<<

Petrology of the , Quarry Quadrangle,

by

S. A. Bi/bey, R. L. Kerns, Jr., and J. T. Bowman

UTAH GEOLOGICAL AND MINERAL SURVEY a division of the UTAH DEPARTMENT OF NATURAL RESOURCES State Capitol, Salt City, Utah

SPECIAL STUDIES 48 PRICE $1.00 APRIL 1974

Petrology of the Morrison Formati~ Dinosaur Quarry Quadrangle, Uta by s. A. Bilbey, R. L. Kerns, Jr., and J. T. Bowman

Dinosaur National Monument Quarry. Dinosaur National Monument, Utah. National Park Service, Department of the Interior.

UTAH GEOLOGICAL AND MINERAL SURVEY a division of the UTAH DEPARTMENT OF NATURAL RESOURCES State Capitol, Salt Lake City, Utah

SPECIAL STUDIES 48 PRICE $1.00 APRIL 1974 CONTENTS

Page Page Abstract ...... 1 References ...... 13

Introduction ...... 1 ILLUSTRATIONS Acknowledgements ...... 2 Figure General Geology ...... 3 1. Index map of the western portion of Dinosaur National Monument ...... 4 Methods ...... 3 2. Stratigraphic columns of measured sections in Dinosaur National Stratigraphy ...... 3 Monument including Upper through Lower Formations ...... 5 Mineralogy ...... 7 3. Relative abundances of montmorillonite, illite, and kaolinite above and below Petrography ...... 9 unit boundaries in section 2 ...... 8

Stratigraphic Correlations ...... 11 Table 1. Distribution of minerals in the Depositional Environments ...... 11 Curtis, Morrison, Cedar Mountain, Models of Clay Formation ...... 11 and Dakota Formations as determined Source Area ...... 12 by X-ray diffractometry ...... 8 ...... 12 2. Physical properties as determined by Morrison Formation, Salt Wash Member ...... 12 petrographic analyses of selected Morrison Formation, Brushy Basin Member ...... 12 samples from section 2 ...... 9 ...... 13 3. Mineralogical properties as determined by petrographic analyses of selected Conclusion ...... 13 samples from section 2 ...... 10

iii PETROLOGY OF THE MORRISON FORMATION, DINOSAUR QUARRY QUADRANGLE, UTAH

by Sue Ann Bilbeyl, Raymond L. Kerns, Jr.2, and James T. Bowman 3

ABSTRACT southern and central Utah to Iowa and (peterson, 1972). The strata later aSSigned to the Mineralogical and petrographic analyses of the Morrison Formation in Dinosaur National Monument Upper Jurassic-Lower Cretaceous units in the vicinity of were originally described as part of the Flaming Gorge the Dinosaur National Monument Quarry near Jensen, Group (Powell, 1876), until the discovery of the dino­ Utah, have clarified the units' characteristics and the saur beds near Jensen, Utah, caused the strata to be locations of formational boundaries. The lower part of formally recognized as the Morrison Formation the Morrison Formation is distinguished by less illite (Gilmore, 1916). and more kaolinite in contrast to the underlying Curtis Formation which contains approximately equal Due to the lack ofa diagnostic age indicator of amounts of illite and kaolinite. The Salt Wash Member the Morrison Formation, there has been considerable and the Brushy Basin Member of the Morrison are controversy over whether it is Jurassic, Cretaceous, or both lithologically and mineralogically identifiable in both. Eldridge (Emmons et ai., 1896) originally as­ this area. Above the boundary between the two, kao­ signed the unit to the Jurassic period, but others (Lee, linite decreases and illite increases. In the strata above 1915; Osborn, 1915) claimed that it is of Cretaceous the Morrison, here recognized as an extension of the age. The consensus of more recent reports is that the Cedar Mountain Formation, kaolinite is the dominant Morrison Formation represents the Upper Jurassic from clay mineral, and illite is almost completely absent. to early Portlandian (Simpson, 1926; The formations in the area represent differing deposi­ Baker et ai., 1936; Imlay, 1952). tional environments: the upper Curtis Formation is a ne ar-shore marine deposit, the members of the In the area of Dinosaur National Monument, the Morrison Formation are fluvial and lacustrine and Morrison Fonnation rests on the Upper Jurassic Curtis possible climatic or depositional changes during the Formation and underlies unnamed Lower Cretaceous depositional period are equated with the changes in the rocks (Reeside, 1923; Untermann and Untermann, clay content, and the Lower Cretaceous sediments now 1949; Bradley, 1952). Stokes (1952; 1955) identified comprising the Cedar Mountain Formation overlying the Cedar Mountain Formation as far north as the the Morrison were formed in a transitional zone south flank of the Uinta Mountains and speculated on (fluvial to littoral) and were eventually covered by the its correlation with the unnamed Lower Cretaceous (littoral). rocks in Dinosaur National Monument. To facilitate the ensuing discussion, the unnamed unit above the INTRODUCTION Morrison and below the Dakota will be called the Cedar Mountain Formation. The Morrison Formation, originally defined as the variegated shales and found in the eastern The Morrison Fonnation has been divided into foothills of the of the four members~the Salt Wash Member (Lupton, 1914; near Morrison, , was named by Cross (I 894). Gilluly and Reeside, 1928), the Brushy Basin Member, Eldridge first described and placed definite boundaries the Westwater Canyon Member, and the Recapture on an incomplete section near Morrison (Emmons and Member (Gregory, 1938). Of these four, only the Salt others, 1896). These boundaries were redefined by Lee Wash and Brushy Basin Members extend into north­ (1920), but the type section was not completely de­ eastern Utah (Craig et ai., 1955). scribed until 1944 (Waldschmidt and Leroy, 1944). The formation has since been recognized over an area The Salt Wash Member is recognized as the oldest of more than 600,000 square miles from southern member of the Morrison Formation, correlative in part Canada to central and , and from with the Recapture Member (Craig et ai., 1955), and is characterized by two lithologies~white to pale brown, 1 Department of Geology and Geophysics, University of Utah, massive, ridge-forming sandstones and greenish-gray to Salt Lake City, Utah 84112. dark reddish-brown siltstones and mudstones. The silt­ 2 Assistant Professor of Geology, Utah State University, Logan, Utah 84322. stones and mudstones are poorly resistant and thick­ 3 Associate Professor of Biology, Utah State University, Logan, bedded (Cadigan, 1967). The origin of these sediments Utah 84322. was mainly a source with some 2 Utah Geological and Mineral Survey Special Studies 48, 1974 evidence for a minor volcanic source (Cadigan, 1967). The presence of dinosaur bones and uranium has The thickening of this deposit and the increase in grain stimulated extensive petrologic and petrographic work size to the west and southwest and the thinning to the on the Morrison. Mook's (1916) discussion of descrip­ east and northeast indicate major source areas in tive petrography and petrology laid the foundation for Arizona, southern Nevada, and western Utah (Mook, many of the studies which followed. Interest in radio­ 1915; Craig et at., 1955; Cadigan, 1967). active minerals has prompted several mineralogical analyses of the clay minerals in the formation (Weeks, The Brushy Basin Member is the younger of the 1953; Keller, 1953, 1959, 1962); other such studies two members present and is correlative with the have been directed toward clarifying the depositional Westwater Canyon Member in New Mexico (Cadigan, environment and source areas (Tank, 1956; Brady, 1967). This is the more easily distinguished of the 1969; Ballard, 1966; Cadigan, 1967; Suttner, 1968; members due to its diagnostic variegated shales and Furer, 1970). Wahlstrom (1966) included some geo­ mudstones. The beds vary in color from pale green to chemical data on the Morrison, and many workers have reddish-brown to purple. The lithology of this member investigated the ore deposits (see Brown, 1961, for a is not restricted, however, to shales. Between some of comprehensive bibliography). these shales are thick-bedded, lenticular, conglomeratic sandstones containing the well-known dinosaur The Cedar Mountain Formation was originally fauna. The source area of the fine-grained sediments is defined on the southwestern flank of Cedar Mountain, the same as that of the Salt Wash, but with lower Emery County, Utah, by Stokes (1944), as part of the gradients, which account for the finer grain size (Craig Cedar Mountain Group which included both the Cedar et al., 1955; Cadigan, 1967). The Brushy Basin also Mountain Formation and the Buckhorn . contains large quantities of volcanic tuff fragments, in­ Stokes (1952) combined the two units. These Lower Cretaceous rocks are found above the Morrison Forma­ dicating a possible volcanic source area to the wes't tion in the area. Stokes (1952) (Hess, 1933; Stokes, 1944; Keller, 1953, 1962; Peter­ measured many sections of the Morrison Formation son, 1966; Cadigan, 1967; Suttner, 1968, 1969; Brady, and the strata above the Morrison along the south 1969; Furer, 1970). flank of the Uinta Mountains. He found the same lithologies and the same stratigraphic relationships as in According to Mook (1916), the deposition of the the San Rafael Swell, where the formation was first Morrison Formation took place on a peneplain fed by identified. several major streams and by many minor intermittent ones in which sediments accumulated in and According to Stokes (1944), the Buckhorn Mem­ floodplain marshes. Mook also postulated that, as on ber of the Cedar Mountain Formation is a massive con­ any flat plain near sea level, there was much shifting of channels and reworking of sediments to form the glomerate with chert pebbles 1.25 inch in diameter and greatly variable lithology, both laterally and vertically. smaller, gradually changi~g to a' thin-bedded, coarse­ The climatic conditions at the time of deposition of grained along the northern edge of the mem­ the Morrison Formation were compared to those of ber. The shales and sandstones of the Cedar Mountain the modern Yangtze and Hwang-Ho plains. Mook Formation above the Buckhorn Member are similar to considered the fossil flora and the semi-aquatic fauna those of the Morrison Formation, however, the colors to be indicative of a wet, hot climate. in the shales are less variable and more subdued. The lower shales are pale red to light purple, grading up­ ward to dull gray and white. There are numerous len­ Stokes (1944), on the other hand, argued that a ticular sandstones which appear to be channel deposits. wet climate is not indicated. He found no strong evi­ In northeastern Utah, this formation is overlain by the dence for great river systems, i. e. no great increase in Dakota Formation. clastic sediments to the west, and very few plant suggesting the existence of ephemeral lakes and inter­ The present study was undertaken to complement mittent streams which provided enough water and existing stratigraphic and paleontologic data in order to vegetation for the . generate a more complete data base for interpreting the phenomena in Dinosaur National Monument. A third environment was proposed by Moberly (1960) who suggested a savannah-like climate with ACKNOWLEDGEMENTS alternate seasons of wetness and dryness. His postu­ lated paleogeography allows radical seasonal changes The authors Sincerely appreciate the critical read­ comparable to the monsoon season in Southeast Asia, ing of the manuscript by Dr. W. L. Stokes. The and accounts of the presence both of 50 feet tall National Park Service expedited the project by granting and of salt precipitates. permission for the field work to be conducted on BUbey, Kerns, and Bowman-Petrology of Morrison Formation, Dinosaur Quarry Quadrangle 3

