fairly planar. Nomineralization was noted in the J2 set either.

Face cleat orientations in all coal beds atBasin Creek average 358º, or N. 2º W. and buttcleats average 89º, or N. 88º E (fig. 2-8).Lengths of cleats could not be readily seen in thisarea because most of the coal beds are weatheredand have to be dug out to see the cleat pattern.Spacing of face cleats ranges from about ¼ inchto 6 inches, spacing of butt cleats is from ¼ inchto a maximum of about 2 inches. Most outcropsof coal have no mineral fillings in the cleats, buttraces of iron were seen at several locations, andthere is abundant iron mineralization of cleats atstation BC33.

For all sandstone beds of the FruitlandFormation at Basin Creek the average orientationof the J1 set is 358º, or N. 2º W. The averageorientation of the J2 set is 270º (fig. 2-8).Exposed lengths of J1 joints in Fruitlandsandstone beds are 1-20 ft, although the topsurfaces of these sandstone beds are rarelyexposed. Spacing is from 2 inches to about 24inches, and many joints in these sandstones areplanar and well-formed. Calcite fillings arecommon in joints in Fruitland sandstone beds, asare coatings of iron oxide. In general, well-cemented, relatively thin sandstones display agreater abundance and better-formed joints thanthick, poorly cemented sandstone beds. J2 jointsin these sandstones have exposed lengths of 1-6ft, are spaced 1-8 ft apart, and are also fairlylinear and planar. The J2 joints also displayfillings of calcite.


StatisticsBasin Creek, Kpc, J1 set

N = 53




Vector Mean = 331.8

Conf. Angle = 16.47

R Magnitude = 0.595

Rayleigh = 0.0000

StatisticsBasin Creek, Kpc, J2 set

N = 44




Vector Mean = 59.2

Conf. Angle = 18.50

R Magnitude = 0.583

Rayleigh = 0.0000

StatisticsBasin Creek, all coals, face cleat

N = 66




Vector Mean = 357.6

Conf. Angle = 5.27

R Magnitude = 0.927

Rayleigh = 0.0000

StatisticsBasin Creek, all coals, butt cleats

N = 66




Vector Mean = 88.8

Conf. Angle = 6.94

R Magnitude = 0.884

Rayleigh = 0.0000

StatisticsBasin Creek, Fruitland sandstones, J1 set

N = 90




Vector Mean = 358.5

Conf. Angle = 6.46

R Magnitude = 0.859

Rayleigh = 0.0000

StatisticsBasin Creek, Fruitland sandstones, J2 set

N = 68




Vector Mean = 270.2

Conf. Angle = 8.47

R Magnitude = 0.822

Rayleigh = 0.0000

Figure 2-8. Summary rose diagrams of joints and cleats in the Basin Creek area.


Carbon Junction

Figure 2-9 shows summary rose diagrams ofjoint and cleat orientations in the Pictured CliffsSandstone, Fruitland Formation coal beds, andFruitland sandstone beds.

In the Pictured Cliffs (including readingsfrom the tongue of Pictured Cliffs) the averageorientation of the J1 set is 77º, or N. 77º E. Theaverage orientation of the J2 set is 310º, or N.50º W, although there is quite a bit of scatter inthe readings obtained from the Pictured Cliffs inthis area. The scatter in these diagrams is aresult of combining the orientations measured atthe individual stations (CJ11, CJ13, CJ 24, CJ27,CJ03, and CJ19, appendix 2-2). Joints of the J1set in the main body of the Pictured Cliffs,measured in Carbon Junction Canyon, areclustered between N. 70º-80º E., whereas thosemeasured southwest of the canyon are orientedstrongly northwest, and those northeast of thecanyon are just a little east of north. J1 joints inthe tongue of Pictured Cliffs are also orientedstrongly northwest to east-west. These divergentdirections all are displayed on the summary roseplot (fig. 2-9). J2 joints are oriented nearly atright angles to those of the J1 set, and theirdivergent directions also are apparent in figure 2-9.

In this area the Pictured Cliffs main bodyand tongue generally lack good jointing, resultingin a small number of readings. Laubach andothers (1991) noted that the outcrop at CarbonJunction Canyon has few fractures, and thatmany of those are surficial. Station CJ11 is at alocality described by Laubach and others (1991)as a fracture “swarm”, where the joints aretightly clustered. Station CJ27 is another areawhere the joints are tightly clustered. Elsewhere,joints may be more a result of stress release or ofweathering.

The J1 joints range in length from 2 to about30 ft, except at station CJ27, where they are aslong as 60 ft or more. Spacing is from less than1 inch in the “swarms” to as much as 10 ft.Most of the J1 joints in this area in the PicturedCliffs are somewhat sinuous, not linear. Mostjoints had either no mineralization or slightamounts of iron coatings, except at station CJ24,where there are abundant iron coatings on jointsurfaces. The J2 joints are somewhat poorlydeveloped and range in length from 6 inches toabout 30 inches. They are spaced from 6 inchesto 15 ft apart. Most of them are also relativelysinuous and unmineralized.

More consistent results were obtained frommeasurements of coal cleats in the CarbonJunction area. The face cleats are tightlyclustered at an orientation of 340º, or N. 20º W.,and the butt cleats are oriented at 69º, or N. 69ºE. (fig. 2-9). In this area, as at the other areas,the total length of the cleats could not beobserved, due to cover. The spacing of facecleats ranges from ¼ inch to 3 inches; thespacing of butt cleats ranges from ¼ inch toabout 2½ inches. Many of the outcrops havefilms of iron oxide coating the cleat surfaces.

Joint orientations of sandstone beds in theFruitland Formation are also fairly tightlyclustered in this area. The average orientation ofJ1 joints is 351º, or N. 9º W.; that of the J2 set is85º, or N. 85º E. (fig. 2-9). A J3 set wasobserved at station CJ20, and the orientation ofthis set is about 296º, or N. 64º W. The J1 setranges from an exposed length of about 1 ft to 8ft and has spacing of from 2 to 36 inches. Theyare relatively well-formed and are planar andlinear in many outcrops. Mineral fillings of ironand calcite are present in many J1 joints inFruitland sandstone beds. The J2 set length isfrom 2 inches to 4 ft, spacing is from 6 inches to4 ft, and they are relatively abundant and well-formed in several outcrops. They also displayedfillings of iron and calcite.


StatisticsCarbon Junction, Kpc, J1 set

N = 52




Vector Mean = 77.7

Conf. Angle = 27.78

R Magnitude = 0.382

Rayleigh = 0.0005

StatisticsCarbon Junction, Kpc, J2 set

N = 33




Vector Mean = 309.5

Conf. Angle = 192.62

R Magnitude = 0.073

Rayleigh = 0.8371

StatisticsCarbon Junction, all coals, face cleats

N = 79




Vector Mean = 339.6

Conf. Angle = 2.54

R Magnitude = 0.982

Rayleigh = 0.0000

StatisticsCarbon Junction, all coals, butt cleats

N = 73




Vector Mean = 68.5

Conf. Angle = 3.75

R Magnitude = 0.961

Rayleigh = 0.0000

StatisticsCarbon Juncton, Fruitland sandstones, J1 set

N = 69




Vector Mean = 351.0

Conf. Angle = 3.86

R Magnitude = 0.959

Rayleigh = 0.0000

StatisticsCarbon Junction, Fruitland sandstones, J2 set

N = 46




Vector Mean = 85.0

Conf. Angle = 6.74

R Magnitude = 0.924

Rayleigh = 0.0000

Figure 2-9. Summary rose diagrams of joints and cleats in the Carbon Junction area.


Florida River

Summary rose diagrams of Pictured CliffsSandstone, Fruitland Formation coal, andFruitland sandstone beds in the Florida Riverarea are shown in figure 2-10. Joint and cleatorientations are fairly tightly clustered for allunits in this area. The average orientation for theJ1 set for the Pictured Cliffs is 337º, or N. 23ºW.; that for the J2 set is 64º, or N. 64º E. Theobserved lengths of J1 joints ranges from 1 to 10ft; spacing ranges from 2 inches to 15 ft. The J1joint set is linear and planar in many outcrops,but somewhat sinuous in others. Except for oneoutcrop at station FR38, which displays calcitecoatings, none of the J1 joint stations wereobserved to have mineral fillings.

The J2 joint set in the Pictured Cliffs ispoorly developed in this area; many of thestations had no J2 joint set. Of those observed,the length varies from about 2 ft to over 5 ft;spacing ranges from 2 inches to 3 ft. Bands ofiron, in a halo effect, are present adjacent to J2joints at station FR03, but no other associatedmineralization was noted.

Face cleats in coal in the Florida River areahave an average orientation of 329º, or N. 31º

W.; butt cleats have an average orientation of58º, or N. 58º E. Spacing of face cleats rangesfrom one-eighth inch to one inch; that of buttcleats ranges from one-eighth inch to one-halfinch. No mineral coatings are present on cleatsin most of the area; iron oxide is present atstations FR37 and FR40, near the Florida canal.

The average orientation of J1 joints inFruitland sandstone beds is 340º, or N. 20º W.;that of J2 joints is 67º, or N. 67º E. J1 joints arefrom 18 inches to in excess of 10 ft long; spacingranges from 2 inches to 10 ft. Most of the J1joints in Fruitland sandstone beds are well-developed, linear and planar. Many of the jointscut multiple beds of Fruitland sands. Ironcoatings were noted at a few stations, and calciteat one station, but many J1 joints do not havemineral coatings.

In contrast, the J2 joint set is poorlydeveloped in Fruitland sands in this area, similarto the situation with the Pictured CliffsSandstone. Where they do occur the J2 set isfrom 1 to 4 ft long, but are so scattered that areliable range of spacing could not bedetermined. Mineral fillings or coatings are alsorare, consisting of minor iron oxide or calcite.


StatisticsFlorida River, Kpc, J1 set

N = 71




Vector Mean = 337.4

Conf. Angle = 5.06

R Magnitude = 0.934

Rayleigh = 0.0000

StatisticsFlorida River, Kpc, J2 set

N = 22




Vector Mean = 63.6

Conf. Angle = 7.68

R Magnitude = 0.947

Rayleigh = 0.0000

StatisticsFlorida River, all coals, face cleats

N = 62




Vector Mean = 329.3

Conf. Angle = 4.08

R Magnitude = 0.957

Rayleigh = 0.0000

StatisticsFlorida River, all coals, butt cleats

N = 50




Vector Mean = 58.2

Conf. Angle = 6.87

R Magnitude = 0.914

Rayleigh = 0.0000

StatisticsFlorida River, Fruitland sandstones, J1 set

N = 55




Vector Mean = 339.9

Conf. Angle = 3.04

R Magnitude = 0.984

Rayleigh = 0.0000

StatisticsFlorida River, Fruitland sandstones, J2 set

N = 14




Vector Mean = 66.6

Conf. Angle = 16.37

R Magnitude = 0.860

Rayleigh = 0.0000

Figure 2-10. Summary rose diagrams of joints and cleats in the Florida River area.


South Fork of Texas Creek

Figure 2-11 shows summary rose diagramsof joint and cleat orientations of the mapped unitsat the South Fork of Texas Creek. In that areathe average orientation of J1 joints in the PicturedCliffs is 351º, or N. 9º W.; the averageorientation of J2 joints is 79º, or N. 79º E.Several areas exist at Texas Creek where astripped dip slope exposes large areas of the topof the Pictured Cliffs, allowing for a moreaccurate assessment of the lengths of joints.Observed lengths of J1 joints range from 20 ft toover 100 ft. J1 joints occur in closely spacedzones in some areas, but are more evenly spacedin other areas. Where tightly clustered, thespacing is less than 2 inches to 1 ft. Otherwise,spacing ranges up to 8 ft. In the good exposuresin this area the pattern of J1 joints is somewhatanastomosing, where one joint will die out intorock or hook into an adjacent joint. A cluster ofjoints will form a long, linear zone that consistsof curvilinear joints. In this area only iron oxidecoatings were seen on the J1 joints.

