Jurassic Stratigraphy of Utah and Colorado Lawrence C

Home , Curtis Formation, Exeter Sandstone, Glen Canyon Group, Nugget Sandstone

New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/2

Jurassic stratigraphy of Utah and Colorado Lawrence C. Craig and Clifford N. Holmes, 1951, pp. 93-95 in: San Juan Basin (New Mexico and Arizona), Smith, C. T.; Silver, C.; [eds.], New Mexico Geological Society 2nd Annual Fall Field Conference Guidebook, 163 p.

This is one of many related papers that were included in the 1951 NMGS Fall Field Conference Guidebook.

Annual NMGS Fall Field Conference Guidebooks Since 1950, the New Mexico Geological Society has held an annual Fall Field Conference that visits some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed papers. These books have set the national standard for geologic guidebooks and are an important reference for anyone working in or around New Mexico.

Free Downloads

The New Mexico Geological Society has decided to make our peer-reviewed Fall Field Conference guidebook papers available for free download. Non-members will have access to guidebook papers, but not from the last two years. Members will have access to all papers. This is in keeping with our mission of promoting interest, research, and cooperation regarding geology in New Mexico. However, guidebook sales represent a significant proportion of the societies' operating budget. Therefore, only research papers will be made available for download. Road logs, mini-papers, maps, stratigraphic charts, and other selected content will remain available only in the printed guidebooks. This will encourage researchers to purchase the printed guidebooks, which are essential references for geologic research in New Mexico and surrounding areas.

Publications of the New Mexico Geological Society, printed and electronic, are protected by the copyright laws of the United States. No material from our website or printed and electronic publications may be reprinted or redistributed without our permission. Contact us for permission to reprint portions of any of our publications. One printed copy of any materials from our website or our print and electronic publications may be made for individual use without our permission. Teachers and students may make unlimited copies for educational use. Any other use of these materials requires permission. This page is intentionally left blank to maintain order of facing pages. I NEW MEXICO GEOLOGICAL SOCIETY * SECOND FIELD CONFERENCE * SAN JUAN BASIN

! JURASS IC FORMATIO NS OF T HE SOUTH AND Thispaper deals with the classification of Jurassic WEST SIDES OF THE SAN JUAN BASIN stratain Coloradoand Utah exceptnorth-central Utah. NEW MEXICO AND ARIZONA The Glen Canyongroup consistsof the Wingate I sandstone,Kayenta formation, and Navajosandstone TheJurassic formations of the southand west in ascendingorder. The age assignmentof the Glen sldesofthe San Juan Basin form an extremelycomplex Canyonis in questionbecause of the lackof diagnostic i systemof sediments.They are nearlyal[ non-marine fossils.This group is tentativelyassigned to the and weredeposited in similarenvironments giving rise Jurassic.A recognizablehiatus is lackingat the to nearlyidentical lithologies and sedimentary structures, base of The Glen Canyon;the componentformations Any discussionof theseformations cannot avoid going are separatedin most placesonly by gradational i far afieldfrom the confinesof the SanJuan Basin andarbitrary contacts. properbecause nearly all of the formationalnames usedhave their type localities beyond the margins The Wingatesandstone and Kayentaformation I of theBasin.Generalizeddescriptions of the form- formtwo broadlens-shapeddeposits extending ationsare dividedgeographically, partly because throughall of southeasternUtah and intosouthwestern of the areasUsed as typelocalities and partlybe- Colorado.The Wingateis mostlyeolian in character causeof the familiarityof the authorswith more in the centerof thisarea but shows increasing effects I localizedoccurrences, of subaqueousdeposition to the northand east.The Kayentais fluviatilein origin.The westernlimit The threepapers which comprise this discussion of the Wingateand Kayentais betweenthe Circle werefirst presented at the conferenceon Jurassic Cllffsand Zion Canyonareas of southwesternUtah. I stratigraphyat the annualmeeting of the New Mex- The characterof thislimit is notclearly described ic0 GeologicalSociety on April 6, 1951. Some in the literatureand considerabledifference of conclusionsin thesearticles may alreadybe outdated opinionprevai[s concerning its position.The north- I becauseof currentfield work by variousbranches of westernand northernlimit lies beneaththe Wasatch the U. S. GeologicalSurvey on mineralresources Plateauand the Uinta Basin.To the east the Wingate and groundwater, continued field work by the and Kayentalose theiridenty along a north-south geologicalstaff of the A. E.C.in the regionand the line in southwesternColorado, as a resultof various i activitiesof privatecompanies and individuals.The combinationsof facieschange convergence,and firstpaper describes the formationsas theyappear erosion.The name Doloresformation has been applied in Coloradoand Utah and servesto introducemuch in southwesternColorado to the intervalthought to I of the nomenclature,Thesecondpaperdescribes containinseparableequivalentsof formationsof the the unitsas theyoccur in the NavajoReservation Glen Canyongroup and the UpperTriassic series. and appliesmost directly to thewest side of theSan Juan Basin.The thirdpaper attemptsto sunxnarize The Navajosandstone forms an irregularwedge I the problemspresented by the firsttwo papersand to of predominantlyeolian sandstone extending through suggestregional distribution patterns and their all southernand easternUtah into southwesternCola- controls, rado. The Navajois thickestin southwesternUtah and correspondsto the even thickerAztec Sandstone i JURASSIC STRATIGRAPHY OF UTAH of southernNevada. The Navajothins to the north AND COLORADO* and east and is correlatedwith the Nuggetsandstone of centralUtah and southwesternWyoming. This unit i LawrenceC. Craig and CliffordN. Holmes** extendssoutheastward into the centralColorado basin as far as Rifle.In southwesternColorado the Navajo (Abstractof a paperpresented before the reachesa featheredge,probably as a resultof both New Mexico GeologicalSociety, depositionalconvergence and pre-SanRafael erosion. I April6, 1951)

