Permian biostratigraphy n' correlation between SE Arizona n' Sonora -- López-Ramos, 1992 -- Bol. Geol. Unison

8/23/2019 Permian biostratigraphy n' correlation between SE Arizona n' Sonora -- Lpez-Ramos, 1992 -- Bol. Geol. Unison

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Bol. Depto. Geol. Uni-Son, 1992, Vol. 9, W 2, p. 1-74

PERMIAN BIOSTRATIGRAPHY AND CORRELATIONBETWEEN SOUTHEAST ARIZONA AND SONORA

Olivia PERFZRAMOSDepartamento e Geologia,Urn-Son,Hermosillo, Sonora,Mexico

ABS1RACfFusulinids are benthic marine microfossils that lived during the late PaleozoicEra (Pennsylvanian-

Permian) n a usually warm shallow water environment.Becauseof their worldwide distribution, greatabundance, nd diversity they areconsidered ood ndex fossils.This study s focusedon Permian ock correlationsbasedon fusulinid faunasobtainedby resamplingpreviouslymeasured ectionsn southeastern rizona, and he measuring nd samplingof threestratigra-phic sections n Sonora,Mexico. Descriptionsof 16 species re given that include the following genera:Monodiexodina,Parajusulina,Schwagerina, araschwagerina nd Pseudoschwagerina..lso given aredescriptionsof six genera ncluding: Schubertella,Fusulinella, Pseudochusenella, arafusulina (Skin-nerella),Schwagerina ndParaschwagerina.In southeastArizona at the Hill 14 locality East of Douglas the Earp Formation was verified asWolfcampian n age. t was deposited n a shallow marine carbonate latform environment. n the samelocality a Late Wolfcampian-EarlyLeonardianagewas assignedo the baseof the Colina Limestone.AnEarly Leonardianage n the middle (?) and upperpart of this formation was also confirmed. A probablelagoonaldepositional nvironment s assignedo the Colina Limestone.In centraleastSonora he Arivechi sectionwas assigned Late Wolfcampian-EarlyLeonardianage. twas also deposited n a shallow marine carbonateenvironment of moderate high energy. In centralSonora he Willard quarry section was designated s Late Leonardian-EarlyGuadalupian n age.TheWillard quarry section I was designated n Early Guadalupiann age.Both sectionswere depositedn ashallowwater marineenvironment.

RESUMENLos fusulinidos son microf6siles marinos bent6nicosque existieron durante el PaleozoicoTardio(pensilvanico - Permico), generalmente n marescilidos y someros.Debido a su amplia distribuci6nestratignffica, ran abundancia diversidadsonconsiderados omo 6siles ndice.En este rabajose conelacionan ocasdel Permicoen basea un estudiosistematico e fusulinidoss.Se

llev6 a cabo un re-muestreoen secciones reviamentemedidadsen el SE de Arizona y la medici6n ymuestreo e tIes secciones stratignificas n Sonora.Sedescriben16 especies ue ncluyen os siguientesgeneros:Monodiexodina,Parafusulina,Schwa-gerina, Paraschwagerinay PseudoschwagerinaTambiense describen generos:Schubertella, usuli-nella,PseudochusenellaParafusulina (Skinerella),Schwagerinay Paraschwagerina.En el SE de Arizona se verific6 que a Formaci6n E~ es de edad Wolfcampiano y de ambientemarino somero.En la misma ocalidad seasign6ala Formaci6nColina, de ambiente agunar, una edad


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WolfcampianoTardIo - LeonardianoTemprano.En el areade Arivechi. Sonorase asign6a a secuenciapermica. de ambiente marino somera y moderadaalta energia. una edad Wolfcampiano Tardio -LeonardianoTemprano.A la secci6nde a CalhidraWillard I rue asignada na edadLeonardiano ardio- Guadalupeano emprano.La secci6nWillard n rue defmida como Guadalupeano emprano.Ambassecciones e econocieron omo depositos e un ambientemarino somero.Seestablecieron uatrozonasbioestratigI1fficas:1) Zona de Pseudoschwagerina.Wolfcampiano; 2)Zona transicional de Monodiexodina . entre Wolfcampiano y Leonardiano; 3) Zona de Schwagerinacrassitectoria. en la base del Leonardiano; (4) Zona de Parafusulina en el Leonardiano y lfurite inferiordel Guadalupeano.

