Devil's Graveyard Formation (New) Eocene and Oligocene Age Trans-Pecos Texas

Devil’s Graveyard Formation (New) Eocene and Oligocene Age Trans-Pecos Texas

James B. Stevens Margaret S. Stevens John A. Wilson

Texas Memorial Museum Bulletin 32 The University of Texas at Austin © 1984 by Texas Memorial Museum The University of Texas at Austin All rights reserved Published September 24,1984 Printed in the United States of America

ISSN 0082-3074-32

A portion of the museum’s general operating funds for this fiscal year has been provided through a grant from the Institute of Museum Services, a federal agency that offers general operating support to the nation’s museums.

The Bulletin is an irregularly published series of technical monographs deriving primarily from research done on Texas Memorial Museum collections and projects.

Texas Memorial Museum • The University of Texas at Austin • 2400 Trinity • Austin, TX 78705 CONTENTS Abstract 1 Introduction 1 Abbreviations 2 Acknowledgments 3 lithostratigraphy, Buck Hill Group 3 Devil’s Graveyard Formation (new) 4 Lower and middle members 4 Bandera Mesa Member (new) 5 Marker beds, lower member 5 Basal Tertiary conglomerate 5 Variegated beds 6 Lunch Locality sandstone 6 Strawberry tuff 6 Marker beds, middle member 7 Titanothere channels and Purple Bench tuff 7 Repeats 7 Marker beds, Bandera Mesa member (new) 7 Skyline channels 7 Cotter channels 19 Upper breccia-conglomerate 19 Upper part of Bandera Mesa Member (new) 19 Summary 20 References 20

ILLUSTRATIONS Figure Page 1. Index map of Texas and Presidio and Brewster Counties 8 2. Sketch map ofTrans-Pecos Texas with volcanic centers 9 3. Geologic map 10 4. Diagrammatic cross section, Devil’s Graveyard Formation(new) 12 5. Diagrammatic stratigraphic section 13 6. Measured section, lower member, lower boundary stratotype 14 7. Measured section, lower and middle members 15 8. Measured section, southern part Bandera Mesa Member (new), North Fork Alamo de Cesario Creek 16 9. Measured section, middle and Bandera Mesa Members (new), South Fork Alamo de Cesario Creek 17 10. Measured section, Bandera Mesa Member (new), upper boundary stratotype.... 18

DEVIL'S GRAVEYARD FORMATION (NEW) EOCENE AND OLIGOCENE AGE TRANS-PECOS TEXAS

James B. Stevens 1 Margaret S. Stevens2 John A. Wilson 3

ABSTRACT Texas west of Texas highway 118, in west-central Brewster and adjacent Presidio counties (fig. 1). The The Devil’s Graveyard Formation (new, Eocene and area includes contiguous parts of the Agua Fria, Oligocene) is described as that part of the Buck Hill Tascotal Mesa, Jordan Gap, and Buck Hill fifteen- Group above the Cretaceous and beneath the Mitchell minute topographic quadrangle maps (fig. 2) where Mesa Rhyolite or the Yellow conglomerate of Moon sediments of the Pruett and Duff formations, Buck (1953). It replaces the terminology used by Moon Hill Volcanic Group (Goldich and Elms, 1949) are (1953) for the lower part of the Buck Hill Group, exposed. The area lies south and west of outcrops of “Buck Hill Group undifferentiated,” as well as “Pruett- the Cottonwood Spring Basalt, the unit that defines Duff” (Erickson, 1953, and Stevens, 1978) and the top of the Pruett and base of the Duff formations “Pruett and Duff undivided” (Barnes, 1979, and (Goldich and Elms, 1949), and embraces an undiffer- Henry and Duex, 1981). The names “Pruett” and entiated stratigraphic section either placed within the “Duff” apply to the northern area in the southern Buck Hill Volcanic Group by Moon (1953), regarded part of the Davis Mountains where their type sections as Pruett-Duff by Erickson (1953) and Stevens are located. The lithology of the Devil’s Graveyard (1978), or called “Pruett and Duff undivided” by Formation is predominately clastic and sufficiently Barnes (1979) and Henry and Duex (1981). different from that of both the Pruett and Duff The study area receives about 12-14 in. (30.5-35.6 formations to warrant its new name. The Buck Hill cm) of precipitation annually, hence is sparsely vege- Group in the Agua Fria-Green Valley area consists tated. Although Pleistocene stream and sediment of the Devil’s Graveyard Formation, the Mitchell deposits mantle the older rocks in certain areas, much Mesa Rhyolite, the Tascotal Mesa Formation, and the of the Eocene and early Oligocene deposits are well Rawls Basalt. The Devil’s Graveyard Formation is exposed. Among the present investigators, Wilson and divided into lower and middle unnamed members and M. Stevens have found abundant vertebrate fossils as an upper Bandera Mesa Member, each separated by well as nonmarine invertebrates in these deposits. concentrations of channel conglomerates. Locally Furthermore, the writers have all found these sedi- useful marker beds that are associated with vertebrate mentary rocks to contain an extensive radiometrically fossil localities are described. The areas of exposure and biostratigraphically datable record of initiation are in west-central Brewster and east-central Presidio and progressive development of volcanic and post- counties, Texas. Laramide tectonic activity for the Trans-Pecos area. In view of this and because the lithology in the Devil’s Graveyard area is distinctive we have decided to name and describe a new herein as the INTRODUCTION unit, designated Devil’s Graveyard Formation, to clarify stratigraphic A thick body of Eocene and early Oligocene volcani- and biostratigraphic relationships of these rocks and clastic fluvial and lacustrine sedimentary rock is to help clarify the regional geology and facilitate exposed in the Big Bend country of Trans-Pecos correlations.

'Assistant Professor of Geology,Department of Geology, Lamar University, Beaumont, Texas. 2 Instructor of Geology, Lamar University of Orange County, Orange, Texas, and Lamar University, Port Arthur, Texas, and Research Associate, Texas Memorial Museum, The University of Texas at Austin. 3 Professor Emeritus, Department of Geological Sciences, and Research Associate, Texas Memorial Museum, The Uni- versity of Texas at Austin. 2 Texas Memorial Museum Bulletin No. 32

