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The Upper Part of the Upper Triassic Chinle Formation and Related Rocks

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The Upper Part of the Upper Triassic Chinle Formation and Related Rocks, . Southeastern U tab and Adjacent Areas By ROBERT B. O'SULLIVAN SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 644-E I Prepared in cooperation with the Bureau of Indian Affairs and the Navajo Tribe i UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1970 UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HICKEL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 40 cents {paper cover) CONTENTS ( Pa~ Abstract----------------------------------------------------------------------------------- E1- Introduction _____________________________________________ -·-'-·- _ _ _ __ _ _ __ _ _ _ _ __ _ _ _ _ _ _ __ _ _ _ _ _ _ _ 1 StratigraphY------------------------------------------------------------------------------- 1 Stratigraphic relations in southern Monument Valley________________________________________ 3 Stratigraphic relations in northeastern Monument Valley_____________________________________ 4 Owl Rock Member_._ _ _ __ _ _ _ __ __ _ __ _ _ _ _ __ _ _ __ _ _ _ __ _ _ _ __ _ _ __ _ _ _ __ _ _ _ _ _ __ _ _ _ _ __ _ _ _ _ _ __ 5 Reddish-orange siltstone member_ _ _ _ _ _ _ __ _ _ _ __ _ _ __ _ _ _ _ _ _ _ __ _ __ _ _ _ _ _ _ __ _ _ _ _ _ _ __ _ _ __ _ _ _ 5 Mule Ear ledge_____________________________________________________________________ 5 Hite Bed--------------------------------------------------------------------------- 5 Unconformity at the base of the Hite Bed_____________________________________________ 9 Division A------------------------------------------------------------------------- 10 Stratigraphic relations in northwe& tern Monument Valley____________________________________ 10 Regional relations____ _ _ __ _ _ __ _ __ _ __ _ __ _ _ __ _ _ _ __ _ _ _ _ __ _ _ _ _ _ _ _ _ __ _ _ __ _ _ _ _ __ _ _ __ _ _ __ _ _ _ _ __ _ _ _ _ _ 11 Grain size__________________________________________________________________________________ 12 Clay minerals----------------------------------------------------------------------------~- 13 Fossils------------------------------------------------------------------------------------- 13 Chinle Formation-Glen Canyon Group contact__________________________________________________ 13 PaleogeographY----------------------------------------------------------------------------- 17 Conclusions________________________________________________________________________________ 21 References cited____________________________________________________________________________ 21 ILLUSTRA'TIONS Pa~ FIGURE 1. Map of northeast Arizona and adjacent areas_________________________________________ E2 2. Nomenclature of Chinle Formation and related rocks of Gregory (1917) _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ 3 3. Graphic sections and stratigraphic diagram showing correlation ·of upper part of Chinle Formation and related rocks along Comb Ridge__________________________________ 6 4. Photograph of Upper Triassic rocks along Comb Ridge________________________________ 8 5. Photograph of west wall of Comb Ridge_____________________________________________ 8 6. Generalized diagram showing stratigraphic relations of Chinle Formation and related rocks_ 12 7. Generalized fence diagram of Chinle Formation and related rocks_______________________ 14 8. Paleogeographic map of northeast Arizona and adjacent areas __________ .:._______________ 19 III J., SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY -.' THE UPPER PART OF THE UPPER TRIASSIC CHINLE FORMATION AND RELATED ROCKS, SOUTHEASTERN UTAH AND ADJACENT AREAS BY RoBERT B. O'SULLIVAN ABSTRACT Wingate Sandstone. Geologic studies by the author in parts of southeastern Utah and northeastern Ariz·ona In northeastern Arizona the Owl Rock Member of the Chinle Formation is overlain by a unit of reddish-orange very fine have yielded some new information on the stratigraphic grained sandstone and siltstone. Previously, this reddish-orange relations of these rocks. The purpose of this report is unit has been referred to informally as division A of the Chinle to review the nomenclature and to summarize the a vail­ Formation. Division A is rerognized throughout northeastern able information about' the Upper Triassic stratigraphy Arizona; stratigraphic studies show that the unit extends not of the area. This report proposes no changes in the exist­ more than 8 miles into southeastern Utah. In different parts of northeastern Arizona, division A is named the Rock Point Mem­ ing nomenclature, but the information presented herein ber of the Wingate Sandstone or the Church Rock Member of may help .to resolve this conflict in nomenclature. the Chinle Formation. In