INTRODUCTIONGeneralities

The depositional history of Upper Paleozoicrocks in southeastArizona has been studied byseveral authors who are in general agreementabout stratigraphicnomenclature, usulinid iden-tifications, and correlations (Gilluly, 1954; Sa-bins, 1957; Ross and Tyrrell, 1965; 1973; Ar-min, 1986). However, the paleogeographic e-constructionand correlationsof Paleozoic ocksin Sonora have been a subject of debate andcontroversy, since most of these sedimentsareconsidered o be of allochthonous rigin (Ander-son, 1979; Noll, 1981; Radelli et al., 1987;Poole, 1988).Paleozoicrocks of central Sonorahavebeendescribedas ectonicallydisplaced ensof kilometers from the Cordilleran belt in NorthAmerica n nonhwesterly rendsacross he SieuaMadre Occidental (Anderson, 1979; Bartolini,1988; Gastil et al., 1991). Radelli et al. (1987)also discuss in central Sonora allochthonousbodies by the presence of overthrusts folds(nappes).n both cases heseallochthonousocksare considered basinal deposits of lowerPaleozoicage which rest upon an early Permianplatfoml.Upper Paleozoic sediments n Sonora wereprimarly deposited in a shallow water marineshelf environment. They contain an abundantbenthic fauna including fusulinids of Wolf-

campian, Leonardian and Guadalupian age.These ocks are usually reported n fault contactwith Ordovician to Pennsylvanian rocks of adeeperwater origin (peiffer, 1987;Poole, 1988).Severalhypotheses avebeenproposed o defmethe edgeof the Paleozoicshelf and o explain hedistinctive depositional facies from thenorthern and central regions of Sonora (Noll,1981; Menicucci et al., 1982; Minjarez, 1985;Peiffer, 1987;Pubellier, 1987).Peiffer (1987), based on fusulinid studies,discussesa possible connect during Paleozoictime between he Ouachita-Marathon rogeny othe east and the Cordilleran belt to the west ntoSonora.Upper Paleozoic ocks n Sonoraare commonand many of them have alreadybeenstudiedbydifferent authors; however most results areunpublishedpapaersor proprietary nformation.This has made paleontological study andcorrelationdiffICult. Permian ocks n this regioncontain abundant usulinids, yet only a few ofthesehavebeen dentified to the speciesevel. Infact, no systematic description of UpperPaleozoic usulinids in Sonoraexists. (Fig. 1).In order to establish correlations for thePermianbetweensoutheastArizona and Sonora,I studied the typical fusulinid faunas rom onelocation n Arizona and wo in Sonora.In southeastArizona fusulinids from LowerPermian ocks of W olfcampian- eonardianagesare abundant n the Earp Fonnation. They are


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absent rom the Colina Limestone except fromone ocality (Hill 14) n southeastern rizona andhave bot been collected from the Epitaph andScherrer ormations.They increase n abundanceagain in the Concha Limestone (Leonardian-Guadalupian). The Earp Formation and theColina Limestoneat the lill14locality, becauseof the fusulinid occurrences, can be used todelineate he Wolfcampian-Leonardianoundary.For this study previously measured ectionsat the Hill 14 locality were resampled. Twodifferent areaswere selected n Sonora.The fIrstis the Willard quarry (two sections)ocatedabout16 km southeast f Hermosillo, and the secondis the Arivechi section, located about 30 kmsouthwestof Arivechi (Fig. 1).Purpose

The purpose of this research s to correlatePermian age sedimentary rock sequences nArizona with those n Sonora,basedon a studyof their fusulinid faunas. Petrography andsystematic paleontology were used to identifychanges in depositional environment and toestablishbiostratigraphiczones.A fmal purposeis to understando someextent he biogeographyand evolutionary lineages of some fusulinidspecies.

Units ill, IV and V with the Earp, Colina, andSchen-eronnations, espectively, n southeasternArizona basedon a study of fusulinids.Himanga's (1977) stratigraphic column forSonora, included a comparison of the TigreLimestone in Sonora with the Naco Group inArizona. Hewett and Schmidt (1978) correlatedthe east-centralSonoraLower Permianwith theEI Tigre Formation n northeasternSonora.Theyused fusulinids where present to equate theirrocks with the Earp Formation, ColinaLimestone,and EpitaphDolomite in southeasternArimna.Wilkinson (1978) also correlated the NacoGroup n southeastern rimna and New Mexicowith the El Tigre Formationand ocks exposed tPuertecitos, ortheasternSonora.Noll (1981) eported he fusulinid fauna n theSierra de Cobachi of central Sonora to beequivalent o that n the NacoGroup n Arizona.Peiffer (1987) established Paleozoic corre-lations for stratigraphiccolumns from northern,eastern and central Sonora, including somelocalities n southeastern rizona.Most recently Lyons (1989) presented on-e-lations of Pennsylvanian-Permian ocks fromseveralsouthwesternU.S. localities, including acorrelationbetweensoutheastern rizona and heEI Tigre Limestoneof northeastern onora.Location and Accessibilityrevious Work

The earliest Upper Paleozoic correlations nSonora were made by Taliafierro (1933) basedupon the dominantly carbonate ock sections nthe Morita Mountainsof northeasternSonora.Hecompared hese ocks with the Naco Limestone(Pennsylvanian)n Arizona. Cooper (1965) usedfusulinids to assign the Monos Formation inCaborca northwest Sonora) o the Guadalupianstage n North America.

