The Glacial/Deglacial History of Sedimentation in Bear Lake (Utah and Idaho) Joe Rosenbaum, Walt Dean, and Richard Reynolds science for a changing world
Jan 20, 2016
The Glacial/Deglacial History of Sedimentation in Bear Lake (Utah and Idaho)
Joe Rosenbaum, Walt Dean,
and Richard Reynolds science for a changing w orld
Interpretations based largely on changes in provenance of detrital material and the transition from siliciclastic to carbonate sedimentation
• Catchment– Relation of Bear River to Bear Lake– Properties of fluvial materials
• Mineralogy and elemental chemistry• Magnetic properties
• Lake sediment cores– Variations in provenance with age– Glacial history
• Comparisons to other records– Rocky Mountains– Lake Bonneville
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Bear Lake and the Bear River
• Headwaters of the Bear River in the northwestern Uinta Mountains
• Bear River is the largest river in the Great Basin
GreatSaltLake
Wasatch
Ra
ng
e
U inta Mtns.
River
Bea
r
Wy
om
ing
Idaho
UtahBearLake
Salt LakeCity
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Bear Lake & Bear River
The Bear River did not enter the lake during much of the Holocene, but did during the last glacial period.
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Geologic Map
Watershed boundary
Geologic Map of the Bear Riverand Bear Lake Watersheds(after Reheis, in press)
Be ar
Lake
42 30 'o
42 30 'o
41 30 'o
41 00 'o
110 30 'o111 30 'o 111 00 'o
0 10 20 km
Wyom ing
Wyo
min
g
U tah
Uta
hW
yom
ing
Ida
ho
UtahIdaho
Evanston
G ardenC ity
R i
v e
r
Pliocene-Pleistocene surficial deposits
Tertiary alluvial and lacustrine rocks
M esozoic and U pper Paleozoicshale, lim estone, and sandstone
Low er Paleozoic lim estone,, and quartzitedolom ite
Upper Precam brian shale and quartzite(including of the Uinta M ountain G roup)
hem atite-rich rocks
53
5149
47
45
4341
3937
35
31
29
27
25
23
21
19
17
15
1311
9
7
1
3
5
33
G lacial till and outw ash
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Magnetic Properties of Fluvial Sediments
• “Magnetite” content– low in Uinta Mtns. and lower
reaches of the Bear River– high in local Bear Lake
catchment– about the same on east and
west sides of lake
• “Magnetite” in the fluvial sediments is largely from dust– variety of magnetite and
titanomagnetite grains that are derived from igneous rocks that do not exist in the catchment
– fine-silt sized grains (<10 m)
Wyo
min
g
Bear LakeCatchm ent
Bear River(upstream )
Uta
h
10 20 30 40 50
Sam ple Num ber
W E Low er Upper
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
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Magnetic Properties of fluvial sediments
• “Hematite” content– higher in Uinta Mtns. than in
other source areas.– about the same in local Bear
Lake catchment as along lower reaches of the Bear River
Note dilution of material from the headwaters of the Bear River downstream so that under present conditions Uinta Mountain material is a minor component of the river sediments.
Wyo
min
g
Bear LakeCatchm ent
Bear River(upstream )
Uta
h
10 20 30 40 50
Sam ple Num ber
W E Low er Upper
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
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Properties of 3 catchment areas
Al/Ti *
Local Bear Lake catchm ent
“Low er” Bear River
Headwaters of the Bear River
M g/CaM S HIRM Dolom iteCalcite
• Local Bear Lake catchment– High dolomite content (Mg/Ca)
& magnetic susceptibility (MS)
– Low HIRM
• Headwaters (Uinta Mtns.)– High HIRM and Al/Ti
– Low MS
• “Lower” Bear River– Low MS, HIRM, & dolomite
content
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Cores
• Composite record from two 4-m-long cores– BL96-2: Largely
carbonate-rich sediments overlying uppermost siliciclastic sediment
– BL96-3: Very thin, incomplete Holocene record overlying more than 3.5 m of siliciclastic sediment
• GLAD800– 120 meters
– Last 240,000 years
Utah
GardenCity
Idaho
42 04' No
41 56’ No
111 12’ No
G23
10
30
50
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Composite Section and Chronology
• The composite record provides a nearly continuous record for most of the Holocene back to about 32 cal. kyr
• Siliciclastic sedimentation 32 – 17 cal. kyr
• Endogenic calcite or aragonite 14.5 cal. kyr - present
BL96-3
BL96-20
1.0
2.0
3.0
4.0D
epth
(m
eter
s)
0
1.0
2.0
3.0
4.0
% Calcite0 20 40 60 80
0 20 40 60 80
% Calcite
Cal. Ages(kyr)
Cal. Ages(kyr)
5.0 13.015.4
23.7
25.725.7
27.5
31.3
3.2
3.74.86.0 6.67.39.2 9.5
12.1
14.916.8
19.322.024.725.126.6
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Ages
