Comparison with Proximal K/Pg Boundary Sites

Home , North Horn Formation, Torrejonian

Sedimentology of the Cretaceous-Paleogene Boundary Interval in the Tornillo Group of West Texas

Jacob Cobb, B.S.

A Thesis

Geosciences

Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of

MASTER OF SCIENCES

Approved

Thomas Lehman Chair of Committee

Dustin Sweet

Paul Sylvester

Mark Sheridan Dean of the Graduate School

August, 2016

Texas Tech University, Jacob Cobb, August 2016

ACKNOWLEDGMENTS

I would like to thank Dr. Lehman for making this study possible and for taking me on as his student, and for all his help and support along the way. Thanks to my parents for their support, and my dad for all his help out in the field. I would like to thank my fiancé for all of her support through this process.

This research was also aided by Texas Tech Geosciences faculty, as professors and students helped support and guide me through my research. Special thanks to Nick

Miller for providing help and knowledge on the picking of charophytes. I would like to thank Mathew Pippin for all the support, and help with SEM imaging. To Tom Shiller,

Zach Wilson, Jenna Kohn, Jenna Hessert, Kevin Werts, and Ethan Backus I appreciate all of the support. Special thanks goes to Ethan Backus for his help throughout this research.

Dr. Sweet and Dr. Sylvester your time, help, and support meant a great deal to me and went a long way in this research. I would like to thank Melanie Barnes for her help, support, and also the use of her lab. Thanks to Dr. Hetherington and Dr. Zhoa for use of the SEM. I also would like to thank my God for providing me this opportunity and seeing me through.

Texas Tech University, Jacob Cobb, August 2016

TABLE OF CONTENTS

ACKNOWLEDGMENTS ...... ii ABSTRACT ...... v CHAPTER 1: INTRODUCTION ...... 1 GEOLOGY OF THE TORNILLO GROUP ...... 3 The Tornillo Basin ...... 3 The Tornillo Group ...... 4 THE K/PG BOUNDARY IN BIG BEND ...... 7 The Dawson Creek Exposure ...... 9 The Rough Run Amphitheater ...... 10 The Rough Run East Exposure ...... 13 THE K/PG BOUNDARY AROUND THE GULF OF MEXICO ...... 14 CHAPTER 2: GEOLOGY OF THE ‘ROUGH RUN EAST’ EXPOSURE ...... 28 Stratigraphic Section at Rough Run East ...... 29 The ‘Odd Conglomerate’ ...... 33 CHAPTER 3: PALEONTOLOGY OF THE ‘ROUGH RUN EAST’ EXPOSURE ...... 46 Sites #1 through #4 ...... 46 Site #5 ...... 47 Site #6 ...... 49 CHAPTER 4: SANDSTONE PETROGRAPHY AND GRAIN MORPHOLOGY ...... 55 Sandstone Petrography ...... 56 Grain Morphology ...... 60 CHAPTER 5: GEOCHRONOLOGY ...... 87 Tom’s Top ...... 88 CHAPTER 6: DISCUSSION ...... 98 Correlation of Rough Run East and Dawson Creek sections ...... 98 Paleontological and Isotopic Age Constraints on the K/Pg Boundary ...... 99 Deposition of the ‘odd conglomerate’ ...... 102

iii

Texas Tech University, Jacob Cobb, August 2016

Significance of Charcoal ...... 106 Sand Grain Morphology ...... 108 Significance of Shocked Quartz ...... 110 Interpretation of the ‘odd conglomerate’ ...... 111 Comparison with modern tsunami deposits ...... 112 Comparison with proximal K/Pg boundary Sites ...... 115 Future work ...... 118 CHAPTER 7: CONCLUSIONS ...... 121 BIBLIOGRAPHY: ...... 124 APPENDIX: ...... 137

Texas Tech University, Jacob Cobb, August 2016

ABSTRACT

A recently discovered outcrop of the Tornillo Group at Rough Run Creek in Big

Bend National Park provides the best exposure of the Cretaceous/Paleogene (K/Pg) boundary interval thus far known in the Big Bend region. An unusual conglomerate bed is exposed here, and vertebrate fossils found above and below the conglomerate, as well as charophyte oogonia found in the bed itself, indicate that it was deposited at or around the time of the K/Pg boundary. The unusual conglomerate appears to occupy the base of a broad paleo-valley incised into underlying strata. The conglomerate bed is generally less than a meter in thickness, but includes very large boulders, and is generally much coarser grained than conglomerates found in typical fluvial channel deposits in the

Tornillo Group. Its composition is also unusual, and consists of rounded sandstone clasts, abraded pedogenic carbonate nodules, mudstone ‘rip-up’ clasts, and charcoal, all derived from local sources. The conglomerate was deposited during or shortly after motion on a small fault that was buried during sedimentation, and at least three successive episodes of sediment transport occurred under rapid (upper flow regime) conditions, with clasts transported only a short distance prior to deposition. Sand grains from the matrix of the conglomerate and from a sandstone layer at its top include quartz grains with planar deformation features, and spherules with ‘splash’ and ‘ablated’ morphologies. These unusual aspects of the conglomerate suggest that it may record the

Chicxulub impact event. The very coarse conglomerate reflects a series of brief, high velocity flow events, perhaps recording the transit of tsunami waves upstream several hundred kilometers from the coastline at that time. If this interpretation is correct, then v

Texas Tech University, Jacob Cobb, August 2016

the conglomerate bed may provide the first documentation of this event in a proximal (within several thousand km from Chicxulub impact) non-marine setting.

Other well studied proximal K/Pg boundary sites around the Gulf of Mexico and

Caribbean are exclusively in marine deposits. Other known continental K/Pg boundary sites are in distal settings where only a thin atmospheric fall-out layer is recorded. Further detailed studies of the chemistry, mineralogy, and precise age of the conglomerate are necessary to determine whether it actually records the K/Pg boundary event.

Texas Tech University, Jacob Cobb, August 2016 List of Tables

4.1. Petrography of Rough Run Creek East Region Sandstone Units.…………………....71 4.2. Petrographic data of time periods within the Tornillo Basin………………………...72 5.1. U/Pb zircon Concentrations at Tom’s Top.………………………………...... 92 5.2. Zircon standard GJ tabulated data……………….…………………………………..93 5.3. Zircon standard Plesovice tabulated data……………………………………………94

vii

Texas Tech University, Jacob Cobb, August 2016

List of Figures

1.1. Geology and structure of the Laramide Tornillo Basin…………………...………….19 1.2. Stratigraphy of the Tornillo Group in Big Bend……………………….……………..20 1.3. Stratigraphy of the K/Pg boundary interval in the Tornillo Group on Dawson Creek ……………………………………………………………………………………...21 1.4. Stratigraphy of the K/Pg boundary interval in the Tornillo Group at the Rough Run Amphitheater…..………………………………………………………………...22 1.5. Geologic map of “Rough Run Amphitheater”………………………………………..23 1.6. Geologic map of south bank of Rough Run Creek.…………………………………..24 1.7. Exposures at “Rough Run East” showing position of the odd conglomerate………...25 1.8. Map of the Gulf of Mexico at end of Cretaceous time, showing comparison of Rough Run Creek East site to Chicxulub impact and location of outcrops with K/Pg sandstone complex deposits……..………………………………………….....26 1.9. Paleogeographic map of Gulf of Mexico at end of Cretaceous time, showing Chicxulub impact site and K/Pg boundary sites……………………….………….....27 2.1. Geologic map of Rough Rough East outcrop………………………………………...38 2.2. Stratigraphic section of Tornillo Group at the Rough Run East……….……………..39 2.3. View to north of lower part of stratigraphic section at Rough Run East showing unit 2 (light gray mudstone) and overlying yellow-weathering sandstone in unit 3……………………………………………………………………………………...40 2.4. View to east of yellow-weathering sandstone in unit 3 (Javelina sandstone #2) and mudstone in overlying unit 4………………………………..…………………..41 2.5. View to northeast of upper part of unit 4 (dark gray mudstone in Black Peaks Formation), unit 5 (prominent red mudstone bed), unit 6 (dark gray mudstone), and unit 7 ….………………………………………………………………………..42 2.6. View to northwest of upper part of stratigraphic section at Rough Run East, showing top of unit 7 (“hoodoo sandstone”), unit 8 (“odd conglomerate”), unit 9 (gray mudstone), unit 10 (“candy-striped beds”), and unit 11..……………………..43 2.7. Detailed geologic map of northwest part of Rough Run East outcrop, showing location of sections A through P measured in the ‘odd conglomerate’……………...44

2.8. Correlation of 16 sections A through P……………….……………………………...45

viii

Texas Tech University, Jacob Cobb, August 2016 3.1. Charophyte gyrogonites……………………………………………………………...51 3.2. Aquatic vertebrate fauna………………...………………………………………...... 52 3.3. Large upper first or second premolar of taeniodontid mammal Psittacotherium multifragum……….………………………………………………...53 3.4. Partial left side of trionychid turtle………………………………….…………….....54 4.1. Photomicrograph of Javelina Sandstone unit 1………………………………………68 4.2. Photomicrograph of ‘hoodoo sandstone’…………………………………………….68 4.3. Photomicrograph of ‘odd conglomerate’…………………………………………….69 4.4. Photomicrograph of sandstone pebble from ‘odd conglomerate’ (Pt. A Hoodoo)…...69 4.5. Photomicrograph of pebble from ‘odd conglomerate’ (ss3)…………………………70 4.6. Ternary diagram comparing basic framework grain composition of Tornillo Group sandstones……………………………………………………………………73 4.7. Ternary diagram comparing lithic grain composition of Tornillo Group sandstones ...... ……………………………………………………………………..73 4.8. Ternary diagram comparing volcanic and carbonate lithic grain composition of Tornillo Group sandstones…………………………………………………………..74 4.9. SEM image of quartz grain showing multiple sets of parallel lamellae……………...74

4.10. Magnified view of same grain shown in figure 4.7………………………………...75

4.11. SEM image of a quartz grain showing deep parallel fractures……………………..75

4.12. Enhanced image of parallel fractures in same grain shown in figure 4.9…………..76 4.13. SEM image of quartz grain that shows intersecting sets of planar deformation features...…………………………………………………………………………...76 4.14. Enhanced view of same grain shown in figure 4.11…………….………………….77

4.15. SEM image of quartz grain displaying two sets of arch-shaped steps……………...77 4.16. SEM image of angular quartz grain with percussion marks and sub-parallel linear fractures………...…………………………………..………………………..78 4.17. SEM image of typical angular quartz grain………………………………………..78 4.18. SEM image of quartz grain with euhedral bipyramidal hexagonal (beta quartz) form and little abrasion……………………………………………………………..79

Texas Tech University, Jacob Cobb, August 2016 4.19. SEM image of quartz grain with vague hexagonal bipyramidal form, subhedral shape, and percussion marks………………………………………...…..79 4.20. SEM image of quartz ‘spherule’ displaying remnant euhedral shape, and higher rounding…………………………………………………………………….80 4.21. SEM image of quartz ‘spherule’………………………………………..….………80 4.22. SEM image of quartz ‘spherule’ displaying high rounding and little or no remnant crystal form, percussion marks and v-fractures………..………………….81 4.23. SEM image of well wounded quartz ‘spherule’ with minor abrasion features……………….……………………………………………………………..81 4.24. SEM image of quartz ‘spherule’ with faint percussion marks………….…………..82

4.25. SEM image of quartz ‘spherule’ with vague tetragonal prism structure…………....82 4.26. SEM image of well rounded quartz ‘spherule’ with possible adhering cement……………………………………………………………………………...83 4.27. SEM image of quartz grain with euhedral triangular crystal face and sub- parallel linear fractures ...……………..…..…………………………………….….83 4.28. SEM image of irregular ‘dumbbell-shaped’ quartz spherule……………………….84

4.29. SEM image of ‘dumbbell-shaped’ quartz spherule with multiple fractures………..84

4.30. Example of a typical subrounded detrital quartz grain with features indicative of prolonged subaqueous transport………………………………………………...85 4.31. SEM image of metal oxide grain consisting of at least three euhedral crystals with pits…………………………………………………………………………….86 4.32. SEM image of pitted subhedral metal oxide grain………………………………....86

5.1. Zircon GJ weighted average 206Pb/238U ages………………….……………….....90

5.2. Zircon GJ weighted average 206 Pb/207Pb………………………...…………….....91

5.3. Zircon Plesovice weighted average 206Pb/238U ages………………………………92 5.4. Probability density plot showing distribution of U/Pb isotopic ages for entire set of 16 zircons in the sample from the “Tom’s Top” bed……….……………...... 95 5.5. Age distribution, mean value and WSMD for 8 youngest zircons in the sample from the “Tom’s Top” bed………………………………………………….96

Texas Tech University, Jacob Cobb, August 2016

5.6. Concordia plot of seven youngest zircons………………...…………………….....97 6.1. Correlation of Dawson Creek, Rough Run Amphitheater, and Rough Run E.………………………………………………………………………………….120

Texas Tech University, Jacob Cobb, August 2016

CHAPTER 1 INTRODUCTION

The Cretaceous-Paleogene (K/Pg) boundary is marked by a major mass extinction event that occurred about 66 million years ago (66 Ma), and has long been a subject of interest to geologists and paleontologists. Over the past several decades, it has become widely accepted that the K/Pg boundary event resulted from the effects of a bolide impact on the northern Yucatan Peninsula in Mexico

(the Chicxulub “crater” structure; reviewed by Renne et al., 2013).

