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Characteristic Marine Molluscan Fossils from the Dakota Sandstone and Intertongued Mancos Shale, West-Central New Mexico

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Characteristic Marine Molluscan Fossils from the Dakota Sandstone and Intertongued Mancos Shale, West-Central New Mexico Characteristic Marine Molluscan Fossils From the Dakota Sandstone and Intertongued Mancos Shale, West-Central New Mexico GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 Characteristic Marine Molluscan Fossils From the Dakota Sandstone and Intertongued Mancos Shale, West-Central New Mexico By WILLIAM A. COBBAN GEOLOGICAL SURVEY PROFESSIONAL PAPER 1009 Brief descriptions, illustrations, and stratigraphic sequence of the more common fossils at the base of the Cretaceous System UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1977 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress Cataloging in Publication Data Cobban, William Aubrey, 1916- Characteristic marine molluscan fossils from the Dakota sandstone and intertongued Mancos shale, West- central New Mexico. (Geological Survey professional paper ; 1009) Bibliography: p. Includes index. 1. Lamellibranchiata, Fossil. 2. Gastropoda, Fossil. 3. Ammonoidea. 4. Paleontology Cretaceous. 5. Paleontol­ ogy New Mexico. I. Title: Characteristic marine molluscan fossils from the Dakota sandstone ***!!. Series: United States. Geological Survey. Professional paper ; 1009. QE811.G6 564'.09789'8 76-26956 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 Stock Number 024-001-03003-9 CONTENTS Page Abstract ________________________________________--__- 1 Introduction ________________________________________ Acknowledgments _____________________________ Stratigraphic summary _________________________ 1 Age of the intertongued Dakota Sandstone and Mancos Shale 3 Earlier records of fossils _______________________ 3 Resume of fossil occurrences _________________________ 10 Geographic distribution of fossils __________________________ 10 Characteristic fossils __________________________________ 10 References cited ___________________________________. 26 Index __________________________________________ 29 ILLUSTRATIONS [Plates follow index] PLATES 1-3. Oak Canyon fossils. 4-5. Oak Canyon and Cubero fossils. 6. Clay Mesa fossils. 7-14. Paquate fossils. 15. Paguate and Whitewater Arroyo fossils. 16-18. Whitewater Arroyo fossils. 19-21. Twowells fossils. Page FIGURE 1. Index map of part of northwestern New Mexico __ 2 2. East-west stratigraphic changes _________. 3 3. North-south stratigraphic changes ________ 4 4. External suture of Tarrantoceras rotatile _______ 23 5. External suture of Acanthoceras amphibolum ___ 24 6. Complete suture of Acanthoceras alvaradoense __ 24 7. External suture of Metoicoceras aff. M. latoventer 25 TABLES Page TABLE 1. Fossils of Clay Mesa Shale Tongue and Paguate Sandstone Tongue _____ . 6 2. Fossils of Oak Canyon Member and Cubero Sandstone Tongue ____________ 8 3. Fossils of Whitewater Arroyo Shale Tongue and Twowells Sandstone Tongue 9 4. Localities where fossils were collected ___________________________________ 10 in CHARACTERISTIC MARINE MOLLUSCAN FOSSILS FROM THE DAKOTA SANDSTONE AND INTERTONGUED MANCOS SHALE, WEST-CENTRAL NEW MEXICO By WILLIAM A. COBBAN ABSTRACT are formally described and named herein. Synono- Molluscan fossils are abundant in marine rocks of early mies include only the original paper in which a spe­ Late Cretaceous age (Cenomanian) on the south and south­ cies was named and, generally, one or two later east flanks of the San Juan Basin in northwestern New papers that have important nomenclature changes Mexico. Here the Cenomanian rocks are characterized by or good illustrations. generally eastward-pointing tongues of Dakota Sandstone separated in part by westward-pointing tongues of Mancos ACKNOWLEDGMENTS Shale. From bottom to top, the sequence consists of the Oak Canyon Member of the Dakota Sandstone, Cubero Sand­ The photographs in this report were made by stone Tongue of the Dakota Sandstone, Clay Mesa Shale Robert E. Burkholder, of the U.S. Geological Sur­ Tongue of the Mancos Shale, Paguate Sandstone Tongue of the Dakota Sandstone, Whitewater Arroyo Shale Tongue of vey. All illustrated specimens are stored in the Na­ the Mancos Shale, and Twowells Sandstone Tongue of the tional Museum of Natural History in Washington, Dakota Sandstone. The lower part of the Oak Canyon D.C. The rest of the fossils, as well as some plaster Member consists of rocks of fluviatile and brackish-water casts of illustrated specimens, are kept in the U.S. origin; the strata of the rest of the member and of all the Geological Survey's Mesozoic invertebrate collec­ overlying intertongued Dakota Sandstone and Mancos Shale are dominantly of shallow-water open-marine origin. tions at the Federal Center, Denver, Colo. Molluscan fossils occur