The best exposure of the Eocene rocks of the members but left the intercalated sediments Devil’s Graveyard Formation occurs along Alamo de unnamed. The techniques of defining a lithologic unit Cesario Creek (fig. 3), a major tributary of Terlingua only on the basis of bracketing flows or by naming Creek, in an area called the Devil’s Graveyard (Moon, only flows within the section make it difficult to 1953:pi. 1). The Devil’s Graveyard, approximately direct attention to the sedimentary units without a 6 by 3 mi (9.7 by 4.8 km) or about 18 square mi (29 long descriptive phase, or to correlate these units square km), lies within a graben and is bounded on accurately when the flows are absent. line of the northwest by a highly irregular pediment- We therefore believe that the vertebrate fossils and and steep slopes to ft (35 to capped cliffs 115 295 the radiometric dates now known for volcaniclastic m) high. 90 sediments of the Buck Hill Group clarify the strati- Eocene and Oligocene rocks closely related to graphy of the extensive sediments below the Mitchell those exposed in the Devil’s Graveyard occur discon- Mesa Rhyolite in the areas of the Jordan Gap, Buck tinuously in an area over 43.5 mi (70 km) long along Hill, Tascotal Mesa, and Agua Fria quadrangles where the Presidio-Brewster county line from Mitchell Mesa the Cottonwood Spring Basalt is absent. on the north to the Rio Grande on the south, and In the absence of useful igneous marker beds almost 18.6 mi (30 km) wide measured from Buck beneath the Mitchell Mesa Rhyolite to the south of Hill on the east to the face of Bandera Mesa on the the present distribution of the Cottonwood Spring west. Areas of notable exposure of sediments directly Basalt (fig. 4), it is necessary to establish the relative the Eocene rocks and of related to making up most positions of geographically separated fossil sites on the the Tertiary deposits in Devil’s Graveyard include the basis of sedimentary stratigraphy. A new forma- the approximately (3-5 km) south- area 1.8-3.1 mi tion with two unnamed lower members and a named Graveyard and base of southeast of the at near the upper member is here formally proposed. Additional the and sides of Fria northern western Agua Moun- informal units below the rank of member but useful tain local (fig. 3), an important landmark. The follow- in local correlation are described. ing areas are defined according to direction and distance away from the Devil’s Graveyard. Early Oli- Tracing of the sedimentary units and measuring of gocene sediments are best exposed along Needle and stratigraphic sections was done mainly by James B. Dogie creeks, 10.8 mi (17.5 km) northwest, as well as Stevens and Margaret S. Stevens. Petrography and sedi- along drainages cutting the eastern face of Bandera mentologic interpretation were the responsibility of Mesa, particularly near Puerto Potrillo, 21 mi (34 km) J.B. Stevens except where otherwise noted. The fos- northwest. Oligocene rocks are also exposed around sils were discovered and collected primarily by R.H. adjacent outlying buttes such as Red Hill, Church Rainey, M. S. Stevens, and J. A. Wilson, and identified Mountain, and McKinney Mountain (fig. 3). by Wilson unless otherwise noted. A brief lithologic description of each marker bed is given for purposes The volcanic rocks of Trans-Pecos Texas have of field identification. Attempts were made to relate received considerable study during the last 25 years, each major collecting locality to marker beds (fig. 5). and their distribution and composition have been the However, the vertical and horizontal extensions of subject of numerous theses, dissertations, and publi- the volume of rock partly occupied by the vertebrate cations. The volcanic centers (fig. 2) are now known faunas do not necessarily coincide with and are not to (Gorski, 1970; Parker, 1976; Cepeda, 1977, 1979). be interpreted as coincident with the lithologic unit. Much of the formal stratigraphic nomenclature of this region has grown by the naming of flow rocks, some Enlarged aerial photographs 27 square in. (68.6 of which define the top and bottom of sedimentary square cm) were used as base maps for field work. units, but until lately little attention has been given Fossil localities were plotted on these photographs, the sediments themselves. Exceptions include study which have been filed in the archives of the Vertebrate of volcaniclastic deposits in the Castolon area, Big Paleontology Laboratory, Texas Memorial Museum, Bend National Park (Stevens, 1969,M. Stevens et al., The University of Texas at Austin. Geology is in part 1969); of sediments within the Vieja Group north- modified from Goldich and Elms (1949), Seward west of Presidio (Walton, 1972; 1975; 1978; 1979); (1950), Moon (1953), and Erickson (1953). Strati- of the Tascotal Formation (Walton, 1978; 1979);and graphic sections were measured with Brunton com- of sediments of the Rawls Formation (Robinson, pass and steel tape. 1976). Schiebout (1974) dealt only with older, pre- volcanic Tertiary deposits. One reason why emphasis has been placed on the volcanic rocks is that some are ABBREVIATIONS excellent marker-beds with extensive lateral conti- ACSN American Commission nuity and have been used to subdivide the strati- on Stratigraphic Nomenclature graphic section. For example, as originally defined, ISSC International Subcommission the Duff Formation of the Buck Hill Group “. . . is on Stratigraphic Classification chiefly rhyolitic tuff with minor breccia and conglom- lUGS International Union erate. The tuff lies on the Cottonwood Spring Ba- of Geological Sciences salt and is overlain by the Mitchell Mesa rhyolite. . .” K-Ar potassium-argon (Goldich and Elms, 1949, p. 1159). Somewhat differ- MS measured section(s) ently, Maxwell et al. (1967) named flows within the my millions of years Chisos Formation, Big Bend National Park, as formal TMM Texas Memorial Museum 1984 Devil’s Graveyard Formation—Lithostratigraphy 3

ACKNOWLEDGMENTS Austin. A summary and evaluation of some 81 perti- This investigation was made possible by the financial nent K-Ar dates is given by him, but not all of them support for field work from the Vertebrate Paleontol- were determined at The University of Texas. Other ogy Laboratory, Texas Memorial Museum, The Uni- K-Ar dates indirectly applicable to this study are versity of Texas at Austin and from Faculty Research given by Gilliland and Clark (1979), Daily (1979), Parker Grants awarded to Margaret Skeels Stevens by Lamar Parker (1978), and McDowell (1979), Henry University, Beaumont, Texas. Additional aid, primar- and McDowell (1982), Keller et al. (1982), and Mauger ily in the form of salary for John A. Wilson prior to and McDowell (1982). Data from the above sources, 1976, was received from the Geology Foundation, as well as dates commissioned from Geochron Labo- Department of Geological Sciences, The University of ratories during the progress of this study, have been Texas at Austin. The Owen-Coates Fund of the Geol- incorporated into the diagrammatic section (fig. 5). ogy Foundation defrayed part of the publication All potassium-argon dates in this report have been expenses. Thin sections and K-Ar dates were made recalculated using the tables of Dalrymple (1979) available through the facilities of the Department of according to the recommendation of the lUGS. Geological Sciences and the Geology Foundation. The authors are grateful to Drs. R. J. Emry, C. D. The Bureau of Economic Geology furnished financial Henry and Amos Salvador for reading the manuscript aid for part of one summer and the drafting of a and making helpful suggestions. Editing, typesetting, and layout were done by Maria de la Luz Martinez. manuscript geologic map of the Jordan Gap Quad- rangle. We are grateful for this continued support. Mr. and Mrs. Billy Pat McKinney, lessees, and J. H. LITHOSTRATIGRAPHY Burton and Macon Richmond, owners of the Agua BUCK HILL GROUP Fria Ranch, provided us with invaluable assistance in The Buck Hill Group was formally defined by the form of shelters and legendary western hospitality. Goldich and Elms (1949) and contained, in ascending The upper reaches of arroyo Alamo de Cesario extend order, the Pruett Formation which includes in its upper into the ranch of Dr. Walter W. Dalquest of Midwest- part the Crossen Trachyte, Sheep Canyon Basalt, and ern State University, Wichita Falls, Texas, who gen- Potato Hill Andesite; the latter three units were mem- erously permitted us to collect vertebrate fossils from bers. The Cottonwood Springs Basalt was described as his land. We are grateful for access to the San Jacinto a formation overlying the Potato Hill Andesite Mem- Ranch, M-Ranch, Coffee Cup Ranch, and the Mont- ber of the Pruett Formation. The Duff Formation gomery ranches in the Jordan Gap and Crystal Creek overlies the Cottonwood Springs Basalt, and the area, owned or leased by Clegg and D’Ette Fowlkes, latter in turn is overlain by the Mitchell Mesa Rhyo- who also most graciously provided shelter. Sincere lite. An unnamed unit was included above the Mitchell thanks also go to Earl Hammond who allowed us Mesa, and Goldich and Seward previously (1948) access to the Rancho Mortillo, and Duncan Cooper gave the name “Tascotal Formation” to the tuffs who allowed us to collect on El Rancho Triste (for- above the Mitchell Mesa Rhyolite and “Rawls Basalt” merly 3-Bar Ranch) in the Hen Egg Mountain area. to the basalt above the Tascotal Formation. Robert H. Rainey, chief preparator at the Verte- McAnulty (1955) elevated the igneous members of brate Paleontology Laboratory, assisted during some the Pruett Formation to formations and restricted the of the field seasons and was co-discoverer with John Pruett Formation to the tuffaceous sediments below A. Wilson of the Whistler Squat local fauna. In 1971, the Crossen Trachyte and above the Cretaceous. Dr. Ann Marie Forsten, Sally Rogers Scanlon, and Because none of the igneous flow units below the Richard P. McCulloh were able field assistants. Mar- Mitchell Mesa Rhyolite extend southward beyond the garet S. Stevens discovered numerous important fossil west-central part of the Buck Hill Quadrangle, or east- sites including Boneanza, Serendipity, Titanothere central part of the Jordan Gap Quadrangles, it proved hill, Skyline, and significant localities at Red Hill, impossible for Moon (1953) and Erickson (1953) to near the old Cotter Ranch headquarters, and Mont- map subdivisions of the Buck Hill Group below the gomery bone bed. J. A.Wilson made an important Mitchell Mesa Rhyolite. Moon (1953) used “Buck Hill discovery at what has been dubbed “Purple Bench.” Volcanic Series” without any formal subdivisions, Dr. Wilson is grateful to his colleagues in the and Erickson (1953) attempted a breakdown using Department of Geological Sciences, The University “Pruett Formation” as a lower unit and “Duff Form- of Texas at Austin, for helpful discussions. Special ation as an upper unit, with a transitionalunit mapped thanks are given to Dr. S. E.Clabaugh and Dr. Donnie as “Pruett-Duff Tuff” and discussed as “Pruett-Duff.” Parker for help with the igneous rocks, and Dr. Fred In the explanation for his map, Erickson shows the W. Dowell for K-Ar dates. J.B. Stevens has had several contact between the Pruett and Duff Formations as valuable discussions with Dr. A. W. Walton, Depart- an arbitrary, roughly north-south dashed line, with ment of Geology, University of Kansas, concerning Pruett-Duff indicated by a blending of the distin- the diagenesis of certain sedimentary rocks in and guishing colors. No line of contact between Pruett around the study area, and the origin of depositional and Duff formations is shown on the map. Instead, episodes. areas of blended color indicate where Pruett-Duff An extremely important and parallel study on meets the Pruett and Duff (formal) Formations. The potassium-argon dating of rocks of the Trans-Pecos areas of contact along indefinite lines do not reflect volcanic field has been progressing under the direc- the attitude of the beds. tion of Dr. Fred W. Dowell (1979) of the Department Earlier papers on the vertebrate fossils from the of Geological Sciences, The University of Texas at Agua Fria Quadrangle by Wood (1972, 1973), Wilson 4 Texas Memorial Museum Bulletin No. 32