The Hill 14 ocality is actually an solatedhilllocated in section 14, T. 24 S., R. 31 E. (Gua-dalupe Canyonquadrangle)about 45 kIn eastofDouglas in the southeastern omer of Arizona(Fig. 1). Access o the area s by a eep trail southfrom the Magoffin Ranch formerly known as heQuimby Ranch)at any time of the year. The hilllies chiefly in the United States with the in-ternational Boundary crossing the toe of thesouth slope.The Arivechi section s locatednear he villageof Arivechi in central eastern Sonora approxi-mately 240 kIn eastof Hermosillo at latitude 28051' 10" North and ongitude 1090 18' 16" West.Rugged opographycharacterizeshe areawhich

Lopez-Ramos 1969), correlatedPrecambrianand Paleozoic ocks from southernArizona withseveral localities in Mexico including Sonora.Tovar (1969), working in the Sierra de Teras ofnortheasternSonora, correlated what he called


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fication of 24 times. Dimensions of the imagewere then read n millimeters. The results of thesemeasmerrents are ncluded in Appendix A.The oriented thin sections were made in theGeology laboratory at the University of TexasArlington, under the supervision of Dr. MerlyndNestell.UPPER PALEOZOIC STRATIGRAPHYOF SOUTHEAST ARIZONA

is boundedby the Sierra SantoDomingo and heReal Viejo. The measured ection s locatednearthe Ebenezermine about 30 kin to the southwestof Arivechi. Access o the area rom Arivechi isvia a primitive one-lane oad with steepmountaingrades. Field work in the rainy season(December-February)s inconvenientbecause froad conditions. n any case,a good ield vehicleis recommendedor accesso this area.The Willard quarry s located n central Sono-ra, about 16 kin southeast f Hermosillo ust 1.5kin eastof a country road. The quarry s locatedat latitude 280 57' 30" North and ongitude 110050' 25" West. Section is on the east side of thequarry and sectionn is on the west side.

GeneralitiesThe Naco Group was originally describedbyRansome 1904) as the "Naco Limestone" For-mation of Pennsylvanianage n the Naco Hills,southof Bisbee, Arizona. Later, Gilluly et al.(1954, 1956), elevated his formation to Groupstatus ncluding all Pennsylvanian Morrowan-Virgilian) and Pemtian (Guadalupian) strata nsoutheast Arizona and New Mexico. Theseformations are in ascending order: HorquillaLimestone, Earp Fomtation, Colina LimestoneEpitaph Dolomite, Scherrer Formation, andConchaLimestone. (Fig. 1). The type localitiesare in the Gunnison Hills in Cochise County,southeast omer of Arizona.

Field and Laboratory Procedures

Earp FormationDescriptioneneral

The selection of samples from the formationsin Hill 14 east of Douglas, Arizona was basedmainly on previously measured sections andfusulinid content (Dirks, 1966, Lyons, 1989),along with extensive reconnaissance of the area.Limited work was done in the Arivechi area ofSonora, because of transportation problems, roadconditions and uncooperative weather.Three measured sections were obtained inSonora: one near the Ebenezer mine in theArivechi area and two in the Willard quarry nearHermosillo. These sections were measured usinga Brunton compass and steel tape. Samples weretaken at each lithologic change; lithologies des-cribed in the field were classified using the ge-neral field textural and compositional terms ofDunham (1962).The laboratory analysis included 50 rock thinsections stained with Alizarin Red-S to determinedolomite content. The microfacies study wasdone with a petrographic microscope usingFolk's (1974) classification for limestones. Over500 oriented thin sections were prepared foridentification and description of the fusulinids.Determination and description of the fusulinidsalso included the measurements of the morpho-logical features (Fig.6). Measurements weremade by choosing the best axial and equatorialcuttings and projecting the image of a specimenfrom a thin section onto a screen at a magni-

The Earp Formation (Upper Pennsylvanian-Lower Pennian) is a thick series of interbeddedred shales, siltstones, chen pebble conglome-rates, and limestones that include some fossilife-rous beds. The chen pebble conglomerate unit isa unique feature of this formation and has beenused as a marker bed (Dirks, 1966; Rea andBryant, 1968; Annin, 1986; Lyons, 1989).The type locality of this formation wasestablished at Earp Hill eight km southeast ofTombstone (Gilluly et al., 1954). The thicknessof the Earp Fonnation at the type locality is nearly500 m. At Hill 14 in the contact with the


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overlying Colina is gradational from the redsandstones nd siltstonesof the Earp to the darkthin bedded imestoneof the Colina. The contactwith the underlying Horquilla is not exposed(Dirks. 1966).