In the Big Bend region of Texas, a record of the K/Pg boundary interval is preserved in sediments of the Tornillo Group. These sediments are predominantly fluvial in origin, and accumulated in a basin (the “Tornillo Basin”) that was several hundred kilometers inland from the shoreline of the Gulf of Mexico at the time of the K/Pg boundary event (Lehman, 1991). Contemporaneous K/Pg marine sediments in northeastern Mexico (e.g., Lawton et al., 2005) and central Texas

(e.g., Bourgeois et al., 1988) are interpreted to record deposition in response to a tsunami generated by the Chicxulub impact. The Tornillo Group section in Big

Bend provides a continental stratigraphic section spanning the K/Pg boundary interval closest to the purported impact site, and modeling of the impact suggests that run-up from the impact-generated tsunami could have passed inland several hundred kilometers – far enough to reach the Big Bend area (e.g., Gault & Sonett,

1982).

Interpretation of the K/Pg boundary interval in the Tornillo Group has,

Texas Tech University, Jacob Cobb, August 2016 however, proven to be problematic (reviewed by Lehman, in Lehman & Busbey,

2007). Fossils are extremely rare in the K/Pg boundary interval, and so it has only been possible to constrain the position of the boundary within a 20 to 80 meter section of strata in most areas (Lehman & Busbey, 2007). Geochemical evidence for the bolide impact (e.g., the “iridium abundance anomaly”) or evidence for a dramatic sedimentation event (e.g., tsunami deposit) has not been discovered

(Lehman, 1990). As a result, it remains uncertain whether the boundary event itself is actually preserved in the Tornillo Group, or if sediments recording the critical time interval were either not deposited or eroded away, resulting in a disconformity.

Recent fieldwork in Big Bend National Park resulted in discovery of a previously unknown exposure of the K/Pg boundary interval. This exposure, referred to in this report as the “Rough Run East” outcrop, is free of structural complexity that makes interpretation of nearby Tornillo Group sections difficult, and offers an opportunity to clarify stratigraphic relationships in the critical K/Pg boundary interval. In addition, the recently discovered exposure exhibits an unusual conglomerate bed that could be interpreted as a tsunami deposit or as a lag accumulation marking a disconformity. The purpose of the present research is to map this exposure in detail, measure the stratigraphic section here, document the occurrence of significant fossil localities in the area, and study the unusual conglomerate bed in detail to determine its origin.

Texas Tech University, Jacob Cobb, August 2016

Geology of the Tornillo Group

The Tornillo Basin

The Tornillo Group accumulated in a relatively small intermontane basin in the Big Bend region known as the Tornillo Basin (Lehman, 1991; Figure 1.1).

This is a Laramide-age sedimentary basin that was active from about 80 to 40 Ma.

During the Laramide Orogeny, the Tornillo Basin formed a discrete depocenter between the leading edge of the Chihuahua Tectonic Belt on the southwest, and the Marathon Uplift on the northeast (Lehman, 1986; Runkel, 1990). These uplifted regions on either side of the basin exposed primarily Lower Cretaceous limestones. The Laramide structure in the Chihuahua Tectonic Belt consists of north-northwest trending folds, some overturned to the northeast, cut by west- southwest dipping imbricate thrust faults and associated tear faults that root in a decollement surface on underlying Jurassic evaporites (Gries and Haenggi, 1970;

Haenggi and Gries, 1970). The Marathon Uplift is bounded by the Santiago Mt –

Sierra del Carmen monocline, overturned to the southwest and cut by a thrust fault, forming the northeast boundary of the Tornillo Basin.

Within the basin there are several structures that are believed to have been active during the Laramide deformational period. The Terlingua-Solitario Dome is a rhombic uplift that lies along the southwest margin of the basin and exposes

Lower Cretaceous limestones (Erdlac, 1990). These limestones are also exposed along the Chalk Draw Fault, a re-activated basement structure along the northern margin of the basin. There is evidence for Laramide left-lateral strike-slip

Texas Tech University, Jacob Cobb, August 2016 movement on numerous faults within and bounding the Tornillo Basin (Cobb and

Poth, 1980; Erdlac, 1990).

The Laramide-age (c. 80 to 40 Ma) basins elsewhere in the Rocky

Mountains are subdivided into four major types described by Chapin and Cather

(1983) as 1) Green River-type basins which are large, broadly symmetrical, bowl- shaped basins with centripetal drainage, and characterized by episodes of lacustrine sedimentation; 2) Denver-type basins which are asymmetric, generally merging with stable craton along one margin, and characterized by a radial drainage pattern, 3) Echo-Park type basins which are narrow, fault-bounded basins arranged en echelon along the axis of the Central Rocky Mountain uplifts, and characterized by through-going drainage; and 4) Piggyback basins developed between thrust sheets within the Cordilleran Overthrust Belt (Mack and Clemons,

1988). The Tornillo Basin of West Texas does not readily fit any of these four types, but is most similar to those of Echo Park type. The sedimentary record of the

Tornillo Basin provides constraints on the timing of deformation in the Big Bend region, and generally supports the “two-phase” tectonic model of Laramide deformation advocated by Chapin and Cather (1983).

The Tornillo Group

The Tornillo Basin preserves a thick sequence of Upper Cretaceous and

Paleogene strata. The Laramide-age strata are subdivided into several formations.

These formations, in ascending order, are the Aguja Formation, the Tornillo

Texas Tech University, Jacob Cobb, August 2016

Group (comprised of three units – the Javelina, Black Peaks, and Hannold Hill formations), and the Canoe Formation (along with correlative parts of the Devil’s

Graveyard, and Chisos formations). With the exception of some lacustrine intervals, these strata are composed almost entirely of fluvial deposits, and consist of conglomeratic sandstone beds that represent river channel and associated levee and splay facies, alternating with thick mudstone deposits that constitute overbank floodplain facies (Lehman, 1991). Coarse- grained alluvial fan facies did not develop along the basin margins, indicating relatively low topographic relief, and through-going drainage was not restricted enough within the basin for extensive lacustrine deposits to form. Thus, the Tornillo Basin appears closest to those of

Echo Park-type as described by Chapin and Cather (1983).

Laramide deformation was initiated near the end of deposition of the Aguja

Formation. The Aguja Formation is Upper Cretaceous (Campanian) in age, and consists of intertonguing marine, deltaic, and terrestrial strata that thin eastwardly across the Big Bend region (Lehman, 1985; Lehman and Busby, 2007). The uppermost progradational deltaic unit in the Aguja Formation is Late Campanian in age (ca. 81 to 78 Ma). Paleocurrent data from this interval indicate that the Late

Campanian strandline prograded northeastwardly across the Big Bend region

(Lehman, 1986). Terrestrial strata above this interval (the upper shale member of

Lehman, 1985) record a shift in paleocurrent direction to the southeast, probably due to incipient rise of the Marathon Uplift, and a change in paleoslope corresponding with onset of the Laramide Orogeny.

The Tornillo Group overlies the Aguja Formation, and is subdivided into

Texas Tech University, Jacob Cobb, August 2016 three formations; in ascending order these are the Javelina, Black Peaks, and

Hannold Hill formations (Figure 1.2). The Tornillo Group is comprised of syn- orogenic strata, mostly of fluvial origin, and consists of alternating stream channel sandstone and overbank mudstone beds.

The Javelina Formation is of latest Cretaceous (Maastrichtian, c. 72 to 67

Ma) age. It consists of yellow-weathering fluvial channel sandstone beds separated by intervals of gray and purple-banded mudstone with paleosols. The

Javelina Formation varies between 85 and 120 m in thickness in the western part of the basin, and 134 to 200 m in the eastern part of the basin (Lehman, 1991).

Paleocurrent data indicate southeastward transport throughout deposition of the formation (Lehman, 1991). Coarse extra-basinal chert clasts are found in channel- lag conglomerates low in the stratigraphic section. The localized occurrence of chert clasts may record the contribution of tributary channels entering from the basin flanks. These chert pebbles were likely derived from multiple sources, but primarily from erosion of Lower Cretaceous conglomerates like the basal Glen

Rose Limestone or Cox Formation (Lehman, 1991).

The Black Peaks Formation spans the K/Pg boundary and extends through middle to late Paleocene time (from about 67 to 57 Ma; Scheibout et al., 1987).

The Black Peaks Formation is generally similar in appearance to the Javelina

Formation, but contains much more extensive mudstone intervals with distinctive paleosols capped by organic- rich black beds that are not found in the underlying

Javelina or overlying Hannold Hill formations (Lehman, 1990). The lowest part of the Black Peaks Formation has distinctive multicolored “candy-striped” mudstone

Texas Tech University, Jacob Cobb, August 2016 beds just above the K/Pg boundary interval (Lehman and Busbey, 2007). The

Hannold Hill Formation is early Eocene (c. 57 to 51 Ma) in age, and consists predominantly of coarse conglomeratic sandstone with lesser amounts of mudstone. It was deposited during the climax of Laramide tectonism, includes the coarsest clastic facies in the Tornillo Group, and obvious evidence for syndepositional deformation (Lehman and Busbey, 2007). Paleocurrent data for both the Black Peaks and Hannold Hill formations record continued southeastward sediment transport throughout deposition (Schiebout, 1974; Hartnell, 1980).

The Tornillo Group is overlain unconformably by the Canoe Formation.

The base of the formation consists of coarse conglomeratic sandstone of middle

Eocene age (c. 51 to 48 Ma). The Canoe Formation consists of post-orogenic strata resting on progressively older strata southwestwardly across the Tornillo Basin

(Lehman, 1991). The upper part of the formation includes volcanic rocks and volcaniclastic sediments correlative with similar deposits in the nearby Devil’s

Graveyard and Chisos formations (Lehman, 1991).

The K/Pg Boundary in Big Bend

The interval spanning the Cretaceous/Paleogene (K-Pg) boundary within the Tornillo Group has been studied since the 1960’s. A historical account of the varied interpretations of this interval was given by Lehman and Busbey (2007), and is summarized here. As part of the original mapping of the Tornillo Group in

Big Bend, during the late 1950’s to early 1960’s, an attempt was made to locate

Texas Tech University, Jacob Cobb, August 2016 the K-Pg boundary on the basis of fossil content, and the formational contact between the Javelina and Black Peaks formations was placed so as to coincide with the system boundary. However, fossils are very scarce in these strata, and so it was not possible to locate the formation contact accurately on this basis in most exposures. It was believed that the Javelina Formation was entirely Cretaceous in age and the overlying Black Peaks Formation was assumed to be entirely Paleocene in age. The K-Pg boundary was thought to be unconformable (e.g., Maxwell et al.,

1967) because the lowermost Paleocene faunas recovered from the Black Peaks

Formation represented a Torrejonian (North American Land Mammal Age) fauna of middle Paleocene age. This suggested that the earliest Paleocene (Puercan) interval was absent in Big Bend, and that the K-Pg boundary was unconformable here. Throughout the 1970’s, it was generally believed that sediments spanning the

K-Pg boundary were either never deposited or eroded away prior to middle

Paleocene time.

In the 1980’s, however, it was found that the K-Pg boundary does not coincide everywhere with the position of the Javelina-Black Peaks formational contact as it was shown on existing maps (e.g., Maxwell et al., 1967). A

Paleocene mammalian assemblage was discovered in the upper Javelina

Formation at a site (“Tom’s Top”) on Dawson Creek (Figure 1.3). Another site in the Javelina Formation (“Dogie”) nearby on Rough Run Creek also yielded a

Paleocene mammalian fauna (Figure 1.4). This suggested that the K-Pg boundary was somewhere within the upper part of the Javelina Formation, at least as those strata were mapped on the western side of Big Bend Park. The “Tom’s Top” and

Texas Tech University, Jacob Cobb, August 2016

“Dogie” sites are about 20 to 80 meters, respectively, above the highest occurrence of dinosaur bones in those areas, leaving open the possibility that undiscovered earlier Paleocene sites might exist in the intervening section.

In the 1990’s, an attempt was made to locate the iridium abundance anomaly, tsunami bed, or any other physical or chemical evidence for the existence of the K-Pg boundary on Dawson Creek. A very weak iridium anomaly was detected, but no compelling evidence for the impact horizon was discovered

(Lehman, 1990). Even so, throughout the 1990’s, it was generally believed that no unconformity was present in the section, and that latest Cretaceous (Lancian) and early Paleocene (Puercan) vertebrate faunas are present within these strata, although no evidence for the K-Pg impact horizon was found (Lehman, 1985,

1988; Standhardt, 1986; Schiebout et al., 1987, 1988).

During the 2000’s, an effort was made to revise the formational contacts within the Tornillo Group, and map these strata more accurately throughout the

Big Bend region (Lehman, 2002, 2004). The Javelina-Black Peaks formational contact was revised to coincide with consistent and more easily recognizable lithologic criteria, and not fossil content. The most recent geologic map of Big

Bend Park (Turner et al., 2011) uses these revised contacts, and where it is possible to identify the K-Pg boundary interval, it is everywhere within the lowermost part of the Black Peaks Formation, just above its contact with the Javelina Formation.

The Dawson Creek Exposure

Texas Tech University, Jacob Cobb, August 2016

The best-exposed and most extensively studied outcrop of the K-Pg boundary interval in Big Bend is along the western edge of Big Bend Park, on the south side of Dawson Creek (Lehman, 1990). The Javelina Formation here is very fossiliferous, and bears middle to late Maastrichtian vertebrate fauna, including the site that yielded the type specimen of the giant pterodactyl

Quetzalcoatlus (reviewed by Lehman, in Lehman and Busbey, 2007; Figure 1.3).