(1972, 1974, 1977), and Wilson and Szalay (1976) other. The measured section shown diagrammatically have referred to the fossils as having been collected in figure 6 (MS 15, fig. 3) includes the lowest beds from the Pruett Formation. However, as work pro- found resting on Cretaceous rocks and is designated a gressed it became impossible to prove that the sedi- lower boundary stratotype. Because it can be shown ments from which the specimens had come were, in (fig. 4 and Wilson et al., 1979) that the Mitchell Mesa fact, Pruett Formation. Some vertebrate fossils have Rhyolite and Yellow conglomerate he on progres- been found at and near the base of the Buck Hill sively older rocks to the south toward the Solitario Group as mapped by Moon (1953). Others have been uplift (fig. 4), the highest units of the Devil’s Grave- collected from sediments mapped by Erickson (1953) yard Formation are found to the north in the south- as “Pruett-Duff tuffs” and still others from Erickson’s central and central portions of the Jordan Gap Quad- Duff Formation. Parts of all of these units contain rangle. The northernmost section of the upper part of the same Whistler Squat local fauna. Like Erickson the Devil’s Graveyard Formation is below elevation and Moon, we have found that a boundary separating 4357 just south of Puerto Potrillo. This section (fig. Pruett from Duff Formation is not mappable south of 10, shown as MS 19 in fig. 3) is designated an upper the limit of the Cottonwood Spring Basalt. For this boundary stratotype. reason we propose a new unit. Measured sections 16, 17, and 18 (figs. 7,8, 9) on figure 3 are diagrammatic representations of sections Devil’s Graveyard Formation* (new) measured by the Stevens’ in the type area and are as reference sections for The name Devil’s Graveyard Formation is given to the designated the formation. the not predominantly volcaniclastic rocks within the Buck Figure 7 (MS 16, fig. 3) shows lower, but low- middle of the Hill Group, from Cretaceous rocks to the base of the est, and parts formation; figure 8 (MS overlying Mitchell Mesa Rhyolite, or to the base of the 17, fig. 3) shows the middle part of the formation on North Alamo de Cesario informal Yellow conglomerate (Moon, 1953), and the Fork, Creek; figure 9 south of an arbitrary vertical cut-off defined by the (MS 18, fig. 3) is, in effect, a continuation of the sec- southernmost outcrops of the igneous members of tion shown in figure 8 and shows a different aspect the the Pruett Formation as defined by Goldich and Elms of the upper unit, as compared to upper boundary Correlation of measured (1949). The upper boundary of the Devil’s Graveyard stratotype (fig. 10). sections, Formation is marked by the base of the Mitchell Mesa admittedly not precise within the type area of the Rhyolite, well exposed along Bandera Mesa, McKinney Devil’s Graveyard Formation, suggests that, conserva- Mountain, and elsewhere in the Jordan Gap Quad- tively, 1550 ft (472 m) of rocks belonging to the for- rangle. At the southeast end of Bandera Mesa, Tasco- mation are exposed there. This is by no means a max- tal Mesa Quadrangle, a conglomerate that is correla- imum thickness of the formation, since much of the tive and lithologically similar to Moon’s (1953) Yellow rock exposed at the upper boundary stratotype (fig. conglomerate appears below the Mitchell Mesa Rhyo- 10) is not included in this thickness, as a result of the lite (fig. 4). South and east of that part of Bandera tilting and beveling. Mesa in the Agua Fria Quadrangle, the Mitchell Mesa Lower and middle members, Devil’s Graveyard Rhyolite thins and becomes discontinuous as channel Formation.-The lower part of the Devil’s Graveyard not fillings within the Yellow conglomerate. The Yellow Formation is formally subdivided, but it has been convenient divide it into conglomerate was described and informally named by to two informal members, the and middle (fig. 5). The two Moon (1953) who mapped it as part of the Buck Hill lower members are a disconformity be “Series.” Erickson (1953) described and mapped the separated by that can traced throughout the type and for lateral continuation of this unit as part of the Tascotal area some distance to north side known Formation. Where it underlies the Mitchell Mesa the along the eastern of the outcrop Graveyard (fig. 3). Rhyolite it was designated Duff Formation. The area of the Devil’s Formation In the eastern area, disconformity above Yellow conglomerate islithologically distinctive, unre- the lies the Strawberry (figs. 7). In the lated to rocks of the Devil’s Graveyard Formation, tuff 5,6, the southwest, disconformity lies the same and makes the most easily recognizable bounding unit on marker bed, a distinctive brick-red mudstone coin- for the Devil’s Graveyard Formation where it is pres- to sandstone. The near cidence of a traceable ent. It is presently intended that the northern bound- marker bed with a disconformity makes recognition of the lower and middle mem- ary of the Devil’s Graveyard formation be defined by practical and the type a line drawn from the east face of Bandera Mesa, 2 bers within near area; but lithologic of mi (3.2 km) northeast of Puerto Potrillo, to hill 4026, distinction in the area contact depends on to Turney Peak, and then southeast to pass south of subtle aspects, including patterns and style of sedi- hill 4140 (west edge of Buck Hill Quadrangle, the mentation, patterns of diagenetic alteration, and southernmost outcrop of Cottonwood Spring Basalt), petrography of the conglomerates. Thus formal status and then northeast to the divide south of Boat Moun- is inappropriate. as of tain and Crossen Mesa. The measured sections can be used examples the rocks referred to the lower and middle members. The type (ISSC, 1976) is the area Devil’s Grave- The measured section of figure 6 (MS 15,fig.3) is rep- yard on the Agua Fria Quadrangle and westward its ofall but the highest part of the lower mem- de resentative extension in the headwaters of Alamo Cesario ber. The lower 150 ft m) of measured section Creek and including the south face of Bandera Mesa (45.7 on the adjacent (west) Tascotal Mesa Quadrangle. No two measured sections in this area are exactly the *Name approved for publication by Geologic Names Com same and no single section is more typical than any mittee, U.S. Geological Survey. 1984 Devil’s Graveyard Formation-Bandera Mesa Member 5