Dinosaur National Monument lands and the coopera­ lower part of the Dakota Formation. Samples were tion of the Monument personnel was invaluable. The taken every 10 lineal feet and obvious lithologic work was completed while Sue Ann Bilbey was a changes were sampled even though they did not occur graduate student in geology at Utah State University. at the regular 10-foot intervals.

GENERAL GEOLOGY Section 2 was chosen as the representative section because it is between the other two, contains some Dinosaur National Monument is located at the facies of both, and is closest to the Dinosaur Quarry. eastern end of the Uinta Mountains in northeastern Precise correlation of the three sections is possible for Utah and northwestern Colorado (figure 1). The Dino­ only a few beds, the most prominent being the quarry saur Quarry is in the western portion of the monu­ layer because the Morrison Formation is a continental ment, seven miles north of Jensen, Utah, in the Dino­ deposit. All three stratigraphic sections are illustrated saur Quarry Quadrangle (USGS map, 7'i6,-minute survey (figure 2), but only the representative section has been series). Within the quadrangle are the three strati­ studied in detail. graphic sections discussed here. The geology of the monument area was studied extensively by Untermann Powder preparations (~3.0 ¢) of all samples from and Untermann (1949), and their work is the basis for the middle section were analysed by X-ray diffraction the following general description. to determine the relative abundances of quartz, dolo­ mite, and calcite and other minor mineral constituents, The geologic structures of the Monument area except the clay fraction. The relative quantities of include minor flank folds and faults of the Uinta illite, montmorillonite, and kaolinite were measured by Mountain system. One of the larger folds is Split analyzing scans of sedimented preparations of particu­ Mountain anticline in which the strata dip slightly at late material ~2 11, both before and after being the crest and plunge steeply (maximum dip 67°) on solvated with ethylene glycol. the flanks. Erosion of these strata has exposed the Morrison Formation almost continuously around the The samples chosen for petrographic analysis were periphery of Split Mountain. Differential weathering selected from among the consolidated sandstones, con­ and erosion of the formations form hogbacks, cuestas, glomerates, , and dolomites of section 2. A and valleys, all of which are essentially free of vege­ total of forty-eight samples were categorized according tation due to the semi-arid climate. to lithology, mineralogy, and grain size and fifteen representative slides were selected for more extensive The stratigraphic sequence exposed within Dino­ analyses; each slide was point-counted to determine the saur National Monument includes the Uinta Mountain approximate percentages of the different minerals in Group () through the Browns Park Forma­ the sample, the mineral grains were classified according tion () with the exception of rocks represent­ to roundness (Powers, 1953), grain size, and sorting, ing the through the periods. The and the entire slide was described according to the Split Mountain anticline exposes rocks from the Madi­ procedures outlined by Folk (1968). From this infor­ son Formation () through the Mancos ma tion, petrologic inferences on the source area, Formation (Upper Cretaceous) in a sedimentary depositional area, and diagenetic changes were made. sequence of limestones, dolomites, sandstones, shales, and mudstones. The Jurassic strata containing the STRATIG RAPHY Morrison Formation in which the Dinosaur National Monument Quarry is located are exposed on the south The Morrison Formation in Dinosaur National flank of the Split Mountain anticline. Monument is characterized by light gray to yellowish­ gray sandstones and conglomerates below variegated METHODS shales and mudstones, and by lenticular, light gray limestones. The sandstones are massive with lenticular, Three sections 0.3 to 0.5 mile apart were strati­ channelled conglomerates and thin shales separating the graphically measured and sampled. The Dinosaur major layers. The shales and mudstones above are thick Quarry is located between sections 1 and 2 and section units recognizable in the weathered valleys between 3 is east of section 2 (figure 1). The measured sections resistant lenticular limestones and conglomerates. A included the upper part of the Curtis Formation, the detailed stratigraphic description of the representative Morrison and Cedar Mountain Formations, and the section (section 2) is shown on page 6. lOgO I 10' I / - "' \. /' " \ ••• r------r---~------·~ ~ ~ I I '- "..-' \ ,,,,' 15° I -~ SQUAW HI ~ -_ ....__ __' .. ---_.I, \ v I , \ I G t­ ex: o UTAH z w => a::: t- r; LV ~-:f::-==-,I ------~: IT Up ~------~------~~'n~' sp \.. \ i /;--,~~ /' I \. DINOSAUR \ \/, ,,\ \", ,,\' I I .. " \ \. NA TIONAL /' \ \ /"<,,,> .,' ' ~------.~----- MONUMENT ... '" \ \,' .'\ Sp\..\i ~i~'