The “Tom’s Top” site is here, within the lowermost part of the Black Peaks

Formation, and it yields a Paleocene mammalian fauna regarded as late Puercan in age by Schiebout et al. (1987). Others, however, interpret the “Tom’s Top” fauna as one of Torrejonian age (Williamson, 1996; Lehman and Busbey, 2007). The c.

20 m interval between the highest in situ dinosaur bones and the “Tom’s Top” site on Dawson Creek has thus far yielded no useful fossils or any unusual lithological features.

The Rough Run Amphitheater

A second exposure subsequently discovered on the south side of Rough Run

Creek, about five miles east of Dawson Creek, also spans the K-Pg boundary interval, but is more difficult to interpret (reviewed by Lehman and Busbey, 2007;

Figure 1.4). The “Rough Run Amphitheater” exposures are cut by at least one significant north-trending fault, and interrupted by a dike along the eastern margin.

Pleistocene pediment gravel covers much of the Tornillo Group bedrock, and vegetated Holocene stream terraces obscure relationships between adjacent

Texas Tech University, Jacob Cobb, August 2016 exposures (Figure 1.5). These complications make it difficult to confidently work out the stratigraphic relationships in this area.

On the west side of the fault, only the lower part of the Black Peaks

Formation is exposed. A particularly prominent red mudstone bed forms the lowest unit in this outcrop, and is overlain by an extensive white-weathering sandstone bed. A gray-green mudstone layer interfingers with the white sandstone at its top. This mudstone bed has yielded abundant specimens of the sauropod dinosaur Alamosaurus (Fronimos and Lehman, 2014). Alamosaurus is the most abundant large vertebrate species found in most exposures up to the K/Pg boundary interval in Big Bend (Woodward, 2005). The highest in situ dinosaur specimen discovered here on the west side of the fault (an isolated tyrannosaurid tooth) was found just above the Alamosaurus-bearing interval (Figure 1.5). Above the dinosaur-bearing zone is a distinctive multicolored series of mudstone layers that Lehman (in Lehman and Busbey, 2007) referred to as the “candy-striped beds.”

These distinctive candy-striped mudstone beds are only known to occur in the

Paleocene part of the Black Peaks Formation in other areas of Big Bend Park. This suggests that the K/Pg boundary may be in the interval above the white sandstone bed near the base of the candy-striped interval, but thus far no diagnostic Paleocene fossils have been found anywhere on the west side of the fault (Lehman, in

Lehman and Busbey, 2007).

East of the fault, the upper part of the Javelina Formation is exposed up to its contact with the Black Peaks Formation, and a significant section of the lower

Black Peaks Formation extends up to a north-trending dike (Figures 1.4, 1.5). The

Texas Tech University, Jacob Cobb, August 2016 upper part of the Javelina Formation here consists of three yellow-weathering sandstone beds separated by intervals of gray and purple mudstone. The lower and middle sandstone intervals have produced a wide variety of dinosaur specimens, as well as fishes, turtles, and crocodylians (the “Bowfin Beach” site described by

Lehman, in Lehman and Busbey, 2007). The upper Javelina sandstone interval has thus far produced only a single isolated pterodactyl bone (Lehman, 2007). The

Javelina/Black Peaks contact is placed at the top of this upper sandstone interval.

The “Dogie” site occurs in a white sandstone bed about 110 m above the top of the

Javelina Formation here. This site has produced a Torrejonian (middle Paleocene) mammalian fauna (Williamson, 1997; Lehman, 2007). The intervening part of the section has yielded no significant fossils, but is marked by an unusual lenticular conglomerate bed described by Lehman (in Lehman and Busbey, 2007) as the

“odd conglomerate.”

What appears to be the uppermost bona fide Cretaceous fossil locality in the Rough Run Amphitheater area is found west of the fault, but the lowermost

Paleocene fossil locality is found east of the fault, and it has not been possible to correlate key stratigraphic units on opposite sides of the fault (Figure 1.4). Based on the presence of the distinctive Paleocene “candy-striped” mudstone beds, the

K/Pg boundary interval may be present west of the fault, but those beds cannot be identified east of the fault (Lehman, in Lehman and Busbey, 2007). In contrast, east of the fault the distinctive Alamosaurus-bearing white sandstone cannot be identified, but the unusual “odd conglomerate” bed occurs. This bed is unlike any other observed in the Tornillo Group, and consists exclusively of

Texas Tech University, Jacob Cobb, August 2016 large reworked sandstone clasts, reworked pedogenic carbonate nodules, and charcoal. This “odd conglomerate” bed is definitely below the “Dogie” fossil locality in that area, but the position of this bed relative to the section exposed west of the fault cannot be determined.

The Rough Run East Exposure

The recently discovered outcrop that is the subject of the present study is about two miles east of the Rough Run Amphitheater and exposes the same stratigraphic interval with minimal structural complexity, and with less extensive cover by Pleistocene and Holocene alluvium (Figure 1.6). This exposure is referred to in the present study as the “Rough Run East” outcrop. The unusual

“odd conglomerate” bed is much more laterally extensive here, widely exposed in this area, and its stratigraphic position within the K/Pg boundary interval is clear

(Figure 1.7). As part of the present project, the Rough Run East area was mapped in detail, the stratigraphic section was measured, the “odd conglomerate” was studied in detail, and an attempt was made to thoroughly prospect this area for fossils.

The “odd conglomerate” bed may be significant in understanding the K/Pg boundary interval, and could be interpreted in several ways.

1) It may represent a basal lag accumulation formed by “normal” lateral stream channel migration. If so, it is unusually thin, unusually coarse-grained, and its clast composition differs significantly from channel lag deposits found at the

Texas Tech University, Jacob Cobb, August 2016 base of fluvial sandstones lower and higher stratigraphically. This would indicate a marked but short- lived change in stream channel hydrology may have occurred at or around the time of the K/Pg boundary.

2) It may represent a lag deposit formed on a disconformity surface that resulted from prolonged erosional downcutting (e.g., due to a significant drop in base level) rather than normal stream channel migration. This could explain some of the unusual features of the bed. If so, some significant time interval, perhaps including the K/Pg boundary itself, may not be recorded in the section.

3) It may represent a deposit produced by run-up of the hypothesized

Chicxulub tsunami, and/or return flow, and accumulated at the time of the K/Pg boundary event itself. If so, some of the clasts represented in the bed may not be indigenous to the Tornillo Basin – for example, marine materials brought inland during the tsunami run-up and/or ejecta accumulated or reworked from the

Chicxulub impact itself. Some deposits elsewhere attributed to tsunami have been interpreted as either triggered directly by the bolide impact (e.g., Bourgeois et al.,

1988) or by associated impact-triggered slope failures (e.g., Olsson et al., 2002). ).

The Big Bend area is in close proximity (less than several thousand km from

Chicxulub impact) to the region where Chicxulub ejecta has been recognized

(Figure 1.8).

The K/Pg Boundary around the Gulf of Mexico

Although most previous studies refer to the terminal Cretaceous extinction

Texas Tech University, Jacob Cobb, August 2016 event, marking the boundary between Mesozoic and Cenozoic eras, as the

Cretaceous-Tertiary (K/T) boundary, authors in recent years instead refer to this as the Cretaceous-Paleogene (K/Pg) boundary. The modern consensus holds that the

K/Pg boundary is marked by the moment of a major bolide impact with Earth, which implies that all sediments generated subsequent to the impact belong to the earliest stage of the Paleocene (the Danian; Molina et al., 2006).

Hypotheses regarding the cause of the K/Pg mass extinction event have been proposed for over a century and include widely varied terrestrial and extraterrestrial mechanisms (reviewed by Melendez and Molina, 2006). Most of these hypotheses have since been discounted, and within the past 20 years only two causal mechanisms have received broad support, either impact of a large meteor, or extensive volcanism on the Deccan Plateau in India. Although debate continues on the subject, the meteor impact hypothesis has gained widespread acceptance, particularly since the discovery of the buried Chicxulub impact site on the northern Yucatan Peninsula.

The subsurface Chicxulub structure on Yucatan was first recognized as a zone of concentric gravity anomalies in surveys conducted in 1948 (Cornejo-

Toledo and Hernandez-Osuna, 1950). This prompted exploratory drilling during the 1950’s. Penfield and Camargo (1981) first proposed that Chicxulub’s unusual features might be interpreted as a large buried impact structure, and Bryars (1981), and Sky and Telescope, ( 1982) suggested that this could be the site of the K/Pg impact event proposed by Alvarez et al. (1980). During the late 1980s and early

1990s, detailed studies of the “boundary clay” at many continental and oceanic

Texas Tech University, Jacob Cobb, August 2016

K/Pg boundary sites provided additional support for the impact hypothesis, and indicated a single continental impact site (Bohor, 1990; Sharpton et al., 1990a,

1990b; Izett et al., 1990). The search for a significant impact crater of appropriate age was then intensified, although some (e.g., Sharpton and Ward, 1990) noted that a large K/Pg impact site on the ocean floor might be difficult to identify, could have been destroyed through plate recycling; or if numerous smaller impact events occurred within a short time period, the impact sites could be very obscure. The attention of K/Pg boundary research in the Gulf of Mexico then returned to the

Chicxulub structure on the Yucatan Peninsula (Sharpton et al., 1990b). Additional gravity and magnetic data were accumulated, and ultimately drilling results convincingly confirmed that the Chicxulub structure is indeed a buried impact crater (Sharpton et al., 1992; Pope et al., 1996; Sharpton, 1993, 1996; Gulick et al.,

2013).

Numerous K/Pg sites within a radius of about 1000 km of the Chicxulub site have been investigated in detail (Figure 1.9). Some of these sites are at exposures on the coastal plains surrounding the Gulf of Mexico, and on the

Caribbean islands. Others are in subsurface areas on the continental shelf and in the deep Gulf of Mexico. At all of these sites, the K/Pg boundary interval is preserved in marine strata. Sites on the island of Haiti (Hildebrand and Boynton,

1990; Izett et al., 1990; Maurrasse, 1980; Maurrasse and Sen, 1991; Sigurdsson et al., 1991), on the Brazos River in Texas (Smit and Romein, 1985; Bourgeois et al.,

1988), in the deep Caribbean (Hildebrand and Boynton, 1988, 1990), and at

Arroyo el Mimbral in northeastern Mexico (Smit et al., 1992) all preserve coarse

Texas Tech University, Jacob Cobb, August 2016 clastic deposits linked in one way or another to the K/Pg boundary (Browler and

Paull, 1998).

Extensive breccia beds, up to 900 m thick, and present within about 100 km of the Chicxulub structure, and interpreted as proximal impact ejecta deposits (e.g.,

Sharpton et al., 1996). Purported tsunami deposits containing decimeter-size rip-up clasts are described at the exposed sections in Texas and northern Mexico over

1000 km from Chixulub (e.g., Bourgeois et al., 1988). Gravity flow deposits at the

K/Pg boundary in Haiti (Maurrasse and Sen, 1991), Cuba (Iturralde-Vinent, 1992),

Chiapas (Montanari et al., 1994), and Belize (O’Campo et al., 1996) are interpreted as a result of mass wasting events triggered by the Chicxulub impact.

Alvarez et al. (1992) correlated coarse-grained basinal deposits in the deep Gulf of

Mexico to the K/Pg boundary impact event.

Debate remains, however, regarding interpretation of the varied deposits at the K/Pg boundary. Deposits interpreted by some authors as a result of impact- generated tsunami (Bourgeois et al., 1988; Smit et al., 1992b; Smit and Romein,

1985) or impact- generated gravity flows (Bohor and Betterton, 1993; Iturralde-

Vinent, 1992; Montanari et al., 1994; O’Campo et al., 1996; Stinnesbeck et al.,

1993) are interpreted by others instead as storm-generated ‘tempestite’ deposits

(Morgan, 1931; Hansen et al., 1987) or lowstand channel infills related to a drop in sea level coincident with the K/Pg boundary (Mancini and Tew, 1993; Sarvda,

1991).

Controversy also remains as to whether or not the K/Pg boundary is conformable at most sections studied. Keller et al. (1993) compared 16 (present

Texas Tech University, Jacob Cobb, August 2016 day) onshore and deep-sea marine sections from the Caribbean, Gulf of Mexico,

Mexico, and western Atlantic regions, and found that the most complete stratigraphic records spanning the K/Pg boundary are found at the onshore marine sections in Mexico, Cuba, and Haiti. Keller et al. (1993) concluded that due to depositional hiatus or erosion, there was not a continuous record of sediment accumulation across the boundary at many sections examined, and that the K/Pg boundary is unconformable throughout the basinal Gulf of Mexico and Caribbean.

A hiatus appears to be present at the K/Pg boundary in many deep sea sections below 1000 m depth (Keller, 1993, MacLeod and Keller, 1991a, 1991b). In contrast, some have suggested that the apparent hiatus reflects the collapse of continental shelf margins around the Gulf of Mexico, and resulting sediment gravity flows generated by large tsunami that produced mixing of sedimentary components from a variety of sources (Bourgeois et al., 1988; Bralower et al.,

1998; Denne et al., 2013).

Texas Tech University, Jacob Cobb, August 2016

Figure 1.1. Geology and structure of the Laramide Tornillo Basin and surrounding region in Trans-Pecos Texas, Chihuahua, and northern Coahuila, Mexico. The Laramide structure (thrust faults, reverse faults, monoclines, anticlines) is adapted from Muehlberger (1980). Outcrop patterns are based on the Geologic Atlas of Texas Van Horn-El Paso, Marfa, and Emory Peak-Presidio sheets (from Lehman, 1991).