16 (fig. 7) are in the lower member, and the suc- processes (Henry and Duex, 1981), giving rise to ceeding approximately 500 ft (152.4 m) to the base white, gray, and pink rocks as hematite becomes of the Bandera Mesa Member are measured in the markedly less dominant. It is also noteworthy that middle member. lacustrine sediments, including gypsiferous clays and limestones, form a prominent part of the southern Bandera Mesa Member * (new) exposures, while rocks in the more northern exposures are characteristic of steeper, smaller alluvial The name Bandera Mesa Member is given to the rocks fans. Additionally, there are three sets of thin basalt in the Devil’s Graveyard Formation extending from flows occurring at 534 ft (162.8 m) above the base of the base of the distinctive red-to-gray (rare) sandstone- the section shown diagrammatically in figure 5. The and conglomerate-filled channels exposed at the tops “basalts,” possibly mugearites or hawaiites in view of of the cliffs at the northern margin of the Devil’s the work by Parker (1976) and Barker (1977), are Graveyard, and in the canyon of the North Fork, found only in the northwest face of Bandera Mesa. Alamo de Cesario Creek, to the base of the Mitchell Potassium-argon dates ranging from 43.9 to 49.7 Mesa Rhyolite or Yellow conglomerate. A major sys- my (fig. 5) on biotite and tuffaceous rocks in the tem of channels informally called the Skyline chan- lower part of the Devil’s Graveyard Formation agree nels occurs at the base of the Bandera Mesa Member. closely with dates given in recent work by Mauger Thus, the boundary is placed at the base of the lowest (1981), Capps (1981), Bockhoven (1981), and Mauger of these ledge-forming channels at any particular sec- and McDowell (1982), who demonstrated the age and tion. Where present, the channel fillings are invariably style of volcanism in several areas in central Chihua- a major influence on the topography of the area. hua. That area may have been a possible source for at Examples of the channels are shown in figures 7,8, least some of the large amount of volcanically-derived and 9. The arbitrary cut-off established for the north- sediment in the lower and middle members of the ern boundary of the Devil’s Graveyard Formation is Devil’s Graveyard Formation. Certainly, the streams intended to apply to the Bandera Mesa Member. that deposited these units flowed from that general The area extending southeast along the front of direction. Work by Cepeda (1977, 1979), Cameron et Bandera Mesa in the south-central part of the Jordan al. (1982), McDowell (1979), and Walton (1978, Gap Quadrangle from Puerto Potrillo to Red Hill, 1979a, 1979b) support the hypothesis that volcanic and then east across Green Valley to McKinney activity in and near the Chinati-Infiernito caldera Mountain, is designated a type area (ISSC, 1976) for complex in West Texas was the source of, and strongly the Bandera Mesa Member. The measured section influenced, the deposition of the upper northern part shown in figure 8 (MS 17, fig. 3) to 413 ft (126 m) of the Bandera Mesa Member. above the zero point is designated as a lower boundary stratotype, and the section shown in figure 10 Marker beds, lower member (MS 19, fig. 3) is designated as an upper boundary A number of thin or discontinuous units within the stratotype. Devil’s Graveyard Formation are locally useful strati- The thickness of the Bandera Mesa Member mea- graphic marker beds (ACSN, 1972) but do not merit sured at the upper boundary stratotype is 789.3 ft member status. They are, however, important in de- (240.6 m). Approximately 6.5 mi (10.5 km) south- tailed correlation, documenting the relative strati- east along the front of Bandera Mesa, just north of graphic positions of fossil localities. Shown diagram- Middle Canyon, Erickson (1953) measured 764 ft matically in figure 5 and on various of the enclosed (232.9 m), and 5 mi (8.1 km) farther southeast, measured sections, these marker beds will be discussed just north of Smuggler’s Gap, the Stevens’ measured in stratigraphic order as informal units. A more de- (unfigured) 810 ft (246.9 m) in the Bandera Mesa tailed lithologic description of these beds is given on Member. These sections are not laterally equivalent each measured section. because of the northward tilting, and because of Basal Tertiary conglomerate. Junction facies. -The erosion of Devil’s Graveyard Formation prior to the lowest marker bed, directly overlying Cretaceous extrusion of the Mitchell Mesa Rhyolite. None of rocks, is called the Junction facies of the Basal these sections includes the lowest part of the Member, Tertiary conglomerate. It consists of small pebble nor is precise correlation of the lower boundary stra- sandy to large medium pebble conglomerate made up totype possible. J. Stevens considers 985 ft (300 m) of very well-rounded limestone and subangular to to be a conservative estimate of the thickness of the subrounded chert clasts overlain by and in some places Bandera Mesa Member. interlayered with more extensive, very coarse to fine The basal part of the Bandera Mesa Member con- feldspathic calclithites and calclithites. To the south sists of pink to brick-red fluvial sedimentary rocks and west, where the conglomerates are generally clast- whenever exposed; the pink to dark brown, coarser supported, some units up to two meters thick are well- sedimentary rocks exposed in the type area are also sorted and imbricated, although major normal grad- of fluvial origin. The southern part of the Bandera ing over minor reverse grading in units 0.5-1.5 m Mesa Member, as exposed in the face of Bandera (1.6-4.9 ft) thick is more common. Flow direction, Mesa, from North Canyon about 0.8 mi (1.3 km) as determined from both imbrication and abundant south of the northern boundary of the Tascotal 0.5-1 m (1.6-3.2 ft) trough cross-bedding sets in the Mesa Quadrangle to the northwest side of the western end of the Devil’s Graveyard, is strikingly dif- *Name approved for publication by Geologic Names Com ferent. Much of the differenceresults from diagenetic mittee, U.S. Geological Survey. 6 Texas Memorial Museum Bulletin No. 32 sandstones, is to the east or slightly southeast. The conglomerate above the quarry site is a Lunch Local- thickness of 55 ft (16.8 m) shown in figure 6 must be ity and is considerably lower in the section. A very nearly a maximum; thicknesses of 25-30 ft (8-9 m) similar, more lithic sandstone occurs as minor lenses are more common. This bed pinches out against pre- within and above a conglomerate directly overlying the existing topography developed on Cretaceous rocks Variegated beds or resting on Cretaceous rocks. Thus, to the northeast of the Devil’s Graveyard and is thin there are two Basal Tertiary conglomerates rather or absent (e.g., fig. 7) in the northwestern part of the than one. The Lunch Locality conglomerate is similar type area (Tascotal Mesa Quadrangle). At three local- to the conglomerate of the Junction facies but con- ities, one near the base of the measured section tains one to three percent very well-rounded silicic shown in figure 6, large numbers of micromammal volcanic pebbles. It is best distinguished from Junc- teeth and a few isolated jaw fragments have been col- tion facies by the clinoptilolitic sandstones associated lected from conglomeratic, very coarse sandstones with it. The upper conglomeratic unit is informally within the Junction facies. called the Northeast facies of the Basal Tertiary con- Variegated beds.- -The smectitic claystones, mud- glomerate and is the lowest Tertiary conglomerate stones, and minor sandstone or conglomerate channel northeast of the Devil’s Graveyard. Together with deposits that overlie the Junction facies or correlative interlayered sandstones, it can be up to 30 ft (9 m) material or rest directly on Cretaceous rocks are infor- thick, but is normally half of this. The textures and mally called the Variegated beds. They are brightly primary sedimentary structures of the Northeast colored-red, orange, purple, light gray, or green. Light- facies are identical with those of the Junction facies. gray layers are nearly pure clay, while the more Both are sheet-like bodies of sandstone and conglom- brightly colored units show substantial amounts of erate. Vertebrate fossils belonging to the Whistler admixed gypsum, quartz, potassium, and sodic felds- Squat local fauna occur in tuffaceous sandstones par. Some of these minerals are diagenetic, but clays above and below the Northeast facies, but the only in various shades of red, purple, and orange are sandy. fossils hitherto found in the conglomerate are large Where the Variegated beds are of clay they show a silicified logs up to 4 ft (1.2 m) in diameter and some characteristic “whaleback” topography (see Moon, 75 ft (22.9 m) long. 1953, pi. 3, fig. 1). A thickness of 108.5 ft (33.1 m) A third conglomerate, informally called the Car is shown in figure 6, and this is believed to be a near Park conglomerate, has approximately 20 percent maximum. The Variegated beds are usually thinner in silicic volcanic pebbles and occurs above the North- the eastern and northeasternpart of the Devil’s Grave- east facies as a basal filling in channels cut in some yard and are often made up of minor channel-filling places well into the Variegated beds. To the northeast muddy sandstone. Elsewhere, the Variegated beds are of the Devil’s Graveyard where the Lower member is believed to be partially lacustrine. Variation in thick- thickest, Car Park conglomerate channels are separated ness is produced by underlying topography, minor from the Northeast facies by an interval