\ I ,\ II" \\11// ", III,.

c" I ••.'.' 11••• / ';', ~ '//1\" -"'1,\,,\ 'III'"

\ " YA M PA PLATEAU " I ------,,'---, I ,II I I , I I I I " \ I I \. , S I I !::l I , I ;:ro J LEGEND I c:'l .,. I " I (1) I 0 I -" I S TA T E BOUNDARY c °0 ~, I\) .. ---~~------' MONUMENT BOUNDARY g, UI... :~ 0 !::l IMPROVED ROADS 0 a

UNIMPROVED ROADS I « ~ TO V E RNA L 0::: ~ o 2 3 4 « ~ AND STREAMS ~ 0 .-J ~ => -::"'I SCALE OF MILES BUILDINGS 0 -- ~ • U ~ CAMPGROUNDS (1) 10 gOI 10' • (':> ~ ~ Figure 1. Index map of the western portion of Dinosaur National Monument. :::: I:l... ~' too ~ ...... '0 ~ Bi/bey, Kerns, and Bowman-Petrology of Morrison Formation, Dinosaur Quarry Quadrangle 5

SECTION I SECTION 2 SECTION 3 EXPLANATION '(]) ,422.5 :::> ~ o DAKOTA 420 p.\h A/\,· fV\.NV: w E~·:· >':