In this area, too, J2 joints are relativelypoorly expressed in the Pictured CliffsSandstone. Their length depends on the spacingof J1 joints, and is therefore quite variable.Spacing of J2 joints is 6 inches to over 5 ft, butaverages about 3-4 ft. In a few places J2 jointsare relatively well-formed, but in general they aredifficult to find. The only mineralization notedon J2 joints is iron oxide.

An interesting feature of the Texas Creekarea is the presence of a third joint set in thePictured Cliffs at some of the stations. Stationswhere this set was observed are TC04, TD01,TD02, TE01, AND TF01 (appendix 2-2).

Except for TF01, the stations are concentrated inthe central part of the mapped area. Theorientation of the J3 set is about 325º, or N. 35ºW. These joints terminate against the J1 and J2sets, and are therefore believed to be youngerthan either of those sets. A fourth set is alsorarely present that is at about right angles to theJ3 set. All four sets are well-expressed at stationTF01, just upslope from the Hobbs property,toward the eastern end of the mapped area. Thissite has an old road leading to it and is easilyaccessible.

Coal cleats in the Texas Creek area havemixed orientations, possibly due to slumping atsome outcrops. The face cleats average 338º, orN. 22º W., and the butt cleats average 68º, or N.68º E., with quite a bit of scatter. The majorityof face cleats are sub-parallel with J1 joints inthe Pictured Cliffs, and the butt cleats are sub-parallel to J2 joints of the Pictured Cliffs.Spacing of both face and butt cleats is one-eighthinch to one inch. No significant mineralizationwas noted on cleats in this area.

In sandstone beds of the FruitlandFormation, the average orientation of J1 joints is1º, or N. 1º E.; the average orientation of J2joints is 271º, or N. 89º W. Length of J1 joints isfrom 1 ft to 15 ft; spacing is about 2 inches to 2ft. As with other mapped areas, the joints inFruitland sandstone beds are well-formed, linear,and planar. Only minor iron oxide mineralizationwas noted on these joints. The J2 joint set variesfrom poorly expressed to common at differentlocalities at Texas Creek. They are commonlyshort, less than 2 ft, and have a spacing of about1-3 ft. Only minor iron oxide coatings werenoted on this set.


StatisticsTexas Creek, Kpc, J1 set

N = 91




Vector Mean = 351.2

Conf. Angle = 4.47

R Magnitude = 0.933

Rayleigh = 0.0000

StatisticsTexas Creek, Kpc, J2 set

N = 66




Vector Mean = 78.9

Conf. Angle = 6.65

R Magnitude = 0.890

Rayleigh = 0.0000

StatisticsTexas Creek, all coals, face cleats

N = 84




Vector Mean = 338.2

Conf. Angle = 19.11

R Magnitude = 0.431

Rayleigh = 0.0000

StatisticsTexas Creek, all coals, butt cleats

N = 77




Vector Mean = 67.6

Conf. Angle = 23.41

R Magnitude = 0.375

Rayleigh = 0.0000

StatisticsTexas Creek, Fruitland sandstones, J1 set

N = 134




Vector Mean = 0.6

Conf. Angle = 3.68

R Magnitude = 0.934

Rayleigh = 0.0000

StatisticsTexas Creek, Fruitland sandstones, J2 set

N = 98




Vector Mean = 270.7

Conf. Angle = 5.72

R Magnitude = 0.876

Rayleigh = 0.0000

Figure 2-11. Summary rose diagrams of joints and cleats in the Texas Creek area.


Pine River

Figure 2-12 shows the average orientationsof joints and cleats in the area between the SouthFork of Texas Creek and the Pine River. Thereis a bit of scatter in average orientations of thePictured Cliffs Sandstone, but J1 joints average5º, or N. 5º E.; J2 joints average 285º, or N. 75ºW. In this area the Pictured Cliffs ischaracterized by relatively few systematic joints.In many outcrops there is abundant surficialjointing, or spalling of blocks of sandstone. J1joints range in length from 10 to 20 ft. Spacingaverages from 6 inches to 10 ft, although there isclustering of joints in some areas where spacingis as close as 2 inches. The J1 set consists oflong, linear, and planar joints. Minor calcite andiron oxide was noted on some joint surfaces.

J2 joints in the Pictured Cliffs are poorlydeveloped. They range in length from 8 inches to5 ft and have spacing of 1-4 ft. Like the J1joints, mineralization is not a significant feature.

The average orientation of face cleats in coalhere is 325º, or N. 35º W.; butt cleat orientationsare 54º, or N. 54º E. Face cleats are spaced one-

eighth inch to 2 inches; butt cleats are spacedone-eighth inch to one inch. Iron oxide was notedat several localities coating both sets of cleats.

There is a good development of J1 joints inFruitland Formation sandstone beds in this area.The average orientation is 7º, or N. 7º E.; theaverage orientation of J2 joints is 279º, or N. 81ºW. The length of J1 joints ranges from less than1 ft to greater than 60 ft. An especially well-exposed dip slope of the number 2 sandstone ispresent at station PR12, where the longest jointsare present. This outcrop is probably typical ofsurface jointing in the Fruitland sandstone bedsin this and other areas. In most places thesesandstones are poorly exposed, making it likelyto underestimate the extent of jointing. Spacingof J1 joints in this area ranges from 1 to 18inches; iron oxide was noted at several localitiescoating the joint surfaces.

J2 joints are also fairly abundant in this areaand range from less than 1 ft to about 3 ft inlength. Spacing is 1 to 3 ft in most localities.Only minor iron oxide was noted on some J2joints; no calcite was seen on this or the J1 set.


StatisticsPine River, Kpc, J1 set

N = 48




Vector Mean = 4.8

Conf. Angle = 13.35

R Magnitude = 0.710

Rayleigh = 0.0000

StatisticsPine River, Kpc, J2 set

N = 12




Vector Mean = 284.9

Conf. Angle = 21.36

R Magnitude = 0.803

Rayleigh = 0.0004

StatisticsPine River, all coals, face cleats

N = 51




Vector Mean = 324.6

Conf. Angle = 10.07

R Magnitude = 0.812

Rayleigh = 0.0000

StatisticsPine River, all coals, butt cleats

N = 47




Vector Mean = 53.5

Conf. Angle = 11.40

R Magnitude = 0.780

Rayleigh = 0.0000

StatisticsPine River, Fruitland sandstones, J1 set

N = 86




Vector Mean = 6.7

Conf. Angle = 3.45

R Magnitude = 0.964

Rayleigh = 0.0000

StatisticsPine River, Fruitland sandstones, J2 set

N = 47




Vector Mean = 279.2

Conf. Angle = 6.69

R Magnitude = 0.916

Rayleigh = 0.0000

Figure 2-12. Summary rose diagrams of joints and cleats in the Pine River area.


Discussion of fractures

Orientations of joints and cleats varysomewhat over the entire study area, but thesevariations are less evident when the area as awhole is considered. Figure 2-7 shows that thereare regional similarities of joint orientations inthe various geologic units studied. However,each individual mapped area has its own identity,as shown in figures 2-8 through 2-12. Morespecific information about individual localities isshown in appendix 2-2.

In each area one main joint or cleat set canbe identified in each geologic unit. This set iscomposed of relatively long, commonly linearjoints, and in some instances joints of this setoccur in narrowly clustered zones. Joint fillingsor coatings consist of iron oxide or calcite, withiron and calcite being abundant at Basin Creek,moderately abundant at Carbon Junction, rare atthe Florida River, and relatively rare at TexasCreek and at the Pine River. No slickensidestriations were noted on any of the J1 or otherjoint sets in the study area. The joints areoriented perpendicular to bedding surfaces inmost instances, which may indicate that thejointing occurred prior to the rocks being upliftedinto their present configuration.

The lithology of the rock unit has animportant impact on the degree of fracturing thatoccurs. Coal is relatively brittle and breakseasily, resulting in the closely spaced face andbutt cleats. Sandstone beds of the FruitlandFormation are relatively thin and firmlycemented, which also promotes the developmentof joints. Thick, weakly cemented rocks,characteristic of the upper part of the PicturedCliffs Sandstone, are the least prone to developgood, systematic joint sets.

In some outcrops, a second joint set is alsopresent. This joint set is commonly at nearlyright angles to and terminates against the mainjoint set. This set is clearly secondary to themain set. This secondary set is also orientedperpendicular to bedding surfaces.

In a few outcrops a third or a fourth joint setwere also observed. These joints terminateagainst both the J1 and J2 joints, indicating that

they are younger than the other two sets.Although a cluster of these joints was found inthe Texas Creek area, they are generally rare inthe entire project area.

The joints and cleats in the study area sharecharacteristics of those in this and nearby areaspreviously described by myself (Condon, 1988,1989, 1995) and by others Close (1993), Closeand Mavor (1991), Laubach and others (1991),Tremain and Whitehead (1990), Tremain andothers (1991a, b).

Fundamental questions in fracture studiesinvolve the cause of fracturing, time offracturing, and predictions of fracture trends inthe subsurface. These topic are briefly discussedbelow.

Joints. Based on surface features and thelack of shear displacement, the joints along thenorthern rim of the basin were interpreted asmode I fractures (Laubach and others, 1991),otherwise known as opening mode or extensionfractures. In sandstones, this type of fracture isthought to initiate at inhomogeneities in the rock,such as fossils, clasts, voids, microcracks, orother features, which concentrate local tensilestresses in an overall compressive stress field(Pollard and Aydin, 1988). Opening modefractures form parallel to the maximumcompressive stress direction and perpendicular tothe least compressive stress direction (Lorenz andothers, 1991). Pore pressure also has beenrecognized as an important component in theformation of natural fractures by decreasing theeffective confining pressure of rocks in thesubsurface (Secor, 1965; Lorenz and others,1991).

The timing of fracture development insandstones of the Fruitland and Pictured Cliffs isnot very well constrained. Before fracturing canoccur the sediments must have been lithified tosome degree. The Pictured Cliffs and FruitlandFormation are Campanian to Maastrichtian inage (roughly 75 to 72 Ma) (Molenaar and Baird,1991). Lorenz (1995) suggested that the FrontierFormation in the Green River basin was lithifiedat a depth of approximately 3,000 ft. In the SanJuan Basin the Pictured Cliffs and Fruitland firstreached that depth of burial at about 60 millionyears ago in the Paleocene and reached a depth of


nearly 7,000 ft in the Miocene (Law, 1992). Acomplicating factor in the San Juan Basin iselevated thermal maturity caused by a thermalevent 40 to 20 m.y. ago, extending from the lateEocene to the early Miocene (Law, 1992).

Law and others (1989) suggested anendogenetic mechanism whereby thermogenic gasgeneration causes overpressuring that eventuallyleads to the creation of fractures in the enclosingrocks. Lorenz and others (1991), however,maintained that pore pressure cannot exceed theleast compressive stress and therefore cannotalone cause tensile fracturing. Differential stressis needed for the development of systematic jointsets.

The tectonic fabric of this part of thesouthwestern USA was established at about1,790 to 1,700 Ma in the Proterozoic duringaccretion of a series of crustal provinces (Condie,1992). Baars and Stevenson (1982) attributedthe orientation of major northwest- and northeast-oriented basement faults and lineaments to north-south compression that formed conjugate shearzones. Given that opening mode fractures formparallel to the maximum compressive stressdirection (Lorenz and others, 1991), it is notunreasonable to expect north-south-orientedfractures in basement rocks of the San JuanBasin. The northwest-northeast pattern ofbasement faults has also been interpreted fromseismic lines (Huffman and Taylor, 1989), andthe pattern of faulting was shown in Huffmanand Condon (1993). Although probably notpropagated upward through the geologic sectionas distinct features, the north-south-orientedfractures may have formed zones of weakness oranisotropy that affected fracture orientations inrocks deposited at later times.

The main compressional tectonic events thatoccurred during and after deposition of thePictured Cliffs Sandstone and FruitlandFormation were the Sevier and Laramideorogenies (Armstrong, 1968; Dickinson, 1978;Hamilton, 1987; Heller and others, 1986; Tweto,1975). Lorenz (1985) provided a concise historyof tectonic events in the nearby Piceance Creekbasin, on the other side of the Uncomphagreuplift, north of the San Juan Basin.