of lacustrine erosion that preceded or accompanied deposition of and palludal sediments with some minor channels overlying tuffaceous, biotite-rich sandstones, and filled by sandstone similar to Lunch Locality sand- growth faulting with maximum displacements of 30 stone. On the southwestern side of the Devil’s Grave- to 42 ft (9 to 13 m). A welded tuff sometimes yard are found places where Junction facies, North- accompanied by two or three much-altered thinner east facies, and Car Park conglomerate are stratigraphi- layers that may be air-fall tuffs, occurs within these cally superimposed with only minor amounts of inter- sandstones and clays. The maximum known thickness lensed sandstone. The lithic portion of the sandstones of the welded tuff immediately underlying the Whistler becomes progressively more volcanic upward. Squat fossil quarry is 20 in (51 cm). The welded tuff Strawberry tuff. -The marker bed informally called is discontinuously exposed from the southwestern to the Strawberry tuff has been mentioned previously as the northeastern corners of the type area of the Devil’s being at or near the top of the Lower member, Devil’s Graveyard Formation. A sample of the tuff gave K-Ar Graveyard Formation. It is present at the top of the dates of 48.6 and 45.8 my (recalculated to 49.7 and section shown in figure 6. In figure 7 the Strawberry 46.9, fig. 5). tuff is comparatively thick and is 152 ft (46.3 m) Lunch Locality sandstone. .—The sandstones asso- above the base of the formation. Clinoptilolite, a ciated with this tuff originally had a high content of white altered glass, occurs in a slightly meandering glass shards, now altered to orange clinoptilolite. channel exposed in relief on the Strawberry tuff in Where this sand is coarser and better washed, it be- the central part of the Devil’s Graveyard. The Straw- comes a zeolitic, volcanic, quartz-bearing, calclithic, berry tuff is recognizable by its lateral persistence, sanidine arkose to feldspathic calclithite sufficiently striking brick-red color, and its tendency to form led- distinct so that, although occurring only as minor ges. It is 2 to 20 ft (0.6 to 6 m) thick and, although lenticular channel fillings, it serves as a local strati- occasionally coarser-grained, is usually a zeolitized graphic field marker bed dubbed the “Lunch Local- (clinoptilolite and analcime) sandy mudstone or mud- ity” sandstone. At Whistler Squat quarry, Lunch stone. The analcime is an exception to the accurate Locality sandstone (capping hill 3395, Moon, 1953, generalization of diagenesis in the Devil’s Graveyard PL 1) occurs 15-20 ft (5-6 m) higher than the welded Formation shown by Henry and Duex (1981, fig. 4). tuff discussed above. Whistler Squat quarry is about Some fossiliferous, pink, suspended-load channel 1,300 yds (1,189 m) east of Whistler Squat and across deposits (Galloway, 1977), 25 to 30 ft (7.6 to 9.1 m) a fault. The conglomerate capping the butte at Whis- thick are exposed at two localities (fig. SC, Serendi- tler Squat is a Titanothere channel filling whereas the pity, and SD, Unio Cliff) in the northeastern part of 1984 Devil’s Graveyard Formation-Marker beds 7 the Devil’s Graveyard where most of the Lower mem- boundary of the Devil’s Graveyard. The tuffs are light ber above the Strawberry tuff is preserved. These are gray, cream, pink, or brilliant red. There is a series of referred to informally as the “Serendipity channels,” three units collectively called the “Repeats,” each although all exposures may be parts of a single channel. consisting of a lower, redder part, and a grayer upper part, and each about 20 to 25 ft (6 to 8 m) thick. Marker beds, middle member The lighter portion is often coarser; in some places it is a cross-bedded tuffaceous sand, whereas the under- Titanothere channels andPurple Bench —The base tuff. lying red portion is usually mudstone. In a few places of the Middle member of the Devil’s Graveyard Form- the red portion shows very small ripple and con- ation is marked by a disconformity having as much as torted ripple cross stratification. Usually only two, 95 ft (29 m) of relief in some places in the northeastern and sometimes only one, of these repeats are exposed, parts of the Devil’s Graveyard. Channel-filling con- and it is often difficult to know which one is present. glomerate (see Moon, 1953, fig. 3), zeolitic volcarenite The two repeats are exposed at approximately 350 ft to zeolitized fine vitric arenite-filled channels at and (107 m) and at 450 ft (137 m) above the base of the slightly above this disconformity, are termed Titan- measured section pictured in figure 8. The lower of othere channels because at one locality limb bones, these repeats forms the base of the measured section teeth, jaws, and skulls of these animals have been in figure 9. found. Titanothere channel conglomerates in at least three locations are directly overlain by orange, altered Marker beds, Bandera Mesa Member (new) (clinoptilolitic), biotite-rich vitric arenites which caused serious stratigraphic confusion in the early Skyline channels..—A series of brick-red to dark-red- stages of this study because of their similarity to zeo- brown to gray sandstone, or deeply-incised conglom- litized sandstones associated with the Northeast facies erate and sandstone-filled channels, determines the conglomerate. Titanothere conglomerate is usually of position of the top of the line of irregular cliffs no great lateral extent, but one channel can be traced (fig. 7) that form the northern margin of the Devil’s for about four mi (6.4 km). Thicknesses are highly Graveyard, from about 1.8 mi (2.9 km) east of the variable but rarely greater than 10 ft (3m). Titan- Devil’s Backbone, a prominent trachyte dike, to 3.9 othere conglomerates are moderately to well sorted, mi (6.3 km) west toward the western end of the grain-supported, small to large medium, pebble con- Devil’s Graveyard. These channels constitute the next glomerates in which normal grading is common, informal lithozone, called the Skyline channels. Fur- reverse grading rare. Flow direction to the east/north- ther examples of these channels are exposed in the east is indicated by imbrication, cross-bedding in pink and red walls of the canyon of the North Fork sandstones, and channel orientation. The well- of Alamo de Cesario (fig. 8). The minor disconformity rounded pebbles are subequally of limestone, silici- with which the slightly sinuous, incised channels are fied limestone, and silicic volcanic rocks with minor associated marks the base of the Bandera Mesa Mem- amount of chert and green silicic quartzarenite. ber, Devil’s Graveyard Formation, and must lie close Hematite in the silica, zeolite, and calcite cements at to an Eocene-Oligocene boundary. The conglomerates most exposures lends a red color, but on weathered are mostly but not always clast-supported, and the surfaces the channel appears dark brown. This color- sorting varies from well-sorted and well-imbricated to ation is in marked contrast to that characterizing the poorly sorted. The clasts range in size from small peb- older conglomerates which appear a yellowish gray, bles to cobbles and boulders, with some boulders of but is common in the remainder of the Devil’s Grave- locally derived, pink tuffaceous sandstone reaching yard Formation. 60 cm (1.97 ft) in intermediate diameter. Some In the western part of the Devil’s Graveyard where depositional units are as much as 3 m (9.8 ft) thick, the buried topography at the base of the Middle mem- but thicknesses of one-half to one-third this are more ber is subdued, a striking purple tuff, a minor ledge- common. The conglomerate and sandstone that fills former called the Purple Bench tuff, can be traced some of the incised channels totals more than 100 ft out of a Titanothere conglomerate channel. The tuff (30 m). Flow direction, judged mainly by tracing is exposed in the banks of Alamo de Cesario Creek individual channels and noting cross bedding, was to close to the eastern edge of the southeastern part of the east. Clasts are well rounded and usually silicic the Tascotal Mesa Quadrangle for 3 mi (4.8 km) and (trachytic) volcanic rock fragments with subequal into the area beween the North and South forks of amounts, approximating a sum of 30 to 70 percent Alamo de Cesario. A large concentration of vertebrate of silicified limestone and limestone pebbles. Mafic, fossils has been found in a nodular, yellow, zeolitized vesicular, and dark-colored volcanic rock fragments vitric arenite approximately 1 to 3 ft (.3 to .9 m) are present in amounts of 5 to 27 percent. The pres- above the Purple Bench tuff. The Purple Bench tuff ence of this lithology is distinctive, inasmuch as mafic is probably an altered airfall ash layer, although it clasts are rare in the Devil’s Graveyard Formation may have been slightly reworked; its lower part is except in the Cotter channels, which are discussed another unusually pure clinoptilolite. The Purple below. Except for the previously noted color, the vol- Bench tuff varies from about 8 in (20 cm) to 2 ft carenites associated with the Skyline channels are not (60 cm) thick, and its base defines the boundary distinctive. A Duchesnean ? vertebrate fauna has been between the lower and middle members. recovered from the Skyline channels. Also, numerous Repeats..—The middle part of the middle member mammal tracks, gastropods, and impressions of palm is a thick section of sedimentary tuff well exposed as fronds have been found along bedding planes of the cliffs (see Moon, 1953, fig. 2) forming the northern Skyline channel sandstones. 8 Texas Memorial Museum Bulletin No. 32