T"--+--_- ... -~ 0:: -+ -4 .. -+ ... -----+--+------..... -...;~ =- =:;:-- ....---~ w_ +-+ .... -- ~ ~ ------+------.... :: = -=..---- en ...... - ... ------.. --+--+--- ~ :::--=+=-=-=-=-::~+~ -+------+- - ..... - ... -- SHALE "'f" - ...... - "1'" - ..... - ...... W -_+_+_-.....--=-+_ ~~~~~::~=;0 -380 ------..... - .... - ..... --+-- ..... - ~ ------.....------...... - ...... ~ ------...... -+- ...... - ..... - _+_~-_4_-_--- .=-~~:~i-=-~=0~..: ------""---+--+------~- ... - ...... -1_-+ - -+.::-= -_-+-..=- .:t-=..- ..------+-+_-4-_ ..... _ ------_--.-+--+- ...... -- ...... MUDSTONE ~:Q~'-~~''''::: -+--+- ...... --+------...... - -4- _ ...... _ ...... _ .. - .. - .. _ .. _. 1-370 ------+ ...... 1~~_~~··i.1~~;-f·1 u MORRISON QUAR RY LAYER SANDY . - .. - .. - .. -. ------+ .... ;...... MUDSTONE <.f) ------.... ----+- ..... - ..... -+-""1"-1_------.... <.f) ------1-360 « -+ - -+ - .... - ..... - .... -:;. - ~ - ~ - -.... - 0::: :::> _... - ---+----~ -::::: .....- ---+-- --~ -.: - ~ =.= -= --::1 .~j,~:~~~~:.~$~:..~~.:

~~~~~\~~ - .. .. - .. - .. - .. -. -- (f) - _- .:: .:: -_ -_- _ -_- - CHERTY :J -::.. ---:.. -:.. ---- -:. :: - LIMESTONE n::: ----=-=---=--=~~_ ~~;:::,.s';_ . l~j_Li:-'; a::l -;__ ::...:-_:::-:._:._:._-= ------·.,i ------'>./ .... ·.• 1-- ? ---j -;;.-,,--=.' : -==- ::::,~ ------QUESTIO NA B LE

SCALE FORMATION o 1-330 ~cs .'(? '/{::;;\: J ::.:- ...... < 0::: W :.' 0... : ..... -320 I:':" 0... ':: 100 :::> I:'; '.' .. :,::::::'.... '::'.::; .. ':. '.: ---- ::.:: '.', :':''': ~:..'..:: '''':'',, '.: :' .- ,-.o....:~ :;:::::- ... ::\: ..: .. :;:::}~ ::..-,,;:: .- '--'.~ 200 IL">' ,:...... FEET lJ'?:j'·": :.::.:-..::\ CURTI S I:;, '/':'::":':/ >:'-: 'Y '.," ,':,:.,:.;<:: '-300 \VVVV\;\ vvvvvvv FORMATION _--- 0.5 MI. ----.----- 0.3 MI. -----_ W----E

Figure 2. Stratigraphic columns of measured sections in Dinosaur National Monument including Upper Jurassic through Lower Cretaceous Formations. 6 Utah GeolOgical and Mineral Survey Special Studies 48, 1974

Section 2: representative section. 10. Conglomeratic sandstone; yellowish-gray; poorly-sorted; fine- to coarse-grained; Location: Dinosaur National Monument; nearly N-S line 0.2 chert pebbles and quartz grains; chalcedony mile east of Dinosaur Quarry; S % central portion Sec. 26, T. cement; "quarry layer"; dinosaur bones; 4 S., R. 23 E., Uintah County, Utah. fresh water clams (Unio); ridge former ...... 19 9. Covered interval; pits reveal weathered Thickness, shaly sandstone grading into mudstone; in feet pale olive gray to greenish-gray; bentonitic with thin lenticular limestones; light Dakota Formation yellowish-gray; weathers pale yellowish- brown; 2 ft beds ...... 60 1. Conglomeratic sandstone; yellowish-gray; 8. Mudstone grading into shale; greenish­ weathers very pale orange; poorly-sorted; gray; bentonitic; lenticular limestone; fine- to coarse-grained; torrential pale yellowish-brown; resistant beds ...... 124 cross-strata; ridge former. Section offset 0.1 mile to the east returning to Sharp contact between conglomerate and poorly original transit. resistant sandstone. 7. Shale; light olive gray to dark greenish- Cedar Mountain Formation gray; weathered on the surface; bentonitic ...... 22

3. Sandstone; yellowish-gray to grayish-orange; Total Brushy Basin Member ...... 435 weathers light brown; well-sorted; fine- to medium-grained; partially covered intervals Sharp contact between shale and conglomerate. with resistant ridges between; parallel bedding with minor low-angle cross-strata ...... 90 Salt Wash Member 2. Shale with one bed of recrystallized dolomite: yellowish-gray to brownish­ 6. Conglomeratic sandstone; yellowish-gray gray; silt near the top; dolomite: to very pale orange; fine- to coarse­ very pale orange; very fine-grained; grained; po orly -sorted; low-angle 2 ft thick ...... 27 scours; dinosaur bone fragments; one 1. Sandstone; light gray to yellowish-gray; lenticular sandy limestone; yellowish-gray . 27 weathers grayish-orange; moderately- to 5. Shale; light olive gray to pale yellowish- well-sorted; fine-grained with a pebbly brown; calcareous ...... 18 base; low-angle cross-strata; ridge former ...... 23 4. Sandstone; yellowish-gray to greenish­ gray; fine- to medium-grained; shaly Total Cedar Mountain Formation ...... 140 sandstone at the base; one lenticular limestone; greenish-gray; marly; Sharp contact of pebbly sandstone with Morrison shales. 3 ft thick ...... 51 3. Conglomeratic sandstone to sandstone; Section offset 0.1 mile to the west following the yellowish-gray to grayish-orange; sandstone ridge. moderately well-sorted; fine- to medium- grained; cross-strata; slightly calcareous ...... 47 Morrison Formation 2. Shale; light olive gray to greenish-gray ...... 19 Brushy Basin Member 1. Sandstone; yellowish-gray to very pale orange; poorly- to moderately-sorted; fine­ 18. Shale; pale red to greenish-gray; silty; up to to medium-grained; thin laminae; scours; 10 ft beds; separated by lenticular dolomite petrified wood; with shale interbedded; beds: yellowish-gray; weathers light light olive gray with reddish-brown brownish-gray; 2 ft beds ...... 57 mottled; 8 ft bed; slightly calcareous ...... 72 17. Covered interval; talus of light gray limestone with chert; pits reveal yellowish-gray Total Salt Wash Member ...... 234 weathered mudstone ...... 14 16. Limestone with chert pebbles and veins; light Total Morrison Formation ...... 669 gray to yellowish-gray; 3 to 4 ft beds; ridge formers; probably source of limestone talus Contact not distinct in the field, base of sandstone in above and below ...... 19 contact with covered interval, pits reveal lithologic 15. Covered interval; talus of light gray limestone; change from sandstone to shaly sandstone. pits reveal weathered mudstone; light gray to brownish-gray ...... 71 Curtis Formation 14. Mudstone; very light gray to greenish-gray 1. Covered interval; pits reveal sandstone grading with 1 ft beds of reddish-brown; one into shaly sandstone; pale olive green to limestone bed 1 ft thick near the base ...... 50 yellowish-gray; poor- to moderate-sorting. 13. Covered interval; talus of yellowish-gray conglomeratic sandstone; pits reveal The formation immediately below the Morrison calcareous shaly sandstones; pale brown ...... 15 Formation is the Upper Jurassic, marine Curtis Forma­ 12. Conglomeratic sandstone; yellowish-gray; tion, containing dull gray shales and light colored, poorly-sorted; coarse-grained; scours; mostly chert pebbles; calcareous cement...... 4 thin-bedded, friable sandstones. The origin is deduced 11. Mudstone; grayish-red ...... 2 from the presence of fossils of belemnites, oysters, and BUbey, Kerns, and Bowman-Petrology of Morrison Formation, Dinosaur Quarry Quadrangle 7

other marine invertebrates. The predominant sandstone been replaced with Si02 and the unit containing the is a medium-grained ridge-fonner near the upper con­ quarry conglomerate has a Si02 (chalcedony) cement tact and includes ripple marks, channel scours, and which is different from many of the other sandstones wonn burrows. In the shaly sandstones immediately and conglomerates in the section haVing a CaC03 above the predominant sandstone there were no fossils cement. Casts of Unio and carbon traces of identified. Just below the contact with the Morrison, are also preserved (White, 1968). The major the lithologies are characterized by easily-weathered, fossil-bearing layer is found from 100 to more than light olive to yellowish-gray, shaly sandstones. 200 feet below the upper contact of the Morrison.

The basal unit of the Morrison Formation is a More lenticular limestones and massive sections of moderately well-sorted, cross-bedded sandstone mem­ shales are found above the quarry layer. Scattered on ber, the Salt Wash, which is yellowish-gray, of variable the surface of the shales are pieces of limestone and thickness, and contains some petrified wood. Higher in well-polished chert pebbles known as "". The the member, in a similar type of sandstone, poorly source of these pebbles, which are probably wind pol­ preserved fossil dinosaur bones are found but no other ished, is not known, but they are thought to have been fossils were 'noted. originated higher in the section and were carried down the weathered shale slopes. None have been found in Intercalated with the sandstones of the Salt Wash association with the fossil dinosaur bones at the are a few thin layers of shale varying in color from quarry. light reddish-brown to greenish-gray, usually averaging only a few feet in thickness with rare exceptions rang­ The upper contact is not always easily located. In ing to 30 feet. The lower shales are characterized by the area studied, a ridge-forming conglomeratic sand­ mottled red and green colors, though neither color stone grading into a fine-grained sandstone was selected dominates and they may be a result of present as the lowermost part of the Cedar Mountain Forma­ wea thering. tion because it overlies the typical greenish-gray and pale red shales