The Sevier thrust belt developed in responseto general east-west compression and crustalshortening along an Andean-type continentalmargin (Coney, 1978). Although much of thecompression was east-west, the configuration ofthe orogenic belt and adjacent foreland basinsuggests a significant southeastward componentto the compressive stress (Heller and others,1986). The effects of the Sevier orogeny arethought to have largely dissipated by about 72Ma, however (Lorenz, 1985), so the sandysediments of the Pictured Cliffs and Fruitlandwould not have been buried deeply enough tolithify and form fractures as a result of Sevier-related stress.

There has been much discussion regardingthe cause of the change in tectonic style betweenthe Sevier and Laramide orogenies and themechanisms for Laramide deformation, topicswhich are beyond the scope of this report.Whatever the causes, Laramide tectonism ischaracterized by basement-cored anticlinal upliftsthat are bounded by deep structural basins. East-west crustal shortening occurred from Montanato New Mexico in Late Cretaceous to late Eocenetime (roughly 75 to 40 Ma) (Coney, 1978;Hamilton, 1987; Lorenz, 1985). This structuralevent would seem to be the most likely to havecaused fracturing in the Pictured Cliffs andFruitland because (1) the units would have beenburied deep enough to have lithified and (2)initial gas generation could have increased thepore pressure to a point favorable for initiation offracturing. The problem with this scenario is thatthe orientations of the main joints in the units arenot parallel to the east-west-oriented stress, andare in fact, nearly perpendicular to it.

The generally north-south orientation of themain joints may be explained by the stressgenerated by the clockwise rotation of theColorado Plateau at this time (Hamilton, 1987)or by late Laramide north-south-orientedcompression (Gries, 1983). The rotation orcompression of the San Juan Basin resulted inconvergence of the basin with the Uncompahgreuplift to the north. The uplift may have acted asa buttress and the stress would have been roughlynorth-south, parallel to the fractures generated inProterozoic time (these directions refer to current


orientations). This collision of the basin with theUncompahgre uplift may also have led to thedevelopment of the reverse fault just west of thePine River (plate 5) and to thrust faults discussedby Huffman and Taylor (this report).

The time between the Laramide and thepresent has been characterized by extension,along with one period of intense volcanism in theOligocene and several periods of regional upliftand erosion (Coney, 1978; Lorenz, 1985).Transform movement along the westerncontinental boundary led to the relaxation of theeast-west Laramide stress, allowing for thepresent extensional mode of the Basin and Rangeprovince (Hamilton, 1987). This time periodseems to lack the necessary compression event orevents that could have caused initial fracturing inthe Pictured Cliffs and Fruitland Formation. TheJ2 and younger sets could possibly have formedduring this time as a result of unloading of theoverburden.

Cleats. Tremain and Whitehead (1990),Tremain and others (1991a, b), and Laubach andothers (1991) summarized the characteristics andorigin of coal cleats in the northern San JuanBasin, and my studies generally support theirconclusions. Important facts to note are that coalcleats are also mode I fractures that formedparallel to the principle compressive stress andperpendicular to the least compressive stress.Close (1993) emphasized that two mechanisms,or a combination of the two, have been proposedfor the formation of cleats. Endogeneticprocesses include dewatering and compaction,while exogenetic processes include paleotectonicor neotectonic responses to stress.

Law and others (1983) noted that peatcontains 80 to 90% water by volume, whichdecreases to about 7% in high-volatile Bbituminous and higher-rank coals. Much of thewater is expelled early in coalification,decreasing to about 20% by volume at thesubbituminous B rank. The mechanisms fordewatering are mainly physical compaction andthermal destruction of functional groups (Lawand others, 1983). Many coal beds in theFruitland are immediately overlain by channelsandstones which contributed to compaction.

The coals of the Fruitland were subjected tothe same stresses that produced joints insandstones, but cleat formation may haveoccurred earlier than the development of joints.Close and Mavor (1993) thought that lithificationof Fruitland coals may have occurred in as littleas 3.4 million years after deposition. Earlyformation of cleats has also been reported inPennsylvanian-age strata in Wales (Gayer andothers, 1996), where coal clasts were erodedfrom coals belonging to the same stage assediments in which the clasts were redeposited.Some of these clasts had already developed cleatas a result of extensional fracturing ofoverpressured coal in response to compression.Another example of early formation of cleats wasreported by Pattison and others (1996). Basedon age dates from mineral fillings in cleats,Pattison and others (1996) interpreted the cleatsto have formed less than 10 Ma after peataccumulation. Cleats were interpreted to haveformed parallel to the maximum horizontalstress.

On the basis of these other studies, it seemslikely that cleats in the Fruitland formedrelatively soon after deposition, possibly as aresult of southeastward-directed compressionfrom the Sevier thrust belt to the west. As withthe joints in sandstone, the possibility exists thatbasement fractures or faults had some influenceon the orientation of stress in the coals of theFruitland.

Fracture trends in the subsurface.Determining joint and cleat trends in thesubsurface is complex and involves manyuncertainties (Grout and Verbeek, 1985; Lorenz,1995; Verbeek and Grout, 1984). Techniquessuch as drilling oriented core and pressure testsbetween nearby wells are of use in limited areas,but cannot usually be extended over a large area.Well log analysis (Johnston and Scholes, 1991;Mullen, 1991) may also be of use in some areas.

Advances in understanding the origin ofjoints and cleats (Lorenz and others, 1991),however, suggest that joint orientations may beconsistent over fairly large areas, so surfacestudies of joints can be of use in predictingsubsurface orientations (Lorenz and Finley,1991). Cleat domain studies (Kulander and


Dean, 1993; Tremain and others, 1991b)indicated that large areas having similar cleatorientations exist, but that there may be overlapof domains and that domains can changeabruptly, depending on local structure.

Even given the uncertainties, it seems likelyto me that the largest, oldest joints in sandstonesof the Pictured Cliffs and Fruitland in thesubsurface of the northern San Juan Basin areoriented north-south and north-northwest tosouth-southeast. I would expect that face cleatsin coal would have a dominantly north-northwestto south-southeast orientation in the subsurface.Within that context, there seem to be a slightclockwise rotation of the joints in sandstone inthe Texas Creek and Pine River areas (figs. 2-6and 2-7).

Summary

1. Joints and cleats in the Pictured CliffsSandstone and Fruitland Formation are openingmode fractures.

2. The main joints in the Pictured CliffsSandstone are oriented N. 14º W. over the wholeproject area, and an orthogonal set trends N. 74ºE. There appears to be clockwise rotation of thesets from west to east across the study area.

3. The main joints in sandstones of the FruitlandFormation are oriented N. 3º W. on average, andan orthogonal set trends East-West. There isalso clockwise rotation of these sets from west toeast across the area.

4. Face cleats in all coals of the FruitlandFormation are at an average orientation of N. 21ºW.; butt cleats are oriented N. 69º E.

5. The most likely time of jointing of PicturedCliffs and Fruitland sandstones was during north-south-oriented Laramide deformation when theSan Juan Basin rotated clockwise into theUncompahgre uplift. Joint trends may have beeninfluenced by previously formed zones ofweakness in basement rocks.

6. The most likely time of cleat formation was inthe Late Cretaceous, probably during or shortlyafter coalification, and in response todeformation in the Sevier thrust belt.

7. Joint and cleat orientations measured at theoutcrop probably extend some distance south intothe subsurface. Differences do exist betweendifferent studied areas of the outcrop, however,so each area must be considered individually.


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Pattison, C.I., Fielding, C.R., McWatters, R.H.,and Hamilton, L.H., 1996, Nature andorigin of fractures in Permian coals fromthe Bowen Basin, Queensland, Australia,in Gayer, R.A., and Harris, I., eds.,Coalbed methane and coal geology:London, The Geological Society, SpecialPublication No. 109, p. 133-150.

Pollard, D.D., and Aydin, Atilla, 1988, Progressin understanding jointing over the pastcentury: Geological Society of AmericaBulletin, v. 100, p. 1181-1204.

Roberts, L.N.R., and McCabe, P.J., 1992, Peataccumulation in coastal-plain mires: amodel for coals of the FruitlandFormation (Upper Cretaceous) ofsouthern Colorado, USA: InternationalJournal of Coal Geology, v. 21, p. 115-138.

Schwochow, S.D., ed., 1991, Coalbed methaneof western North America: RockyMountain Association of Geologists,guidebook, 1991, 336 p.

Secor, D.T., Jr., 1965, Role of fluid pressure injointing: American Journal of Science,v. 263, p. 633-646.

Tremain, C.M. and Whitehead, N.H., III, 1990,Natural fracture (cleat and joint)characteristics and patterns in UpperCretaceous and Tertiary rocks of the SanJuan Basin, New Mexico and Colorado,in Ayers, W.B., Jr., and others, Geologicevaluation of critical productionparameters for coalbed methaneresources, part 1, San Juan Basin:Chicago, Gas Research Institute, GRI-90/0014.1, p. 73-98.

Tremain, C.M., Laubach, S.E., and N.H.Whitehead III, 1991a, Coal fracture(cleat) patterns in Upper CretaceousFruitland Formation, San Juan Basin,Colorado and New Mexico: Implicationsfor coalbed methane exploration anddevelopment, in Ayers, W.B., Jr., andothers, Geologic and hydrologic controlson the occurrence and producibility ofcoalbed methane, Fruitland Formation,San Juan Basin: Chicago, Gas ResearchInstitute, GRI-91/0072, p. 97-117.

Tremain, C.M., Laubach, S.E., and N.H.Whitehead III, 1991b, Coal fracture(cleat) patterns in Upper CretaceousFruitland Formation, San Juan Basin,Colorado and New Mexico—implications for coalbed methaneexploration and development, inSchwochow, S.D., ed., Coalbed methane


of western North America: RockyMountain Association of Geologists,1991 guidebook, p. 49-59.

Tweto, O.L., 1975, Laramide (Late Cretaceous-Early Tertiary) orogeny in the SouthernRocky Mountains, in Curtis, B.F., ed.,Cenozoic history of the Southern RockyMountains: Geological Society ofAmerica Memoir 144, p. 1-44.

Verbeek, E.R., and Grout, M.A., 1984,Prediction of subsurface fracturepatterns from surface studies of joints—an example from the Piceance Creek

Basin, Colorado, in Spencer, C.W., andKeighin, C.W., eds., Geologic studies insupport of the U.S. Department ofEnergy's Multiwell Experiment: U.S.Geological Survey Open-File Report 84-757, p. 75-86.

Zapp, A.D., 1949, Geology and coal resources ofthe Durango area, La Plata andMontezuma Counties, Colorado: U.S.Geological Survey Oil and GasInvestigations Preliminary Map 109.


APPENDIX 2-1.