Texas Tech University, Jacob Cobb, August 2016

Figure 1.2. Stratigraphy of the Tornillo Group in Big Bend National Park, Texas (from Lehman, 2007).

Texas Tech University, Jacob Cobb, August 2016

Figure 1.3. Stratigraphy of the K/Pg boundary interval in the Tornillo Group on Dawson Creek in Big Bend National Park, Texas (from Lehman, 2007).

Texas Tech University, Jacob Cobb, August 2016

Figure 1.4. Stratigraphy of the K/Pg boundary interval in the Tornillo Group at the Rough Run Amphitheater in Big Bend National Park, Texas (from Lehman,

2007).

Texas Tech University, Jacob Cobb, August 2016

Figure 1.5. Geologic map of “Rough Run Amphitheater” area in western Big Bend National Park, Texas. Kjf = Javelina Formation, Tbp = Black Peaks Formation, Tac = Alamo Creek Basalt, Tch = Chisos Formation (undivided), Ig = igneous intrusive rocks, Qal = Quaternary alluvial terrace deposits (from Lehman & Busbey, 2007).

Texas Tech University, Jacob Cobb, August 2016

Figure 1.6. Geologic map of south bank of Rough Run Creek in western Big Bend National Park, showing the “Rough Run Amphitheater” and the area of present study at “Rough Run East.” Kjf = Javelina Formation, Tbp = Black Peaks Formation, Tig = Tertiary igneous intrusive rocks, Qal = Quaternary alluvial terrace deposits (from Lehman & Busbey, 2007).

Texas Tech University, Jacob Cobb, August 2016

Figure 1.7. Exposures at “Rough Run East” showing position of the ‘odd conglomerate’ within the K/Pg boundary interval in the study area (above), and view (below) showing the thin character of the bed, bounded above and below by fine-grained overbank floodplain facies. The man in the bottom image is about 6 feet and 2 inches for scale.

Texas Tech University, Jacob Cobb, August 2016

Figure 1.8. Paleogeographic map of the Gulf of Mexico at end of Cretaceous time, showing position of “Rough Run East” location to Chicxulub impact site, and location of outcrops with K/Pg sandstone complex deposits and sites that preserve spherules. 603, 390A, 536, and 540 are Deep Sea Driling project sites (Smit et al., 1996).

Texas Tech University, Jacob Cobb, August 2016

Figure 1.9. Paleogeographic map of Gulf of Mexico at end of Cretaceous time, showing Chicxulub impact site and K/Pg boundary sites in Texas, Mexico, Belize, and Cuba, as well as Deep Sea Drilling Project (DSDP) sites and industry deep- water well sites that penetrate the K/Pg boundary interval (from Denne et al., 2013).

Texas Tech University, Jacob Cobb, August 2016

CHAPTER 2

GEOLOGY OF THE ‘ROUGH RUN EAST’ EXPOSURE

The ‘Rough Run East’ study area is located on the south side of Rough Run

Creek, immediately northwest of Burro Mesa (Figure 2.1). Two intermittent tributaries of Rough Run Creek flow westward through this region. For this study, an area of about 4 km2 was mapped to show units within the K/Pg boundary interval in greater detail (Figure 2.1). Bedrock in the map area consists entirely of lower Tornillo Group (Javelina and Black Peaks formations) generally dipping gently to the northwest. Quaternary alluvial deposits covering the Tornillo Group were divided into three units: 1) high-level Pleistocene pediment gravels (Qal3) that cap mesas and form the high points (above 3000’) in the topography, 2) intermediate-level Holocene (Qal2) alluvial stream terrace and colluvial deposits that form benches above the level of modern floodplains, and 3) low-level

Holocene (Qal1) alluvial deposits on the modern floodplains and within the present stream drainages (elevations about 2880’). Although alluvial deposits are extensive throughout the map area, the underlying Tornillo Group is well exposed, free of surface soil and vegetation, and forms ‘badlands’ topography.

Strata of the Tornillo Group in the map area generally dip between 5° and

20° to northwest except for exposures on the southeast side of the area where the dip is instead to the southeast. This dip reversal may be due to drag along a prominent northwest- trending normal fault that passes along the eastern side of the map area, and results in a broad open anticline in the Tornillo Group along the

Texas Tech University, Jacob Cobb, August 2016 upthrown side of the fault. A second, less significant, west-trending normal fault interrupts the Tornillo Group, but shows displacement of less than a meter or so, and is only observed to cut three units within the Black Peaks Formation.

Major lithologic units within the Javelina Formation and Black Peaks

Formation below and above the K/Pg boundary interval were mapped individually. The lowest stratigraphic unit exposed in the map area is within the upper part of the Javelina Formation (unit 1 = “Javelina sandstone #1”). Three units in the Javelina Formation are shown (units 1 to 3; Figure 2.3). The distributions of nine units in the lower part of the Black Peaks Formation are shown (units 4 to 11; Figures 2.4-2.6), including the “odd conglomerate” (unit 8).

The lowermost mudstone interval in the Black Peaks Formation (unit 4) is very thick and exposed over a broad area of deeply dissected terrain; its thickness shown in the stratigraphic section (Figure 2.2) may be exaggerated due to the irregularity of this outcrop. That part of the Black Peaks Formation above unit 11 is mapped as an undivided unit (KTbp).

Stratigraphic Section at Rough Run East

The stratigraphic section exposed at Rough Run East was measured using a Brunton compass and Jacob staff along a route immediately west of the major fault crossing the map area (path shown in Figure 2.1).

Unit 1 (“Javelina sandstone #1”) is coarse-grained sandstone that represents a fluvial channel deposit. The base of this unit may not be exposed in this area, but

Texas Tech University, Jacob Cobb, August 2016 there are lenses of caliche-pebble conglomerate within the lower part of the exposed sandstone. Unit 2 is thin but laterally extensive light gray calcareous mudstone bed separating the two Javelina sandstone intervals (units 1 and 3). This unit is broadly exposed on the floor of the southernmost valley in the area (Figure

2.1). Unit 3 (“Javelina sandstone #2) is a coarse-grained fluvial channel sandstone deposit very similar in appearance to Unit 1. This sandstone has a yellow- weathering granule-pebble conglomerate bed with veins of gypsum at the base.

Abraded indeterminate dinosaur bone fragments occur in the conglomerate (fossil locality 1; Figure 2.1). This unit is not well consolidated, and forms a low bench along the drainage divide between the southern and northern stream valleys in the area, but locally forms a well-indurated dark brown ledge at its top – marking the contact between Javelina and Black Peaks formations (Figures 2.3 and 2.4).

Unit 4 is the lowest division of the Black Peaks Formation. This unit is a very thick, dark gray mudstone interval with horizons of large cylindrical calcite nodules and concretions in its lower part. The cylindrical calcite concretions have distinctive radial crystal fabric, and appear to represent large filled burrows. At least the lower part of this mudstone interval is thinly bedded and may have accumulated in a lacustrine environment. A poorly preserved indeterminate dinosaur bone was found in the lower part of this unit (fossil locality 2; Figure

2.1).

Unit 5 is thin but distinctive and laterally extensive dark red mudstone bed.

This bed has very high clay content (“popcorn” weathering pattern) and lacks the calcite nodules typically found in other Tornillo Group mudstones. A few

Texas Tech University, Jacob Cobb, August 2016 fragmentary tyrannosaurid limb bones were found near the top of this unit (fossil locality 3; Figure 2.1). Unit 6 is a thin dark gray mudstone bed that also has high clay content and lacks calcite nodules (Figure 2.5). Several large isolated titanosaurian sauropod bones were found near the top of this unit – one is a badly weathered femur; the other is an ulna (fossil locality 4; Figure 2.1). Unit 7 is informally referred to as the “Hoodoo sandstone.” This unit consists of friable fine-grained sandstone that weathers to a nearly white surface, and has a zone of large reddish-brown sandstone concretions that support distinctive ‘hoodoo’ pedestals. Local lenses of caliche-pebble conglomerate occur at the base. A few fragmentary bones of titanosaurian sauropods were found near the top. This unit forms a broad lenticular fluvial channel deposit that thins both to the west and east of the line of section.

Unit 8 is the bed informally referred to here as the “odd conglomerate.”

This unit is described in detail in a following section. This bed is typically less than about one meter in thickness, but varies substantially across the map area, and intermittently pinches out for short distances (Figure 2.1). Along the line of section, this bed is separated from the underlying “hoodoo sandstone” (unit 7) by a thin mudstone; however, both to the east and west, the base of the “odd conglomerate” rests directly on the “hoodoo sandstone.” A diverse charophyte algal gyrogonite assemblage was recovered from the top of unit 8 (fossil locality

5; Figure 2.1).

Unit 9 is a thick bed of dark gray mudstone lacking calcite nodules. Sparse unionid bivalve shells occur in the base of this unit (fossil locality 5; Figure 2.1).

Texas Tech University, Jacob Cobb, August 2016

This unit thins and pinches out both to the east and the west in the map area, and appears to be truncated at the base of unit 10 (Figure 2.1). Unit 9a is a local lens of white-weathering fine-grained sandstone that occurs in the upper part of unit 9 only near the western border of the map area (Figure 2.1). Unit 9a is not seen in the original path taken to acquire the overall strat column in the study region. Due to its localized locality it was labled unit 9a as this unit was not included in the original strat column so was added in as 9a rather than being unit 10. This sandstone lens is a fluvial channel deposit with a conglomeratic zone near that base that preserves abundant turtle shell fragments, crocodylian teeth, and gar scales

(fossil locality 6; Figure 2.1).

Unit 10 is referred to here as the ‘candy-striped beds.” This unit consists of multicolored alternating layers of black, light gray, and red mudstone beds with interfingering thin beds of white-weathering fine sandstone (Figure 2.6). This unit extends across the entire map area. The multicolored beds probably represent paleosol horizons similar to those described by Lehman (1990) on Dawson Creek.

Unit 11 is referred to here as the “Dogie-like sandstone” due to its similarity in appearance and stratigraphic position to the unit that preserves the “Dogie” site at the Rough Run Amphitheater farther west. This unit consists of fine-grained white-weathering sandstone with sparse conglomerate along the base. This unit is not laterally extensive, and represents a local fluvial channel deposit. Units 12 and

13 consist of yellow-weathering sandy mudstone beds. These are the highest stratigraphic units exposed in the map area, and were included in the undivided upper Black Peaks Formation on the present map (Figure 2.1).

Texas Tech University, Jacob Cobb, August 2016

The ‘Odd Conglomerate’

The ‘odd conglomerate’ (unit 8) is variably exposed in an irregular outcrop extending about 1 km across the map area. Measured sections were taken at 16 sites

(see Appendix I) and labeled A through P along the length of this outcrop to show variation in this unit; a detailed map was prepared to show the location of these sections (Figure 2.7). The measured sections were correlated to show trends within unit 8 along the length of its outcrop (Figure 2.8). The bed is best exposed along the north bank of an intermittent stream between sites D and L. Additional observations were made at points between the measured sections.

The ‘odd conglomerate’ varies in thickness across the map area from a minimum of about 15 cm (site C; see Appendix, figure 2.10) to a maximum of about 2 m (site L; see Appendix figure 2.19). The thickness does not vary in a regular pattern, although it is generally greatest in the area from site L to P, and thinner southwest of that. The bed appears to pinch out intermittently along the outcrop belt, but this may only reflect superficial burial in the weathering zone by downslope slumping or creep of the overlying mudstone (unit 9) at the surface.

Where the bed is fully exhumed by erosion, or exposed with excavating tools, it is laterally continuous. At the northeast and southwest ends of the outcrop belt, the

‘odd conglomerate’ bed and overlying mudstone (unit 9) thin and pinch out (or are truncated) at the base of the overlying ‘candy-striped beds’ (unit 10; see Figure

2.1).

Texas Tech University, Jacob Cobb, August 2016

The ‘odd conglomerate’ is thickest (2 m) immediately northeast of the small normal fault that interrupts the section, and consists here of a single conglomeratic bed with few obvious breaks (Figure 2.8). The section here (site L) rests on the hanging wall of the normal fault, while immediately to the southwest, on the footwall of the fault, the bed is dramatically thinner and contains the largest boulders observed anywhere along the outcrop (sites J and K). These observations suggest that the fault was active during sedimentation of the ‘odd conglomerate.’

Toward the edges of the outcrop belt, both to the northeast and southwest the unit includes more interbedded sandstone, and in places it consists of at least three distinct depositional units (labeled 1, 2, and 3 in Figure 2.8). Each depositional unit consists of a basal conglomeratic bed that fines-upward to sandstone.

The “odd conglomerate” appears to alternate along strike from single to multiple depositional units. In some cases, however, this may be due to incomplete exposure (e.g., at site C the upper part of the “odd conglomerate” may not be exposed due to modern erosion). In other cases, this may be due to direct superposition of the basal conglomerate of one depositional unit atop another without an intervening sandstone bed (e.g., at site L and M there are vague erosional surfaces within the conglomerate that may equate with depositional breaks). It is possible, therefore, that three depositional units are present throughout the “odd conglomerate” but poorly preserved or only vaguely expressed in some sections. The individual depositional units appear to merge laterally by thinning of the finer grained sandstone intervals and their truncation at the base of overlying conglomeratic beds.