Jurassicrocks of the ColoradoPlateau are I dividedinto threemajor units -- the Glen Canyon group,San Rafaelgroup and Morrlsonformation in *Publicationauthorized by the D~rector,U.S. ascendingorder. This classificationcan be extended GeologicalSurvey. I to mostof the Jurassicrocks of Utahand Colorado. ** Geologists,U. S. GeologicalSurvey. ! 93 | | NEW MEXICO GEOLOGICAL SOCIETY *SECOND FIELD CONFERENCE * SAN JUANBASIN "

ggg~ I TheSan Rafael group is divldedinto’four form- greenishsandstone and minor greenish shale; the ations-- the Carmelformation, Entrada sandstone, Summervilleis predominantly redsilty shale and Curtisformation and Summervilleformation, in sandstone.Both overlie the Entrada conformably n ascendingorder. The Carmelhas beendated as exceptin centralUtah, where an angularuncon- II earlyUpper Jurassic and theCurtis as middleUpper formitylocally marks the baseof theCurtis. The Jurassicfrom marine invertebrate fossils. The Curtisformation has beenrecognized in southwestern, gg Entradaand Summerville lack diagnosticfossll remains, centraland northeastern Utah and in northwestern g Colorado.Unfossiliferous thln-bedded sandstones and The Carmelformation was depositedthroughout shalesalong the northern part of theFront Range in southernUtah. It is notpreserved west of south- Coloradomay be equivalentto the Curtis.Thick n westernUtah. It thinsto thenortheast and reaches gypsumdeposits southwest of the AncestralUncompahgre U a featheredgein southwesternColorado. A limes- Upliftand southeast of theAncestral Front Range stone-and gypsum-bearing sandstone and shale Upliftprobably formed in restrictedparts of theCurtis gg Sea.The Summervilleformation has beenrecognized faciesin centraland southwesternUtah has been ¯mm dlstinguishedfrom a redsilty sandstone facies in throughoutsouth-central and southeasternUtah and southeasternUtah. A criticalstudy of faciesrelations partof southwesternColorado. Where both formations in southeasternUtah is necessaryto determinethe arepresent the Summerville overlies the Curtis. In ¯ extentof thered silty sandstone facies of theCarmel northeasternUtah and northwestern Colorado the II intoNew Mexicoand Arizona. Curtisoccupies the entire interval between the Entradasandstone and the Morrlsonformation. South- TheEntrada sandstone was deposited throughout eastwardfrom central and south-central Utah~ the g southernand eastern Utah and most of Colorado.It Curtisgrades into the Summerville and theSummer- HI correlateslocally with the Garo sandstone (Stark et villeoccupies the entire interval between the Entrada al.,1949) Exeter sandstone (Lee, W. T. 1902) and the Morrison.In a north-southbelt through Moab, [] thelower part of theSundance formation in central Utah,the Moabtongue of theEntrada sandstone occupies g and easternColorado. A red earthysandstone facies mostof theinterval between the Entrada and the in centraland southwestern Utah has been distinguished Morrlson.To the eastand westof Moab,and to the froma cleansandstone facies in Coloradoand eastern southon thewest flank of the AbajoMountains, it ¯ Utah.The earthy sandstone facies is largelyof sub- tonguesand grades out into the red shales of the aqueousorigin, and thecleansandstone facies was Summery¯lie.The Bluff sandstone of southeasternmost depositedin an alternatTngsubaqueous and subaerial Utahwas defined as a basalmember of the Morrison mm environment.The Entradapinches out against the formation;butitsdePositionalcharacteristicsrelate g AncestralRockies in southwesternand central Cola- it to theSon Rafae] group and it tonguesand grades radoand locally contains basal conglomerates of northwardinto red shales of the Summerville.In igneousand metamorphic rocks where it restson the partof southwesternColorado the intervalbetween ¯ pre-Cambrianof the positive elements, the Entradaand theMorrison is occupiedby the_Wan" : akahformation, formerly considered a member of the Wherethe Enffadasandstone overlies the Carmel Morrison.The Wanakahformation is subdividedinto formationthe basal contact is an arbitrarylithologic threemembers of varyinggeographic extent -- the n boundary,but in mostofColorado the Carmel,as PonyExpress limestone member, the BilkCreek sand- HI wellas underlyingunits of the GlenCanyon group, stonemember, and a marlmember. A fourthunit-- areabsent and the base of theEntrada is a sharp theJunction Creek sandstone, here considered a n erosionalbreak, with the Entrada resting on Triassic memberof the Wanakah--is presentat the topof the or upperPaleozoic sedimentary rocks. Wanakahin the Durango,Piedra River, and Dolores areas.The Junction Creek has alsobeen treated as a Theinterval between the top of theEntrada memberof theM0rrison formation and as a separate ¯ sandstoneand the base of the/V~orrisonformation is formation.The JunctionCreek is slmilarto and complicatedby numerousfacies changes and several appearsto occupythe same stratigraphic positio n as formationand membernames. The Curtisand Summ- theBluff sandstone. The relation of theJunction err¯lieformations are the main units occupying this Creekto theMorrison formation has not beenldeflnltely ¯ interval.The Curtis is predominantlygrayish to establishedand an upperpart may havebeen deposited :!: ! !

