A PROVENANCE STUDY OF THE TRIASSIC DEPOSITS OF NORTHWBSTEIIN TEXAS IK>WARD WILLIAM KIATTA, B. S. A THESIS IN GEOLOGY Submitted to the Graduate Faculty of Texas Technologlcal College in Partial Fulflllment of the Requirements for the Degree of ItASTER OF SCIENCE Approved May, 1960 ^0<b 11 •no. II ACEIK»nL£OGlfERT£ Appreclatlon is acknowledged to tbe &r.tlr& stalf of tbe gøology department without whose cooperation asd as&Ã.£t&j.co tn.LE tbesis wDuld not have been poaslble. The writer express«s special gxatitTule to ttae members of his conmittee, Dr. Wllliaa B. Arper, Br. Jc.:i.-^ F. .^.^, and Dr. Lola Beth Qreen, for their supervistoti nxiã. IseipiiL cTíri:-.sa throogh- out the preparation of this work. TABLS OF CONTENTS Page LIST OF TABLES v LIST OF ILLUSTSATIONS vi ABSraACT viii I. INTROØdCflOíc 1 Nature and Purpose of Study 1 Geographic Location and Extent .... 1 History of Previous Investigations .... 2 Procedure 6 II. STRATIGRAPHY 8 Tecovas Fonaation 11 Trujillo Fomation 12 Chinle Formation 15 III. ANALYSIS OF SEDIIfSNTARY STRUCTURES 18 Crossbedding. 18 Other Structures 21 IV. SEDIMENTARY ANALYSIS OF SANDSTONES 32 Texture 32 Mineralogy 32 Llght Minerals 32 Quartz 32 Chert 34 Feldspar 34 Calclte 35 Rock Fragments 35 Heavy Minerals 36 iii iv V. INTERPRETATIONS 45 Environment of Depositlon 45 Lithologic Character of the Provenance 47 Location of the Provenance 49 VI. CONCLUSKmS 53 BIBLI06RAPHY 55 APPENDIX 58 Measured Sections 58 y LIST OF TABLES Page l. Relative Percentage of Heavy Minerals • • 37 ... '... ÍÍ-V- »«•'*« LIST OF ILLUSTRATIONS Figure Page 1. Hap Showing Sxtent of Dockum Beds and Locati<»i of Outcrops Sampled 3 2. Permian and Triassic Beds in Palo Ouro Canyon State Park 10 3. Permian-Triassic Contact at Roaring Springs, Motley County 10 4. Tecovas-Trujillo Contact In Tule Canyon, Briscoe County 17 5. Dockuffl Ssuidstone Underlying Camp Springs Congloraerate, Scurry County 17 6. Triassic-Pliocene Contact in Palo Ouro Canyon State Park 17 7. Compass Diagram of Crossbed Measurements 20 8. Map Showing Orientation of Crossbeds in the Dockum Sandstones 22 9. Crossbeddlng in the Tecovas Formation in Palo Ouro Canyon State Park 24 10. Crossbedding in the Trujillo Formation in Palo Duro Canyon, Armstrong County 24 11. Crossbedding in the Trujillo Formation, Armstrong County 24 12. Crossbedding In Oockum Sandstone, Los Lingos Canyon, Briscoe County 26 13. Crossbedded Trujillo Sandstone, Los Lingos Canyon, Briscoe Coimty 26 14. Crossbeddlng in Oockum Sandstone in Pole Canyon, Briscoe County 26 15. Crossbedding in Triassic Sandstone in Pole Canyon, Brlscoe Ccî'nty 28 16. Reworked Shale Conglomerate in Los Lingos Canyon, Briscoe County 28 vi vli 17. Section of a Stream Channel in Trujlllo Formation, Palo Ouro Stete Park 31 18. Large Dockum Streaia Channel, Palo Duro Canyon, Armstrong County 31 19. Stream Channel in Trujillo Formation, Tule Canyon, Briscoe County 31 20. Thin Section of Sandstone Sas^le 42 21. Thin Sectioii of Sandstone Sample . 42 22. Thin Section of Sandstone Sample 42 23. Thin Section of Ssuidstone Sample . , 44 24. Photomicrograph Showing the Variety of Shapes Exhibited by Tourmaline Grains in the Oockum Sandstones . 44 25. Map Showing the Proposed Source Areas and Their Controlling Structural Features 52 viii ABSTRACT Continental deposits of the Upper Triassic Oockum Oroup are exposed along the eastem escarpment of the Southern High Plains in northwestern Texas. Three formatlons are present: the Tecovas, the Trujillo, and the Chinle, generally represMiting the floodplain, stream channel, and floodplain environments respectively. Analyses of the sedimentary structures were made to determine the dlrection of the source of tbese beds. Mlneralogieal studies were conducted in an eífort to establisb the lithologic character of the source rocks. Results indicate that the provenance consisted chiefly of a terrane ot sedimentary rooks to the east and southeast. Specific source areas are proposed and some paleogeographic reconstructions are suggested. CHAPTER I INTRODUCTION Nature and Purpose of Study Triasslc rocks of conslderable thickness and extent occur in north- westem Texas. Tbese beds, the largest occurrence of Triasslc rocks in Texas, have been named the Dockum Group. Because of lack of economic importance the deposits have not been studied intensively. They do, however, offer important areas of Interest in sedlmentation, stratigraphy, and vertebrate paleontology. The purpose of this work is to present data which may indicate the character and location of the provenance of the Oockum sediments. Approach to this problem is twofold: first, an analysis of the sedimentary struc- tures in an effort to determine the dlrection of the paleocurrents which deposited these sediments, thereby establishing the location of the prov- enance; and second, to perform a detailed study of the minerals contained in the Dockum sandstones and conglomerates in order to determine