Figure 1.-Map of Texas with Presidio and Brewster counties shaded. Enlarged map shows location of principal fossiliferous areas; Big Bend National Park shaded. 1984 Devil’s Graveyard Formation-Figure 2 9

Figure 2.-Sketch map of Trans-Pecos Texas and adjacent Mexico showing extent of igneous and volcaniclastic rocks, known and inferred volcanic centers, and the location of geologic quadrangles. AF, Agua Fria Quadrangle (Moon, 1953); BH, Buck Hill Quadrangle (Goldich and Elms, 1949); BM, Bofecillos Mountains Quadrangle (McKnight, 1970); CM, Cathedral Mountain Quadrangle (McAnulty, 1955); JG, Jordan Gap Quadrangle (Seward, 1950); TM, Tascotal Mesa Quadrangle (Erickson, 1963). Modified from Gorski (1970). 10 Texas Memorial Museum Bulletin No. 32 1984 Devil’s Graveyard Formation-Figure 3 11 measured Figure sections. 3.-Geologic map of parts of the Agua Fria, Tascotal Mesa, and Jordan Gap quadrangles to show areas exposureof of Devil’s Graveyard Formation (new) and location of 12 Texas Memorial Museum Bulletin No. 32

Figure 4.-Fence diagram of Buck Hill Group from the Southern Davis Mountains to the west side of Agua Fria Mountain and South Lajitas Mesa to Tule Mountain. The diagram was not drawn to scale and most faulting was removed. Positions of samples for potassium-argon dates shown as K-Ar 1 through 7: (all dates corrected to 1976 lUGS standards) K-Ar 1, Alamo Creek Basalt, 40, 44, 39, 43 my; K-Ar 2, tuff directly underlying Whistler Squat Quarry (TMM 41372), 49, 46 my; K-Ar 3, micaceous tuff above Whistler Squat Quarry and below Strawberry tuff, 43 my; K-Ar 4, upper basalt on Bandera Mesa, 33 my; K-Ar 5, Mitchell Mesa Rhyolite, average of 18 dates 32.28 ± .6 my; K-Ar 6, Basalt (Rawls 2, Bofecillos Mountains), 28 my; K-Ar 7, ash beneath Skyline channel at Tepee Canyon (TMM 41578), 42 my. 1984 Devil’s Graveyard Formation-Figure 5 13

Figure 5.-Diagrammatic stratigraphic section of the Buck Hill Group, Devil’s Graveyard-Bandera Mesa area, Brewster and Preside Couties, Texas, to show approximate relative thickness and stratigraphic position of fossil localities, local faunas, and North American land mammal ages. Radiometric dates (in millions of years) are from McDowell (1979) except the following which are from Geochron Laboratories; 42.7 (biotite-bearing ash, just below Skyline channel); 33.0 (whole rock basalt, lowest basalt on Bandera Mesa). The number in parentheses following the date signifies the number of samples. All dates on this diagram have been corrected to conform to lUGS recommendation Subcommision on Geochronology and will therefore differ from those given in Wilson (1980), Wilson and Schiebout (1981), Wilson and Schiebout (1984). Letters A through J refer to stratigraphic position of one or more fossil localities. A. Junction, 41443; .6 mi east of Junction, 41444; B. Whistler Squat no. 2 quarry, 41372; C. Serendipity, 41745; D. Unio Cliff, 41784; E. Titanothere Hill, 41723; F. Purple Bench, 41672; G. Skyline, Tepee Canyon, 41578, H. Horseshoe stone coral, 41853; I. Red table, 41965; J. Red Hill, 41781. 14 Texas Memorial Museum Bulletin No. 32 Figure 6.—Measured section of lower member, boundary stratotype, and of Devil’s Graveyard Formation (new). This is measured section 15 on figure 3. 1984 Devil’s Graveyard Formation—Figure 7 15

Figure 7.-Measured section, lower and middle members, Devil’s Graveyard Formation (new). This is measured section 16 on figure 3. 16 Texas Memorial Museum Bulletin No. 32 Formation Figure (new). This 8.-Measured is section measured of section North 17Fork on of figure Alamo 3. de Cesario Creek showing the lithology of the southern part of the Bandera Mesa Member (new) of the Devil’s Graveyard 1984 Devil’s Graveyard Formation-Figure 9 17

Figure 9.-Measured section of middle member and Bandera Mesa Member of Devil’s Graveyard Formation (new) on South Fork of Alamo de Cesario Creek. This is section 18 on figure 3. 18 Texas Memorial Museum Bulletin No. 32 Quadrangle, Figure Presidio 10.—Measured County, section, Texas. upper This is boundary section 19 on stratotype figure of 3. Bandera Mesa Member (new), Devil’s Graveyard Formation (new) at southeast corner of Puerto Potrillo, Jordan Gap 1984 Devil’s Graveyard Formation-Cotter channels 19

Cotter channels. —No well-exposed section imme- Mountain and at Whirlwind Spring it occurs in the diately above the Skyline channels was available for upper part of the Pruett Formation (Goldich and Elms, study to clarify the stratigraphic relationship between 1949, p. 1148). McAnulty (1955, p. 545) reported the Skyline channels and the overlying sediments. A fossil bones now identified as early Oligocene from set of channels occurs stratigraphically above the Sky- the upper breccia at Cottonwood tank just west of line channels near the old Cotter Ranch headquarters Boat Mountain. However, Seward (1950) did not map on Needle Creek (Erickson, 1953, pi. 1), and is infor- any Pruett Formation where the Upper breccia- mally called the Cotter channels. The best exposed parts conglomerate is exposed on the Jordan Gap Quad- of these sinuous to highly sinuous channels are point- rangle and must therefore have included it within the bar deposits encountered along Needle, Dogie, Crystal, Duff Formation. Early Oligocene fossils are also pres- and Musgrave creeks, on the Tascotal Mesa and Agua ent in the lower part of the Bandera Mesa Member Fria Quadrangles. The strongly-graded conglomerates which was mapped by Seward (1950) as Duff Forma- are usually not clast supported and are poorly to tion. This is made more understandable by the east- moderately well-sorted, medium to very small pebble west cross section of Henry and Duex (1981) in deposits. They have little lateral continuity and depo- which they show that their clinoptilolite and mont- sitional units of conglomerate or sand conglomerates morillonite diagenetic zone extends from the Duff are rarely thicker than 0.5 m (19.6 in) in the point Formation down into the western biostratigraphic bars and are more commonly half that figure. The equivalent of the Pruett Formation. small exposures prevent precise estimates of point- From Puerto Potrillo southeastward, the Upper bar thickness, but 22 to 34 ft (7 to 10 m) is prob- breccia-conglomerate is represented by basal fillings able in some places. The streams depositing the sedi- and lateral bar deposits in straight to slighly sinuous ments filling the Cotter channels flowed generally channels which indicate an eastward flow direction. eastward. Labile pebbles of locally derived tuffaceous The southernmost of these channels is known from a sand-and-mudstone and calcitic nodules of tuffaceous set of large down-dropped blocks at the base of the fine sandstone are abundant and constitute one-half southern and western sides of Red Hill. Conglomeratic, to two-thirds of the pebbles in given exposures, and altered, vitric volcarenites 168 ft (51.2 m) above the more in the eastern exposures of the Cotter channels. base of the measured section at Puerto Potrillo (fig. 10) The durable pebbles are rounded to well-rounded and are lateral to the top of one of these channels. The consist of subequal amounts of limestone, silicified stratigraphically highest fossils recovered thus far limestone, and silicic (trachytic) volcanic pebbles, from the Devil’s Graveyard Formation come from with a relative increase in the number of volcanic peb- 60 to 80 ft (18 to 24 m) below the Upper breccia- bles upward in the section. Sandstones in the point- conglomerate, Bandera Mesa Member, at Red Hill, bar deposits are medium to fine, except basally, and Montgomery tank area (Montgomery bone bed) and are volcarenites laterally and vertically gradational at the base of the southwestern face of McKinney with zeolitized (clinoptilolite) and montmorillonized Mountain.

