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Stratigraphy of the Uppermost Triassic and the Jurassic Rocks of the Navajo Country John W

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Stratigraphy of the Uppermost Triassic and the Jurassic Rocks of the Navajo Country John W New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/9 Stratigraphy of the uppermost Triassic and the Jurassic rocks of the Navajo country John W. Harshbarger, C. A. Repenning, and J. H. Irwin, 1958, pp. 98-114 in: Black Mesa Basin (Northeastern Arizona), Anderson, R. Y.; Harshbarger, J. W.; [eds.], New Mexico Geological Society 9th Annual Fall Field Conference Guidebook, 205 p. This is one of many related papers that were included in the 1958 NMGS Fall Field Conference Guidebook. Annual NMGS Fall Field Conference Guidebooks Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores 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 geoscience papers. These books have set the national standard for geologic guidebooks and are an essential geologic reference for anyone working in or around New Mexico. Free Downloads NMGS has decided to make peer-reviewed papers from our Fall Field Conference guidebooks available for free download. Non-members will have access to guidebook papers two years after publication. Members 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 our operating budget. Therefore, only research papers are available for download. Road logs, mini-papers, maps, stratigraphic charts, and other selected content are available only in the printed guidebooks. Copyright Information Publications of the New Mexico Geological Society, printed and electronic, are protected by the copyright laws of the United States. No material from the NMGS website, or printed and electronic publications, may be reprinted or redistributed without NMGS permission. Contact us for permission to reprint portions of any of our publications. One printed copy of any materials from the NMGS 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 explicit permission. This page is intentionally left blank to maintain order of facing pages. 98 NEW MEXICO GEOLOGICAL SOCIETY 0' NINTH FIELD CONFERENCE STRATIGRAPHY OF THE UPPERMOST TRIASSIC AND THE JURASSIC ROCKS OF THE NAVAJO COUNTRY By J. W. HARSHBARGER, C.A. REPENNING, and J. H. IRWIN2 The Navajo country comprises parts of northeastern mation of the San Rafael group. In accordance with rec- Arizona, northwestern New Mexico, and southeastern Utah. ommendations of Craig and others (1955), the members It is comparable in size to the State of West Virginia. of the Morrison formation are used without their original Jurassic rocks crop out in about two-thirds of this area. lithologic adjectives. The area lies in the southwestern part of the Colorado GLEN CANYON GROUP Plateaus province and includes the Black Mesa basin and The Glen Canyon group overlies the Triassic Chinle the western part of the San Juan Basin. Associated with formation and underlies the Carmel formation, which is these basins are the Zuni uplift, the Defiance uplift, and of Middle and Late Jurassic age (Imlay, 1952, p. 963). the Monument Valley upwarp. The interpretation of faunal and stratigraphic evidence pre- INTRODUCTION sented in the present paper indicates that the Glen Canyon NOMENCLATURE group should be assigned to both the Triassic and Jurassic Stratigraphic nomenclature in this report closely fol- systems. lows that recommended by Baker, Dane, and Reeside Lower boundary of the Glen Canyon group (1936, p. 37. 1947). The subdivision of the Morrison In the western, southwestern, and southeastern parts formation in this report follows that suggested by Stokes of the Navajo country, the lower boundary of the Glen (1944, p. 962-965). Figure 1 shows charts listing the Canyon group is marked by an erosional surface showing terminology used for the uppermost Triassic and the Ju- minor relief and in most places is overlain by a veneer of rassic rocks at the following selected areas in the Navajo conglomerate 1-3 inches thick. The conglomerate is com- country: Kachina Point, Navajo Creek, Mexican Water, posed mainly of pebbles derived from the Chinle forma- and Fort Wingate. The detailed stratigraphic relationships tion. In the southern and central parts of the Navajo of the units are shown on the fence diagrams ( pls. 2 and country, no indication of a break in deposition between the 3 in pocket). Chine and the Glen Canyon group has been found, and The uppermost unit of the Chinle formaton, the "A" the boundary is quite arbitrary. There it is based on lith- division as defined by Gregory (1917), has been removed ologic differences and is placed at the top of the highest from the Chinle and placed in the Wingate