diagnostic of the Morrison. Although Lenticular conglomerates are closely interbedded this sandstone appears to be lenticular, it has moderate with sandstones in the upper part of the Salt Wash lateral extent, and its mineralogy is more similar to the Member. These conglomerates occur as cross-cut thickly-bedded sandstones above than to those of the channel deposits within the sandstones and contain Morrison. This Cedar Mountain basal unit may corre­ pebbles greater than 2 cm in diameter set in a matrix late with the Buckhorn Member of Stokes (1944, of smaller pebbles, sand, silt, and clay. Most of the 1952). Bradley (1952) correlated the shales and sand­ pebbles are sub-rounded chert fragments. The enclosing stones above the contact with the Cedar Mountain sandstone contains both quartz and chert grains. Formation, and Stokes (1952) speculated that these beds are, indeed, an extension of the Cedar Mountain The upper Brushy Basin Member includes a large Formation. amount of variegated shales and mudstones. These rocks, which are best recognized by the well-segregated MINERALOGY color variations and sharp boundaries between beds, range from grayish-red to light gray to greenish-gray to The X-ray diffraction scans of the samples from pale reddish-purple. The grayish-green mudstones are section 2 showed differences in the mineralogies of the bentonitic, showing typical "pop-corn" texture. Curtis Formation and the Morrison Formation, of the members of the Morrison Formation, and of the Within these shales and mudstones are lenticular, Morrison and the beds above it. Scans of the powdered thin-bedded, yellowish-gray to light gray limestones. samples revealed varying amounts of quartz, feldspar, They are very fine-grained, with an occasional calcite, dolomite, and barite throughout the section -like structure noted in the field, but no fossils (table 1). Unfortunately, no direct correlation could be appeared in thin sections. Abundant secondary calcite made from these data in identifying boundaries. and chalcedony fill fissures and partially replace the limestone. The lithologic changes at the contacts between the units are reflected in the corresponding clay­ The lenticular conglomerates and sandstones of mineral suites (figure 3). Near the top of the Curtis the Brushy Basin Member forming ridges are relatively Formation, in a mixture of sandstones, shales and scarce in this area with one important exception, the shaly sandstones, the relative abundances of illite, quarry layer. This cross-bedded conglomeratic sand­ montmorillonite and kaolinite are variable but stone contains the fossil remains of at least fourteen approximately equal. Just above the contact between species of dinosaurs, three species of , and two the Curtis and the Morrison Formation (Salt Wash species of (White, 1968). The bones have Member), illite disappears almost entirely from the 8 Utah Geological and Mineral Survey Special Studies 48, 1974

Z illite gradually disappears from all lithologies, but is f­ not accompanied by a reappearance of kaolinite. ~ MONTMORILLONITE ILLITE KAOLIN ITE a: 410 Above the contact between the Morrison and the « o Cedar Mountain Formation, an increase in kaolinite is w u ------~______J correlated with the return of sandstone.

Montmorillonite is present, with few exceptions, as the dominant clay mineral throughout the entire section. Its abundance shows no marked change from below the lower contact of the Morrison through the contact between the members of the Morrison, though in some parts of the Brushy Basin Member, especially the middle and upper portion, it is the only clay >- I (/l present in measurable quantities. There is, however, a :::> a: marked relative decrease in total montmorillonite con­ CD tent near the upper Morrison contact and through the z beds above . 0 (/l - a: a: Apart from the three major clays, only two other 0 ~ I types appear in the scans. One is chlorite, which was (/l « 3: found in only two samples in the entire section, both near the bottom: one in the Curtis and the other in f- the lower part of the Morrison. The other clay is a -l « (/l mixed-layer illite-montmorillonite. It appears four times, once in the Salt Wash Member and three times in the Cedar Mountain Formation above the Morrison. (/l The mixed-layer clays may actually be more prevalent f- a: I :::> 0 5 10 0 5 10 0 5 10 than indicated by the scans, since solvating the clay u may have resulted in preferential identification of montmorillonite. Figure 3. Relative abundances of montmorillonite, illite, and kaolinite above and below unit boundaries in section 2. Dolomite was rare in the scans of powdered sandstones. The relative abundance of kaolinite de­ samples except near the lower and upper boundaries of creases above the contact of the Salt Wash , with the the Morrison. The microcrystalline carbonate rocks Brushy Basin paralleling the change of sandstone to which appear throughout the upper member are, for shales and mudstones which contain appreciable the most part, limestones. Even where dolomite is quantities of illite. Near the top of the Brushy Basin , abundant, near the top, some calcite is also present. Table 1. Distribution of minerals in the Curtis, Morrison (Salt Wash and Brushy Basin Members), Cedar Mountain, and Dakota Formations as determined by X-ray diffractometry. Entries are number of samples and, in parentheses, percentage of samples which contained detectable quantities of each mineral.

Quant' (100%) Feldspar CalCite Dolomite a , Barite (100%) , Montmorillonite (' 100~ )

I Very low relative abundance in 31 of the 33 samples. 2 Includes 11 limestones. 3 As dolomite in upper Brushy Basin and lower Cedar Mountain. "Predominant clay in upper half. 5 Very low relative abundance in sandstones and conglomerates. 6 Absent at top. 7Very low relative abundance in shales and mudstones. Bilbey, Kerns, and Bowman-Petrology of Morrison Formation, Dinosaur Quarry Quadrangle 9

This situation holds through the upper contact and The conglome ra te (324) is classified as a into the beds above. moderately-sorted conglomeratic sandstone : calcitic and chalcedonic, submature, tuffaceous chert-arenite. PETROGRAPHY The detrital grains include quartz, chert, and devitrified tuff fragments. The chert and tuff fragments are Detailed data from the petrographic analyses are morphologically similar except that the tuff fragments recorded in tables 2 and 3 which should be consulted have shard remnants in the recrystallized material. This in connection with the following descriptions. The conglomeratic sandstone is a cross-bedded, channel classifications of the sandstones and conglomerates are deposit. taken from Folk (I 968). The limestones and dolomites are classified by the scheme used by Bissell and Chilin­ The limestones (332) found in the lower member ger (1967). are classified as detrital micritic varieties. A crypto­ crystalline calcite matrix constitutes most of the rock; The sample (300) selected for petrographic study fissures are filled with sparry calcite cement. The silt­ of the upper portion of the Curtis Formation is a sized to very fine sand-sized quartz, chert, and feldspar well-sorted, silty, very fine sand: calcitic, submature, are trapped in the matrix of the limestone. subchertarenite. Its main terrigenous constituents are quartz and chert; other minerals and rock fragments Most of the rocks of the upper Brushy Basin are minor. The bonding agent is sparry calcite cement Member of the Morrison are shales and mudstones. which fills all the spaces between the grains, making Within these layers are lenticular limestones, dolomites, the porosity of the rock very low. In the field, cross­ and conglomerates. Each of these was sampled, and bedding and rippl~ marks are present in this unit. No representative examples were described petro­ fossils were found in the sampled stratum although graphically. gastropods and belemnites were observed lower in the formation. Detrital micritic limestones represented in tables 2 and 3 by sample 360B, consist predominantly of The lower Salt Wash Member of the Morrison cryptocrystalline calcite matrix in the lower and Formation is divisible into several lithologies , primarily middle portions of the upper member, with calcite spar sandstone and conglomerate, with minor limestone and fllling the fissures within the matrix. Fine-grained de­ shale. One sample of each of these except the shale trital quartz is present in very minor quantities. No was chosen for detailed petrographic analysis. The fossils were seen in the thin sections, although a few sandstone (313) is classified as a moderately well­ ostracod-like structures were seen in the field. sorted, medium sandstone: calcitic, submature, sub­ chertarenite. The detrital sediments include quartz, In tables 2 and 3, sample 389 is listed as repre­ chert, and chalcedony, with minor quantities of feld­ sentative of the crypotocrystalline micritic dolomite spar and volcanic rock fragments with clay in the observed in the upper portion of the upper member. It matrix. Sparry calcite cement fills the pore spaces has the same texture and appearance as the calcite in within the rock. the limestones except for more extensive brecciation