vitric arenites. Stratigraphically higher channels, Upper part of the Bandera Mesa Member (new). - apparently gradational with the Cotter channels, are This part of the Bandera Mesa Member is known to the seen along the east face of Bandera Mesa and are simi- authors only from exposures in the face of Bandera lar to the low sinuosity channels characteristic of Mesa, on McKinney Mountain, and along Puerto depositing streams for most of the Devil’s Graveyard Potrillo. The bulk of this unit, as with other parts, is Formation. The Cotter channels yield both vertebrate made up of fine to very fine calcitic, zeolitized vitric and invertebrate fossils. arenites, with minor 1 to 3 ft (30 to 91 cm) thick Upper breccia-conglomerate. ,-Goldich and Elms calcitic, zeolitic volcarenites. The boundary between (1949, p. 1146) named and described this unit, situ- the clinoptilolite-opal-montmorillonite and clinoptilo- ated 60 ft (18.3 m) below the top of the Pruett lite-montmorillonite diagenetic facies of Henry and Formation, and stated that it covered many square Duex (1981) occurs close to North Canyon, at the miles and (by implication) that it extends west from northern boundary of the Tascotal Mesa Quadrangle, the area of Boat Mountain and Whirlwind Spring in where the color change previously mentioned takes the north-central part of the Buck Hill Quadrangle, place. Depositionally, the principal differences can be into the Jordan Gap Quadrangle (Goldich and Seward, seen by contrasting sediments northwest of South 1948). The present writers observe that in the Jordan Canyon with those to the southeast. As Wilson et al. Gap Quadrangle north of McKinney Mountain and (1979) and Stevens (1979) noted, the southern part west to the base of Antelope Mesa the Upper breccia- of the section has been thinned by pre-Mitchell Mesa conglomerate is exposed as a broad sheet of hematitic, Rhyolite and pre-Yellow conglomerate erosion. Fan- zeolitized, angular to subrounded conglomerate glomerates in the original sense are absent with one, resistant to erosion, and weathering dark brown to possibly Yellow conglomerate-related, exception. Con- nearly black. Thickness of Upper breccia-conglomerate glomerates contain rounded to well rounded, medium varies from 15 in. to 11.5 ft (0.4 to 3.5 m). Its strati- pebbles, although they are usually not well sorted. graphic position is shown on figure 5. Higher up, limestone and silicified limestone pebbles The Upper breccia-conglomerate of Goldich and become important or even dominant. Lake deposits Elms (1949) provides a valuable stratigraphic marker including limestone units up to 20 ft (6 m) thick are bed from the northern part of the Buck Hill Quad- found low in the upper part of the Bandera Mesa rangle at Boat Mountain westward to the Jordan Member and interlayered with the highest Cotter Gap Quadrangle near McKinney Mountain. At Boat channels, at and near Smugglers Gap. Discontinuous, 20 Texas Memorial Museum Bulletin No. 32

thin basalt layers recur high in the section from just the upper part of the Bandera Mesa Member north of north of South Canyon to the point about 1 mi (1.6 South Canyon. There are few conglomerates above km) from the southeast end of Bandera Mesa where the Upper breccia-conglomerate, but near the top, basalt flows were beveled by erosion prior to extru- there is a major fanglomerate, represented in figure sion of the Mitchell Mesa Rhyolite. 10 by a 40-ft (12.2-m) interval starting 601 ft Stevens’ (1979) description of an upper informal (183.2 m) above the base of the section. This very member of the “Pruett-Duff” unit applies mainly to coarse fanglomerate is also exposed high on McKinney Mountain.

SUMMARY

A thick section of volcaniclastic sediments is named Bandera Mesa Member yielded a Chadronian fauna the Devil’s Graveyard Formation. Vertebrate fossils named the Coffee Cup local fauna. The Pruett and of the early late Eocene Whistler Squat local fauna Duff formations of the Buck Hill Group were occur in the basal conglomerate and in the lower bounded by lava flows, the stratigraphic positions of member of the formation. Late Eocene vertebrate which were not possible to locate in the area of expo- fossils, the Serendipity local fauna, were found in the sure of the Devil’s Graveyard Formation. Lower mid- middle member and a small vertebrate fauna, the Sky- dle and upper stratotype sections and the strati- line local fauna, was discovered in red conglomerates graphic position of important vertebrate fossil local- and is probably of Duchesnean age. The upper or ities were given.

REFERENCES

American Commission on Stratigraphic Nomenclature geology of the Trans-Pecos volcanic field of Texas. (ACSN), 1972. Code of stratigraphic nomencla- Bur. Econ. Geol., Univ. Texas—Austin, Guide- ture. Amer. Assoc. Petroleum Geologists, Tulsa, book 19:92-96. Okla., pp. 1-21, 2nd printing. Dalrymple, G.8., 1979. Critical tables for conversion Barker, R. S., 1977. Northern Trans-Pecos magmatic of K-Ar ages from old to new constants. Geology province: introduction and comparison with the 7:558-560. Kenya rift. Geol. Soc. Amer. Bull. 88:1421- Erickson, R.L., 1953. Stratigraphy and petrology of 1427. the Tascotal Mesa Quadrangle, Texas. Geol. Soc. Barnes, V. E., Project Director, 1979. Atlas of Texas Amer. Bull. 64(12):1353-1386. Emory Peak-Presidio Sheet. Bur. Econ. Geol., Galloway, W.E., 1977. Catahoula Formation of the Texas—Austin. Univ. Texas coastal plain: depositional systems, com- Bockoven, N. T., 1981. Tertiary stratigraphy of the position, structural development, ground water Sierra Del Gallego area of Chihuahua with com- flow history, and uranium distribution. Bur. the parisons to Pena Blanca uranium district. In Econ. Geol., Univ. Texas—Austin, Rept. Invest. Amer. Assoc. Petroleum Geologists, Studies in 87. 56 pp. Geology (13), Uranium in volcanic and volcani- Gilliland, M.W., andH.C. Clark, 1979. Paleomagnetism clastic rocks, 181-187. of early Tertiary volcanics of the Big Bend, Texas. Cameron, Maryellen, K.L. Cameron, and J.C. Cepeda, In Cenozoic geology of the Trans-Pecos volcanic 1982. Geochemistry of Oligocene volcanic rocks field of Texas. Bur. Econ. Geol., Univ. Texas— from the Chinati Mountains, West Texas. Geol. Austin, Guidebook 19:48-54. Soc. Amer., South Central Section, Abstracts with Goldich, S. S., and M.A. Elms, 1949. Stratigraphy and Programs, 16th Ann. Mtng., p. 106. petrography of the Buck Quadrangle, Texas. Capps, R. C., 1981. Geology of the Rancho ElPapalote Hill Geol. Soc. Amer. Bull. 60:1133-1183. Area, Chihuahua, Mexico. In Amer. Assoc. Petro- Goldich, Green Valley- leum Geologists, Studies in Geology (13), Urani- S. S., and C. L. Seward, 1948. um in volcanic and volcaniclastic rocks, 243-264. Paradise Valley field trip. West Texas Geol. Soc. Cepeda, J.C., 1977. Geology and geochemistry of the Field Trip, Oct. 29-31. igneous rocks of the Chinati Mountains, Presidio Gorski, D.E., 1970. Geology and trace transition ele- County, Texas. Unpubl. Ph.D. dissertation, Univ. ment variation of the Mitre Peak area, Trans-Pecos Texas—Austin. 154 pp. Texas. Unpubl. master’s thesis, Univ. Texas— , 1979. The Chinati Mountains caldera, Presi- Austin. 200 pp. dio County, Texas. In Cenozoic geology of the Henry, C.D., and T.W. Duex, 1981. Uranium in dia- Trans-Pecos volcanic field of Texas. Bur. Econ. genesis of the Pruett, Duff, and Tascotal forma- Geol., Univ. Texas—Austin, Guidebook 19:106- tions, Trans-Pecos Texas. In Amer. Assoc. 125. Petroleum Geologists, Studies in Geology (13), Daily, Michael, 1979. Age relations in alkaline rocks Uranium in volcanic and volcaniclastic rocks, from the Big Bend region, Texas. In Cenozoic 167-180. 1984 Devil’s Graveyard Formation-References 21