Composite Stratigraphic Section of the Fruitland Formation in the Texas Creek Area(Described by S.M. Condon and R.C. Milici)

Kirtland Shale Kk Sandstone and mudstone thickness not measured

Leaf beds Mudstone, some slightly silty, carbonaceous, light olive gray to olivegray; with abundant impressions of leaves and other plant fossils, slightlyrooted, with muscovite flakes; some beds massive, jointed; with interbedsof silty, yellowish gray to dusky yellow sandstone; irregularly bedded,hackly weathering, with abundant muscovite flakes and finelydisseminated carbonaceous material, rooted; 10 feet exposed

Sandstone Sandstone, very fine grained, clay rich, with interstitial kaolinite(?),limonite, grayish orange to yellowish gray, with rip-up clasts of olive-graymudstone, impressions of plants; bedding is massive to tabular; three feetmeasured; minimum thickness estimated to be about 25 feet

Fruitland Formation total thickness about 350 feet

Upper part Kfu Mudstone, slightly silty, pale yellowish brown, with finely disseminatedcarbonaceous material; 8-10 feet thickShale, carbonaceous, medium-dark gray; 2-3 feet thickCoal, weathered; 2-3 feet thickShale, carbonaceous, medium dark to dark gray; 1-2 feet thickMudstone, olive gray; 3 feet thickSandstone, very fine grained, and very slightly calcareous siltstone, withfinely disseminated carbonaceous material and muscovite flakes;irregularly bedded, beds 6 to 8 inches thick; with septaria of dolomiticlimestone up to 2 feet across in upper part; with plant fossils; 5 feet thickMudstone, olive gray, and dark-gray carbonaceous shale, with leafimpressions; 5 feet thickSandstone, very fine grained, argillaceous, very slightly calcareous, withmuscovite flakes, finely disseminated carbonaceous material; irregularlybedded, weathers grayish orange; 2 feet thickMudstone, light gray to olive gray; 45 feet thick

No. 4 sandstone Kf4 Sandstone, very fine to fine grained, well sorted, with white interstitialminerals, black accessory minerals, carbonaceous material on beddingsurfaces; weathers yellowish gray, grayish yellow; beds generally rangefrom 1 to 10 inches thick; basal bed is about 5 feet thick; some beds withabundant leaf impressions, twigs, sticks; few beds with abundantinvertebrate fossils, including gastropods and pelecypods; estimatedthickness about 35 feet


No. 3 sandstone Kf3 Sandstone, fine grained, light olive gray, weathers grayish red to darkreddish brown; well sorted, subangular to subrounded; moderatelycalcareous, argillaceous, with black accessory minerals, feldspathic, withabundant interstitial limonite; contains yellowish-orange septarianconcretions; bedding up to 18 inches thick, massive and cross-bedded nearbase, ripple bedded at top, with some slumped, contorted bedding;minimum thickness about 50 feet

d coal zone Kcd Occurs at top of No. 2 sandstone; 2-4 feet thickSkeleton bed Not mapped separately; occurs between c and d coal zones; outcrops

consist of lenticular masses of septarian limestone up to 10 feet long, 2 to3 feet across, and one or two feet thick; exhibits radial and concentricfracture patterns; septae are filled with white calcite crystals and anotherdark brown carbonate minerals; limestone consists of light-olive graydolomitic micrite; weathers dark yellowish orange

c coal zone Kcd Overlies No. 2 sandstone; 3-4 feet thick

No. 2 sandstone Kf2 Sandstone, very fine grained, well sorted, grayish red, with finelydisseminated hematite, very slightly calcareous; basal unit cross bedded,with scour base; tightly cemented, with quartz overgrowths; overlain byfine-grained, light-to medium-gray, irregularly bedded sandstone, rippledat base, horizontally laminated at top; bedding up to one foot thick; withwoody debris, plant fragments, fossil pelecypods; thickness estimated tobe up to 100 feet

ab coal zone Kfab Coal; occurs where No. 1 sandstone thins to a parting and the two coalzones combine into one; thickness, including partings, about 50 feet

b coal zone b Coal; thickness about 20-25 feet

No. 1 sandstone Kf1 Sandstone, upper beds are very fine grained, very well sorted, slightlycalcareous, well cemented with quartz overgrowths; light brownish gray tolight olive gray; bedding about 1 inch to 1 foot thick, some rippled, someburrowed, with clay chips; basal unit consists of 6 inches of irregularlybedded, carbonaceous, argillaceous to silty, fine- to medium-grainedsandstone that is overlain by 3 feet of medium-gray mudrock; No. 1sandstone thins to east; estimated thickness up to 25 feet

a coal zone a Coal; estimated thickness 15-20 feet, including partings

Pictured CliffsSandstone Kpc Sandstone, fine grained, very light to light gray, medium to thick bedded,

irregularly bedded, with abundant Ophiomorpha in upper part; dividedinto two main units; the lower is massively bedded, the upper is thinnerbedded; in general, bedding is uneven and wavy, some is massive or crossbedded; top is marked by grayish-black rooted sandstone; sandstone dikesthat are locally several inches thick occur in places in the upper beds ofthe unit; thickness not measured.


APPENDIX 2-2. ROSE DIAGRAMS AT INDIVIDUAL FRACTURE

STATIONS.

Tables 2-7 through 2-11 show a breakdown of which geologic unit each joint or cleat station wasrecorded in. Rose diagrams of the individual stations are also grouped by geologic unit.

Table 2-7. Joint and cleat stations established in the Basin Creek study area, grouped bygeologic unit. Station locations are shown on plate 1.Kpc Kft Kpct Kflc Kfls Kfmc Kfms Kfuc KfusBC01 BC03 BC05 BC02 BC11 BC33 BC10 BC15 BC16BC04 BC08 BC06 BC18 BC12 BC17 BC25BC21 BC09 BC07 BC23 BC14 BC28 BC26

BC31 BC13 BC45 BC27 BC30 BC29BC46 BC19 BC32 BC35 BC36

BC20 BC34 BC37 BC38BC22 BC44 BC39 BC40BC24 BC42 BC41

BC47 BC43Kpc - Pictured Cliffs Sandstone, main body; Kft - coal below tongue of Pictured Cliffs; Kpct - tongue ofPictured Cliffs Sandstone; Kflc - coal in lower part of Fruitland Formation; Kfls - sandstone in lower part ofFruitland; Kfmc - coal in middle part of Fruitland Formation; Kfms - sandstone in middle part of Fruitland;Kfuc - coal in upper part of Fruitland; Kfus - sandstone in upper part of Fruitland.

Pictured Cliffs Sandstone, main body:

StatisticsBC01

N = 22




Vector Mean = 284.4


R Magnitude = 0.082

Rayleigh = 0.8635

StatisticsBC04

N = 8




Vector Mean = 20.1


R Magnitude = 0.060

Rayleigh = 0.9715


StatisticsBC21

N = 10




Vector Mean = 305.9


R Magnitude = 0.124

Rayleigh = 0.8570

Coal below tongue of Pictured Cliffs Sandstone:

StatisticsBC03

N = 10




Vector Mean = 310.8


R Magnitude = 0.104

Rayleigh = 0.8978


Pictured Cliffs Sandstone, tongue:

StatisticsBC05

N = 18




Vector Mean = 347.7


R Magnitude = 0.096

Rayleigh = 0.8467

StatisticsBC08

N = 15




Vector Mean = 356.8


R Magnitude = 0.084

Rayleigh = 0.8990

StatisticsBC09

N = 16




Vector Mean = 17.6


R Magnitude = 0.121

Rayleigh = 0.7898

StatisticsBC31

N = 5




Vector Mean = 350.4

Conf. Angle = 52.68

R Magnitude = 0.600

Rayleigh = 0.1657

StatisticsBC46

N = 14




Vector Mean = 337.2

Conf. Angle = 71.98

R Magnitude = 0.287

Rayleigh = 0.3162


Fruitland Formation, coal in lower part:

StatisticsBC02

N = 10




Vector Mean = 29.3


R Magnitude = 0.063

Rayleigh = 0.9611

StatisticsBC06

N = 8




Vector Mean = 318.7


R Magnitude = 0.104

Rayleigh = 0.9174

StatisticsBC07

N = 10




Vector Mean = 320.8

Conf. Angle = INF

R Magnitude = 0.004

Rayleigh = 0.9999

StatisticsBC13

N = 8




Vector Mean = 55.5


R Magnitude = 0.115

Rayleigh = 0.8996


StatisticsBC19

N = 9




Vector Mean = 348.3


R Magnitude = 0.116

Rayleigh = 0.8855

StatisticsBC20

N = 8




Vector Mean = 311.9


R Magnitude = 0.168

Rayleigh = 0.7971

StatisticsBC22

N = 8




Vector Mean = 31.9


R Magnitude = 0.035

Rayleigh = 0.9904

StatisticsBC24

N = 8




Vector Mean = 40.4


R Magnitude = 0.134

Rayleigh = 0.8666


Fruitland Formation, sandstone in lower part:

StatisticsBC11

N = 5




Vector Mean = 1.1


R Magnitude = 0.229

Rayleigh = 0.7697

StatisticsBC18

N = 6




Vector Mean = 324.6


R Magnitude = 0.018

Rayleigh = 0.9980

StatisticsBC23

N = 10




Vector Mean = 75.3


R Magnitude = 0.143

Rayleigh = 0.8145

StatisticsBC45

N = 4




Vector Mean = 46.5


R Magnitude = 0.017

Rayleigh = 0.9988

Fruitland Formation, coal in middle part:

StatisticsBC33

N = 4




Vector Mean = 316.5


R Magnitude = 0.061

Rayleigh = 0.9853


Fruitland Formation , sandstone in middle part:

StatisticsBC10

N = 18




Vector Mean = 322.9


R Magnitude = 0.025

Rayleigh = 0.9884

StatisticsBC12

N = 6




Vector Mean = 353.0

Conf. Angle = 95.99

R Magnitude = 0.326

Rayleigh = 0.5284

StatisticsBC14

N = 10




Vector Mean = 341.5


R Magnitude = 0.234

Rayleigh = 0.5782

StatisticsBC27

N = 7




Vector Mean = 13.9


R Magnitude = 0.165

Rayleigh = 0.8274


StatisticsBC32

N = 10




Vector Mean = 357.1


R Magnitude = 0.219

Rayleigh = 0.6181

StatisticsBC34

N = 8




Vector Mean = 34.7


R Magnitude = 0.207

Rayleigh = 0.7105

StatisticsBC44

N = 8




Vector Mean = 358.9


R Magnitude = 0.257

Rayleigh = 0.5903


Fruitland Formation, coal in upper part:

StatisticsBC15

N = 10




Vector Mean = 314.0


R Magnitude = 0.215

Rayleigh = 0.6307

StatisticsBC17

N = 5




Vector Mean = 11.0


R Magnitude = 0.203

Rayleigh = 0.8139

StatisticsBC28

N = 8




Vector Mean = 312.6


R Magnitude = 0.176

Rayleigh = 0.7795

StatisticsBC30

N = 4




Vector Mean = 333.0


R Magnitude = 0.199

Rayleigh = 0.8536

StatisticsBC35

N = 4




Vector Mean = 45.3


R Magnitude = 0.052

Rayleigh = 0.9892

StatisticsBC37

N = 6




Vector Mean = 328.5


R Magnitude = 0.018

Rayleigh = 0.9981


StatisticsBC39

N = 8




Vector Mean = 308.8


R Magnitude = 0.065

Rayleigh = 0.9670

StatisticsBC42

N = 4




Vector Mean = 65.5


R Magnitude = 0.009

Rayleigh = 0.9997

StatisticsBC47

N = 8




Vector Mean = 38.2


R Magnitude = 0.164

Rayleigh = 0.8068


Fruitland Formation, sandstone in upper part:

StatisticsBC16

N = 10




Vector Mean = 324.3


R Magnitude = 0.087

Rayleigh = 0.9264

StatisticsBC25

N = 5




Vector Mean = 11.2


R Magnitude = 0.195

Rayleigh = 0.8261

StatisticsBC26

N = 10




Vector Mean = 345.6

Conf. Angle = 56.95

R Magnitude = 0.419

Rayleigh = 0.1722

StatisticsBC29

N = 6




Vector Mean = 354.0

Conf. Angle = 97.85

R Magnitude = 0.325

Rayleigh = 0.5310

StatisticsBC36

N = 7




Vector Mean = 340.8


R Magnitude = 0.216

Rayleigh = 0.7217

StatisticsBC38

N = 6




Vector Mean = 51.6


R Magnitude = 0.130

Rayleigh = 0.9031


StatisticsBC40

N = 6




Vector Mean = 338.5

Conf. Angle = 83.97

R Magnitude = 0.374

Rayleigh = 0.4323

StatisticsBC41

N = 8




Vector Mean = 348.6


R Magnitude = 0.006

Rayleigh = 0.9997

StatisticsBC43

N = 8




Vector Mean = 1.1

Conf. Angle = 98.55

R Magnitude = 0.278

Rayleigh = 0.5385


Table 2-8. Joint and cleat stations established in the Carbon Junction study area, grouped bygeologic unit. Station locations are shown on plate 2.Kpc Kft Kpct Kflc Kfls Kfmc Kfms Kfuc KfusCJ11 CJ02 CJ03 CJ01 CJ14 CJ06 CJ05 CJ07 CJ08CJ13 CJ26 CJ19 CJ04 CJ20 CJ22 CJ15 CJ09 CJ10CJ24 CJ12 CJ16 CJ17 CJ23CJ27 CJ25 CJ18

CJ21Kpc - Pictured Cliffs Sandstone, main body; Kft - coal below tongue of Pictured Cliffs; Kpct - tongue ofPictured Cliffs Sandstone; Kfcl - coal in lower part of Fruitland Formation; Kfls - sandstone in lower part ofFruitland; Kfmc - coal in middle part of Fruitland Formation; Kfms - sandstone in middle part of Fruitland;Kfuc - coal in upper part of Fruitland; Kfus - sandstone in upper part of Fruitland. Note that stations CJ26and CJ27 are not shown on the map because they are located in or near the Ewing Mesa gravel pit,outside the map boundary.