Table 2. Physical properties as determined by petrographic analyses of selected samples from section, ~.

Grain f s~e Median(mm) Silt

CUrtis Formation 300 93 60 0.05-0.33 0.11 0.11 0.5 +0.30 0 74 26 Salt Wash Member of the Morrison f<'ormation 313 101 76 0.07-0.90 0.2'6 0.31 +'0.10 0 100 0 324 97 71 ' 0.05-2.25 0:65/, 1.00 +0.04 ' 5 94 1 f 33f···:·; 21 [5 ,, 0.02-0.10 0;03.; 0.04 NA o. 29 7L Brushy Ba~nMember of the Morrison Form'ation 360B 16 13 0.02-0.11 0,.05 0.07 NA NA 0 50 50 363.5 77 55 0.13-2.25 1'.00 1.10 1.0 +0.14 13 87 0 389 7 5 0.03-0.14 0.05 0.06 NA NA 0 43 57 Cedar Mountain Formation 94 68 0.05-0.52 0.13 0.16 0.8 -0.40 0 97 3 0 0 10 Utah Geological and Mineral Survey Special Studies 48, 1974

Table 3. Mineralogical properties as determined by petrographic analyses of selected samples from section 2.

'Salt Wash Memher «'<- <- ,,: 15-0'.33, :'0 ..2£) 67 33 () cl'; 07.;-q. 52 0:26 35': 63 ... o O.13-(J.52: 0;:20 703ci, o Q"tS:-O;90 0: ',2~ 67 33 o 0: 19~0 '. 52; , .0.33 67 >' 33, o ', 0: 15'dJ'.90 0:)'5 0' 10Et , o

50 :' 50 0 &0,' 20 0 50 : 50 0 "0 < 100 0

Dolo. mat, Fe slain ':',

1 C = Chalcedony; Ch = Chert; CI = Clay; H = Hematite; M = Microcline; P = Plagioclase; Q = Quartz; RF = Rock fragments; S = Sanidine; T = Tourmaline; TF = Tuff fragments. 2U = Undulatory; N = Non-undulatory; P = Polycrystalline. 3 SA = Subangular; SR = Subrounded; 0 = Other; R = Rounded. ~c.cem. = Chalcedony cement; Cal. cern. = Calcite cement; Cal. mat. = Calcite matrix; Cl. mat. = Clay matrix; Dolo . ma t. = Dolomite matrix; Fe stain = Iron stain; Qtz. ogr. = Quartz overgrowth. Bilbey, Kerns, and Bowman-Petrology of Morrison Formation, Dinosaur Quarry Quadrangle 11

within the rock itself. Dolomite in the thin sections By comparison with the descriptions by Stokes was identified by X-ray diffraction analysis of the en­ (1944, 1952), the strata above the Morrison cor­ tire rock which also revealed the presence of quartz in re s po n d stratigraphically and lithologically to the minor amounts, whereas only rare detrital quartz grains Lower Cretaceous Cedar Mountain Formation. The and undeterminable carbonates appeared in petro­ lower member of the Cedar Mountain, the Buckhorn graphic preparations. Conglomerate, is apparently absent; the only layer which might be considered temporarily correlative to it Usually the conglomerates are rare lenses within is the lowermost sandstone of the formation. This the mudstones; the predominant one at the Dinosaur sandstone has a pebbly base which might represent the quarry (363.5) is classified as a poorly sorted, con­ Buckhorn. Without further investigations, however, the glomeratic sandstone: chalcedonic, submature, tuffa­ validity of this suggestion can not be confirmed. ceous, chert-arenite composed mainly of chert and devitrified tuff fragments. In this lens are the silicified DEPOSITIONAL ENVIRONMENTS bones of dinosaurs, turtles, and crocodiles. Models of Clay Forma tion The beds of the Cedar Mountain Formation above the upper Morrison contact are typified by moderately The physico-chemical and geological conditions well-sorted sandstones, shales, and finely-crystalline for the formation of montmorillonite are discussed at dolomites. The shales were not studied petrograph­ length by Millot (1970). The association of mont­ ically. morillonite and volcanic tuff fragments suggests that the former may have arisen from the latter since vol­ The sandstones represented in the tables by canic tuff fragments, when deeply buried, may change sample 397.1 grade from moderately well-sorted, fine diagenetically to montmorillonite. Another alternative sandstone: dolomitic and calcitic, submature, sub­ gives the same result: if the tuff should fall into a chert arenite to well-sorted, fine sandstone: chalcedonic, sedimentary basin which has moderate drainage and an mature, sublitharenite. All contain large quantities of alkaline environment, it could crystallize into chert and feldspar. The differences are minor: the montmorillonite. Such an alkaline environment may chalcedonic cement replaces the calcite and dolomite result either from semi-arid climatic conditions or from cements, and the rounding and sorting improves to­ lacustrine or marine conditions. A third explanation ward the top of the section. for the fonnation of montmorillonite is based on lateritic soil. According to this model, abundant rain The dolomite (404B) in the Cedar Mountain water percolates through the soil and dissolves metal Formation is finely-crystalline. Dolomite rhombs are ions causing the solution to become increasingly more seen through the microscope, though in hand specimen alkaline. If the water is restricted to an area with poor the rock appears the same as any of the other carbon­ drainage, the metal ions combine with silicate anions ates. No detrital grains were seen, but X-ray diffraction to form montmorillonite and other clays. revealed a minor amount of quartz. Although illite formation, as described by Millot STRATIGRAPHIC CORRELATIONS (1970), can occur in a variety of depositional regimes, the process is restricted to alkaline environments, The Morrison Formation and the beds overlying it where it fonns most readily under marine conditions have been discussed at length in the literature. Al­ by the combination of potassium cations with silicate though the Morrison in Dinosaur National Monument anions. In a wet, hydrologically well-circulated, terres­ has been described stratigraphically in detail, the Salt trial regime, detrital illite will alter to kaolinite, but if Wash and Brushy Basin Members have not been iden­ the ground water becomes sufficiently enriched in tified specifically nor has the boundary between the metal cations the process will reverse. Illite also forms Morrison and the overlying beds of the Cedar in lacustrine (in which the pH is 7.5 to 8.5) and in Mountain Formation, been set. semi-arid and arid terrestrial environments where the water sequestered in basins is alkaline. Under these North of Vernal, Utah, near Steinaker Reservoir, conditions illite from older sedimentary source rocks is Craig et al. (1955) identified 285 feet of Salt Wash not altered since not enough water circulates through and 600 feet of Brushy Basin. The data of the present the system to carry away the metal ions. study show that these members extend into the monu­ ment area where they are approximately 230 feet and The fonnation of kaolinite, according to Millot 450 feet thick, respectively. Their lithologic properties (1970), is restricted to acidic environments such as are consistent with those descriptions given by Cadigan streams, which are generally slightly acidic. In this (1967) in his survey of the Morrison Formation in the process some detrital illite is altered to kaolinite which Colorado Plateau. is relatively stable, even though its long-term stability 12 Utah Geological and Mineral Survey Special Studies 48, 1974

depends on hydrologic circulation to maintain the level A change from marine to fluvial deposlts near the of dissolved metal cations below that required for con­ boundary between the Curtis Formation and the Salt version back to illite. Wash Member of the Morrison Formation is indicated by the presence of fossil marine fauna in the former and fossils of a terrestrial fauna in the latter. The sand­ Source Area stones and shales of the Curtis are moderately well­ The petrographic data suggest the sediments sorted, whereas those of the Salt Wash are variable. which formed the Curtis, Morrison, and Cedar The relative abundances of illite and calcite decrease Mountain Formations in the Dinosaur National and kaolinite is present in greater relative abundance in Monument area were derived from either a single large the Salt Wash sandstones and conglomerates, but small or several smaller source areas which were quite simi­ amounts of calcite and illite are found in almost all the lar. The sandstones and conglomerates contain minor samples. These data present a problem: the three amounts of chert, chalcedony, and other sedimentary minerals present are not all stable under the same con­ rock fragments and the quartz grains present are sub­ ditions. Considering the models of clay formation dis­ angular to subrounded and equant, which indicates cussed above, it appears that the kaolinite is primary, reworking of quartz from sedimentary rocks. Potassium having been formed in a regime characterized by effi­ and sodium feldspars are present in minor quantities cient water circulation, and the illite and calcite are (0-5%), as shown by point-counting grains in thin sec­ probably secondary, having been formed in an alkaline tions and by X-ray diffraction data, and heavy minerals ground-water regime. This interpretation is supported are