Texas Tech University, Jacob Cobb, August 2016

Clasts in the conglomerate are typically in the granule to coarse pebble size range (0.4 to 6 cm) with rare cobbles (6 to 20 cm); however, there are very large boulders at several sites (J, K, and L) ranging from 38 to 125 cm in largest diameter

(Appendix, figures 2.17-2.19). At site K, the largest boulder projects above the top of the bed in which it rests (Figure 2.18). The conglomeratic part of each depositional unit is poorly sorted, and shows crude horizontal stratification.

Grading within each depositional unit is ‘coarse-tail’ grading due primarily to segregation of most granule to pebble sized clasts in the lower part of the bed.

In places, the clasts show some preferred orientation or imbrication with clasts dipping ~10° NW, but in other areas dip is in the opposite direction

(Appendix, figure 2.12.); the fabric is typically grain-supported, but in places appears matrix-supported (sites, I, J, K, M, and P). Most of the clasts in the granule to pebble size range are subrounded to well-rounded; those in the cobble to boulder range are subangular. The upper sandy part of each depositional unit exhibits better sorting, with only sparse granule or pebble clasts, and well- developed parallel lamination. Soft sediment deformation is present at one site (I) where a truncated ‘flame’ structure distorts the internal lamination (Figure 2.23).

Low-angle cross-stratification is present in a few areas (E, H, L, and M) and the larger clasts in those areas are aligned parallel to the depositional dip. Both conglomeratic and sandy intervals show distinct parallel lamination and low angle cross-stratification at several sites (D, F, G, and I).

The conglomerate clast composition is relatively limited and uniform throughout the outcrop belt. Most of the granule- to pebble-size clasts are

Texas Tech University, Jacob Cobb, August 2016 composed of 1) weakly indurated laminated white sandstone; fewer clasts consist of 2) reddish-brown well- indurated sandstone, 3) carbonate concretions (paleo- caliche nodules), 4) abraded charcoal clasts, and 5) purple mudstone clasts. At one site (H) the conglomerate includes an abraded dinosaur bone fragment. The common white sandstone clasts are similar in appearance to the sandstone in the underlying “hoodoo sandstone” (unit 7), and the reddish-brown well-indurated sandstone clasts (which include the largest boulders) are similar to the concretions also found within that unit. The purple mudstone and carbonate nodule clasts resemble those in underlying mudstones (unit 4). None of the clasts examined in the “odd conglomerate” appear to have an extra-basinal origin, and all could have been derived through erosion of underlying or nearby strata. No ‘exotic’ clasts were identified through examination of hand samples (or within thin-sections, see below).

In conclusion, the ‘odd conglomerate’ (unit 8) and overlying mudstone

(unit 9) are lenticular units that appear to occupy a broad paleo-valley, about 1 km across, overlain by the ‘candy-striped’ beds (unit 10) which extend laterally beyond the limits of these valley-filling units. Deposition of the ‘odd conglomerate’ appears to have been contemporaneous with movement on a small normal fault (about 2 m displacement) that cuts the conglomerate as well as underlying units (5, 6, and 7). Three similar fining-upward depositional events are variably recorded in the ‘odd conglomerate’. Clasts in the conglomerate are limited in composition and uniform in each depositional unit, and consist largely of sandstone clasts that may have been derived through erosion of nearby or

Texas Tech University, Jacob Cobb, August 2016 underlying Tornillo Group strata.

Texas Tech University, Jacob Cobb, August 2016

Figure 2.1. Geologic map of Rough Rough East outcrop showing major units in the Javelina and Black Peaks formations (numbered), Quaternary alluvial cover, normal faults, significant fossil localities discussed in text, and the path taken to measure the stratigraphic section shown in figure 2.2.

Texas Tech University, Jacob Cobb, August 2016

Figure 2.2. Stratigraphic section of Tornillo Group at the Rough Run East outcrop, showing major numbered units and significant fossil localities.

Texas Tech University, Jacob Cobb, August 2016

Figure 2.3. View to north of lower part of stratigraphic section at Rough Run East showing unit 2 (light gray mudstone) and overlying yellow- weathering sandstone in unit 3 (Javelina sandstone #2; photo taken by Brian Cobb).

Texas Tech University, Jacob Cobb, August 2016

Figure 2.4. View to east of yellow-weathering sandstone in unit 3 (Javelina sandstone #2) and mudstone in overlying unit 4 (base of Black Peaks Formation; photo taken by Brian Cobb).

Texas Tech University, Jacob Cobb, August 2016

Figure 2.5. View to northeast of upper part of unit 4 (dark gray mudstone in Black Peaks Formation), unit 5 (prominent red mudstone bed), unit 6 (dark gray mudstone), and unit 7 (white-weathering “hoodoo sandstone”; photo taken by Brian Cobb).

Texas Tech University, Jacob Cobb, August 2016

Figure 2.6. View to northwest of upper part of stratigraphic section at Rough Run East, showing top of unit 7 (“hoodoo sandstone”), unit 8 (“odd conglomerate”), unit 9 (gray mudstone), unit 10 (“candy-striped beds”), and unit 11 (“Dogie-like sandstone”; photo taken by Brian Cobb).

Texas Tech University, Jacob Cobb, August 2016

Figure 2.7. Detailed geologic map of northwest part of Rough Run East outcrop, showing location of sections A through P measured in the ‘odd conglomerate’ (unit 8); numbered map units are the same as those shown in Figure 2.1.

Texas Tech University, Jacob Cobb, August 2016

Figure 2.8. Correlation of 16 sections A through P measured in the ‘odd conglomerate’ (unit 8), depositional units 1 to 3, and position of normal fault shown in figure 2.7.

Texas Tech University, Jacob Cobb, August 2016

CHAPTER 3

PALEONTOLOGY OF THE ‘ROUGH RUN EAST’ EXPOSURE

While conducting fieldwork mapping the Rough Run East exposures, an attempt was made to locate any significant fossils that might help constrain the position of the K/Pg boundary within the stratigraphic section. Six fossil localities were discovered (locations of sites #1 through #6 shown in figure 2.1, and stratigraphic positions shown in figure 2.1).

Sites #1 through #4

Sites in the upper Javelina and lowermost Black Peaks formations yielded only isolated dinosaur bones that were not collected. Specimens found at site #1 were too fragmentary to identify, although their size and structure indicate they pertain to dinosaurs. These specimens occur in a conglomerate bed and were transported and abraded prior to burial. Specimens at sites #2 and #4 are preserved in situ, and sufficiently complete to identify as titanosaurian sauropod bones. Specimens found at site #3 are also preserved in situ, but consist only of fragments of tyrannosaurid limb and rib bones. The highest insitu dinosaur bones found in the area occur at site #4 in the “hoodoo sandstone” (unit 7). Collectively, specimens found at these sites indicate that at least units 1 through 7 are within the Upper Cretaceous.

Texas Tech University, Jacob Cobb, August 2016

Site #5

A diverse assemblage of charophyte algal gyrogonites was recovered from the upper fine interval of the “odd conglomerate” (unit 8) at site #5.

Approximately 65 specimens were recovered by picking through a washed sample of the sand fraction from this locality. Charophyte gyrogonites are probably common throughout the uppermost sandy interval of the “odd conglomerate” but a representative sample was obtained only at site #5. At least four species are represented in the assemblage (Figure 3.1). The most abundant species is

Platychara compressa (Peck and Reker, 1948) recognized primarily on the basis of its distinctive oblate-spheroidal shape; however, all of the specimens recovered have a slightly smaller diameter than those measured by Peck and Forester (1979).

Also abundant is Strobilochara sp., with pronounced tuberculate ornamentation

(see Mebrouk et al., 2009); although all of the specimens recovered are incomplete, none preserves the apical part of the gyrogonite, and the species cannot be identified with certainty. Very small specimens, referred to Microchara cf. M. leiocarpa (Grambast, 1971) are also common, and these are relatively well preserved. A few specimens are referable to Porochara gildmeisteri (Koch and

Blissenbach, 1960), and several others remain unidentified (Figure 3.1).

This assemblage appears to be very similar to one found in the Upper

Cretaceous (Maastrichtian) part of the North Horn Formation in central Utah

(Fouch et al., 1987). The North Horn charophyte flora includes Platychara compressa, Porochara gildmeisteri, Microchara cf. M. cristata, Microchara cf.

Texas Tech University, Jacob Cobb, August 2016

M. leiocarpa, Strobilochara n.sp., and Retusochara n. sp.

Platychara compressa is typical of Upper Cretaceous strata in North

America, although Peck and Forester (1979) report an occurrence also in the lower

Paleocene of Alberta. Microchara cristata and M. leiocarpa are known from

Maastrichtian strata of Europe (Grambast, 1971) but Microchara spp. extend through the Paleocene (Riveline et al., 1996). Strobilochara spp. are typical of

Maastrichtian strata in Europe and North Africa (Mebrouk et al., 2009).

Porochara gildmeisteri is known from Maastrichtian strata of South America

(Musacchio, 2000). If these species are correctly identified, taken together they indicate a Maastrichtian age for the charophyte flora found directly above the “odd conglomerate” (unit 8).

Scattered shells of unionid bivalves also occur at site #5 in dark gray mudstone within the lower part of unit 9, just above the charophyte-bearing interval in the uppermost part of unit 8. Most of these shells are poorly preserved and fragmentary; however, a few fairly complete examples were collected (Figure

3.2). The shells are all generally similar in form, and appear to represent a single species. They are ovate or elongate in shape, and other than faint concentric umbonal corrugations, lack any distinctive sculpture on their external surface.

These specimens resemble most closely Plesielliptio spp. but similar species have been reported from both Upper Cretaceous and Paleocene strata. Collectively, the charophytes in unit 8 and unionid bivalves in unit 9 indicate that a period of lacustrine sedimentation occurred following deposition of the “odd conglomerate.”

Texas Tech University, Jacob Cobb, August 2016

Site #6

A sparse vertebrate fauna of middle Paleocene (Torrejonian) age was recovered at site # 6 (field number = TL 15-01 in T. Lehman field notes) in unit

9a. Vertebrate bones and teeth occur here as isolated, abraded, and fragmentary elements in the coarse basal lag of a lenticular fluvial channel deposit. Scales of lepisosteiid fishes (Figure 3.2) and pieces of turtle carapace and plastron are particularly abundant at this site (Figure 3.4).

A large trionychid turtle (Aspideretes sp., Figure 3.4) is represented by most of the left side of a carapace. Shells of similar large ‘soft-shelled’ turtles are common throughout Upper Cretaceous and Paleogene strata in western North

America, many species assigned to Aspideretes or closely-related genera have been named, but their validity is doubtful (Tomlinson, 1997). Of those described, the present specimen most closely resembles Aspideretes reesidei from the

Nacimiento Formation in New Mexico (Gilmore, 1919). Additional distinctively sculptured plastron fragments indicate that two species of baenid turtle and a small chelydrid turtle are also present at the site. Isolated teeth of crocodylians with varied morphology indicate that a small alligatorine (Figure 3.2), and a second small species with slender recurved conical teeth (Figure 3.2) are present, as well as a large species with stout, blunt teeth (Figure 3.2).

A single large upper first or second premolar of a taeniodontid mammal was also recovered at this site (Figure 3.3). This specimen likely pertains to

Psittacotherium multifragum (T. Williamson, personal communication to T.

Texas Tech University, Jacob Cobb, August 2016

Lehman, 11/2015). The first occurrence of this species in the San Juan Basin of

New Mexico is in middle Torrejonian Protoselene opisthacus – Ellipsodon granger Zone (P-E zone of Williamson, 1996), but its range extends throughout the remainder of the Paleocene. Site # 6 can therefore be no older than middle

Torrejonian in age.

Texas Tech University, Jacob Cobb, August 2016

Figure 3.1. Charophyte gyrogonites from unit 9 near site 5. 1-5) Platychara compressa, 1) specimen #5, basal, and 2) apical view, 3) specimen #8, basal view, 4) specimen #46, lateral view, 5) specimen #1, lateral view. 6-7) Porochara gildmeisteri, specimen #31 in 6) apical, and 7) lateral view. 8-13) Microchara cf. M. leiocarpa, specimen #43 in 8) apical, 9) basal, and 10) lateral view; specimen #12 in 11) apical, 12) basal, and 13) lateral view. 13-17) Strobilochara sp., specimen #24 in 13) basal, and 14) oblique lateral view; 15) specimen #60, basal view; 16) specimen #27, basal view, 17) specimen # 28, lateral view. 18-20) specimen #11, basal, 19) apical, and 20) oblique lateral view.

Texas Tech University, Jacob Cobb, August 2016

Figure 3.2. Aquatic vertebrate fauna from site 6 in unit 9a (= TL 15-01); tooth of small alligatorine crocodylian in 1) oral, and 2) lateral view; 3-4) indeterminate crocodylian teeth in lateral view; 5) large lepisosteiid fish scale in lateral view. Unionid bivalve Plesielliptio sp. from site 5 in unit 9; 6) right valve in medial view, and left valve in 7) lateral view, and 8) medial view.

Texas Tech University, Jacob Cobb, August 2016

Figure 3.3. Large upper first or second premolar of taeniodontid mammal Psittacotherium multifragum from unit 9a at site 6.

Texas Tech University, Jacob Cobb, August 2016

Figure 3.4. Partial left side of trionychid turtle (Aspideretes sp.) carapace from unit 9a site 6 (C1 to C7 = costal bones, pN = preneural, N1 and N3 = parts of neural bones).