StatisticsCJ11

N = 15




Vector Mean = 72.8

Conf. Angle = 58.82

R Magnitude = 0.336

Rayleigh = 0.1842

StatisticsCJ13

N = 8




Vector Mean = 72.5

Conf. Angle = 53.14

R Magnitude = 0.495

Rayleigh = 0.1411

StatisticsCJ24

N = 12




Vector Mean = 337.0


R Magnitude = 0.078

Rayleigh = 0.9294

StatisticsAF11

N = 30




Vector Mean = 65.9


R Magnitude = 0.087

Rayleigh = 0.7955

Note: Station AF11 renamed CJ27.


Coal below tongue of Pictured Cliffs Sandstone:

StatisticsCJ02

N = 12




Vector Mean = 24.6


R Magnitude = 0.041

Rayleigh = 0.9804

StatisticsAF09

N = 30




Vector Mean = 304.4


R Magnitude = 0.040

Rayleigh = 0.9528



StatisticsCJ03

N = 10




Vector Mean = 89.3

Conf. Angle = 59.76

R Magnitude = 0.404

Rayleigh = 0.1955

StatisticsCJ19

N = 10




Vector Mean = 272.9

Conf. Angle = 37.13

R Magnitude = 0.604

Rayleigh = 0.0261


Fruitland Formation, coal in lower part:

StatisticsCJ01

N = 16




Vector Mean = 316.5


R Magnitude = 0.032

Rayleigh = 0.9838

StatisticsCJ04

N = 6




Vector Mean = 284.6


R Magnitude = 0.007

Rayleigh = 0.9997

StatisticsCJ12

N = 12




Vector Mean = 23.7


R Magnitude = 0.043

Rayleigh = 0.9776

StatisticsAF07

N = 30




Vector Mean = 19.8


R Magnitude = 0.098

Rayleigh = 0.7489


Fruitland Formation, sandstone in lower part:

StatisticsCJ14

N = 15




Vector Mean = 3.5


R Magnitude = 0.204

Rayleigh = 0.5365

StatisticsCJ20

N = 18




Vector Mean = 332.2

Conf. Angle = 48.99

R Magnitude = 0.366

Rayleigh = 0.0895


Fruitland Formation, coal in middle part:

StatisticsCJ06

N = 11




Vector Mean = 341.8


R Magnitude = 0.109

Rayleigh = 0.8781

StatisticsCJ22

N = 8




Vector Mean = 21.9


R Magnitude = 0.039

Rayleigh = 0.9878


Fruitland Formation, sandstone in middle part:

StatisticsCJ05

N = 12




Vector Mean = 29.8


R Magnitude = 0.035

Rayleigh = 0.9855

StatisticsCJ15

N = 13




Vector Mean = 343.6

Conf. Angle = 54.46

R Magnitude = 0.386

Rayleigh = 0.1446

StatisticsCJ16

N = 9




Vector Mean = 335.8

Conf. Angle = 40.19

R Magnitude = 0.588

Rayleigh = 0.0445

StatisticsCJ18

N = 13




Vector Mean = 77.1


R Magnitude = 0.054

Rayleigh = 0.9629

StatisticsCJ21

N = 2




Vector Mean = 16.0


R Magnitude = 0.208

Rayleigh = 0.9172


Fruitland Formation, coal in upper part:

StatisticsCJ07

N = 8




Vector Mean = 333.5


R Magnitude = 0.251

Rayleigh = 0.6030

StatisticsCJ09

N = 9




Vector Mean = 343.0


R Magnitude = 0.111

Rayleigh = 0.8953

StatisticsCJ17

N = 10




Vector Mean = 342.7


R Magnitude = 0.208

Rayleigh = 0.6480


Fruitland Formation, sandstone in upper part:

StatisticsCJ08

N = 13




Vector Mean = 295.4


R Magnitude = 0.090

Rayleigh = 0.9001

StatisticsCJ10

N = 18




Vector Mean = 335.5

Conf. Angle = 60.58

R Magnitude = 0.303

Rayleigh = 0.1907

StatisticsCJ23

N = 9




Vector Mean = 334.6


R Magnitude = 0.136

Rayleigh = 0.8467


Table 2-9. Joint and cleat stations established in the Florida River area, grouped by geologicunit. Station locations are shown on plate 4.Kpc Kftc Kfts Kpct Kfab Kf1 Kf2 Kf3c Kf3s KfucFR01 FR04 FR30 FR11 FR12 FR10 FR19 FR37 FR20 FR21FR02 FR06 FR14 FR13 FR17 FR31 FR40 FR23 FR22FR03 FR09 FR15 FR16 FR35 FR24FR05 FR25 FR26 FR18 FR36 FR32FR07 FR29 FR33 FR27FR08 FR39 FR34FR28FR38Kpc - Pictured Cliffs Sandstone, main body; Kftc - Fruitland Formation, tongue, coal; Kfts - FruitlandFormation, tongue, sandstone; Kpct - Pictured Cliffs Sandstone, tongue; Kfab - Fruitland Formation,lower coal interval; Kf1 - Fruitland Formation sandstone number 1; Kf2 - Fruitland Formation sandstonenumber 2; Kf3c - Fruitland Formation, coal below sandstone number 3; Kf3s - Fruitland Formationsandstone number 3; Kfuc - Fruitland Formation, upper interval coal.


StatisticsFR01

N = 7




Vector Mean = 358.6

Conf. Angle = 38.29

R Magnitude = 0.667

Rayleigh = 0.0443

StatisticsFR02

N = 8




Vector Mean = 339.5

Conf. Angle = 52.12

R Magnitude = 0.501

Rayleigh = 0.1347

StatisticsFR03

N = 16




Vector Mean = 327.1

Conf. Angle = 37.92

R Magnitude = 0.486

Rayleigh = 0.0229

StatisticsFR05

N = 7




Vector Mean = 356.0


R Magnitude = 0.168

Rayleigh = 0.8201


StatisticsFR07

N = 4




Vector Mean = 342.3

Conf. Angle = 7.97

R Magnitude = 0.989

Rayleigh = 0.0200

StatisticsFR08

N = 7




Vector Mean = 334.6

Conf. Angle = 6.00

R Magnitude = 0.995

Rayleigh = 0.0010

StatisticsFR28

N = 4




Vector Mean = 283.1


R Magnitude = 0.155

Rayleigh = 0.9081

StatisticsFR38

N = 9




Vector Mean = 352.8

Conf. Angle = 55.56

R Magnitude = 0.449

Rayleigh = 0.1624

Coal in tongue of Fruitland Formation:

StatisticsFR04

N = 6




Vector Mean = 335.2

Conf. Angle = 86.59

R Magnitude = 0.363

Rayleigh = 0.4536

StatisticsFR06

N = 8




Vector Mean = 20.0


R Magnitude = 0.044

Rayleigh = 0.9849


StatisticsFR09

N = 5




Vector Mean = 333.1


R Magnitude = 0.196

Rayleigh = 0.8254

StatisticsFR25

N = 4




Vector Mean = 323.0

Conf. Angle = 55.12

R Magnitude = 0.631

Rayleigh = 0.2037

StatisticsFR29

N = 7




Vector Mean = 354.8


R Magnitude = 0.232

Rayleigh = 0.6869

Sandstone in tongue of Fruitland Formation:

StatisticsFR30

N = 5




Vector Mean = 339.6

Conf. Angle = 7.13

R Magnitude = 0.987

Rayleigh = 0.0076



StatisticsFR11

N = 6




Vector Mean = 328.3

Conf. Angle = 42.21

R Magnitude = 0.659

Rayleigh = 0.0737

StatisticsFR14

N = 4




Vector Mean = 343.5

Conf. Angle = 73.80

R Magnitude = 0.499

Rayleigh = 0.3689

StatisticsFR15

N = 5




Vector Mean = 331.2

Conf. Angle = 10.12

R Magnitude = 0.975

Rayleigh = 0.0086

StatisticsFR26

N = 5




Vector Mean = 348.4

Conf. Angle = 10.08

R Magnitude = 0.983

Rayleigh = 0.0080

StatisticsFR33

N = 6




Vector Mean = 332.8


R Magnitude = 0.310

Rayleigh = 0.5628

StatisticsFR39

N = 5




Vector Mean = 63.9


R Magnitude = 0.197

Rayleigh = 0.8244


Fruitland Formation, lower coal interval:

StatisticsFR12

N = 8




Vector Mean = 285.8


R Magnitude = 0.013

Rayleigh = 0.9986

StatisticsFR13

N = 8




Vector Mean = 5.4


R Magnitude = 0.100

Rayleigh = 0.9238

StatisticsFR16

N = 8




Vector Mean = 19.9


R Magnitude = 0.100

Rayleigh = 0.9232

StatisticsFR18

N = 8




Vector Mean = 18.0


R Magnitude = 0.043

Rayleigh = 0.9850

StatisticsFR27

N = 10




Vector Mean = 329.9


R Magnitude = 0.194

Rayleigh = 0.6855

StatisticsFR34

N = 6




Vector Mean = 317.1

Conf. Angle = 89.42

R Magnitude = 0.352

Rayleigh = 0.4764


Fruitland Formation, sandstone No. 1:

StatisticsFR10

N = 9




Vector Mean = 340.7

Conf. Angle = 77.85

R Magnitude = 0.330

Rayleigh = 0.3743

StatisticsFR17

N = 6




Vector Mean = 338.8

Conf. Angle = 41.31

R Magnitude = 0.669

Rayleigh = 0.0683


StatisticsFR19

N = 5




Vector Mean = 342.6

Conf. Angle = 7.11

R Magnitude = 0.993

Rayleigh = 0.0072

StatisticsFR31

N = 6




Vector Mean = 350.1

Conf. Angle = 42.17

R Magnitude = 0.660

Rayleigh = 0.0730

StatisticsFR35

N = 5




Vector Mean = 323.0


R Magnitude = 0.220

Rayleigh = 0.7855

StatisticsFR36

N = 8




Vector Mean = 344.9

Conf. Angle = 51.14

R Magnitude = 0.506

Rayleigh = 0.1288


Fruitland Formation, coal below sandstone No. 3:

StatisticsFR37

N = 8




Vector Mean = 15.2


R Magnitude = 0.236

Rayleigh = 0.6402

StatisticsFR40

N = 10




Vector Mean = 337.6


R Magnitude = 0.220

Rayleigh = 0.6152


StatisticsFR20

N = 7




Vector Mean = 340.4

Conf. Angle = 34.92

R Magnitude = 0.711

Rayleigh = 0.0289

StatisticsFR23

N = 6




Vector Mean = 343.5

Conf. Angle = 42.97

R Magnitude = 0.654

Rayleigh = 0.0765

StatisticsFR24

N = 6




Vector Mean = 335.3

Conf. Angle = 6.51

R Magnitude = 0.988

Rayleigh = 0.0029

StatisticsFR32

N = 6




Vector Mean = 338.5

Conf. Angle = 95.29

R Magnitude = 0.331

Rayleigh = 0.5185


Fruitland Formation, upper interval coal:

StatisticsFR21

N = 8




Vector Mean = 291.1


R Magnitude = 0.061

Rayleigh = 0.9710

StatisticsFR22

N = 8




Vector Mean = 294.9

Conf. Angle = 73.10

R Magnitude = 0.370

Rayleigh = 0.3344


Table 2-10. Joint and cleat stations established in the South Fork of Texas Creek area, groupedby geologic unit. Stations marked with an asterisk (*) provided data from more than onegeologic unit. No orientations were recorded at stations TA06, TA07, TA09, and TB06. Stationlocations are shown on plate 6.

