BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA VOL. 36. PP. 439*454 SEPTEMBER 30. 1925 CRETACEOUS AND TERTIARY FORMATIONS OP THE WASATCH PLATEAU, UTAH * BY EDMUND M. SPIEKER AND JOHN B. REESIDE, JR. {Read before the Geological Society December SO, 1925) CONTENTS Page Introduction.......................................................................................................................... 435 General features of plateau........................................................................................... 436 Location and surface features............................................................................. 436 Structure.......................................................................................................................436 Mancos shale........................................................................................................................ 436 General statement...................................................................................................... 436 Lower shale member................................................................................................. 437 Ferron sandstone member...................................................................................... 438 Middle shale member............................................................................................... 438 Emery sandstone member...................................................................................... 439 Upper shale member...........................................................................'....................439 Mesa verde group........................................................................................................................ .•........ 441 The Mesa verde group in Colorado, New Mexico, and Utah......................441 . Subdivisions of the group in the Wasatch Plateau.................................... 442 Star Point sandstone................................................................................................ 442 Blackhawk formation............................................................................................... 443 Price River formation..............................................................................................445 Tertiary formations........................................................................................................... 448 Wasatcli formation.................................................................................................... 448 Boundary between Cretaceous and Eocene................................................... 450 Green River formation and later beds........................................................... 451 Summary of geologic history....................................................................................... 451 Discussion...............................................................................................................................453 I ntroduction This paper is intended to present, in summary fashion, some of the results of stratigraphie work by the senior author in the Wasatch Plateau of Utah.. In this study he has had the advantage of extensive conference, both in the field and in the office, with the junior author, who contributes * Published by permission of the Director, U. S. Geological Survey. Manuscript received by the Secretary of the Geological Society April 13, 1925. XXIX—B u l l . G eol. Soc. A m ., V o l . 36, 1924 • (435) Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/36/3/435/3429887/BUL36_3-0435.pdf by guest on 02 October 2021 486 CRETACEOUS AND TERTIARY OF THE WASATCH PLATEAU, UTAH to the paper the paleontologie part of the work and many of the com­ parisons with other regions. General F eatures op P lateau LOCATION ANI) SURFACE FEATURES The Wasatch Plateau lies in central Utah. It is the northeastern unit of the great group of high plateaus that borders the northern part of the Colorado Plateau on the west and separates it from the Great Basin. The plateau is a fairly well-defined tableland, about 90 miles long and 20 to 30 miles broad, whose summits commonly reach elevations 10,000 to 11,000 feet above sealevcl and 5,000 to 6,000 feet above Castle Valley on the east and Sanpete and Sevier valleys on the west. Castle Valley is entirely. erosional in origin and it represents a broad platform in the great steplike succession of benches rising from the Colorado River to the High Plateaus. Sanpete and Sevier valleys, on the other hand, are primarily structural in origin and are due to a great downfolded and faulted block that parallels on the west the eastern tier of the High Plateaus. On the north the Wasatch Plateau merges with the higher land at the western end of the Uinta Basin; on the south it is separated from the Fish Lake Plateau by an erosional depression about 20 miles broad. The location of the plateau is shown on the index map, figure 1. STRUCTURE In the eastern part of the plateau the formations lie nearly level or dip gently westward. The basal slopes are made by Mancos shale, above which are cliffs of sandstone and shale of the Mesaverde group; and above them in turn, forming the summits, the Wasatch formation. On the western flank the beds plunge downward in a huge monocline that borders on the east the first of the great series of faults in the structural province of the Great Basin. This western border presents great dip slopes, chiefly in the beds of the Wasatch formation, but locally of the underlying Cretaceous. In places within the plateaus the rocks arc broken by zones of normal faults, some of them rather complex. M a n g o s S h a l e GENERAL STATEMENT The Mancos shale here consists of five well-defined members, as shown in the columnar section for the southern part of the Wasatch Plateau. The lower two members do not really form the surface of any part of the plateau, but are well shown in the adjacent valleys and certainly under­ lie the plateau. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/36/3/435/3429887/BUL36_3-0435.pdf by guest on 02 October 2021 MANCOS SHALE 4 37 LOWER SHALE MEMBER The lowest member, unnamed, is a gray marine shale about 600 feet thick, with Gryphea newberryi, Inoceramus labiatus, Metoicoceras, and other fossils characteristic of a widespread faunal zone in the lower part F ig u re 1.—Index Map of Utah, shotting Location of Wasatch Plateau Numerals in circles indicate location of sections given in figure 2. of the Colorado group. It is equivalent to the “Tununk shale” of Gil­ bert’s section in the Henry Mountains and to the Graneros and Green­ horn formations east of the Rockies. This shale underlies the eastern Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/36/3/435/3429887/BUL36_3-0435.pdf by guest on 02 October 2021 43§ CRETACEOUS AND TERTIARY OF THE WASATCH PLATEAU, UTAH part of Castle Valley and borders the San Bafael Swell. Locally it rests on a sandstone that has been called Dakota, but at many places it is in direct contact with variegated beds probably of Morrison age (upper part, of the McEImo formation of many geologists). FERRON SANDSTONE MEMBER The next higher member, the Perron sandstone, fully described by Lupton1 and Clark,2 is a variable group of brown sandstone, gray shale, and local coal beds. It contains a fauna, with such species as Scaphites warreni, Prionocyclus wyomingensis, Prionotropis hyatti, Inoceramus fragilis, Inoceramus dimidius, and. Ostrea lugubris, that correlates it with a widespread zone in the Colorado group especially well typified by the Carlile shale 'east of the Rockies. It is the faunal equivalent of the Tununk sandstone of Gilbert’s section in the Henry Mountains. The Perron sandstone contains considerable coal at the southern end of Castle Valley, but north of Emery, 60 miles south of the Denver and Rio Grande Western Railroad, coal is lacking at the outcrop. The sand­ stone also thins northward along the outcrop from a thickness of 700 feet south of Emery to 50 feet near Farnham. A recent drilling near Price, on the Denver and Rio Grande Western Railroad and 10 miles west of the outcrop, shows the sandstone to be 200 feet thick there and to contain several beds of coal, one of which is 7% feet thick. The re­ gional tendency of the Cretaceous beds to change westward from marine to littoral, to continental and coal-bearing sediments, is well shown by this occurrence. MIDDLE SHALE MEMBER Above the Ferron sandstone is the middle member of the Mancos, a gray marine shale, also unnamed. It ranges in thickness from 1,650 feet at the south end of the Wasatch Plateau to 2,650 feet at the north end. Farther east, along the Book Cliffs, it is inseparable from the upper member. Within .the Castlegate Quadrangle, at' the northern end of Castle Valley, this shale contains in the upper part a lenticular sandstone named by Clark in his unpublished paper the Garley Canyon sandstone member of the Maneos shale. Much, if not all, of the middle shale mem­ ber is Niobrara in age, and it contains at a number of horizons such dis­ tinctive fossils as Scaphites vermiformig, Scaphites ventricosus, Inocer­ amus deformis, IAoceram-us undulatoplicatus, and other undetermined but very large species of Inoceramus. 1 C. T. Lupton: The geology and coal resources of Castle Valley, Utah. V. S. Geol. Survey Bull. 628, 1016. 2 F. R. Clark: The geology and coal resources of the Sunnyside, Wellington, and Castlegate quadrangles. U. S. Geol.