Texas Tech University, Jacob Cobb, August 2016

CHAPTER 4:

SANDSTONE PETROGRAPHY AND GRAIN MORPHOLOGY

The most common pebbles and cobbles in the ‘odd conglomerate’ (unit 8) are sandstone clasts that appear to have been derived from nearby sandstone beds in the Javelina or Black Peaks formations. Examples of individual sandstone clasts taken from the conglomerate were selected for petrographic examination, and to compare with samples of sandstone taken from the underlying Javelina

Formation (units 1 and 3) and the Black Peaks Formation (unit 7 – the “hoodoo sandstone”) as well as with sandstones in the Tornillo Group more broadly. The goal of this analysis is to evaluate whether clasts in the ‘odd conglomerate’ were derived locally or from outside the Tornillo Basin.

Eleven examples of sandstone pebbles from the “odd conglomerate” (Table

4-1; labeled pt.A hoodoo, ss1a through c, ss2a and 2b, ss3, p5 to p5-2, and p6), two samples from Javelina sandstone unit 1 (jv-ss1), two samples of Javelina sandstone unit 3 (jv-ss2) and one sample of the “hoodoo sandstone” (labeled “hoodoo”) were sectioned (Table 4- 1). The samples were cut into slabs; all were weakly indurated, and required epoxy impregnation prior to trimming into billets for thin-sections.

A straightforward examination of the thin-sections indicates that the Javelina

Formation sandstones are litharenites, with predominately carbonate and volcanic lithic grains and small amounts of plagioclase in clay matrix with calcite cement

(Figure 4.1). The “hoodoo sandstone” in the Black Peaks Formation is also a

Texas Tech University, Jacob Cobb, August 2016 litharenite with carbonate rock fragments and small amounts of plagioclase in clay matrix and calcite cement (Figure 4.2). The sandy matrix of the ‘odd conglomerate’ likewise consists predominantly of quartz, volcanic and carbonate rock fragments, and plagioclase (Figure 4.3). Pebbles in the ‘odd conglomerate’ (Figures 4.4 and

4.5) are also primarily lithic sandstones with carbonate and volcanic rock fragments, plagioclase, clay and calcite cement. A superficial examination therefore indicates that pebbles and sandy matrix of the ‘odd conglomerate’ are very similar to sandstones in the underlying Javelina and Black Peaks formations.

Sandstone Petrography

Point counts (minimum of 100 framework grains) were conducted for each of the 16 thin-sections. In addition to essential framework grains (quartz, feldspar, and lithic grains), the amounts of accessory minerals, cements, and detrital clay matrix were also tallied. The compositions determined for each sample are shown in table 4.1. The composition of the Rough Run East sandstones can be compared with those reported by Lehman (1991) for the Tornillo Group elsewhere in Big

Bend (Table 4.2). Lehman (1991; his table 2) reported average values for point counts of a total of 30 thin-sections in three stratigraphic intervals; Javelina

Formation (Lancian, n = 9), lower Black Peaks Formation (Puercan-Torrejonian interval, n = 8), and upper Black Peaks Formation (Tiffanian-Clarkforkian interval, n = 13).

The Rough Run East samples and the average Tornillo Group values from

Texas Tech University, Jacob Cobb, August 2016

Lehman (1991) are compared here using conventional ternary diagrams. A traditional QFL diagram (Figure 4.6) compares the basic framework grain composition (quartz, feldspar, and lithic grain abundances). A second ternary diagram (Figure 4.7) compares the relative abundances of lithic grains

(recalculated percentages of volcanic, metamorphic, and sedimentary rock fragments), and a third diagram (Figure 4.8) plots volcanic and carbonate lithic grain abundance, with all other sedimentary rock fragments (clastic lithic grains and chert) included instead with metamorphic lithic grains.

The QFL diagram (Figure 4.6) shows that all samples from Rough Run

East, and the average Tornillo Group values reported by Lehman (1991) are lithic- rich subquartzose sandstones with relatively low feldspar content. The quartz content varies between 30 and 70%, but all samples plot close to the lithic side of the diagram. The average values reported by Lehman (1991) have slightly higher feldspar content, comparable to several of the Javelina sandstone samples from

Rough Run East. The pebbles from the “odd conglomerate” all have very low feldspar content, comparable to the “hoodoo sandstone” sample. Although all of these sandstones have similar bulk composition, the “odd conglomerate” pebbles plot closest to those from the “hoodoo sandstone.”

The lithic grain plot compares the abundance of volcanic, sedimentary, and metamorphic rock fragments (Figure 4.7) and shows that all Rough Run East sandstones, and the average Tornillo Group values reported by Lehman (1991) are similar in having essentially no metamorphic lithic grains. They vary substantially, however, in the ratio of volcanic to sedimentary lithic grains. The Tornillo Group

Texas Tech University, Jacob Cobb, August 2016 averages reported by Lehman (1991) show very high volcanic lithic grain abundance, higher than any of the samples from Rough Run East, although the

Javelina sandstones also have somewhat higher volcanic lithic content. In contrast, the pebbles from the “odd conglomerate” and the “hoodoo sandstone” have high sedimentary rock fragment abundance. The greater abundance of sedimentary rock fragments in the Rough Run East samples distinguishes them from typical sandstones in the Javelina and Black Peaks formations.

The plot showing relative abundance of volcanic and carbonate rock fragments (Figure 4.8) includes all other sedimentary rock fragments (chert and clastic lithic grains) at the metamorphic lithic pole. Thus, showing the metamorphic and sedimentary rock fragments grouped together. This shows that the average Tornillo Group sandstones reported by Lehman (1991) have not only higher volcanic lithic grain content, but also slightly higher chert and clastic rock fragment content. The Javelina sandstone samples from Rough Run East are intermediate in composition between the Tornillo Group averages and the remaining samples - the “hoodoo sandstone” and pebbles from the “odd conglomerate” which have almost exclusively carbonate rock fragments as the primary lithic grain. Close examination of the carbonate rock fragments shows that they are composed almost exclusively of microcrystalline calcite similar to the pedogenic ‘caliche’ nodules found in underlying Black Peaks mudstone beds, and also found as reworked pebbles in the ‘odd conglomerate.’ The carbonate clasts do not contain skeletal (fossil) grains that would indicate derivation from marine limestone, and no reworked carbonate skeletal grains other than charophyte

Texas Tech University, Jacob Cobb, August 2016 oogonia (described previously) were found.

In addition to general similarities in the basic framework grain composition and lithic grain abundances, there are also similarities in varieties of quartz, feldspar, and accessory minerals in the Rough Run East and typical Tornillo Group sandstones. All of the Rough Run East sandstones have much higher monocrystalline compared to polycrystalline quartz (Table 4.2), and the same is true for average Tornillo Group sandstones reported by Lehman (1991) – although this may reflect the fine grain size of the sandstones (typically fine to medium- grained). All of the Rough Run East sandstones have little or no microcline; instead plagioclase is the dominant feldspar (Table 4.2), and the same is true for the average values reported by Lehman (1991). Even samples that have very low feldspar content – the “hoodoo sandstone” and pebbles from the “odd conglomerate” have plagioclase as the dominant feldspar. Opaque oxides and micas are the dominant accessory minerals in all of the sandstones, and all exhibit relatively high clay matrix and/or clay cement content (Table 4.1).

These comparisons make it clear that the sandstone pebbles in the “odd conglomerate” could have been derived through erosion of sandstones in the

Tornillo Group. The pebbles exhibit compositions like those of Tornillo Group sandstones, and do not suggest a source area that was ‘exotic’ or outside the

Tornillo Basin itself. The great abundance of carbonate lithic grains in the sandstone pebbles from the “odd conglomerate” and in the “hoodoo sandstone” suggests that the pebbles could have been derived directly from erosion of sandstone in the underlying Black Peaks Formation, if not from the “hoodoo

Texas Tech University, Jacob Cobb, August 2016 sandstone” itself.

Grain Morphology

Individual sand grains were segregated from the matrix of the “odd conglomerate” (unit 8) and from the laminated sandstone bed at its top, to examine the grain morphology, and to determine whether any of the distinctive grain features reported from K/Pg boundary samples elsewhere may be present here

(e.g., ‘shocked’ quartz grains, microspherules). The primary objective of this analysis was to determine if the presence of any unique grain microtextures or compositions could help indicate the origin of the “odd conglomerate.”

The bulk sediment samples were first disaggregated and washed to remove clay and silt-sized particles. The disaggregation process consisted of completely drying the sample, soaking it in K1 (kerosene), then running the sample through hot water, and sieving the sample using a 230 mesh (62 micron) sieve. The resulting sand concentrate was picked under a binocular microscope to select grains with any unusual surface microtextures or spherule form. A sample of approximately 122 grains was selected for detailed examination using scanning electron microscopy (SEM). This sample strategy is of course a biased one, and the grains included were only chosen if they exhibited planar or lamellar features, spherical form, or were otherwise unusual and warranted examination to determine their composition.

The grains were mounted on an aluminum stub with double coated carbon

Texas Tech University, Jacob Cobb, August 2016 paper, and sputter coated with gold-palladium. The Hitachi S4300 SEM with tungsten filament was set at 15 kV accelerating potential, brightness value of 1, and energy-dispersive spectrum (EDS) analysis was used to assess chemical composition of grains. Not all of the grains examined were quartz, some appeared to be glass spherules (identified also through microscope), some grains segregated by magnetic-separation were also examined, and one charcoal grain was examined.

A few grains initially identified as quartz under binocular microscope were found to not be composed of SiO2 using EDS analysis under SEM.

Of the 122 grains examined, four groups are represented; these are 1) common quartz grains, 2) altered quartz grains, 3) quartz prisms and spherules, and

4) metallic oxide grains. Other grain types were examined but not of primary interest.

Altered quartz grains - Four quartz grains display sets of planar micro- features. Three of these grains show multiple prominent sets of planar lamellae, and one grain shows these sets on multiple faces (Figure 4.9). In this grain, the lamellae within each set appear to be parallel to one another, with spacing between

5 and 20 microns. It is difficult to determine if the lamella thickness is uniform throughout; this could reflect abrasion of the grain surfaces during transport or non-uniform grain coating applied prior to SEM examination. The lamellae intersect at angles that together form ridges on the grain surface. It is not clear whether these ridges form a perfectly straight intersection, or if the intersection exhibits ‘side-stepping.’ Although in places the intersection appears to show

‘side-stepping’ (Figure 4.10), this could be due to actual interaction between the

Texas Tech University, Jacob Cobb, August 2016 two sets of lamellae or a result of ‘plucking’ due to abrasion.

Parallel sets of micro-fractures are also present on another quartz grain

(Figure 4.11) The fractures do not appear to extend across the entire grain, smaller fractures are evident between more prominent ones, and some of the fractures have splays at their ends (Figure 4.12). The spacing between fractures can only be measured in a few places, where it is found to be 20 microns.

Another quartz grain displays two sets of lamellar structures that intersect on the same face at about 120 degrees (Figure 4.13). The intersections are not in line with one another, but definitely side-step. Furthermore, the intersecting lamellae appear to cut across one another. The lamellae sets are parallel, and appear to be equally spaced throughout, but the surface is not clear in some areas.

Individual lamellae are straight, with the exception of minor curves at their ends where lamellae are cut by intersecting sets of lamellae (Figure 4.14). Apart from displaying multiple sets of lamellae, this grain also shows minor abrasion, and appears to exhibit a subhedral overall shape.

These four grains show at least some of the features reported in quartz grains subject to ‘shock’ metamorphism, as is typically associated with bolide impact sites and ejecta. ‘Shocked’ quartz grains exhibit two types of planar microstructure (‘shock lamellae’) that are thought to distinguish them: planar fractures, and planar deformation features (Stoeffler and Langenhorst, 1994).

Planar fractures form from sets of parallel open fissures that have spacing of approximately 20 microns, and are oriented along crystallographic planes

(Mahaney, 2002). At least these four grains from the ‘odd conglomerate’ (Figures

Texas Tech University, Jacob Cobb, August 2016

4.11, 4.12) show planar features that appear to match the descriptions given by

Mahaney (2002) and compatible with an origin by shock metamorphism.

Quartz grains with ‘common’ microtextures – Many of the grains examined show microtextures that are more commonly observed on detrital quartz grains from a variety of settings. Arc-shaped steps are exhibited on some grains, as are cross-cutting sets of arc-shaped steps (Figure 4.15). Arc-shaped steps are deep breaks in the quartz grain fabric that may be caused by grain-to-grain impact, such as results from high velocity stream transportation. These features are similar to conchoidal fractures but have deeper penetrations into the grain and typically have a wider spacing (>5 microns; Mahaney, 2002). Figure 4.16 illustrates a grain with sub-parallel linear fractures. In contrast to planar deformation features, sub- parallel linear fractures are not evenly spaced, not parallel, or straight. The sub- parallel linear fractures are curved, and vary in relief, shape, and length. Sub- parallel linear fractures are also shown in other grains (Figure 4.16; this grain also has high angularity, and displays percussion abrasion marks). The angular grain in figure 4.17 also shows sub-parallel linear fractures along with abrasion

(percussion) marks. These quartz grains (Figures 4.16 and 4.17) illustrate ‘normal’ quartz grains with microtextures more typical of that expected in detrital sand grains. They are noticeably more angular compared to those showing planar fractures or planar deformation features, or compared to the quartz spherules and altered euhedral quartz grains described below.

Quartz prisms and spherules – Many grains in the sample superficially appear to be glass spheres when examined under reflected light. These grains are

Texas Tech University, Jacob Cobb, August 2016 clear to translucent, and rounded to well rounded, but display a limited degree of surface abrasion, and were found to be composed primarily of SiO2 when examined using EDS under SEM. These grains appear to represent a spectrum from some exhibiting a perfectly euhedral crystal form to others that are completely round anhedral grains. These grains are described below in order from euhedral to anhedral.