Kpc a coal Kf1 b coal Kf2 c coal Kf3 Kf4 Kfu KirtlandShale

TA04* TA01 TC03* TA11 TA03 TC06* TA08 TC07 TB07 TB03TA05 TA02 TC03* TD02* TD04 TB01 TD05 TB08 TC08TA10 TA04* TF03 TE04 TC05 TE05 TE07 TD07TB02 TB04* TG02 TE06 TC06*TB04* TB05* TI01 TF04 TD06TB05* TC01 TJ01 TJ03 TI02TC02 TD02*TC03* TD03TC04 TE02TD01 TF02TD02* TG01TE01 TJ02TE03TF01TH01Kpc - Pictured Cliffs Sandstone; Kf1 - Fruitland Formation sandstone number 1; Kf2 - Fruitland Formationsandstone number 2; Kf3 - Fruitland Formation sandstone number 3; Kf4 - Fruitland Formation sandstonenumber 4; Kfu - Fruitland Formation, upper part; Kk - Kirtland Shale


Pictured Cliffs Sandstone:

StatisticsTA04 JOINTS

N = 16




Vector Mean = 14.0


R Magnitude = 0.029

Rayleigh = 0.9864


N = 9




Vector Mean = 17.2


R Magnitude = 0.111

Rayleigh = 0.8944


N = 9




Vector Mean = 17.2


R Magnitude = 0.168

Rayleigh = 0.7749

StatisticsTB02 JOINTS

N = 11




Vector Mean = 14.7


R Magnitude = 0.181

Rayleigh = 0.6977


N = 10




Vector Mean = 322.0


R Magnitude = 0.053

Rayleigh = 0.9720


N = 14




Vector Mean = 329.4

Conf. Angle = 54.95

R Magnitude = 0.374

Rayleigh = 0.1408


StatisticsTC02 JOINTS

N = 14




Vector Mean = 356.9

Conf. Angle = 66.47

R Magnitude = 0.312

Rayleigh = 0.2549

StatisticsTC03 JOINTS (Kpc)

N = 2




Vector Mean = 357.5


R Magnitude = 0.087

Rayleigh = 0.9849


N = 16




Vector Mean = 337.8

Conf. Angle = 42.63

R Magnitude = 0.442

Rayleigh = 0.0441

StatisticsTD01 JOINTS

N = 19




Vector Mean = 336.4

Conf. Angle = 81.26

R Magnitude = 0.223

Rayleigh = 0.3892

StatisticsTD02 JOINTS (Kpc)

N = 24




Vector Mean = 336.2

Conf. Angle = 52.98

R Magnitude = 0.298

Rayleigh = 0.1195

StatisticsTE01 JOINTS

N = 18




Vector Mean = 336.6

Conf. Angle = 65.94

R Magnitude = 0.276

Rayleigh = 0.2534



N = 9




Vector Mean = 78.2


R Magnitude = 0.100

Rayleigh = 0.9142

StatisticsTF01 JOINTS

N = 22




Vector Mean = 356.8


R Magnitude = 0.120

Rayleigh = 0.7298

StatisticsTH01 JOINTS

N = 7




Vector Mean = 350.3

Conf. Angle = 34.84

R Magnitude = 0.715

Rayleigh = 0.0280


Fruitland Formation, a coal:

StatisticsTA01 CLEATS

N = 6




Vector Mean = 11.5


R Magnitude = 0.070

Rayleigh = 0.9714


N = 3




Vector Mean = 356.9


R Magnitude = 0.343

Rayleigh = 0.7027


N = 8




Vector Mean = 299.9


R Magnitude = 0.273

Rayleigh = 0.5497

StatisticsTB04 CLEATS

N = 8




Vector Mean = 357.6


R Magnitude = 0.022

Rayleigh = 0.9961


N = 2




Vector Mean = 291.0


R Magnitude = 0.139

Rayleigh = 0.9620

StatisticsTC01 CLEATS

N = 8




Vector Mean = 66.5


R Magnitude = 0.017

Rayleigh = 0.9976


StatisticsTD02 CLEATS

N = 8




Vector Mean = 5.0


R Magnitude = 0.017

Rayleigh = 0.9976


N = 8




Vector Mean = 325.0


R Magnitude = 0.009

Rayleigh = 0.9994

StatisticsTE02 CLEATS

N = 8




Vector Mean = 283.7


R Magnitude = 0.035

Rayleigh = 0.9901

StatisticsTF02 CLEATS

N = 8




Vector Mean = 2.9


R Magnitude = 0.006

Rayleigh = 0.9997

StatisticsTG01 CLEATS

N = 8




Vector Mean = 335.8


R Magnitude = 0.026

Rayleigh = 0.9946

StatisticsTJ02

N = 6




Vector Mean = 338.0

Conf. Angle = 95.00

R Magnitude = 0.333

Rayleigh = 0.5143



StatisticsTC03 JOINTS (Kf)

N = 3




Vector Mean = 326.5

Conf. Angle = 98.93

R Magnitude = 0.437

Rayleigh = 0.5633

Fruitland Formation, b coal:


N = 8




Vector Mean = 300.9


R Magnitude = 0.082

Rayleigh = 0.9474


N = 8




Vector Mean = 282.5


R Magnitude = 0.091

Rayleigh = 0.9353




N = 12




Vector Mean = 41.5


R Magnitude = 0.186

Rayleigh = 0.6602

StatisticsTD02 JOINTS (Kf)

N = 13




Vector Mean = 16.3

Conf. Angle = 55.57

R Magnitude = 0.382

Rayleigh = 0.1502

StatisticsTF03 JOINTS

N = 14




Vector Mean = 304.2


R Magnitude = 0.050

Rayleigh = 0.9662

StatisticsTG02 JOINTS

N = 15




Vector Mean = 346.5


R Magnitude = 0.072

Rayleigh = 0.9252

StatisticsTI01

N = 9




Vector Mean = 349.3

Conf. Angle = 58.14

R Magnitude = 0.434

Rayleigh = 0.1830

StatisticsTJ01 JOINTS

N = 16




Vector Mean = 2.4

Conf. Angle = 30.11

R Magnitude = 0.589

Rayleigh = 0.0039


Fruitland Formation, c coal:


N = 7




Vector Mean = 9.4


R Magnitude = 0.230

Rayleigh = 0.6905


N = 8




Vector Mean = 307.6


R Magnitude = 0.061

Rayleigh = 0.9707


N = 8




Vector Mean = 60.6

Conf. Angle = INF

R Magnitude = 0.005

Rayleigh = 0.9998


N = 6




Vector Mean = 354.6

Conf. Angle = 89.96

R Magnitude = 0.347

Rayleigh = 0.4850

StatisticsTF04 CLEATS

N = 8




Vector Mean = 300.1


R Magnitude = 0.065

Rayleigh = 0.9665

StatisticsTJ03

N = 8




Vector Mean = 28.2


R Magnitude = 0.177

Rayleigh = 0.7787




N = 13




Vector Mean = 354.6

Conf. Angle = 90.59

R Magnitude = 0.239

Rayleigh = 0.4758


N = 12




Vector Mean = 347.0

Conf. Angle = 59.88

R Magnitude = 0.368

Rayleigh = 0.1975


N = 15




Vector Mean = 16.0

Conf. Angle = 96.72

R Magnitude = 0.209

Rayleigh = 0.5188


N = 7




Vector Mean = 325.5


R Magnitude = 0.233

Rayleigh = 0.6842


N = 14




Vector Mean = 24.4

Conf. Angle = 86.33

R Magnitude = 0.244

Rayleigh = 0.4334

StatisticsTI02

N = 9




Vector Mean = 14.5

Conf. Angle = 75.98

R Magnitude = 0.335

Rayleigh = 0.3632




N = 6




Vector Mean = 345.4

Conf. Angle = 69.89

R Magnitude = 0.438

Rayleigh = 0.3160


N = 10




Vector Mean = 336.2

Conf. Angle = 75.93

R Magnitude = 0.324

Rayleigh = 0.3509


N = 11




Vector Mean = 19.1


R Magnitude = 0.101

Rayleigh = 0.8939

Fruitland Formation, upper part:


N = 3




Vector Mean = 355.0


R Magnitude = 0.330

Rayleigh = 0.7211


N = 14




Vector Mean = 0.5


R Magnitude = 0.166

Rayleigh = 0.6807



N = 8




Vector Mean = 306.1


R Magnitude = 0.048

Rayleigh = 0.9819

Kirtland Formation sandstones:


N = 12




Vector Mean = 314.3


R Magnitude = 0.075

Rayleigh = 0.9350


N = 13




Vector Mean = 27.3


R Magnitude = 0.172

Rayleigh = 0.6801


N = 16




Vector Mean = 339.8

Conf. Angle = 80.85

R Magnitude = 0.244

Rayleigh = 0.3862


Table 2-11. Joint and cleat stations established in the Pine River area, grouped by geologic unit.Station locations are shown on plate 6.Kpc Kfab Kf1 Kf2 Kfcd Kf3 Kf4PR01 PR03 PR07 PR02 PR13 PR15 PR18PR04 PR06 PR11 PR12 PR16 PR17PR05 PR08 PR23 PR19 PR31 PR32PR09 PR14 PR21 PR34 PR33PR10 PR20 PR26 PR37 PR35PR22 PR25 PR30 PR36PR24 PR28PR27 PR29PR38

Kpc - Pictured Cliffs Sandstone; Kfab - Fruitland Formation, lower coal interval; Kf1 - Fruitland Formationsandstone number 1; Kf2 - Fruitland Formation sandstone number 2; Kfcd - Fruitland Formation, middlecoal interval; Kf3 - Fruitland Formation sandstone number 3; Kf4 - Fruitland Formation sandstone number4

Pictured Cliffs Sandstone:

StatisticsPR01

N = 8




Vector Mean = 334.6

Conf. Angle = 30.47

R Magnitude = 0.742

Rayleigh = 0.0123

StatisticsPR04

N = 6




Vector Mean = 26.9


R Magnitude = 0.296

Rayleigh = 0.5914

StatisticsPR05

N = 7




Vector Mean = 18.0

Conf. Angle = 34.93

R Magnitude = 0.711

Rayleigh = 0.0290

StatisticsPR09

N = 6




Vector Mean = 47.7

Conf. Angle = 42.09

R Magnitude = 0.663

Rayleigh = 0.0716


StatisticsPR10

N = 7




Vector Mean = 334.0

Conf. Angle = 6.00

R Magnitude = 0.996

Rayleigh = 0.0010

StatisticsPR22

N = 5




Vector Mean = 10.4

Conf. Angle = 16.05

R Magnitude = 0.954

Rayleigh = 0.0106

StatisticsPR24

N = 9




Vector Mean = 15.2

Conf. Angle = 77.65

R Magnitude = 0.332

Rayleigh = 0.3705

StatisticsPR27

N = 4




Vector Mean = 333.8

Conf. Angle = 77.15

R Magnitude = 0.482

Rayleigh = 0.3941

StatisticsPR38

N = 7




Vector Mean = 8.0

Conf. Angle = 68.32

R Magnitude = 0.416

Rayleigh = 0.2972


Fruitland Formation, lower coal interval:

StatisticsPR03

N = 8




Vector Mean = 350.5


R Magnitude = 0.117

Rayleigh = 0.8955

StatisticsPR06

N = 4




Vector Mean = 319.5

Conf. Angle = 75.73

R Magnitude = 0.487

Rayleigh = 0.3870

StatisticsPR08

N = 8




Vector Mean = 84.6


R Magnitude = 0.130

Rayleigh = 0.8732

StatisticsPR14

N = 8




Vector Mean = 359.2


R Magnitude = 0.095

Rayleigh = 0.9306

StatisticsPR20

N = 8




Vector Mean = 81.4


R Magnitude = 0.120

Rayleigh = 0.8916

StatisticsPR25

N = 8




Vector Mean = 11.4


R Magnitude = 0.048

Rayleigh = 0.9818


StatisticsPR28

N = 8




Vector Mean = 6.3


R Magnitude = 0.082

Rayleigh = 0.9474

StatisticsPR29

N = 8




Vector Mean = 322.6


R Magnitude = 0.159

Rayleigh = 0.8166


StatisticsPR07

N = 8




Vector Mean = 17.7

Conf. Angle = 44.31

R Magnitude = 0.574

Rayleigh = 0.0715

StatisticsPR11

N = 7




Vector Mean = 12.3


R Magnitude = 0.216

Rayleigh = 0.7224

StatisticsPR23

N = 7




Vector Mean = 7.4

Conf. Angle = 35.00

R Magnitude = 0.708

Rayleigh = 0.0299



StatisticsPR02

N = 7




Vector Mean = 16.3

Conf. Angle = 66.07

R Magnitude = 0.432

Rayleigh = 0.2700

StatisticsPR12

N = 14




Vector Mean = 54.8


R Magnitude = 0.018

Rayleigh = 0.9954

StatisticsPR19

N = 10




Vector Mean = 13.7

Conf. Angle = 58.40

R Magnitude = 0.411

Rayleigh = 0.1851

StatisticsPR21

N = 6




Vector Mean = 5.7

Conf. Angle = 36.13

R Magnitude = 0.727

Rayleigh = 0.0419

StatisticsPR26

N = 8




Vector Mean = 319.4


R Magnitude = 0.172

Rayleigh = 0.7885

StatisticsPR30

N = 8




Vector Mean = 325.7


R Magnitude = 0.086

Rayleigh = 0.9421


Fruitland Formation, middle coal interval:

StatisticsPR13

N = 8




Vector Mean = 14.8


R Magnitude = 0.030

Rayleigh = 0.9927

StatisticsPR16

N = 8




Vector Mean = 28.7


R Magnitude = 0.016

Rayleigh = 0.9980

StatisticsPR31

N = 8




Vector Mean = 9.3


R Magnitude = 0.142

Rayleigh = 0.8506

StatisticsPR34

N = 8




Vector Mean = 3.6


R Magnitude = 0.035

Rayleigh = 0.9904

StatisticsPR37

N = 6




Vector Mean = 314.0

Conf. Angle = 95.64

R Magnitude = 0.328

Rayleigh = 0.5234



StatisticsPR15

N = 7




Vector Mean = 19.7

Conf. Angle = 86.07

R Magnitude = 0.336

Rayleigh = 0.4535

StatisticsPR17

N = 13




Vector Mean = 356.5


R Magnitude = 0.082

Rayleigh = 0.9160

StatisticsPR32

N = 10




Vector Mean = 4.5

Conf. Angle = 32.69

R Magnitude = 0.660

Rayleigh = 0.0129

StatisticsPR33

N = 6




Vector Mean = 2.4

Conf. Angle = 99.05

R Magnitude = 0.317

Rayleigh = 0.5472

StatisticsPR35

N = 9




Vector Mean = 336.3

Conf. Angle = 40.01

R Magnitude = 0.593

Rayleigh = 0.0422

StatisticsPR36

N = 9




Vector Mean = 15.8

Conf. Angle = 60.23

R Magnitude = 0.417

Rayleigh = 0.2097



StatisticsPR18

N = 10




Vector Mean = 53.6


R Magnitude = 0.151

Rayleigh = 0.7968



INTRODUCTION

The objective of this part of the study was todetermine what influence deep-seated controlsmight have exerted on fracturing and faulting inthe Fruitland Formation and related rocks in LaPlata County. In order to hold down costs, theinvestigation was limited to existing seismic anddrill hole data in the vicinity of the Los PinosRiver. The USGS had a seismic reflection lineowned by Maxus Exploration Company (Natomasline AAC-1, 2,and 3) from a previous study andAmoco Production Company contributed threeshallow high-resolution seismic reflection lines(HXS-1,-2,-3). The recording parameters of theMaxus line were designed to best resolve reflec-tors at depth (Pennsylvanian) while the Amocolines were designed to resolve the shallow (Creta-ceous) reflectors best. Fortunately, one of theAmoco lines (HXS-3) was recorded coincidentwith part of Maxus line 1 which enabled us tosuperimpose the two, thus recovering detail fromthe entire section, not possible using either of thelines separately. However, due to the lack ofdetail and accuracy on the shot-point map wereceived from Amoco, we are unable to preciselycorrelate the two lines nor are we able to accu-rately describe or locate any interpreted features.Also, because we had no east-west seismic lines inthe area, we are unable to fully describe thegeometry of the interpreted features.

In addition to the seismic lines, Amoco alsomade available an unpublished 1994 report, “PineRiver Fruitland Coal Outcrop Investigation”, puttogether by the Southern Rockies Business Unit ofAmoco Production Company. K.N. Energy Inc.contributed three seismic lines acquired byFuelco. These lines were too far away from thearea of study to be directly applicable but were ofconsiderable use in obtaining a regional perspective

because they were also designed to resolve theshallow part of the section and were far enoughremoved from the basin margin faulting that wecould use them for comparative purposes. Alsouseful were previous studies performed by theauthors in various parts of the San Juan Basin.

Thrust faulting underlying the HogbackMonocline along the northwestern rim of the SanJuan Basin was first described by Taylor andHuffman (1988) and this interpretation was laterexpanded to include the monoclines along thenorthern and northeastern rims (Huffman andTaylor, 1989). Huffman and Taylor (1989) alsoreported an orthogonal pattern of basementfaulting throughout the San Juan Basin. Thispattern is reflected in the overlying sedimentarysection and has influenced the occurrence andproduction of energy resources throughout thebasin (Huffman and Taylor, 1991). Huffman andCondon (1993) used these faults to help explainPennsylvanian and Permian depositional patterns.Analysis of effects on Cretaceous deposition andstructure, however, has been largely conjectureprimarily due to the lack of good seismic data inthe shallower part of the section. The lines sup-plied by Amoco are the first high resolutionseismic data we have been able to work with andalthough the data have serious shortcomings, theyhave provided new insights into the structure andtectonic style along the margins of the basin.

SEISMIC AND BOREHOLE DATA

As part of the La Plata County study, the U.S.Geological Survey received three shallow highresolution seismic lines from Amoco. A coarselocation map, paper copies of the lines, and digitalSEG-Y tapes of the processed data were alsoincluded. The USGS asked for, and did receive,copies of the side labels for the seismic lines.

Seismic Structure Studies of the Pine River GasSeep Area, La Plata County, Colorado

By A. Curtis Huffman, Jr. and David J. Taylor


This provided us with acquisition informationneeded in order to perform additional processingon the seismic data.

Using the Landmark/Advance ProMAXseismic data processing system we re-displayedall three lines at a common scale. Unfortunately,we could not correlate the CDP numbers from theSEG-Y headers on tape with the shot numbers onboth the location map and the original papercopies of the data. Therefore, we were forced toestimate the correlation between the shot locationsfrom the map and the seismic data. The resultingconfiguration is shown in figure 3-1 and, althoughwe recognize that the positions are not exact, wefeel confident that they allow a reasonablyaccurate representation of the data.

Synthetic seismograms generated from logsfor the following four wells were used to correlatesubsurface horizons with seismic reflectors.

Locations of the wells are shown in figure 3-1.

Natomas North America Inc.Ward McCoy 1-9SW of the NW: T35N, R7W, Section 9TD 9,350'

Natomas North America Inc.Richardson 1-25NW of the SE: T35N, R8W, Section 25TD 7,350'

Natomas North America Inc.Jones 1-32SE of the NW: T35N, R6W, Section 32TD 7,000'

Bush Drilling CompanyRaso 1NE of the NW: T35N, R6W, Section 7TD 1,160'

3136

30

19

18

7

6

31

30

25

24

13

12

1

36

25

32

29

20

17

8

5

32

33

28

21

16

9

4

33

34

27

22

15

10

3

34

35

26

23

14

11

2

35

36

25

24

13

12

1

36

31

30

19

18

7

6

31

32

29

20

17

8

5

33

28

21

16

9

4

32 33

34

27

22

15

10

3

34

30 29 28 2729 28 27

26

25

T 36 N

T 35 N

T 35 N

T 34 N

R 8

W

R 7

W

R 7

W

R 6

W

Natomas North America, Inc. Ward McCoy 1-9 TD 9530'

HX

S-1

HXS

-1

HX

S-2

HX

S-2

HX

S-3

HX

S-3

State Hwy 284

US Hwy 160

U.S. Geological Survey LaPlata, Co. Colorado ProjectScale : 1" = 2,500'

Los Pinos River

Natomas North America, Inc. Richardson 1-25 TD 7350' Natomas North America, Inc.

Jones 1-32 TD 7000'

AA

C -

1

AA

C -

1

AA

C -

2

AAC - 2

AAC - 3

AA

C - 3

Bush Drilling Co. Raso No. 1 TD 1160'

N

Figure 3-1. Map showing location of well and seismic data used in the study.


The McCoy well is located about 2 miles eastof the north end of seismic line HXS-1 and 2.3miles west-northwest of the north end of seismicline HXS-3. The Richardson well is locatedapproximately 1.2 miles south of the southern endof seismic line HXS-1 and 4.5 miles west of thesouthern end of seismic line HXS-3. The Joneswell is located about 1 mile south of the southernend of seismic line HXS-2 and 3.3 miles east-southeast of the southern end of seismic lineHXS-3. The Raso well is located 1.5 milesnorthwest of the northern end of seismic lineHXS-2.

SYNTHETIC SEISMOGRAMS

A synthetic seismogram is generated bycalculating a reflection coefficient series froman acoustic velocity log (and optionally, adensity log) measured in a borehole. Thereflection coefficient series is then convolvedwith an estimate of the seismic source wave-form to produce the final synthetic seismicresponse. The object is to create a close matchbetween the synthetic seismogram and the surfaceseismic section. Once the match is made identifi-cation of reflecting interfaces observed on thesurface seismic section can be made.

A reflection coefficient is defined as the ratioof the amplitude of a reflected wave to that of theincident wave. For normal incidence on aninterface which separates media of densities (gm/cc) pn and pn+1 and velocities (ft./sec.) Vn and Vn+1,the reflection coefficient can be calculated by:

(pn+1

Vn+1

- pn V

n ) / (p

n+1 V

n+1 +

p

n V

n )

where n is the sample number of the density oracoustic velocity log.

In the absence of a measured density log, wecan use a constant value for the density, or densitycan be estimated using a number of empiricalrelationships between velocity and density.Similarly in the absence of a measured acousticvelocity log a sonic log can be estimated usingone of several empirical relationships betweenresistivity measurements and acoustic velocity.

Sonic and density logs were digitized for theJones well. A sonic log was digitized for the Rasowell, but no density log was available. No sonic

logs were available for the McCoy and Richardsonwells, so the dual induction - SFL logs weredigitized for these wells instead. Sonic logs weregenerated from these resistivity logs using Faust’sequation (Faust, 1951 and Faust, 1953) as de-scribed below.

106 / SONIC = 1948 (Z1/6) (R1/6)or

SONIC = 1948 ( Z1/6) (R1/6) / 106

where “Z” is the depth in feet “R” is the resistivityvalue in ohms at that depth, and “SONIC” is theresultant acoustic velocity value in µs/ft.

The Raso well did not have a density logavailable so a conversion was used to create onefrom the sonic log. Using Lindseth’s equation(Lindseth, 1979), described below, a pseudodensity log in gm/cc was generated.

p = (V-3460) / (V(.308))

where “p” is the density value in gm/cc and “V”is the compressional wave velocity in ft/sec whichis derived using the equation:

V (ft/sec) = 106/SONIC (µs/ft)

Sonic and density values were used to producethe impedance and reflection coefficient logs.Figures 3-2 through 3-5 are plots of the variouslogs used to create the reflectivity series withgeologic tops annotated. Sonic logs were alsoused to create depth, and velocity logs.