sandstone, the limestone in the "B" division of the Chinle. In the area lowermost formation in the Glen Canyon group, because along the New Mexico-Arizona State line, the contact in of lithologic and stratal relationships (Harshbarger, Re- most places is marked by a thin granule conglomerate penning, and Jackson, 1951). This unit is referred to in which is particularly persistent to the south. At Thoreau, this paper as the Rock Point member of the Wingate sand- N. Mex. (pl. 1), the conglomerate is in channels having stone. The upper unit of the Wingate sandstone in herein a relief of 2 or 3 feet, and at Lupton, Ariz., the basal referred to as the Lukachukai member. This member con- Wingate contains several thick conglomeratic lenses. In stitutes the entire Wingate sandstone at the original type the Shiprock area and in the area between the San Juan locality at Fort Wingate, N. Mex. A sequence of rocks and Colorado Rivers in Utah, the Chinle formation and the overlying the Wingate sandstone in the western part of Glen Canyon group appear to represent a continuous se- the area is herein referred to as the Moenave formation. quence of deposition. For the most part, conspicuous Where the Wingate is absent, the Moenave is the basal breaks in sedimentation between the Chinle and Glen Can- formation of the Glen Canyon group. The Dinosaur Can- yon are in the western and southeastern parts of the Nav- yon sandstone, a unit described by Colbert and Mook ajo country, whereas in the central part the contact ap- (1951, p. 151) as equivalent to the "orange-red sand- pears to be conformable. stone" of Ward (1901, p. 4131, is recognized in this Wingate sandstone paper as the lower member of the Moenave formation. In the Navajo country the Wingate sandstone com- The Springdale sandstone member of the Chinle formation prises two mappable units. The lower unit consists of (Gregory, 1950) is believed to be a part of the Moenave reddish-orange parallel-bedded, thin-bedded siltstone and formation and is treated in this report as the upper mem- sandstone. This unit is described as the Rock Point ber of the Moenave. In the southwestern part of the member from typical exposures near Rock Point School, Navajo country the Kayenta formation of the Glen Canyon Apache County, Ariz. (fig. 3). The upper unit consists group consists of a sequence of intercalated fine-grained of reddish-brown fine-grained sandstone which is cross- sandstone and mudstone beds. Owing to the distinctive bedded on a large scale and commonly forms vertical lithology of these rocks as compared to those at the type massive cliffs. This unit is herein referred to as the Luka- locality of the Kayenta formation, they are discussed sep- chukai member, from typical exposures along the escarp- arately in this report and are referred to as the silty facies ment north of Lukachukai, Apache County, Ariz. The Luka- of the Kayenta formation. chukai is the only member of the Wingate sandstone that The Cow Springs sandstone was defined by Harsh- is present at the type locality near Fort Wingate. The Rock barger, Repenning, and Jackson (1951) as a formation Point and Lukachukai members are closely related, as indi- laterally equivalent to parts of both the San Rafael group cated by their lithologic character and strata! relations. and the Morrison formation and is so used in this report. Rock Point member The Bluff sandstone is referred to as the uppermost for- The name Rock Point member of the Wingate sand- 1 Publication authorized by the Director, U. S. Geological Survey. Abstracted from U. S. Geological Survey Prof. Paper 291, 1957. 2 Geologists, U. S. Geological Survey. UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY PROFESSIONAL PAPER Ast Pit 1r e Mesa 'XiY NAVAJO ..., / MONUMENT C CORNERS MONTEZUMA CAD _ 1 . _ _ ■.,.1- a . e SAN :JUAN . _ mesa - - --"T-EAN JUAN CO V ALLEY IIi- 977: .ist 4" /2 CINexican ater -..-7- - - --. FOUR 9 I 1, -L■ 6 13 • ') 1 "4b_, ls\ CARRIZOat _,_„,. SS"i 9 _ ll ,.0. 1Sitla, iiBito _ ..0Dinnehoteo 04, 1 1 ii,i 1 3 El Tvend• a 0 , , Shiprock l;, 0 1-. -• III- I I ,q,, $ Mesa ,11, c., ._ _ • 6 A ' MOUNTAINS < ° -9- I II __,‘,Far mine° I /I/ Kayentaii 1A,, , 8 . -- ' ...,,,, Rock PointIti 1 9 Betatakin ci e frf Ruin I c, r 9/ 113 4,, .2 0 Red Ree,,, Z / I Kaibito / // I BLACK-, G. // I ) ) ,‘ ,s,,,/, : it C R X. °Round Rock ,....,"‘% ,-.., i 9I I .9/ IIS • - -- -41 X //,_ , II '1 1 : ,. _w , . - ., rs.: "-. - / /1,h-- , ,s9.74,-, 7 ,, 1 S .9-. 5 7/ I Roughmi = .-_ _ 0 LukachukiQ/ 74 7 : s--° 0, , '% 1 i I Rock Yak N . / M it A ,-,7,/ 9, / 0, / Many pis ' , , Farms '' I ' / //i 2 818 i Sr 7Gap ..f°Recl Lake 1 I ,Li/d'- ..- /I -SI i o .1\ : 9 1," I C/ I i oToadleNnT ..(\ // / ./ 1 .
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