Figure 4.18 illustrates a quartz grain that is almost perfectly euhedral and shows minimal abrasion. This grain displays the hexagonal bipyramidal (beta quartz) form typical of quartz phenocrysts in volcanic and shallow intrusive rocks.

Figure 4.19 shows a grain that partly retains the euhedral bipyramidal shape, but with possible resorption pits, percussion marks, and with edges of the hexagonal crystal faces rounded. The grain in Figure 4.20 exhibits even greater abrasion, and only vaguely retains the original euhedral shape. This grain approaches the rounded spherical form of some others. Figure 4.21 shows a grain that has only faint suggestion of the original crystal faces. This grain shows a change in texture across the surface from the original pyramidal edges to the more spherical interior.

Figure 4.22 shows a grain that is nearly entirely round, with little expression of an original euhedral shape. There are large v-shaped cracks as well. Figures 4.23 and

4.24 show grains that are entirely spherical or oblong with no expression of crystallographic features, and minimal abrasion.

Several grains also included in the ‘spherule’ category display unusual form and microtexture. One grain retains a rounded but vaguely euhedral form (Figure

4.25) but instead appears to have originally had a tetragonal prism structure. The

Texas Tech University, Jacob Cobb, August 2016 surface has round and oblong pits and grooves within the pits have perpendicular grooves, and EDS indicates that the grain is SiO2. Figure 4.26 shows a spherule grain that is very well rounded with minor abrasion, but this grain has an unusual projection (possibly an adhering bit of cementing agent that is still composed of silica) attached to the top. Another example is an angular quartz grain with sub- parallel linear fractures that retains some adhering clay cement on its surface, but also displays an unusual triangular prism face surrounded by deep grooves (Figure

4.27).

Other grains have a general spherule form with quartz composition, but do not show any evidence for having ‘evolved’ from a hexagonal bipyramidal structure. Figures 4.28 and 4.29 show ‘dumbbell-shaped’ grains that resemble two spheres joined together. Both of these grains show minor percussion abrasion features, but are rounded to subrounded. These grains somewhat resemble the most rounded of the bipyramidal grains in having a more bulbous spherical interior surrounded by a thinner external flange.

In general, grains included here in the ‘spherule’ category appear to fall in two categories. One group includes those that almost certainly represent quartz phenocrysts derived from erosion of felsic volcanic or shallow intrusive igneous rocks, and subject to varied degree of abrasion due to transport (e.g., Fig. 4.18,

4.19). However, many of these show very limited abrasion on the euhedral crystal faces, which could indicate that they were deposited directly nearby as crystal-rich air fall ash, and not reworked from older volcanic rocks. A second group includes very well rounded grains that lack any evidence for the former presence of a

Texas Tech University, Jacob Cobb, August 2016 euhedral form. These tend to have a thick bulbous center surrounded by a thin external flange that gives the grain a ‘saucer’ shape (Fig. 4.21, .22,

.23, and .26). The ‘dumbbell’ shaped grains (Fig. 4.28, .29) also show this distinct external flange. Although this second group of spherule grains is well rounded, their surfaces are nearly smooth and show little evidence for abrasion (percussion) marks. The surfaces of quartz grains that are rounded due to prolonged transport in water or air typically display numerous v-shaped percussion cracks (Figure 4.30).

Metallic oxide grains – Several grains separated from the sample using a hand- held magnet were examined under SEM to observe their form and composition, and to determine for example if they might represent microtektites.

These grains (Figures 4.31 and 4.32) are composed of metal oxides. Figure 4.31 shows a grain that consists of at least three pitted subhedral crystals joined together. EDS indicates that the grain is composed predominantly of Fe and Ti.

Figure 4.32 shows a similarly pitted but anhedral grain that instead is composed predominantly of Mg, V, and Nb. Neither grain has significant Ni content. Both grains have large cavities that probably represent lost inclusions of other minerals.

These grains appear to be authigenic ferromagnesian oxide minerals, and do not exhibit the characteristic form or composition of microtektites.

In summary, SEM examination of selected sand grains from the ‘odd conglomerate’ (unit 8) indicates that the bulk of these grains exhibit features typical for detrital quartz grains. However, some of the grains are unusual. A few quartz grains (about 4 of 122 examined) appear to show planar deformation features or planar fractures of the sort commonly attributed to shock metamorphism, and

Texas Tech University, Jacob Cobb, August 2016 associated with bolide impacts (Mahaney, 2002). A few of the grains (about 6 of

122 examined) have unusual smooth ‘saucer’ or ‘dumbbell’ shapes of a sort that are comparable to splash form tektites, which are known to occur from impact events (Glass, 1990).

Texas Tech University, Jacob Cobb, August 2016

Figure 4.1. Photomicrograph of Javelina Sandstone unit 1 (jvss-1) thin-section (cross-polarized light at 4x, width of field of view about 2.5 mm), loose grain mount, showing carbonate lithic grains and quartz, with minor plagioclase.

Figure 4.2. Photomicrograph of ‘hoodoo sandstone’ (unit 7) thin-section (cross- polarized light at 4x, width of field of view about 2.5 mm), showing alternating quartz-rich and carbonate lithic grain-rich laminations.

Texas Tech University, Jacob Cobb, August 2016

Figure 4.3. Photomicrograph of ‘odd conglomerate’ (thin-section MD; cross- polarized light at 4x, width of field of view about 2.5 mm), showing larger carbonate lithic grains and sandstone clasts with finer quartz, plagioclase, and volcanic rock fragments in interstitial space.

Figure 4.4. Photomicrograph of sandstone pebble from ‘odd conglomerate’ (Pt. A Hoodoo thin section; cross-polarized light at 4x, width of view about 2.5 mm) showing quartz and carbonate lithic grains and calcite cement.

Texas Tech University, Jacob Cobb, August 2016

Figure 4.5. Photomicrograph of pebble from ‘odd conglomerate’ (ss3 thin- section, cross-polarized light at 4x, width of view about 2.5 mm) showing quartz, plagioclase, volcanic lithic and carbonate lithic grains, calcite and clay matrix.

Texas Tech University, Jacob Cobb, August 2016

Table 4.1. Thin-section point count data for sandstone samples from the Rough Run East exposure; Javelina Formation sandstone units (labeled jvss), “hoodoo sandstone” in the Black Peaks Formation (labeled hoodoo), and sandstone pebbles from unit 8 - the “odd conglomerate” (labeled ss and p).

Texas Tech University, Jacob Cobb, August 2016

Table 4.2. Petrographic data for major stratigraphic intervals in the Tornillo Group (from Lehman 1991); average values for 8 to 16 samples from sandstone units.

Texas Tech University, Jacob Cobb, August2016

Figure 4.6. Ternary diagram comparing basic framework grain composition of Tornillo Group sandstones (average values reported by Lehman, 1991) with Rough Run East samples of Javelina, Black Peaks, and sandstone pebbles from ‘odd congl’.

Figure 4.7. Ternary diagram comparing lithic grain composition of Tornillo Group sandstones (average values reported by Lehman, 1991) with Rough Run East samples of Javelina Fm, Black Peaks Formation, and sandstone pebbles from ‘odd conglomerate’.

Texas Tech University, Jacob Cobb, August2016

Figure 4.8. Ternary diagram comparing volcanic and carbonate lithic grain composition of Tornillo Group sandstones (average values reported by Lehman, 1991) with Rough Run East samples of Javelina Fm, Black Peaks Fm, and sandstone pebbles from ‘odd conglomerate’.

Figure 4.9. SEM image of quartz grain showing multiple sets of parallel lamellae on several faces (image taken by Matthew Pippin).

Texas Tech University, Jacob Cobb, August2016

Figure 4.10. Magnified view of same grain shown in figure 4.9 indicating (with thin black line) how the two intersecting sets of planar lamellar structures do not form a straight contact (image taken by Matthew Pippin).

Figure 4.11. SEM image of a quartz grain showing deep parallel fractures (image taken by Matthew Pippin).

Texas Tech University, Jacob Cobb, August2016

Figure 4.12. Enhanced image of parallel fractures in same grain shown in figure 4.11 showing splays at the ends of fractures (image taken by Matthew Pippin).

Figure 4.13. SEM image of quartz grain that shows intersecting sets of planar deformation features (image taken by Matthew Pippin).

Texas Tech University, Jacob Cobb, August2016

Figure 4.14. Enhanced view of same grain shown in figure 4.13 illustrating intersection between the two sets of parallel lamellae (image taken by Matthew Pippin).

Figure 4.15. SEM image of quartz grain displaying two sets of arch-shaped steps. One set cuts across the other (image taken by Matthew Pippin).

Texas Tech University, Jacob Cobb, August2016

Figure 4.16. SEM image of angular quartz grain with percussion marks and sub- parallel linear fractures (image taken by Matthew Pippin).

Figure 4.17. SEM image of typical angular quartz grain (image taken by Matthew Pippin).

Texas Tech University, Jacob Cobb, August2016

Figure 4.18. SEM image of quartz grain with euhedral bipyramidal hexagonal (beta quartz) form and little abrasion (image taken by Matthew Pippin).

Figure 4.19. SEM image of quartz grain with vague hexagonal bipyramidal form, subhedral shape, and percussion marks (image taken by Matthew Pippin).

Texas Tech University, Jacob Cobb, August2016

Figure 4.20. SEM image of quartz ‘spherule’ displaying spherical center and external flange (image taken by Matthew Pippin).

Figure 4.21. SEM image of quartz ‘spherule’ with bulbous interior and marginal ‘flange’ (image taken by Matthew Pippin).

Texas Tech University, Jacob Cobb, August2016

Figure 4.22. SEM image of quartz ‘spherule’ with subtle external flange, abrasions, and v-fractures (which are percussion marks created by transportation of sediment) (image taken by Matthew Pippin).

Figure 4.23. SEM image of well wounded quartz ‘spherule’ with vague flange and minor abrasion features (image taken by Matthew Pippin).

Texas Tech University, Jacob Cobb, August2016

Figure 4.24. SEM image of quartz ‘spherule’ with faint abrasions and v- shaped cracks (image taken by Matthew Pippin).

Figure 4.25. SEM image of quartz ‘spherule’ with vague tetragonal prism structure. Large pits may represent former inclusions (image taken by Matthew Pippin).

Texas Tech University, Jacob Cobb, August2016

Figure 4.26. SEM image of well rounded quartz ‘spherule’ with marginal flange and possible adhering cement (image taken by Matthew Pippin).

Figure 4.27. SEM image of quartz grain with euhedral triangular crystal face and sub-parallel linear fractures (image taken by Matthew Pippin).

Texas Tech University, Jacob Cobb, August2016

Figure 4.28. SEM image of irregular ‘dumbbell-shaped’ quartz spherule (image taken by Matthew Pippin).

Figure 4.29. SEM image of ‘dumbbell-shaped’ quartz spherule with multiple fractures (image taken by Matthew Pippin).

Texas Tech University, Jacob Cobb, August2016

Figure 4.30. Example of a typical subrounded detrital quartz grain with features indicative of prolonged subaqueous transport - bulbous edges and multiple v-shaped percussion cracks with some partially abraded fractures; this grain is from Nile Delta sediments (from Mahaney, 2002).

Texas Tech University, Jacob Cobb, August2016

Figure 4.31. SEM image of metal oxide grain consisting of at least three euhedral crystals with pits from former inclusions (image taken by Matthew

Figure 4.32. SEM image of pitted subhedral metal oxide grain (image taken by Matthew Pippin).

Texas Tech University, Jacob Cobb, August2016

CHAPTER 5 GEOCHRONOLOGY

Samples were collected from multiple beds in the Rough Run East outcrop, and from the K/Pg boundary interval at the Rough Run Amphitheater and Dawson

Creek outcrops, to determine whether any tuff beds suitable for U/Pb isotopic age determination might be present that could help constrain the ages of key units within the K/Pg boundary interval. All of the beds sampled, when examined in thin-section did not show evidence for a tuffaceous origin, and zircons extracted from those beds were clearly detrital and yielded a wide range of ages much older than the likely depositional ages of the units. However, one bed sampled immediately above the “Tom’s Top” sandstone on Dawson Creek (see Figure 1.3) appears to be a reworked tuff, and yielded a significant sample of zircons with similar U/Pb ages that almost certainly record the depositional age for that unit.

Zircons were analyzed in-situ for U, Th, and Pb isotope composition by laser- ablation using the NU instrument Plasma HR-MC-ICP-MS multi-collector at U.C. Santa Barbara. The laser ablation spot size diameter was 60 microns.

Accuracy of the analyses was monitored through repeated measurement of the GJ reference zircon (Concordia age = 602.5 ± 1.8 Ma, mean square weighted deviation (MSWD) of concordance = 1.6, probability of concordance = .008, n=

39) as well as the Plesovice reference zircon. Individual charts were made to derive the mean for each U/Pb age (figures 5.1, 5.2, and 5.3). Results for GJ are in agreement with the published values of 602.0 ± 3.0 Ma (2σ) and 602.4 ± 3.7 Ma

Texas Tech University, Jacob Cobb, August2016

(2σ) for the GJ zircon (Chen et al., 2011). There were no 207Pb/206Pb measurements taken for the Plesovice zircon for the Big Bend data by laser ablation, so Concordia could not be plotted (Mean age = 337.99 ± .78 Ma, MSWD of concordance = 1.2, probability of concordance = 1.5, n = 39; see Figure 5.4).

Results are in agreement with the published values of 206Pb/238U yeilding 337.13

± .37 Ma for the Plesovice zircon (Slama et al. 2008).