essentially absent. Tuff fragments were conSistently by the observation that the calcite fills the pore spaces found, however, these may have originated near the between the grains as a coarsely crystalline spar. The depositional site and later have been carried by streams higher relative abundance of the illite and calcite in the or by the wind into the basin of deposition. fine-grained sediments is probably due to deposition in an area of restricted drainage, e.g. a lake, or a semi-arid to arid climate. Since these types of environments are Curtis Formatior. alkaline, illite would persist, calcite would form, and kaolinite would alter to illite. The montmorillonite in The rocks determined to be part of the Curtis the system probably formed from volcanic tuff, based Formation in the field have fossil and clay-mineral on observations of tuff fragments in petrographic thin assemblages indicative of a near-shore marine deposit. sections. Devitrification of the tuff could have The presence of moderately well-sorted sandstones con­ occurred in each of the three ways previously taining both illite and kaolinite is consistent with the discussed. model proposed by Smoot (1960; Millot, 1970) des­ cribing a sedimentary source area of weathered clay minerals which recrystallize to illite in the sea. Kaolin­ Morrison Formation, Brushy Basin Member ite is deposited with the sands in an acidic, fresh-water, environment. At the interface of the two depositional At the boundary between the Salt Wash Member environments, (stream mouths) mixing occurs by wave and the Brushy Basin Member of the Morrison, the and current action, preserving the kaolinite by rapid lithology changes from a dominantly sandstone unit to burial. Such a phenomenon may account for the mixed a dominantly shale unit. This lithologic change is illite and kaolinite found in the upper part of the accompanied by a reversal of the relative abundance of Curtis Formation. kaolinite and illite indicating an abrupt change from an acid to an alkaline environment. The disappearance of kaolinite and the increase in relative abundance of illite Morrison Formation, Salt Wash Member and the carbonates emphasize this change (Keller, 1956; Millot, 1970). This point, of course, assumes no As the Curtis sea withdrew, rivers and streams compositional change of the source area. carried continental deposits into a basin of deposition, the Morrison plain, covering the marine sediments. Kaolinite, which was the dominant clay in the Heavy rainfall, with consequent vigorous streams, or a sandstones of the Salt Wash, decreases appreciably in close source area could account for the moderately­ the shales and mudstones of the Brushy Basin; illite to poorly-sorted sandstones and conglomerates in the increases proportionally. One possible explanation is Salt Wash Member of the Morrison. Thin limestone that the climate changed from humid to semi-arid and beds within the sandstones indicate an entrapment of the mudstones may have been deposited on a flood­ surface water where the pH increased and carbonate plain where reduced" circulation of water enhanced the precipitated as a very fine micritic mud. The very fine stability of illite and montmorillonite. The thinly· detrital sand found in the limestones was probably of bedded limestones, containing fossil and algal aeolian origin. mounds, were most likely formed in persistent lakes. Hi/bey, Kerns, and Bowman-Petrology of Morrison Formation, Dinosaur Quarry Quadrangle 13

The conglomerates may have been formed by flash the corresponding lithologies. The boundary between floods carrying heavy loads of sediment. Another the marine Curtis Formation and the fluvial Salt Wash possible explanation is that at least some of the mud­ Member of the Morrison Formation is denoted by a stones and shales formed in a lacustrine environment. change from a marine sandstone and shale with a Under lacustrine conditions illite is stable, montmoril­ montmorillonite, illite, and kaolinite suite to fluvial lonite may form from volcanic ash, and calcite precipi­ sandstones characterized by montmorillonite and kao­ tates, but the dominance of these minerals in the linite. A reversal from the presence of kaolinite and Brushy Basin does not necessarily indicate a lacustrine lack of illite to the lack of kaolinite in the shales of environment since they can be formed under other the Brushy Basin Member reinforces the placement of conditions. Among the criteria listed by Picard (1957) the boundary between these members. Another change for distinguishing lacustrine deposits, is the presence of is noted in the clay minerals as the lithologies change mudstones which are brown, gray, or green; indurated; at the boundary of the Morrison and the Cedar sub waxy and resinous; include iron sulfides, chert, and Mountain Formations where illite, which is found in saline minerals; cemented with calcite, dolomite or very small quantities through the shales in the upper silica; varved and shaly; and associated with extensive portion of the Brushy Basin, completely disappears in and varied limestones and dolomites. Fluvial mud­ the sandstones of the Cedar Mountain and kaolinite stones, on the other hand, are red or green; friable; becomes the diagnostic clay mineral. earthy; cemented by calcite; poorly-bedded; and are associated with thin, spotty limestones. Since mud­ The clay-mineral suites are good indicators of stones satisfying both of these sets of criteria are changes in the depositional environments. The illite­ found in the Brushy Basin, it is quite possible that kaolinite suite in the upper Curtis Formation indicates each of the two types of environment occurred at an interface between marine and fresh-water environ­ different times during deposition. ments with rapid deposition. The presence of kaolinite and reduced abundance of illite in the fluvial sand­ An increase of dolomite in the upper portion of stones in the Salt Wash Member of the Morrison the Morrison suggests a period of aridity. The dolo­ indicate an acidic environment, i. e., a wet climate with mites resemble the limestones morphologically, but do enough water to carry heavy sediment loads in the show an increase in shrinkage brecciation. With streams and to dissolve the carbonates and illite which increased aridity, illite decreases in abundance and interfere with the formation of kaolinite. The Brushy grades into montmorillonite (Millot, 1970), consistent Basin Member is typified by mudstone, lenticular lime­ with the upper strata of the Brushy Basin. stomes, conglomerates, and a clay suite including montmorillonite and illite, which indicates an alkaline Cedar Mountain Formation environment, possibly either a variable semi-arid c1ima te or a lacustrine environment. The Cedar A pronounced lithologic change takes place above Mountain Formation, like the Salt Wash Member of the boundary between the Morrison and the Cedar the Morrison, contains an appreCiable amount of kao­ Mountain Formations. Paralleling an increase in sand­ linite in the sandstones, which again suggests a humid stone, kaolinite reappears sporadically near the base of climate. Also, the change in the sorting of the sand­ the unit and the carbonate minerals decrease appre­ stones indicates a progression from fluvial deposits to cia bly, leaving only quartz, kaolinite, and minor the littoral deposits of the Dakota Formation. quantities of montmorillonite. This profile of mineral­ ogical and physical characteristics indicates a deposi­ REFERENCES tional environment resembling that of the Salt Wash. Higher in the section, the sorting improves in the sand­ Baker, A. A., et aI., 1936, Correlation of Jurassic formations of stones, and the Cedar Mountain grades into a littoral parts of Utah, Arizona, and Colorado: U. S. Geol Survey deposit, the Dakota Formation, retaining the same Prof. Paper 183. clay-mineral assemblage. Ballard, W. W., 1966, Petrography of Jurassic and Cretaceous sandstones, north flank of Little Belt Mountains, CONCLUSION , in Symposium, Jurassic and Cretaceous strati­ graphic traps, Sweetgrass Arch: Billings GeoL Soc., 17th The area studied in this work is in Dinosaur Ann. Field Conf. Guidebook., p. 56-70. National Monument, at the Dinosaur Quarry, near Jensen, Utah. The sections in the Morrison _.Formation Bissell, H. J., and G. V. Chilinger, 1967, Classification of sedi­ chosen for study flank the quarry on the east and mentary carbonate rocks, in Developments in sedimentol­ ogy, v. 9A, Carbonate rocks-Origin, occurrence, and west. These were measured stratigraphically and classification: Amsterdam, Elsevier Publ. Co., p. 87-168. sampled at regular intervals. The samples were analyzed by X-ray diffraction and petrographic techniques. Data Bradley, W. A., 1952, Jurassic and pre-Mancos Cretaceous collected by X-ray diffractometry indicate a different stratigraphy of the eastern Uinta Mountains, Colorado­ clay-mineral assemblage for each unit correlating with Utah: UnpubL M. S. thesis, Univ. of Colo., Boulder, Colo. 14 Utah Geological and Mineral Survey Special Studies 48, 1974