the litho- logic cbaracter of the rocks comprlsing the provenance. This paper Is the result of approxlraately one year of field, labo- ratory, and library work under the directlon of the geology faculty. Geographic Location and Extent Dockum beds are exposed in northwestern Texas and in eastern New Mexico. In Texas they crop out along the Canadian River in Oldham and Potter countlesy and in a narrov belt aloag the eastem escarpment of tho Southern High Plains froa Armstrong County aouthward to Sterllng County. They are present in the subsurfsuse underlying the PIains« and crop out again in San Mlguel, Harding, Quay, Guadalupe, Oe Baca, and Chaves coun- ties, New Mexico. Figure 1 shows the geographiéal extent of the exposed Dockum beds in Texas. The quality of tbe Texas exposures dependa to a large extent on the sharpness of the eaetern eecariMient of the Plaias. Thie escarpmmit, whicb lies roughly along loagitude 101** West, ia protected by a massive ealcium carbonate deposit kaown as the "caproek caliche." The steep descent of this slope affords excellent exposures of tbe underlying Plio- cene and Triassic beds. On the southern end of the Soutbern High Plains the escarpment is abseht, the plains topography becomes contintious witb tbe Edwards plateau, and the Triassic outcrop widens oonsiderably. This study is restricted to the Triaasic deposits in northwestern Texas. The New Mexico exposures are omitted beoause of obviotis practical linitation in covering too large an aroa, and beoauee they appear to offer geologic problems whicb ciiffer frcm those of the Texas deposits. History of Previous Investigations TAf- earliest known referenoe to the Triassic deposits in this region was made by Ci^tain R. B. Haroy in 1850 in a report of his 1849 routelinding expedition. He described thick sandstone units along the Canadian Eiver and near the Oouble Mountain Fork of the Brasos Blver. Conceming tbe latter he wrote: . sandstones of different kinds, some dark and highly impregnated with iroo and having tbe appearance of volcanic productions; otbersin very thin slabs or piates and of an exceedingly fine texture, the fracture reseabling that of a bone (Marcy, 1850, p. 72). I L MAP SHOWING EXTENT OF DOCKUM BEDS AND LOCATION OF OUTCROPS SAMPLED ARABIC NUMERALS REFER TO SAMPLES ROMAN NUMERALS REPRESENT MEASUREO SECTION 0 10 20 3 0 SCALE IN MILES Figure 1 4 G. G. Sfaumard, a member of the 1852 Marcy expedition, noted these rocks in Palo Duro Canyon but assigned them to the Cretaceous System (Shumard, 1852, p. 187). The French scientist Jules Marcou, while accom- panylng an expeditlon through this region iu 1853, observed and described the sandstones along the Canadian River at the edge of the Llano Estacado (Blake, 1856, p. 25-26). He further described these deposits in a sepa- rate geology book and recognized them as Triasslc on the basis of the contained vertebrate fauna (Marcou, 1856, p. 28). In 1889 in the first report of the Geological Survey of Texas, Cummins described Triassic deposits in Oickens County and named them "Dockum beds" because of the exposures near the settlement of Oockum in northern Oiekens County (Cummins, 1889, p. 189). The followlng year he described in greater detail the Dockum beds in Oickens and Crosby counties and drew the Permian-Triassic contact near Dickens (Cufflnd.ns, 1890, p. 424- 430). In 1892, Drake conducted the first comprehenslve study of the Triassic deposits in Texas and New Hexico pointing out several ways to distinguish them from the underlying Permian (Drake, 1892, pp. 227-247). He described the geographic extent of the Triassic in this region and divided it into three distinct units: a lower unit of sandy clay, a middle unit of sandstone and congloaerate with some clay, and an upper unit of sandy clay. He accepted the name Oockum for the complete sequence but did not assign names to the three separate units. The next important contribution was made in 1907 by Gould who studied the Triassic deiMsits in the Panhandle in connection with a United States Geological Survey. water resources survey. He divided the Triasslc into two foraations: a lower sandy clay whicii he naæd the Tecovas, and an upper unlt of sandstone and conglomerate which he called the Trujillo 5 (Gould, 1907, p. 21). Baker concluded later that Orake's two lower units were synoncMBOus with Gould's Tecovas and Trujlllo formations (Baker, 1915, p. 17). Another twofold division of the Triassic was offered by Hoots who studied the deposits in the southeastern part of the High Plains area in connection with a United States Geological Survey investigatlon of salt and potash deposits. He noted a lower unit of red clay and giray crossbedded sand, and an upper unit of red clay. He attempted to cor- relate his division with those of Drake and Gould, suggesting that Gould's Tecovas and Trujillo graded into his lower unit, and that his upper unit was the same as that of Drake (Hoots, 1926, p.