in all the members. Most speci­ Dr. Annie Dhondt, Institut royal des Sciences mens are found in silty limestone concretions, in calcareous naturelles de Belgique, kindly examined photographs siltstone or sandstone concretions, and in very fine grained of Neithea from the Paguate Sandstone Tongue of sandstone and siltstone beds. The upper part of the Oak the Dakota Sandstone and Camptonectes from the Canyon Member and the Paguate Sandstone Tongue contain Twowells Sandstone Tongue of the Dakota, and she the greatest variety of fossils. Fifty-two kinds of bivalves, 38 gastropods, and 15 ammonoids from these two units are offered suggestions regarding their specific names. present in the collections of the U.S. Geological Survey. STRATIGRAPHIC SUMMARY INTRODUCTION Landis, Dane, and Cobban (1973a, b) observed The basal part of the Cretaceous System in west- that the intertonguing of the Dakota Sandstone and central New Mexico consists of a generally trans- Mancos Shale was formed best in the Grants-Laguna gressive sequence of intertongued sandstone, silt- area in the southern part of the San Juan Basin stone, and shale. The stratigraphic framework and (fig. 1). Here the sequence, from oldest to youngest, terminology of this sequence was summarized in two consists of Oak Canyon Member of the Dakota recent papers by Landis, Dane, and Cobban (1973a, Sandstone, Cubero Sandstone Tongue of the Dakota b). Many of the characteristic molluscan fossils Sandstone, Clay Mesa Shale Tongue of the Mancos were recorded, but no attempt was made to show Shale, Paguate Sandstone Tongue of the Dakota either stratigraphic ranges or geographic distribu­ Sandstone, Whitewater Arroyo Shale Tongue of the tions. This paper has been prepared as a paleon- Mancos Shale, and Twowells Sandstone Tongue of tologic supplement to the stratigraphic work of the Dakota Sandstone. Northwestward from Grants, Landis, Dane, and Cobban. However, this paper is the lower part of the sequence (Oak Canyon Mem­ not intended as a detailed systematic study of the ber and Cubero, Clay Mesa, and Paguate Tongues) fauna, but rather as a generalized guide to the com­ grades into a dominantly sandstone unit identified mon fossils and their distribution. No new species as the main body of the Dakota Sandstone (fig. 2). MARINE MOLLUSCAN FOSSILS, WEST-CENTRAL NEW MEXICO 109° 108° 107° 37C I COLORADO Shiprock Q Farmington SAN JUAN RIO ARRIBA O NJ I 36C MC KINLEY 12 X x72 22-24 H ! X 10 X13 x O 3,4 Fort Wingate •) 5.21 O X 14 ' x °Manuelito x 25-26 11 .———- v ,, Mt. Taylor \ 39,40 * Seboyeta£————^\- _ Grants O Vf^l T>_ __ _ J. ^\ x' 35° l X 50 56-59 X R1 X60 c_x\ <,\o VALENCIA x 51-53 x ^Acoma pueblo 67 ^ X 54,55 X62-65 8 x O Atarque -68 x 69,70 CATRON 71 x 0Riley SOCORRO 20 30 MILES 10 20 30 KILOMETERS FIGURE 1.—Part of northwestern New Mexico showing localities of mollusk collections referred to in the text and in table 4. EARLIER RECORDS OF FOSSILS Southeastward from Grants, the Cubero and Pagu­ WEST MOUNT EAST ate Sandstone Tongues grade into shale referred GALLUP AREA POWELL GRANTS LAGUNA (Cliff Dwellers AREA AREA AREA to as the lower part of the Mancos Shale. The Canyon section) nomenclature of the Grants-Laguna area is appli­ cable northeastward from Laguna for about 50 miles (80 km) to north-central Sandoval County where the Cubero and Paguate Sandstone Tongues disappear into the lower part of the Mancos Shale, which overlies a thick main body of the Dakota Sandstone and underlies a very thin Twowells Sand­ stone Tongue of the Dakota Sandstone (fig. 3). AGE OF THE INTERTONGUED DAKOTA SANDSTONE AND MANCOS SHALE The oldest molluscan fossils occur in dark-brown- weathering ferruginous silty to sandy concretion­ ary beds above the middle of the Oak Canyon Mem­ ber. An ammonite, described from the Woodbine Formation of Texas as Acanthoceras wintoni by Adkins (1928, p. 234, pi. 25, figs. 2, 3), occurs sparsely in the ferruginous concretions in the Oak Canyon Member. This ammonite is middle Cenoma- nian in age. The youngest fossils are found in the upper part of the Twowells Sandstone Tongue. Among the am­ monites are Calycoceras obrieni Young and frag­ ments of Metoicoceras resembling M. defordi Young and M. muelleri Cobban, which are of late Cenoma- nian age. In Wyoming, these ammonites occur with Morrison Dunveganoceras conditum Haas, a guide to the Formation first ammonite zone older than that of Sciponoceras gracile (Shumard), which is of latest Cenomanian age. EXPLANATION EARLIER RECORDS OF FOSSILS Fossil mollusks of Cretaceous age have been re­ corded from west-central New Mexico in many papers during the past century. Most authors, how­ ever, have made only passing remarks such as not­ ing the local abundance of "Exogyra columbella" or "Gryphaea newberryi." Calcareous C. A. White was probably the first person to de­ Formational scribe Cretaceous mollusks from
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