Brady, L. L., 1969, Stratigraphy and petrology of the Morrison ----1920, Type section of the Morrison Formation: Am. Formation of the Canon City, Colorado area: Jour. Sed. Jour. Sci, ser. 4, v. 49, p. 183-188. Pet., v. 39, p. 632-648. Lupton, C. T., 1914, Oil and gas near Green River, Grand Brown, A., 1961, Geologic investigations of radioactive de­ County, Utah: U. S. Geol. Survey Bull 541. posits, 1942-1960, in A bibliography of U. S. Geological Survey publications on the geology of radioactive Millot, G., 1970, Geology of clays: Springer-Verlag, New York. deposits: U. S. Geol Survey Rept. TEI-777.

Cadigan, R. A., 1967, Petrology of the Morrison Formation in Moberly, R., Jr., 1960, Morrison, Cloverly, and Sykes the Colorado Plateau region: U. S. Geol. Survey Prof. Mountain Formations, northern Big Horn Basin, Paper 556. and Montana: Geol. Soc. Am. Bull., v. 71, p. 1137-1176.

Craig, L. C., et af., 1955, Stratigraphy of the Morrison and Mook, C. c., 1915, Origin and distribution of the Morrison related formations, Colorado Plateau region, a preliminary Formation: Geol. Soc. Am. Bull., v. 26, p. 315-322. report: U. S. Geol. Survey Bull. 1009-E. ----1916, A study of the Morrison Formation: New York Cross, C. W., 1894, Description of the Pikes Peak quadrangle, Acad. Sci Annals, v. 27, p. 39-191. Colorado: U. S. Geol. Survey Geol. Atlas, Folio 7. Osborn, A. F., 1915, Close of Jurassic and opening of Emmons, S. F., et al., 1896, Geology of the in Cretaceous time in : Geol. Soc. Am. BulL, Colorado: U. S. Geol. Survey Mono. 27. v. 26, p. 295-302.

Folk, R. L., 1968, Petrology of sedimentary rocks: He mph ills, Peterson, J. A., 1966, Sedimentary history of the Sweetgrass Austin. Arch, in Symposium, Jurassic and Cretaceous stratigraphic traps, Sweetgrass Arch: Billings Geol. Soc., 17th Ann. Furer, L. c., 1970, Petrology and stratigraphy of non-marine, Field Conf. Guidebook. Upper Jurassic-Lower Cretaceous rocks of western Wyoming and southeastern Idaho: Am. Assoc. Petrol. ----1972, Jurassic System, in Geologic atlas of the Rocky Geol. Bull., v. 54, p. 2282. Mountain Region: Hirschfeld Press, Denver, Colo.

Gilluly, J., and J. B. Reeside, Jr., 1928, Sedimentary rocks of Picard, M. D., 1957, Characteristics of fluvial and lacustrine the San Rafael Swell and some adjacent areas in eastern rocks in Tertiary beds of Uinta Basin, Utah: Jour. Sed. Utah: U. S. Geol. Survey Prof. Paper 150-D. Pet., v. 27, p. 373-377.

Gilmore, C. W., 1916, Description of a new species of tortoise Powell, J. W., 1876, Report on the geology of the eastern from the Jurassic of Utah: Annals Carnegie Museum, v. portion of the Uinta Mountains: U. S. Geol. and Geog. 10, p. 7-12. Survey Terr.

Gregory, H. E., 1938, The San Juan country: U. S. Geol. Powers, M. C., 1953, A new roundness scale for sedimentary Survey Prof. Paper 188. particles: Jour. Sed. Pet., v. 23, p. 117-119.

Hess, K. F., 1933, Uranium, vanadium, radium, gold, silver, Reeside, J. B., Jr., 1923, Notes on the geology of Green River and molybdenum sedimentary deposits, in Ore deposits of Valley between Green River, Wyoming and Green River, the western states (Lindgren volume): Am. Inst. Min. Met. Utah: U. S. Geol. Survey Prof. Paper 132. Eng., p. 450-481. Simpson, G. G., 1926, The age of the Morrison Formation: Imlay, R. W., 1952, Correlations of the Jurassic formations of Am. Jour. Sci., ser. 5, v. 12, p. 198-216. North America, exclusive of Canada: Geol. Soc. Am. Bull., v. 63, p. 953-960. Smoot, I. W., 1960, Clay mineralogy of pre- sandstones and shales of the Illinois Basin, part III-Clay Keller, W. D., 1953, Clay minerals in the type section of the minerals of various facies of some Chester formations: Morrison Formation: Jour. Sed. Pet., v. 23, p. 93-105. Illinois State Geol. Survey, v. 293, p. 1-19.

----1956, Clay minerals as influenced by environments of Stokes, W. L., 1944, Morrison Formation and related deposits their formation: Am. Assoc. Petrol. Geol. Bull., v. 40, p. in and adjacent to the Colorado Plateau: Geol. Soc. Am. 2689-2710. Bull., v. 55, p. 951-992.

----1959, Clay minerals in the mudstones of the ore­ ----1952, Lower Cretaceous in Colorado Plateau: Am. bearing formations, in R. M. Garrels and E. S. Larsen, Assoc. Petrol. Geol. Bull., v. 36, p. 1766-1776. Geochemistry and mineralogy of the Colorado Plateau uranium ores: U. S. Geol. Survey Prof. Paper 320, p. ----1955, Correlation of formations of Utah: 113-119. Am. Assoc. Petrol. Geol. Bull., v. 39, p. 2003-2019.

----1962, Clay minerals in the Morrison Formation of Suttner, L. J., 1968, Clay minerals in the Upper Jurassic-Lower the Colorado Plateau: U. S. Geol. Survey Bull. 1150. Cretaceous Morrison and Kootenai Formations, south­ western Montana: Earth Sci. Bull., v. 1, no. 4, p. 5-14. Lee, W. T., 1915, Reasons for regarding the Morrison an intro­ ductory Cretaceous formation: Geol. Soc. Am. Bull., v. ----1969, Stratigraphic and petrographic analysis of 26, p. 303-314. Upper Jurassic-Lower Cretaceous Morrison and Kootenai Bi/bey, Kerns, and Bowman-Petrology of Morrison Formation, Dinosaur Quarry Quadrangle 15

Formations, southwestern Montana: Am. Assoc. Petrol. Waldschmidt, W. A., and L. W. Leroy, 1944, Reconsideration Geol. Bull., v. 53, p. 1391-1410. of the Morrison Formation in the type area, Jefferson County, Colorado: Geol. Soc. Am. Bull., v. 55, p. Tank, R. W., 1956, Clay mineralogy of Morrison Formation, 1097-1113. area, Wyoming and : Am. Assoc. Petrol. Geol. Bull., v. 40, p. 871-878. Untermann, G., E., and B. R. Untermann, 1949, Geology of Weeks, A. D., 1953, Mineralogic study of some Jurassic and Green and Yampa River canyons and vicinity, Dinosaur Cretaceous claystones and siltstones from western National Monument, Utah and Colorado: Am. Assoc. Colorado and eastern Utah: U. S. Geol. Survey Rept~ Petrol. Geol. Bull., v. 33, p. 683-695. TEI-285. Wahlstrom, E. E., 1966, Geochemistry and petrology of the Morrison Formation, Dillon, Colorado: Geol. Soc. Am. White, T. E., 1968, Dinosaurs at home: Vantage Press, Inc., Bull., v. 77, p. 727-739. New York. UTAH GEOLOGICAL AND MINERAL SURVEY

103 Utah Geological Survey Building University of Utah Salt Lake City, Utah 84112

TIlE UTAH GEOLOGICAL AND MINERAL SURVEY, a Division of the Utah Department of Natural Resources, operates with a professional staff under the guidance of a policy-making Board appointed by the Governor of Utah from various representatives of industry and the public as specified by law.

The Survey is instructed to investigate areas of geOlogic and topographic hazards, to survey the geology and mineral occurrences, and to collect and distribute reliable information concerning the mineral industry and mineral resources, topography and geology of the state so as to contribute to the effective and beneficial development of the state. The Utah Code, Annotated, 1953 Replace­ ment Volume 5, Chapter 36, 53-36-1 through 12, describes the Survey's functions.

Official maps, bulletins, and circulars about Utah's resources are published. (Write to the Utah Geological and Mineral Survey for the latest list of available publications.)

THE LIBRARY OF SAMPLES FOR GEOLOGIC RESEARCH is a library for stratigraphic sections, drill cores, well cuttings, and miscellaneous samples of geologic significance. Initiated by Lhe Utah G(~o]ogical and :Mineral Survpy in cooperaLion with the departments of geolog~ of the universities in the state, the ULah Geological Society, and the Intermountain Association of Petro­ leum Geologists, the library was made possible m 1951 by a grant from the University of Utah Research Fund and is maintained hy donations of collections from mineral resource companies operating in Utah. It collects, catalogs, and systematically files geologically significant specimens for library reference, comparison, and research, particularly cuttings from important wells and explora­ tory holes drilled in Utah, and from strategic wells in adjacent states. For catalogs, facilities, hours and service fees, contact the Utah Geological and Mincral Survey.

THE SURVEY'S BASIC PHILOSOPHY is that of the U. S. Geological Survey, i. e., our employees shall have no interest in lands wiLhin Utah where there is a conflict of interest deleteri­ ous to the goals and objectives of the Survey; nor shall they obtain financial gain by reason of information obtained through their work as an employee of the Survey. For permanent employees this restriction is lifted after a two- absence; for consultants employed on special problems, therc is a similar Lime period which can be modified only after publication of the data or after the data have been acted upon. For consultants, there are no restrictions beyond the field of the problem, except where they are working on a broad area of the state and, here, as for all employee~, we rely on their inherent integrity.

Diredors: Donald T . .McMillan, 1974- William P. Hewitt, 1961-1974 Arthur L. Crawford, 1949-1961