Age

Lithology and Micropaleontology

In the ower memberof the Earp Formation nHill 14, Dirks (1966) reports the presence ofseveral usulinida of Wolfcampian age ncludingin ascendingorder: Schwagerina, Schubertellakingi, Oketaella,Pseudoschwagerina, riticites,Staffella, and Rugosofusulina.In the same locality were identified thefollowing species, from the base to the top:Pseudochusenella sp. A (Pl. 2, figs. 2-3),Paraschwagerina cf. P. fax (Thompson andWheeler) (Pl. 2, figs. 4-6), Rugosofusulina sp.A (pl. 3, figs. 1-3), Schwagerina sp. A (Pl. 3,figs. 7-8). Schwagerina providens Thompsonand Hazzard (Pl. 3, figs. 5-6) Pseudoschwa-gerina beedei Dunbar and Skinner (Pl. 4, figs. 4-5) and Pseudoschwagerina ddeni (Beed~andKniker) (pl. 4, figs. 1-3). This faunal associationis also ndicative of a Wolfcampian age (Dunbarand Skinner, 1937; Needham.1937; Thompson,1946, 1954; Newell, 1953; Sabins and Ross,1963).Environment of deposition

Based upon the paleontology and the petto-graphic study of the limestones of the lowermember of the Earp Formation, I interpret theenvironmentof deposition o havebeena shallowmarine platform in a warm sea.The areaunder-went continuousdepositionof calcareousmud ina ow energy,aerobicenvironment.The great faunal abundance and diversitysuggestshat the areawas optimal for carbonateproduction.The encrustingalgaeTubiphytes andMizzia fragmentsare mportant componentsofthe imestones.The crinoid-fusulinid-paleotextu-larida community observed in this area fallswithin the rangeof fossil assemblagesommonlyfound in offshore normal marine waters, wherefactors such as salinity and depth appear o haveremainedconstant hrough the time-span epre-sent by the faunal assemblage Bretsky, 1968;Stevens, 1966, Yancey, 1981). According toStevens (1966, 1969), a benthic fauna assem-blage dominatedby fusulinids and paleotextula-rida in association with bryozoa and crinoids

At Hill 14 the thickness of the Earp Fonnationis about 133 meters, and it may be divided intoupper and lower members (Dirks, 1 966 ;Armin,1987). The upper member comprises 68meters of unfossiliferous red siltstone with darkmicritic furestone layers.The lower member comprises 65 meters of redor reddish orange fusulinid-rich limestonesinterbedded with red siltstones (Dirks, 1966;Armin, 1987). In this member I collectedunevenly spaced samples rom the base o the topof this section. The limestones gradually changein color from dark gray to brownish, yellowish,and orange as a result of variations in iron contentand the extent of iron oxidation.Furthermore, the limestones contained abun-dant fusulinids (fusulinid packstone), and fossilhash, including crinoid stems, echinoid spines,bryozoa, some brachiopods and gastropods.The petrographic study of the limestonesshowed them to be dominated by a calcareousmud matrix, without terrigenous clastics, andgreat number of foraminifera, including fusu-linids and paleotextularida. Most fusulinids arecomplete; a few are broken and randomly orien-ted and show signs of wear. (See Appendix, p.133).Well preserved paleotextularida such asClimacammina Tetrataxis (pl. I, fig. 6) andGlobivalvulina (Pl. I, fig.7) and othertrochospiral and tubular forms (Tuberitina ) werealso observed. Finally algal debris such asCalcisphaera, Mizzia, and the encrusting algaTubiphytes were also found. This assemblage scommonly found in rocks of Permian age(Toomey, 1977; Flugel, 1978).Besides foraminifera, crinoid plates, bryozoa,brachiopoda, scarce trilobite and mollusk frag-ments, rounded micrite intraclasts, and dispersedhematitic grains are readily visible in thin section.


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suggests a water depth of 20 to 50 meters.However nmature usulinids could live in wateras shallow as4 meters Stevens,1966).Large, subglobose speciesof Pseudoschwa-gerina andParaschwagerinamay be ndicativeoflow energy environments Yancey, 1981).Theyare likely to have been floating or suspendedforms at or near the water surface where theycould be easily moved by currents (Coogan,1960; Ross, 1963).

consists of thin-and-thick bedded light gray,weathering brownish gray limestone with inter-beddeddolomitesand scattered ilty laminationsand cross laminations. In general the outcropshows egular bedding.Benthic macrofauna and microfauna areusually found in concentrated zones withinindividual bedsand consistmainly of gastropods,brachiopods, some corals, and fusulinids.Petrographic study showed patchesof partiallyrecrystallizedmicrite along with minor silicifica-tion as well scatteredhematitic patches. Somebrachipods, bryozoa and echinoid plates wereobserved. Abundant fusulinids, but of lowdiversity, were found mainly in the upperpart ofthe section. Other foraminifera such as Paleo-textularia (Pl. I, fig. 5), Globivalvulina (pl. I,fig. 7) and Tuberitina also occur. Algal debrissuch as Tubiphytesand Calcisphaera and abun-dant Mizzia fragmentswere also ound.