m I NEW MEXICO GEOLOGICAL SOCIETY* SECONDFIELD CONFERENCE * SAN JUAN BASIN I synchronouslywith lower beds of theMorrison in positionof partof theSan Rafael group and the southwesternColorado: Morrisonformation, or theMorrison formation may havebeen removed by pre-Dakotaerosion in this I The Morrisanformation was deposited through- area. out Coloradoand eastern Utah. It reachesa featheredgein the Kaiparowits Plateau of south- LowerCretaceous formations overlie the centralUtah, probably as a resultof increasing Morrisonin Coloradoand mostof easternUtah. In I erosiontoward the southwest prior to depositionof placesthe Lower Cretaceous beds are difficult to the Dakotasandstone of UpperCretaceous age. The separatefrom the upper part of theMorrisan because northwesterlyextent of theMorrisonin Utah is not of similarlithologic characteristics. : i known,but theformation has beenreported in the vicinityof SaltLake City and Sallna in central Utah.In eastern¯ Utahand westernColorado, the Morrisonmay be dividedinto an upperpart and a JURASSIC STRATIGRAPHY OF THE NAVAJO I lowerpart, but in centralColorado these units COUNTRY* Cannotbe separated.The SaltWash sandstone memberoccupies the lowerpart of theMorrison in J.W.Harshbarger, C. A. Repenning,R. L. Jackson** I easternUtahandwesternColorado.Itconsists of interstratifiedfluviatile sandstones and claystones. Introduction Theorientation of cross-lamlnae and increasein thicknessand coarseness indicate that the source of At therequest of theoffice of IndianAffairs, I theSalt Wash lay southwest of south-centralUtah, the GroundWater Branch of the UnitedStates Geo- probablyin west-centralArizona. Beds equivalent logicalSurvey is makingan investigationof the to the saltWash were probably deposited in central ground-waterresources of the Navajo¯country. It Colorado~but because of theabsence of scour-fill becameapparent early in thisinvestigation, that a I sandstonesthey cannot be differentiatedfrom the studyof regionalstratigraphic relationships was upperpart of the Morrison.The upper part of the essential.Certain phases of sucha studyare now SaltWash intertongues and ¯gradesinto the Recapture beingcarried on. This paper is a preliminaryreport i shalemember of theMorrison formation in southon theJurassic stratigraphy of the Navaio country. easternUtah, south of Blanding.The Recaptureis extensivein northeasternArizona and northwestern TheNavajo country comprises parts of north- New Mexico.The BrushyBasin shale member easternArizona, southeastern Utah and northwestern I occupiesthe upper part of theMorrlson formation in New Mexico(pl. I). The Jurassicrocks of the Black ¯ easternUtv, h andwestern Colorado and consists of Mesabasin and the southwestern part of theSan Juan thevariegated claystanes with minor lenticular sand- Basinare discussed in this paper. ill stones,conglomerates andlimestones. It is thought I to representcombinations of fluviatile and playa Intertonguing,lateral gradation and facies changes depositsand it probablycontains large contributions in theformations considered to be Jurassicand Jurassic of volcanicash. These deposits cannot be differen- (?)¯ obscure the regional correlations. This paper I tlatedfrom the lower part of theMorrison in central presentsonly preliminary concluslons as to correlations Colorado.The Brushy Basin is similarto thetypical amongthe strata. Morrlsonof mostof thewestern interior of the UnitedStates. In the Blandingarea of southeastern The nomenclatureused in thispaper follows closely I Utahthe WestwaterCanyon sandstone member of the thatrecommended by Baker,Dane and Reeside(I 936, Morrisonintertongues and gradesinto the lower part p.37;1947) and Gregory’s subdivision (1938,p. 58) 0f the BrushyBasin member. The WestwaterCanyon i memberis extensivein northeasternArizona and northwesternNew Mexico. * Publicationauthorized by theDirector, U.S. GeologicalSurvey. The Winsorformation of centralKane County, **Geologists,Ground Water Branch, U.S. Geological I: southwesternUtah, may occupythe stratigraphic Survey. ! I 95 !