• 14C ages– AMS ages on pollen
concentrates (pollen + other refractory organic material)
– Pollen is plentiful and well preserved in carbonate sediments
– Pollen is sparse and in poor condition in the siliciclastic sediments
– Ages are in good stratigraphic order and there is no apparent discontinuity
BL96-3
BL96-20
1.0
2.0
3.0
4.0D
epth
(m
eter
s)
0
1.0
2.0
3.0
4.0
% Calcite0 20 40 60 80
0 20 40 60 80
% Calcite
Cal. Ages(kyr)
Cal. Ages(kyr)
5.0 13.015.4
23.7
25.725.7
27.5
31.3
3.2
3.74.86.0 6.67.39.2 9.5
12.1
14.916.8
19.322.024.725.126.6
science for a changing w orld
Properties vs age“Hematite”
0 4 8 12
“Magnetite”
0 2 4 6
Mg/Ca (leach)
0.0 0.2 0.4 0.6
10
15
20
25
30
CaCO (%)3
0 40 80
Cal
. Ag
e k
yr
BP
Al/Ti (bulk)
20 25 30 35
Quartz (%)
20 40 60 80
I. Quasi-cylical variations in magnetic properties and elemental ratios
II. Decreasing HIRM and Al/Ti
III. Increasing MS and Mg/Ca
IV. Transition to carbonate
V. Constant carbonate (alteration of Fe-oxides)
VI. Aragonite precipitation
Observations
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MS vs. HIRM for Zone I
• Strong negative relation between content of material from Uinta Mountains and from the local Bear Lake catchment
0 2 4 60
2
4
6
8
10
from local catchm ent
fro
m U
inta
Mo
un
tain
s
“Magnetite”M S x 10 (m kg )-7 3 -1
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Detrital material from the Uinta Mountains is glacial flour:
• High content of material from the Uinta Mountains requires enhanced erosion.
• There was extensive Pinedale-equivalent glaciation in the Uinta Mountains.
• Sediment with high content of Uinta Mountain material is finer-grained.
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Properties vs age 2“Hematite”
0 4 8 12
“Magnetite”
0 2 4 6
Mg/Ca (leach)
0.0 0.2 0.4 0.6
10
15
20
25
30
CaCO (%)3
0 40 80
Cal
. Ag
e k
yr
BP
Al/Ti (bulk)
20 25 30 35
Quartz (%)
20 40 60 80
Uinta Mtns.Bear Lake
Catchment (BLC)
I. Variations in glacial extent with material from BLC replacing Uinta Mt. Material and vice versa.
III. Increasing input from BLC
IV. Progressive loss of river
II. Decreasing glaciation
V. Little if any input of Bear River sediment
VI. Increasing salinity
Interpretations
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Magnetic properties from BL96-3 and
GLAD800
• Unequivocal correlation based on magnetic susceptibility
• Base of BL96-3 just captures the base of the zone with high values of HIRM
GLAD800M S x 10 (volum eSI)-6
0 20 40
8
10
12
14
16
18
20
GLAD800HIRM x 10 (Am )-3 -1
0 4 8 12
0
1
2
3
4Dep
th in
GL
AD
800
(me
ters
)
Dep
th i
n B
L96
-3 (
met
ers)
BL96-3M S x 10 (m kg )-7 3 -1
0 2 4 6
BL96-3HIRM x 10 (Am kg )-4 2 -1
2 6 1 0
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Comparison to other records of glacial extent• Upper Klamath
Lake– Millennial-scale
variations– Peak at about 19
to 18 cal. kyr
• Rocky Mts.– Peak at about the
same time– Major
deglaciation somewhat later
• Southern Uintas (Laabs) and Wasatch (Lips)– Cosmogenic ages
indicate significantly later deglaciation
0 2 4
HIRMBear Lake
( this study)
NorthwesternUinta M ountains
10
20
30
40
0 50 100
Glacier length (% )(m odified from Porter, 1983;
Pierce, 2004)
Ca
len
dar
ag
e 1,
000
yr
B.P
.
RockyM ountains
1965 m odel
1983 m odel
?
?
?
?
0 40 80
SouthernCascade Range
Flux of glacial flourUpper Klam ath Lake
(Rosenbaum and Reynolds, 2004)
10
20
30
40
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Comparison to Lake Bonneville
• Onset of glaciation at same time as initial growth of Bonneville
• Increase to max. glaciation corresponds to rise following SO
• Deglaciation occurs while Bonneville continues to rise
• River leaves Bear Lake (Zone IV) during fall from Provo shoreline
• Salinity increases (Zone V/VI boundary) during fall from Gilbert (i.e., at end of YD)
IIIIIIIVVVI
1550
1450
1350
1250Lak
e B
on
nev
ille
Ad
just
ed
ele
va
tio
n (
me
ters
) B
P
G SSO
10 15 20 25 30 35
Calibrated age (kyr)
0
1
2
3
4
5
U2
U1
U3 modified fromOviatt, 1997
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Summary
• Bear Lake contains glacial flour from the headwaters of the Bear River in the Uinta Mountains. The record suggests:– onset of glaciation at 32 cal. kyr
– maximum glaciation from 25-24 cal.
– deglaciation during later stages of growth of Bonneville and earlier than indicated by recent dating of moraines in the southern Uinta and Wasatch mountains
• The Bear River abandoned Bear Lake 17-14.5 cal/kyr
• The salinity of Bear Lake increased at the end of the Younger Dryas
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