Colina LimestoneGeneral Description

Age

The Colina Limestone consists of dark graylimestone of micritic texture with scattered chertnodules and interbedded dolomite. Gastropods,echinoid spines, scaphopoda tubes andbrachiopod shells occur, while fusulinids,ammonites, bryozoa, corals, and trilobites arerare (Gilluly, 1954; Dirks, 1966; Wilt, 1969,1990; Lyons 1989).The type locality is Colina Ridge in theTombstone Hills about 3 km south ofTombstone, Arizona. Thickness of the ColinaLimestone is 155 m at the type locality (Gilluly etal., 1954); however, the greatest thickness (302m) is found at the Southeast Ridge section in thesame area (Wilt, 1990). At Hill 14 east ofDouglas the Colina Limestone is 290 m thick(Dirks, 1966; Lyons, 1989).The contact of the Earp Formation with theoverlying Colina is comfonnable and gradationalfrom the red siltstone of the Earp to the darklimestone of the Colina (Gilluly et aI., 1954,1956; Dirks, 1966; Lyons, 1989). The uppercontact of the Colina with the Epitaph Dolomite isexposed in the Quimby Hills (located north ofHill 14) where intercalated limestones anddolomites of the Colina grade into the mottleddolomitic limestone and dolomite of the EpitaphDolomite (Dirks, 1966).

On Hill 14 fusulinids in the Colina Limestoneare locally abundant. A few species have beenreported in the Mule Mountains, PedregosaMountains, and Guadalupe Mountains (Hill 14),in southeastArizona.In the Mule Mountains Hayes and Landis(1965) reported Triticites sp. aff. T. ventricosus(Meek and Hayden) at the base of the formation,but these collections may represent EarpFormation lithologies. In Limestone Mountain inthe Pedregosa Mountains Triticites californicusThompson and Hazzard, Schwagerina sp. andStaffella sp. are reported to occur at the base ofthe section (Epis, 1956).A Wolfcampian age is assigned to the lowerpart of Colina Limestone in these areas (Hayesand Landis, 1965; Epis, 1956).

Hill 14 in the Guadalupe Mountains has thehighest reported fusulinid content from the ColinaLimestone (Dirks, 1966; Lyons, 1989). Dirksreports the presence of Staffella (about 50 mabove the base of the section) as well asSchwagerina and Parafusulina upsection. Lyonsmentions a similar faunal assemblage to thatreported by Dirks, including Nankinella andLithology and Micropaleontology

On Hill 14 sampled he Colina Limestone. t


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linids of the samespecieswhich decreasen sizenear the top of the section (i.e. Schwagerinaguembeli Dunbarand Skinner);4. the abundance of Mizzia, a calcareousgreen algae common in marine lagoons (Johnson,1961; Wray, 1977); and5. the lack of obvious current bedding nthe outcrop.PERMIAN CORRELATIONS INSOUTHEAST ARIZONA

Endothyra. Lyons also reportsParafusuIina andSchwagerina in the upper part of the formation.This fusulinid fauna helps o assign o the ColinaLimestone as Early Leonardian age (Lyons,1989).Approximately50 metersabove he baseof theColina, an Endothyridae (Upper Devonian-Lower Permian) (Pl. 1, figs. 1,2) andSchubertella sp. (Upper Pennsylvanian-LowerPermian) pl. 1, Figs. 3-4-8) were collected.Thelong stratigraphic range of these genera couldplace these orms in the Late Wolfcampian age.The highest usulinid contentwasobserved bout50 to 60 meters below the top of the Colinawhere abundantSchwagerinaguembeli Dunbarand Skinner (Pl. 5, figs. 2-4) were identifiedalong with a few S. dugoutensis Ross, (Pl. 7,figs. 1-3). These speciesare typical of an EarlyLeonardianage Ross,1960; 1962)In sample600, the following fusulinids werefound: Parafusulina cf. P. deltoides Ross (Pl.5, fig. 6), P. leonardensisRoss (Pl. 5, fig. 1), P.ct. P. brooksensisRoss (Pl. 7, figs. 4-5); scarceSchwagerinadugoutensisRossand S. guembeliDunbarand Skinnerwere identified as well.Most of the species escribed uggest eonardianages. (Ross, 1960, 1962; Magginetti, 1988).Unfortunately, t was not possible o ascertain hestratigraphic position of sample600. Topogra-phically it is found betweensections I A and IB of the Colina Limestone on Hill 14, andprobably represents he middle or upper part ofthe Colina.Environment of Deposition