southeastern Utah and parts of north­ The. author is grateful to R. A. Cadigan, M. E. eastern Arizona a fluviatile sandstone-the Hite Bed-is at the Cooley, L. C. Craig, J. H. Stewart, J.D. Strobell, and top of the Chinle Formation, and stratigraphic studies show it D. G. Wyant for helpful suggestions and comments to be equivalent to division A. In much of southeastern Utah a unit of reddish-orange very fine grained sandstone and siltstone about terminology and regional geology made during a is present below the Hite Bed and is also called Church Rock field conference in Monument Valley. The author ex­ Member of the Chinle Formation. However, the stratigraphic presses particular thanks to D. G. Wyant, who first relations, grain-size analyses, clay minerals, and fossil content recognized the significance of an important unconform­ show that it is a separate unit equivalent to the Owl Rock Mem­ ity within the rock units discussed in this report. J. H. ber of the Chinle Formation. It is the author's opinion that rocks formerly assigned to division A of the Chinle Formation be Stewart aided in measuring a stratigraphic section and everywhere called the Rock Point Member of the Wingate Sand­ examined some of the stratigraphic relations herein stone and that the so-called Church Rock of southeastern Utah described, but he does not necessarily agree with any of be renamed. the conclusions in this report. A widespread unconformity that separates the Chinle Forma­ The work on which this report is based is part of a tion, as here defined, from overlying rocks extends from south­ ern Nevada across southwestern Utah and northeastern Arizona continuing study of the geology of the Navajo In­ to northwestern New Mexico. The unconformity overlies the dian Reservation and was done on behalf of the U.S. Owl Rock Member in most of northeastern Arizona and overlies Bureau of Indian Affairs in cooperation with theNavajo older parts of the Chinle Formation to the west in Nevada and Trilbe. to the east in northwestern New Mexico. In southeastern Utah STRATIGRAPHY the unconformity probably lies at the base of rocks equivalent to the Hite Bed, where present, or .at the base of the Wingate Stratigraphic subdivisions recognized by Gregory Sandstone. (1917, p. 37-50) in northeastern Arizona and adjacent INTRODUCTION parts of' southeastern Utah include, in ascending order, Part of the Upper Triassic rocks of northeastern Ari­ the Shinarump Conglomerate, the Chinle Formation, zona and adjacent areas (fig. 1) includes the Chinle and the Wingate Sandstone. Gregory (1917, p. 42-43) Formation and the overlying Wingate Sandstone. The distinguished four units (fig. 2)' of the Chinle For­ uppermost subdivision of the Chinle Formation, in the mation, which he .referred to as divisions D, C, B, and Monument Valley area, is the same unit that, in the De­ A in ascending order. Gregory later (1950, p. 67) used fiance Plateau area, is assigned to the basal part of the the name Petrified Forest Member in the Zion Park E2 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Delta 0 /Line of generalized diagram I I I .......... ........_ __ j_r-I ..-r---- __j oBlanding oCortez 0 Paria (abandoned) 37" oTuba City 1l r )> -1 fT1 )> c oGallup 0 Fort Wingate Thoreau 0 oF!agstaff Fence Lake 0 50 100 MILES FIGURE 1.-Map of northeastern Arizona and adjacent areas showing approximate outcrop distribution of division A (solid). Compiled in part from Dane and Bachman (1957); Cooley, Harshbarger, Akers, and Hardt (1004); and M. E. Cooley (written commun., 1966). Hase from U.S. Geological Survey, 1: 1,000,000 State base maps. CHINLE FORMATION AND RELATED ROCKS, SOUTHEASTERN UTAH AND ADJACENT AREAS E3 <: .·; South of Laguna Creek the same sequence of strata is Reddish-orange and reddish-brown to be known as the Rock Point Member of the Wingate Wingate Sandstone massive crossbedded sandstone Sandstone" (Witkind and Thaden, 1963, p. -34). Al­ though two different names are used for division A, Division Reddish-orange sandstone and A siltstone there appears to be no dispute about the correlation of the unit across Laguna Creek (fig. 1) in northeastern ..,. Pale-red shale and interbedded reddish­ Arizona . Division orange siltstone and conglomeratic B gray, light-green, and pink limestone Stewart, Williams, Albee, and Raup (1959, p. 518) and pale-red sandstone -- ~ -~-~~() recognized, in addition to these formal members, an­ Chinle -- other unit-the Rite Bed-at the top of the Chinle and Formation - -- 1-- -- Division Gray, pale-blue, pale-red, and brown below the Wingate Sandstone over a large part of south­ c shale and variegated siltstone and -- -( eastern Utah. The Rite Bed in much of Utah is 10-50 shale - ---- feet thick and consists of pale-~red and light-greenish­ ---1----- gray very fine grained
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