Figure 3-6 is a plot of the wavelet used togenerate the synthetic seismograms. It is a zerophase bandpass wavelet with a frequency contentof 12 to 55 hertz. This wavelet matches theprimary frequency content of the seismic data.Because the seismic data has been deconvolved, azero phase wavelet is appropriate. Figure 3-7 is aplot showing all of the final synthetic seismo-grams for the four wells used in the study.

SEISMIC DATA—PROCESSING

As mentioned previously, the U.S. GeologicalSurvey received three shallow high-resolutionmultichannel seismic lines from Amoco. Initialexamination of the data showed that these lineswere processed through CDP stack with no


Figure 3-2. Display of the (A) measured resistivity log, (B) sonic log generated using Faust’sequation, and (C) density log generated from the sonic log utilizing Lindseth’s equation used togenerate a synthetic seismogram for the Ward McCoy No. 1-9 well.

migration applied. There was also a significantamount of noise in the section and what weinterpreted to be interbed multiples below thestrong reflectors of the Dakota Formation.

We used several post-stack processing techniques inan effort to decrease the noise content of the data withoutdegrading the signal. These included spike and noiseburst reduction, F-X deconvolution, and bandpassfiltering. All of these processes attacked a specific noiseproblem and produced a section that was easier tointerpret after they were applied. The post-stackprocessing sequence included:

*SEG-Y Tape Input*Disk Data Input*Spike Burst Edit*Noise Burst Edit*F-X Deconvolution*Bandpass Filter (8-12-55-60 Hz.)*Automatic Gain Control*Disk Data Output

Once a satisfactory stacked section wasproduced, the data were migrated to collapsethe diffractions and move the reflectors to theirtrue subsurface location using a Kirchoff timemigration algorithm.

Because the original field data were notavailable to us we could not determine migrationvelocities directly from the seismic data, there-fore, we converted the sonic and velocity informa-tion from the wells to RMS velocities and used theresults for the migration. Key reflecting horizonswere picked and the RMS velocities within thosehorizons were averaged. The averaged RMSvelocities were then held constant across thesection but the application time window wasvaried according to the dip of the key reflectinghorizons. This procedure produced a satisfactoryresult as the section did not seem to be severelyunder or over migrated. The horizons and theaveraged RMS velocities used were:


Figure 3-3. Display of the (A) measured resistivity log, (B) sonic log generated using Faust’sequation, and (C) density log generated from the sonic log utilizing Lindseth’s equation used togenerate a synthetic seismogram for the Ward McCoy No. 1-9 well.

Top of Data 8860 ft/sec. (2700 m/sec.)Top of Lewis Shale 10700 ft/sec. (3261 m/sec.)Base of Lewis Shale 11400 ft/sec. (3475 m/sec.)Dakota Formation 13000 ft/sec. (3962 m/sec.)Cutler Formation 14650 ft/sec. (4465 m/sec.)Paradox Formation 15420 ft/sec. (4700 m/sec.)Base of Data 18500 ft/sec. (5639 m/sec.)

The following post migration processing wasperformed.

*Disk Data Input*Trace Muting (mute pattern duplicated from Amoco

processed sections)*Bandpass Filter (8-12-60-64 Hz.)*Automatic Gain Control

Final results were displayed at various scales.A scale of 10 inches per second two-way traveltime in the vertical direction and 20 traces per

inch in the horizontal direction proved to be thebest for the interpretation.

SEISMIC DATA—INTERPRETATION

Line figure interpretations of the Amoco linesare shown in figures 3-8, 3-9, and 3-10. Severalfeatures are common to all of the Amoco lines: (1)the Dakota sandstone is a strong continuousreflector with few discontinuities; (2) theFruitland Formation is a strong continuousreflector with few discontinuities; (3) there is littlethickness change between the Dakota and theFruitland except at the northern end of each line;(4) the Mancos and Lewis shales are highlydeformed in the northern and central portions ofeach line and; (5) the Mesaverde Group is broken


Figure 3-4. Display of the (A) measured sonic log and (C) density log generated from the soniclog utilizing Lindseth’s equation used to generate a synthetic seismogram for the Jones No. 1-32well.

and offset in a number of places on all lines. Weinterpret these features to indicate a certainamount of into-the-basin movement along glideplanes in the shales with associated thrust faultingand back thrusting related to thrust faultingunderlying the basin margin monocline.

Some of the apparently uplifted ordowndropped ( but not actually faulted) portionsof certain reflectors, such as that in the Fruitlandin the central part of line HXS-3, (fig. 3-10) couldbe attributed to: (1) a parallel fault underlying theline such that the line passes back and forth acrossthe fault or; (2) to two separate faults at depthcrossing the line at some angle. Such ambiguitiescannot be totally resolved without a line at rightangles to HXS-3. In this particular case, we preferthe underlying parallel fault interpretation becausethe apparent lithologic character of the Fruitland is

the same on either side of the uplifted block butdifferent from that within the block which wouldbe more likely if the two downfaulted sides wereactually part of a continuous section rather thantwo separate fault blocks. The Maxus line was ofno help in this case because of data degradation atthe ends of two of the line segments (AAC 1 and2) immediately beneath the structure. In what maybe a similar situation, the Dakota is offset byeither a single underlying parallel fault or twocross-cutting faults in the southern part of lineHXS-2 (fig. 3-9).

The northernmost end of line HXS-3 inter-cepts the basin margin thrust fault as well as arather complicated set of thrusts and back thrustsassociated with it. These associated faults alsosuggest that the apparent north verging reversefault noted by Condon in this report could be a


back thrust (it should be noted that these interpre-tations are first approximations and only serve toillustrate the style and complexity of the structure).

Many lithologic variations can be seen,particularly in the Fruitland and Mesaverde of lineHXS-3, as well as in the Mancos and Lewis shalesof all the lines. Tongues of sand and shale enterthe northern end of the marine units in all of thelines, particularly in the Lewis Shale, and we haveinterpreted a number of channels or delta lobes inthe continental and marginal marine parts of thesection. Some of the lithologic changes may havebeen localized by faulting at depth but most are

probably the result of the position of the areawithin the Cretaceous seaway.

We interpret the apparent thickening betweenthe Dakota and the Fruitland seen in the northernportion of the lines, particularly line HXS-2 (fig.3-9), to be primarily tectonic in origin. Southverging thrust faults related to the basin marginthrust are most prominent in HXS-2 but arepresent in the other lines as well. The overalleffect of thrust faulting is to thicken the section;the basin margin thrusts interpreted in HXS-2have caused a dramatic thickening in the UpperCretaceous part of the section.

Figure 3-5. Display of the (A) measured sonic log and (C) density log generated from the soniclog utilizing Lindseth’s equation used to generate a synthetic seismogram for the Raso No. 1well.


Figure 3-6. Plot showing the shape and frequency spectrum of the wavelet utilized to generatethe synthetic seismograms for all of the wells used in the study area.

Line HXS-1 (fig. 3-8) contains the best evidence fora glide plane in the basal Mancos Shale. Thrust faultscoming off this detachment surface, as well as associatedback thrusts, break the Mesaverde into a number ofblocks and significantly disrupt the Lewis Shale.

The only large though-going faults seen on anyof the seismic lines available to this study areassociated with the basin margin thrusting thatunderlies the monoclinal folding on three sides of theSan Juan Basin. These thrust faults are typicallymultiple faults as they approach the surface (Taylorand Huffman,1988) and one or more of the branchesmay be seen to offset the Fruitland near the outcrop(figs. 3-8 and 3-9). We would expect a greater degreeof fracturing in the vicinity of these faults than mightotherwise be present. We can not comment on theprobability of any north-south striking faults becauseof the absence of any east-west oriented data. Thevicinity of the wind and water gaps and areas ofchanges in direction of the hogback would be likelyplaces to look for such faults.

CONCLUSIONSLittle information specific to fracturing was

gathered during the course of this study. The

original intent was to compare faulting at depth tofracturing at the Fruitland Formation level andabove. For the reasons cited previously, we wereunable to map the faulting in the area so we wereunable to compare the fracture patterns determinedin other parts of this study with underlying faultpatterns. Based on our experiences elsewhere in thebasin, we would expect there to be an orthogonalfault system offsetting the basement through thePermian part of the section and for that pattern to bereflected in the depositional patterns and fracturepatterns of the overlying units. We are unable todemonstrate such a relationship based on the findingsof this investigation.

With the notable exception of the basinmargin thrust fault, we have found no relationshipof faulting in the Fruitland Formation with struc-ture at depth in the study area but the data we hadto work with are somewhat limited and do notallow for unambiguous interpretations. Severalcritical structures , such as the problematic north-south oriented faulting, could be easily resolvedwith a tie line or two and a small 3-D survey in thearea of interest would undoubtedly resolve anumber of the questions. We do not have enough


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Figure 3-8. Line Drawing Interpretation of Amoco line HSX-1.



data in the right location to say there is or is not apattern of faulting in the Fruitland that reflects theorthogonal basement pattern we have seen else-where in the basin.

The following is a summary of our principalconclusions:

1. The Dakota Sandstone is a strong continuousreflector with few offsets at a scale resolvableby the Amoco seismic data provided for thisstudy.

2. The Fruitland Formation is a strong continu-ous reflector with few offsets at a scaleresolvable by the Amoco seismic data.

3. In this area, the entire Cretaceous section,including the Fruitland, is offset by the basinmargin thrust faults.

4. Much of the movement on the basin marginthrust is apparently taken up along a detach-ment surface in the lower Mancos and alongrelated thrusts and back thrusts in the Mancosand Lewis Shales.

5. The Mesaverde is extensively broken andoffset by the thrusts and back thrusts.

6. It is impossible to determine the pattern offaulting and its relationship to fracturing inthe Cretaceous without more data, particularlysome lines at right angles to the existing data.

ACKNOWLEDGMENTS

We are grateful to Amoco Production Com-pany, Maxus Exploration Company, and K.N.Energy, Inc. for providing the data necessary forthis study. We also benefited from discussionswith a number of people, particularly HarryTerBest, Tom Ann Casey, and Curt Johnson, aswell as from review comments by Chris Potter andJohn Miller. The interpretations and conclusionsexpressed, however, are ours alone.

REFERENCES CITED

Faust, L.Y., 1951, Seismic velocity as a functionof depth and geologic time: Geophysics, v. 16,no. 2, p. 192-206.

Faust, L.Y., 1953, A velocity function includinglithologic variation: Geophysics, v. 18, no. 2,p. 271-288.

Huffman, A.C., Jr., and Condon, S.M., 1993,Stratigraphy, structure, and paleogeographyof Pennsylvanian and Permian rocks, San JuanBasin and adjacent areas, Arizona, Colorado,New Mexico, and Utah: U.S. GeologicalSurvey Bulletin 1808-O, 44 p., 18 pl.

Huffman, A.C., Jr., and Taylor, D.J., 1989, SanJuan Basin faulting—more than meets the eye

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Fi 10 Li D i I t t ti f A li HSX 3

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Mesaverde

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Basin Margin Thrust Fault



(abs): American Association of PetroleumGeologists Bulletin, v.73, no. 9, p. 1161.

Huffman, A.C., Jr., and Taylor, D.J., 1991,Basement fault control on the occurrence anddevelopment of San Juan Basin energyresources (abs): Geological Society ofAmerica Abstracts with Programs: v. 23, no. 4,p. 34.

Lindseth, R.O., 1979, Synthetic sonic logs—aprocess for stratigraphic interpretation:Geophysics, v. 44, no. 1, p. 1-26.

Taylor, D.J., and Huffman, A.C., Jr., 1988,Overthrusting in the northwestern San JuanBasin, New Mexico—A new interpretation ofthe Hogback Monocline, in Programs andAbstracts, 1988 McKelvey Forum: U.S.Geological Survey Circular 1025, p. 60-61.

GEOLOGY AND STRUCTURE OF THE PINE RIVER, FLORIDA RIVER, … · 2005-02-07 · Fruitland Formation coal beds in the Pine River, Florida River, Carbon Junction, and Basin Creek gas-seep

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