Pemrian stratigraphic correlations that havebeen made in southeastArizona are based onlithological and facies changes, stratigraphicposition, faunal assemblages,and particularlyfusulinid content.Sabins (1957), Ross (1963), Sabins andRoss, (1963, 1965) and Ross and T~l (1965)have established biostratigraphic correlationsusing fusulinids in the Chiricahua,Dos Cabezasand Whetstone Mountains within the EarpFormation and the ConchaLimestone (Virgilianthrough Guadalupian).The Colina, Epitaph andScherrer onnationsare considered eonardian nage basedon fossil assemblages,acies change,and stratigraphic osition.McClymonds (1959) correlated PaleozoicNaco Group rocks from several localities incentralPima County with the GunnisonHills andTombstoneHills in centralCochiseCounty.Dirks (1966), working at the Quimby Ranch(now the Magoffin Ranch) locality in theGuadalupeMountains assigneda Wolfcampian-Leonardian age to the Earp-Colina beds basedupon fusulinids. His fusulinid collection fromColina Limestone beds came from the Hill 14locality and epresentshe first fusulinids to havebeen collected from the Colina Limestone insoutheast rizona. Fusulinidswere also abundantin the EarpFormationon Hill 14 and he hills justto the north of Hill 14 and eastof the old QuimbyRanchhouse.Wilt (1969) redescribed he Colina Limestonein the TombstoneHills using modem carbonaterock tenninology. She measuredand correlatedsix new measuredsections. Correlations were

The Colina Limestone was deposited in a lowenergy environment, of a quiet, stable platformwith restricted circulation - perhaps in a shallowlagoon where salinity increased from time totime. This is indicated by:1. the presence of calcareous mud andscattered silty laminations, showing probablyseasonalvariations;2. the scarcity of metazoanmarine faunaand benthic oraminifera ncluding the fusulinidaandpaleotextularida;3. the lack of variety but abundant usu-

.


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basedchiefly on lithologies and a meager ossilassemblage. This research helped others torecognize he Colina environment of depositionand the various lithologies in other mountainblocks. .

Armin (1986)establishedegionalcorrelationsfor the Earp Formation (Pennsylvanian-Permian)using numerous sections in southeastArizonaand southeast New Mexico. The correlationswere based mainly on lithologies and faunalassemblages,ncluding fusulinids, and the po-sition of a prominent red chert pebble conglo-meratebed.The Naco Group rocks of southeast Arizonaalso have been correlated with those in the GrandCanyon section. The facies changes from thedominantly carbonate and nonclastic deposits ofsoutheastern Arizona to the considerably sandierdeposits in northern Arizona is remarkable(Stoyanow, 1936, 1942; Gilluly, 1954; Ross,1978; Wilkinson, 1978; Blakey, 1990).UPPER PALEOZOIC STRATIGRAPHYOF SONORA

Generalities

Lower Pennian agehave beendescribed.This isthe only areaknown in northern Sonorawhere arelatively complete Permian sequenceoccurs.This section can be correlated with the NacoGroup of southeast Arizona except for theConchaLimestone peiffer, 1987).According toMaldonado 1954),La Morita shouldbe the typelocality of the Naco Group n Sonora.Lower Permian sediments in these areas aredisconformably overlain by Lower Cretaceousrocks of the Bisbee Group (Imlay, 1939; Peiffer,1987).Noll (1981) proposed hat the Picacho Colo-rado Limestone in Sierra de Cobachi, Sonorashould be designated as the type locali ty forLower Pennianage strataof central Sonora Fig.2). The locality comprises about 145Om ofMississippian,Pennsylvanian nd Pennianstrata.However, these sediments are considered ofallochthonous rigin (Noll, 1981).In SierraEI Encinal and La Zacatera, bout 14km south of Bacanora (Fig. 2), Hewett (1978)and Schmidt(1978) describeda 1019m hicknessof Lower Permian rocks. They correlated heserocks with the EI Tigre Formation in northernSonora (Fig. 4). However, Minjarez and Torres(1987) proposed he tenD SantoDomingo Groupfor the EI Encinal sequence escribedby Hewettand Schmidt arguing that the variety andthickness of this sequenceallowed its divisioninto several ormations(Fig. 4).Other localities have been reported by otherauthors in the north and along an east-westtransect hroughcentralSonora.They are isted nTable I. Most of them havebeenconsideredo beWolfcampian-Leonardian rocks based on thepresenceof benthonic foraminifera, includingfusulinids and paleotextularida,as well crinoids,bryozoans, some mollusks, brachiopods, andalgae.

Arivechi SectionGeneral Description

The most extensive rocks described in theArivechi areaare represented y limestonesand

Rocksof Pennianageare widely distributed nthe nonhern,easternand central parts of Sonora.Because onnal stratigraphicunits have not beenestablished,a brief review of the main works isnecessaryor reference.EI Tigre Fonnation, described by Imlay(1939), along Canon Santa Rosa in thenortheasternSonorahas about 168Om f Penno-Carboniferous imestone with chert and inter-beddedshales ich in fusulinids. Approximately1080mbelong to the Permian sequence Imlay,1939). According to Alvarez (1949), Hewett(1978), Schmidt (1978) and Lopez Ramos(1985) this section can be considered he typelocality, though the sequences incomplete.Thefusulinids Parafusulina skinneri Dunbar and P.sonoraensisDunbar were fonnally describedbyDunbar 1939) asLeonardian n age.In Cerro La Morita, 40 km nonh of Cananea(Fig. 2), 185m of partially sandy dolomites of