Henry, C.D., and F.W. McDowell, 1982. Timing, dis- Seward, C. L., 1950. Geology of the Jordan Gap Quad- tribution, and estimates of volumes of silicic vol- rangle, Texas. Unpubl. master’s thesis, Texas canism in Trans-Pecos Texas. Geol. Soc. Amer., A&M Univ. 72 pp. South Central Section, Abstracts with Programs, Stevens, J. 8., 1969. Geology of the Castolon area, Big 16th Ann. Mtng. p. 113. Bend National Park, Brewster County, Texas. International Subcommission on Stratigraphic Classi- Unpubl. Ph.D. dissertation, Univ. Texas—Austin. fication (ISSC), 1976. International stratigraphic 129 pp. guide, ISSC of International Union of Geol. , 1979. Eocene-Oligocene volcaniclastic sedi- Sciences (lUGS) Commission on Stratigraphy. ments, West-Central Brewster County and adja- H.D. Hedberg, ed., John Wiley and Sons, New cent Presidio County, Trans-Pecos Texas. In York. 200 pp. Cenozoic geology of the Trans-Pecos volcanic Keller, P.C., N.T. Bockoven, and F.W. McDowell, field of Texas, Bur. Econ. Geol., Univ. Texas— 1982. Tertiary volcanic history of the Sierra del Austin, Guidebook 19:150-156. Gallego area, Chihuahua, Mexico. Geol. Soc. Stevens, M.S., J.B. Stevens, and M.R. Dawson, 1969. Amer. Bull. 93:303-314. New early Miocene Formation and vertebrate Mauger, R. L., 1981. Geology and petrology of the local fauna, Big Bend National Park, Brewster central part of the Calera-del Nido block, Chi- County, Texas. Texas Memorial Mus. Pearce- huahua, Mexico. In Amer. Assoc. Petroleum Sellards Ser. 15. 53 pp. Geologists, Studies in Geology (13), Uranium in Walton, A.W., 1972. Sedimentary petrology and zeo- volcanic and volcaniclastic rocks, 181-187. litic diagenesis of the Vieja Group (Eocene-Oligo- Mauger, R. L., and F.W. McDowell, 1982. K-Ar dating cene) Presidio County, Texas. Unpubl. Ph.D. dis- of igneous rocks in central Chihuahua, Mexico. sertation. Univ. Texas—Austin. 264 pp. Geol. Soc. Amer., South Central Section, , 1975. Zeolitic diagenesis in Oligocene vol- Abstracts withPrograms, 16th Ann. Mtng. p. 116. canic sediments, Trans-Pecos Texas. Geol. Soc. Maxwell, R. A., J.T. Lonsdale, R. T. Hazzard, and J. A. Amer. Bull. 86:615-624. Wilson, 1967. Geology of Big Bend National Park. , 1979. Volcanic sediment apron in the Tasco- Univ. Texas Publ. 6711. 320 pp. tal Formation (Oligocene?), Trans-Pecos Texas. McAnulty, W.N., 1955. Geology of the Cathedral J. Sed. Pet. 49; 303-314. Mountain Quadrangle, Brewster County, Texas. , b.1979 Sedimentology and diagenesis of the Geol. Soc. Amer. Bull. 66:531-578. Tascotal Formation: a brief summary. In Ceno- McDowell, F.W., 1979. Potassium-argon dating in the zoic geology of the Trans-Pecos volcanic field of Trans-Pecos Texas volcanic field. In Cenozoic Texas. Bur. Econ. Geol., Univ. Texas—Austin, geology of the Trans-Pecos volcanic field of Texas. Guidebook 19:157-171. Bur. Econ. Geol., Univ. Texas—Austin, Guide- Wilson, J.A., 1972. Vertebrate biostratigraphy of book 19:10-18. Trans-Pecos Texas and northern Mexico, in the McKnight, J.F., 1970. Geologic map of Boffecillos geologic framework of the Chihuahua tectonic Mountain area, Trans-Pecos Texas. Bur. Econ. belt. West Texas Geol. Soc., R.K. DeFord Sym- Geol., Univ. Texas—Austin, Geol. Quad. Map. 37, posium, pp. 157-166. with text. , 1974. Early Tertiary vertebrate faunas Vieja Moon, C.G., 1953. Geology of Agua Fria Quadrangle, Group and Buck Hill Group, Trans-Pecos Texas: Brewster County, Texas. Geol. Soc. Amer. Bull. Protoceratidae, Camelidae, Hypertragulidae. Tex- 61:151-196. as Memorial Mus. Bull. 23. 34 pp. D.F., 1976. Petrology and eruptive history of Parker, , 1977. Early Tertiary vertebrate faunas Big an Oligocene trachytic shield volcano, nearAlpine, Bend area Trans-Pecos Texas: Brontotheriidae. Texas. Unpubl. Ph.D. dissertation, Univ. Texas— Texas Memorial Mus. Pearce-Sellards Ser. 25. Austin. 184 pp. 15 pp. , ThePaisano volcano: stratigraphy, age, 1978. Wilson, J.A., J.B. Stevens, and M.S. Stevens, 1979. and petrogenesis. In Cenozoic Geology of the New cross section from the southern Davis Moun- volcanic field of Bur. Econ. Trans-Pecos Texas, tains to northeast Solitario. In Cenozoic Geology Univ. Texas—Austin, 19: Geol., Guidebook of the Trans-Pecos volcanic field of Texas. Bur. 97-105. Econ. Geol., Univ. Texas—Austin, Guidebook 19: Parker, D.F., and F.W. McDowell, 1979. Stratigraphy 147-149. and K-Ar geochronology of Oligocene volcanic Wilson, J.A., and F.S. Szalay, New adapid pri- Davis and Barrilla Mountains, Trans-Pecos 1976. rocks, mate of European affinities from Geol. Soc. Amer. Bull. Pt. 1, 90:1100 Texas. Folia Texas. Primat. 25(4):294-312. 1110. Robinson, 8.R., 1976. Stratigraphy and environment Wood, A.E., 1972. An Eocene hystricognathous ro- of deposition of member 9 of the Rawls Forma- dent from Texas: its significance in interpretation, Presidio County, Texas. Unpubl. master’s tions of continental drift. Science 175: 1250- thesis, Univ. Houston, 151 pp. 1251. Schiebout, J.A., 1974. Vertebrate Paleontology and , 1973. Eocene rodents, Pruett Formation, Paleoecology of the Paleocene Black Peaks For- southwest Texas; their pertinence to the origin mation, Big Bend National Park, Texas. Texas of the South American Caviomorpha. Texas Memorial Mus. Bull. 24. 88 pp. Memorial Mus. Pearce-Sellards Ser. 20. 41 pp.