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Fig. 2 - Map showing he localities of Permianoutcrps n SonoraState.Mexico. Ages and microfaunaare isted n Table I.

palafox, 1985; Minjarez, 1987, Pubellier, 1987).The Permian units and the clastic rocks ofJurassic- Cretaceous age are thought to beallochtonous (Minjarez et al., 1985; Pubellier,1987).

interbedded clastics and chert of Permiansequences in fault contact with Jurassic andCretaceous volcanoclastics (King, 1939, Flinn,1977, Himanga.1977, Hewett, 1978, Schmidt,1978, Ornelas, 1984, Palafox et al; 1985;

-


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11O. PerezRamos

The term "Santo Domingo Group" was flfStapplied in Sierra Santo Domingo to the EI Ca-joncito and Cerro Real Viejo sections Minjarezand Torres, 1987); this is close to the Arivechisection,which was the areachosen or my study(Figs. 1 and 3).Lithology and Micropaleontology

Tetrataxis (Pl. 1, fig. 6); brachiopods,molluscfragments,and ooids, scarce rilobite fragments,the encrustingalgae Tubiphytes..algal (?) piso-lites, and dark colored organic matter. A similarfaunal assemblagewas found in the silty andsandy limestones, but in lesser amounts.However: fusulinids were remarkably abundanin the calcareous iltstone.In most of the samples he fusulinids, crinoidstemsand other fossil fragmentsshowedcun-enorientation, which indicates paleocurrentdirec-tion. In this this locality the walls of the fusu-linids were much thicker than specimensobser-ved n southeastern rizona (Hil114).Age

Fusulinids dentified through he entire Arive-chi sectionwere:Parafusulina Skinnerella)brevis Skinner (Pl.8, fig. 2), Parafusulina c/. P. brooksensis Ross(Pl. 7, figs. 4-5), P. cf P. allisonensis Ross(Pl. 6, figs. 5-6), Schwagerina crassitectoriaDunbar and Skinner (Pl. 5, fig. 5) S. guembeliDunbar and Skinner (Pl. 5, figs. 2-4) andMonodiexodina linearis (Dunbar and Skinner)(Pl. 5, figs. 2-4).This faunal association is indicative of anEarly Leonardian age (Dunbar and Skinner,1937; Thompson, 1954; Knight, 1956; Ross,1960, 1962; Skinner, 1971), with exception ofM. linearis (mainly in the middle of the section)which has been reported also in rocks of lateWolfcampian age (Dunbar and Skinner, 1937;Ross, 1963). Thus, a Late Wolfcampian-EarlyLeonardian age is presented for the Arivechisection Fig. 3).Also near the middle of the section (sample8c), Fusulinella sp. indicative of middle Penn-sylvania age (Atokan) was found. This samplemay be in fault contact with Permian ocks, or itmay represent erosion from older fusulinidbearing ocks nto Permiandeposits.Environment of deposition

The Arivechi section s a 170m hick sequenceof reddish-brown sandy imestone, nterbeddedwith thin- and thick-bedded, sometimessandy,blocky red sandstone nd siltstone (20 to 50 cmthick) as well gray massive aminated imestone.Horizontal and cross-beddedsandy layers arecommon, along with iron concretions andfusulinid casts. Fusulinids and crinoidal debrisare abundant; bryozoa and brachipods arecommon;andcoralsand mollusksare scarceLarge, thick-shelled fusulinids are embeddedmainly in sandy limestone. In some samplesfusulinids are aligned with the orientation ofcross bedding.A petrographic study showed several sharpcontacts from fossiliferous to unfossiliferouscalcareous siltstone and sandstone.The sandylimestonesnear he baseof the sectioncontainedless quartz sand and more dark colored organicmatter.Petrographically,most samplesare fossiliferoussilty and sandy limestones, which are slightlydolomitized in patches. The quartz grains are"floating" in the microcrystalline carbonate ma-ttix; sometimesauthigenic quartz (crystal over-growth) is present. n general he quartz grains,which are angularand subangular, re within therange of silt and very fine sand. Also, thislithology includes grains of plagioclase, mica,zircon, and a few metamorphic ock fragments.Roundeddetrital chert grainsvarying n size romless han 1 to 2 or 3 mm, were also found. Mag-netite grains altered o hematiteoccur as solatedcrystals and in well developed aminations of asingle grain thickness.The massive, laminated limestones have amicritic mattix, usually with abundantcrinoidalplates and bryozoa,some oraminifera includingfusulinids, a few arenaceous forms such as The rocks of the Arivechi section suggestdeposition in an open shelf, shallow marine


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12 O. PerezRamos

The Sierra Santa Teresa preserves the thickestUpper Paleozoic rock sequence hat outcrops nearHermosillo. In this area Peiffer (1987) describesa 1500m thickness of Pennsylvanian-Pennianunits, comprising limestones, sandy limestonesand black nodular and bedded chen. The faunalassemblage ncludes crinoids, bryozoa, brachio-pods, corals, fusulinids and other foraminifera(paleotextularida), and some algae.Two Permian sections were measured in theWillard quarry east of Sierra Santa Teresa:Section I is on the west side of the quarry. Itcomprises 110m of thin bedded crinoidallimestone that is panially recrystallized, dolo-mitized, silicified and hematized Benthonic faunain this section are deformed, broken and badlypreserved. Section II is on the east side of thequarry. It comprises 180m thick section ofrecrystallized cheny limestones, with silicifiedfusulinids being poorly preserved.In general, this area was strongly folded andfractured by post-Paleozoic intrusions andregional tectonism (Rodriguez, 1981).Willard Section I

Lithology and Micropaleontology

environment affected by waves or currentswithan intem1ittent supply of terrigenousmaterial.Evidence for this includes the fossiliferouscalcareous iltstone,with the commonalignmentof the fusulinids, the cross-bedding,occasionalinterruptions in lithology, worn and brokenfusulinid shells, and disarticulated rinoidal stemplates. The broken faunal material indicatestransportor reworking of the bioclastics.The elongate, ylindrical shape f the usulinidtest (like Monodiexodina and Parafusulina andtheir low bulk density as well as heir thick shellsspecialize hem or life in shallow,agitatedwater(Coogan, 1960; Ross, 1961; Scholle, 1983).This type of fauna s an deal current ndicator. nthis case it indicates moderately high energybecausemost of the clasticmaterial s well sorted.The presenceof angularand subangularsilt-sizequartzalong with someplagioclase,mica, zircon,and rounded rock fragments, ndicates a sourcenot far away.During heavy stormsor storm tides the samegrainscould have been ransported omedistanceaway rom the shorelineand deposited n slightlydeeperwaters. This statement s basedupon theobservation that most terrigenous grains are"floating"in micrite which suggestsransportationto and ultimate deposition in quiet marineenvironmentAlso, the interbedded silty or sandy blockybeds in the limestones are suggestive of anincreasen clastic supply rom time to time.Willard sections I and II

General DescriptionThe Willard quarry, located about 16 kmsoutheast f Hermosillo, exposesMississippian,Pennsylvanianand Permian imestonesand do-.lomites (some metamorphosed), andstones ndchert (Flores, 1929; Rodriguez,1981; Peiffer,1987). The limestones are rich in crinoids,bryozoans, orals, brachiopods, nd usulinids.The Willard quarry has beenopened n smallhills located 3 to 4 km to the west of the CerroPrieto and SierraSantaTeresa Figs. 1 and 4).

Poorly resistant ferruginous shale wasobservedat the baseof the section.Units higherin the section were mostly thin-to thick- bedded(10 to 30 cm) and blocky (50 cm ) crinoidallimestones of dark gray to reddish color andslightly silty. Near the middle of the sectionfusulinids and bryozoawere abundant n a whiteyellowish bedded imestone.The uppermost nitsare limestones that tend to be darker andbrownishand have ewer fossils.A petrographic study shows that the shalesalso contain some angular and subangularsilt-sizequartz.The matrix is silicified and hematizedand shows a few micas. The position of thehematite helps to recognize laminations. Nofossils were observed.In general, he limestone consistsof micritethat was partially recrystallized, dolomitized,silicified, andhematized.Also, some authigenic


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O. PerezRamos4

APPENDIX BList of Algae and Foraminifera mentioned in this study

Algae:TubiphytesMizziaCalcisphaera

Foraminifera:TuberitinaPaleotextularia sp.Tetrataxis sp.Climacammina sp.Giobivalvulina sp.EndothyridaeFusulinella spAPseudochusenella pAMonodiexodinainearis (DunbarandSkinner)Parafusulina eonardensisRossParafusulinacf. P. deltoidesRossParafusulinacf. P. allisonensis RossParafusulinacf. P. brooksensisRossParafusulina Skinnerella)c/. P. (S.) sonoraensisDunbarParafusulina Skinnerella)brevis SkinnerParafusulina Skinnerella) spAParafusulinacf P. durhami Thompson ndMillerParafusulinaempirensis SabinsandRossSchwagerina rovidens Thompsonand HazzardSchwagerina rassitectoriaDunbarandSkinnerSchwagerina uembeli Dunbarand SkinnerSchwagerina ugoutensisRossSchwagerina pARugosofusulina p.AParaschwagerina r. P fax (Thompson ndWheeler)Paraschwagerina pAPseudoschwagerinaeedei DunbarandKnicker

Permian biostratigraphy n' correlation between SE Arizona n' Sonora -- López-Ramos, 1992 -- Bol. Geol. Unison

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