Tom’s Top bed

A sample of 16 zircons was obtained from the reworked tuff bed overlying the “Tom’s Top” sandstone. The zircons yielded 206Pb/238U isotopic ages ranging from c. 188 to 63 Ma (Table 5.1). The entire set of U/Pb ages is compiled here in a probability density plot to show peak ages for all 16 zircons (Figure 5.4). All of the zircons that yielded apparent ages older than c. 68 Ma provided data were considered problematic for various reasons (e.g., likely inheritance, laser shots that crossed multiple zones, apparent lead loss, or discordant ages). As a result of these problems, those data shown (struck through) in Table 4.1 were not considered in the resulting age assessment. The remaining 8 zircons yielded concordant ages in a tight grouping from c. 63.6 to 64.5 Ma, and a mean age of 63.70 ± 0.47 Ma

(Figures 5.5, 5.6). The mean square weighted deviation (MSWD) for this average is 2.4, but this is due primarily to one ‘outlier’ value somewhat below the average age. If that outlier is removed, the MSWD is 1.13, and the mean remains substantially unchanged at 63.63 ± 0.51 Ma (Figure 5.6).

This age determination is in accord with the Torrejonian (middle

Texas Tech University, Jacob Cobb, August2016

Paleocene) age assessment based on the mammalian fauna recovered from the

Tom’s Top sandstone (e.g., Williamson, 1996). An ash bed of approximately the same age (40Ar/39Ar age 64.0 ± 0.40 Ma) was recently described in Torrejonian strata of the Nacimiento Formation in New Mexico, which indicates that the

Puercan/Torrejonian boundary is at about 64.4 Ma (Fassett et al., 2010).

Texas Tech University, Jacob Cobb, August2016

Age (Ma)

206PB/238U

Figure 5.1. Zircon GJ weighted average 206Pb/238U ages shown.

Texas Tech University, Jacob Cobb, August2016

Age (Ma)

PB206/PB207

Figure 5.2. Zircon GJ weighted average 206 Pb/207Pb shown.

Texas Tech University, Jacob Cobb, August2016

Age (Ma)

206PB/238U

Figure 5.3. Zircon Plesovice weighted average 206Pb/238U ages shown.

Table 5.1. U/Pb concentrations, measured isotopic ratios and isotopic ages for the zircon sample from the “Tom’s Top” bed on Dawson Creek.

Texas Tech University, Jacob Cobb, August2016

Table 5.2. Zircon standard GJ tabulated data.

Texas Tech University, Jacob Cobb, August2016

Table 5.3. Zircon standard Plesovice tabulated data.

Texas Tech University, Jacob Cobb, August2016

Figure 5.4. Probability density plot showing distribution of U/Pb isotopic ages for entire set of 16 zircons in the sample from the “Tom’s Top” bed.

Texas Tech University, Jacob Cobb, August2016

Figure 5.5. Age distribution, mean value and MSWD for 8 youngest zircons in the sample from the “Tom’s Top” bed.

Texas Tech University, Jacob Cobb, August2016

Figure 5.6. Concordia plot of seven youngest zircons (youngest age excluded to tighten group). Not able to distinguish grains due relatable ages by errors, so grains are treated as one. Dotted line effectively shows correction for common lead and yields an age of 63.63 Ma with error of .52.

Texas Tech University, Jacob Cobb, August2016

CHAPTER 6 DISCUSSION

The Rough Run East outcrop provides an excellent exposure of the K/Pg boundary interval in the Tornillo Group. In particular, the ‘odd conglomerate’ bed described by Lehman and Busbey (2007) at Rough Run Amphitheater, about two miles to the west, is continuously exposed here for a distance of about a kilometer.

In the following discussion, basic constraints on the K/Pg boundary at Rough Run

East are assessed, and features of the ‘odd conglomerate’ and its constituents are evaluated in light of several possible interpretations of the section exposed here.

Correlation of Rough Run East and Dawson Creek sections

The ‘odd conglomerate’ (unit 8) and overlying gray lacustrine mudstone

(unit 9) are lenticular units that appear to occupy a broad ‘paleo-valley’ about a kilometer across, extending from northeast to southwest across the Rough Run East outcrop (see figure 2.1, chapter 2). The ‘odd conglomerate’ is best developed in the floor of this local paleo- valley, and this is likely the reason the ‘odd conglomerate’ is not more widely exposed around Big Bend Park. The same paleo- valley may be exposed at the Rough Run Amphitheater, about two miles to the west; however, it is not evident at Dawson Creek another four miles farther west

(Figure 6.1).

Although precise correlation between these areas is not possible, the general

K/Pg boundary interval, for example from the top of the Javelina Formation to the 98

Texas Tech University, Jacob Cobb, August2016 lowermost occurrence of Paleocene fossil vertebrates, thins dramatically to the west

(from about 100 m at Rough Run East to 40 m at Dawson Creek; figure 6.1). The entire Tornillo Group generally thins from east to west (e.g., Lehman, 1991) and so this may simply indicate that sedimentation rates during the K/Pg transition were much lower in the Dawson Creek area. Two Laramide-age structures (the

Terlingua Monocline and Maverick Anticline; see Lehman, 1991) bracket the

Dawson Creek area on the north and northeast, and so it is also possible that uplift of those structures led to lower sedimentation rates or intermittent erosion in the

Dawson Creek area.

In all three areas, the lowermost Paleocene vertebrate fossil sites known are of Torrejonian (middle Paleocene) age. It seems clear from study of the Rough

Run East exposure that if an earliest Paleocene (Puercan) fauna were to be found, it would be in the c. 20 m interval of gray mudstone (unit 9) above the ‘odd conglomerate’ and this unit also appears to only occupy the local paleo-valley floored by the ‘odd conglomerate’ itself. The full extent of this paleo-valley is not known, and whether others of the same kind may be present in the region is also unknown, and this may explain why early Paleocene fossils have yet to be discovered in Big Bend.

Paleontological and Isotopic Age Constraints on the K/Pg Boundary

Isolated dinosaur bones occur throughout the lower part of the section exposed at Rough Run East, from the upper sandstone of the Javelina Formation

(unit 3) to the lower Black Peaks Formation (unit 7). The highest dinosaur bones 99

Texas Tech University, Jacob Cobb, August2016 found are titanosaurian sauropod bones in the base of the ‘hoodoo sandstone’

(fossil locality 4) about 20 m below the ‘odd conglomerate.’ These bones are large, well preserved, and preserved in place (unlikely to have been reworked from older strata). Fronimos and Lehman (2014) described the partial skeleton of a titanosaur from about the same stratigraphic level at the Rough Run Amphitheater, and compared this titanosaur with others known to be latest Cretaceous (Maastrichtian, c. 71 to 65 Ma) in age. In addition, a tuff bed in the middle of the Javelina

Formation several miles east of the Rough Run area provided a U/Pb age of

69.0 ± 0.9 Ma (Lehman et al., 2006); the dinosaur-bearing part of the section at

Rough Run East is well above that stratigraphic level, and therefore must be younger than c. 69 Ma.

The matrix of the ‘odd conglomerate’ and the sandy bed at its top (unit 8) contains a diverse assemblage of charophyte algal oogonia (fossil locality 5). The overall assemblage is comparable to that found in latest Cretaceous (Maastrichtian) strata elsewhere in North America. The oogonia exhibit varied states of preservation; however, some are well preserved and show little or no abrasion, others are highly abraded, smoothed, or broken. Their preservation in the matrix and sandy upper layer of the ‘odd conglomerate’ indicates that most or all of the oogonia were transported prior to burial, but their delicate nature suggests that they could not have been transported for an extended time. There have been few detailed studies of charophyte stratigraphic distribution across the K/Pg boundary, and so it is not clear whether some or all of the typical Maastrichtian species became extinct precisely at the K/Pg boundary. For example, the most abundant

100

Texas Tech University, Jacob Cobb, August2016 charophyte in the ‘odd conglomerate,’ Platychara compressa, is common in

Maastrichtian strata of North America; but it has also been reported from the early

Paleocene of Alberta (Peck and Forester, 1979). The simplest assessment of the charophyte assemblage would indicate that the ‘odd conglomerate’ is Maastrichtian in age, however, the likelihood of reworking, and uncertainty in species distribution makes this assessment equivocal.

The lowermost fossil locality above the ‘odd conglomerate’ (fossil locality 6 in unit 9a) yielded a variety of turtles, crocodylians, and a single tooth of the taeniodontid mammal Psittacotherium multifragum, which has an earliest known occurrence of middle Paleocene (Torrejonian age; Williamson, 1996). Fossil locality 6 is about 25 m above the ‘odd conglomerate.’ A similar site with a mammalian fauna also believed to be of Torrejonian age nearby on Dawson Creek

(‘Tom’s Top’) has at its top the reworked tuff bed that yields a U/Pb age of 63.70 ±

0.47 Ma (reported here in chapter 5).

Isotopic age determinations indicate, therefore, that the section exposed at

Rough Run East must be between c. 69 and 64 Ma, and spans the K/Pg boundary

(c. 65.5 Ma). Paleontological evidence indicates that the K/Pg boundary itself must be in the interval between the ‘odd conglomerate’ (unit 8) and the base of unit 9a. The only fossils found in this 25 m interval are shells of unionid bivalves that have yet to be confidently identified (see chapter 3). It is possible that the

K/Pg boundary is at the ‘odd conglomerate’ bed itself, because the charophyte assemblage found there could be interpreted in different ways, for example, as an in situ Maastrichtian flora, or instead as a reworked assemblage derived from

101

Texas Tech University, Jacob Cobb, August2016 underlying Maastrichtian strata.

Deposition of the ‘odd conglomerate’

The ‘odd conglomerate’ was apparently deposited at or around the time of the K/Pg boundary, and records an unusual sedimentation event at that time. This bed is unusual in being very thin, very coarse grained, including large boulders, and in consisting predominantly of reworked sandstone clasts. Typical fluvial channel sandstones in the Tornillo Group range from 3 to 7 m in thickness

(averages reported by Lehman, 1991), whereas the ‘odd conglomerate’ is generally less than 1 m thick. Typical fluvial channel sandstones in the Javelina and Black Peaks formations also have only thin lenses of gravel lag at their base, usually less than 30 cm thick, overlain by several meters of cross-bedded, parallel- laminated, and ripple cross-laminated sandstone; for example, as in units 1 and 3 in the Javelina Formation, and the ‘hoodoo sandstone’ (unit 7) at Rough Run East, which also represent typical fluvial channel deposits. The ‘odd conglomerate’ is instead composed predominantly of gravel lag with little or no overlying sandy channel bar facies. The gravel is also much coarser grained, including large cobbles and boulders. Fluvial channel lag deposits in the Javelina and Black Peaks formations do not contain clasts larger than medium pebble size (< 4 cm diameter; see Lehman, 1991), and in no other case is the conglomerate composed predominantly of sandstone clasts. Reworked soil carbonate nodules, abraded petrified wood, bone, and chert are the usual clast types in Javelina and Black

Peaks fluvial channel gravels (Lehman, 1991). Therefore, whatever process was 102

Texas Tech University, Jacob Cobb, August2016 responsible for depositing the ‘odd conglomerate’ it had not occurred prior to or following that time during deposition of the Tornillo Group.

Multiple episodes of sedimentation are recorded in the ‘odd conglomerate;’ it is not the result of a single event. At least three depositional events are evident in some exposures (sites D through G), and the absence of multiple deposits in other exposures may only be due to later erosion or ‘amalgamation’ of successive beds (erosion of intervening sandy intervals and superposition of gravel base of later deposits on top of previous ones). Each of the three depositional events is similar, and consists of a pebble- cobble conglomerate abruptly grading upward to coarse- or medium-grained sandstone. The thickness of each conglomerate bed generally diminishes upward, as does the thickness of each of the three deposits overall.

The conglomerate and sandstone beds exhibit primarily horizontal bedding and parallel-lamination with only local low-angle cross-stratification, suggesting that deposition took place under rapid (upper flow regime) conditions. The abrupt transition from conglomerate to sandstone indicates that each depositional event records a rapid reduction in flow velocity or depth. Abrupt gravel-to-sand transitions in bed material are observed in many fluvial channel deposits

(Sambrook Smith and Ferguson, 1995; Heitmuller and Hudson, 2009), so this is not particularly unusual. However, no trough or tabular cross-bedding, or ripple cross-lamination is present, even in the intervening sandstone intervals, that might indicate tranquil (lower flow regime) conditions during or following depositional events. And, no bioturbation features or mud ‘drapes’ were observed that might

103

Texas Tech University, Jacob Cobb, August2016 indicate extended periods of calm or stagnant water conditions intervened between depositional events.

Overall, the ‘odd conglomerate’ shows no change in clast composition vertically (between the three successive conglomerate beds), or over its c. 1 km lateral extent. At all sites studied, the clasts consist of sandstone, mudstone, pedogenic carbonate nodules, and charcoal. These same clast types are also found sparsely distributed in the sandstone intervals between conglomerate beds, and indicate that the source area for the sediment remained consistent throughout deposition. All of the clasts are of local derivation. No extra-basinal or ‘exotic’ clast types were found. Petrographic study of the sandstone clasts indicates that they were probably derived from erosion of sandstones in the Javelina or Black

Peaks formations, perhaps even directly from the underlying “hoodoo sandstone”

(unit 7) in the Rough Run area (see chapter 4). The mudstone ‘rip-up’ clasts and carbonate rock fragments were also likely derived from erosion of nearby mudstone beds with pedogenic carbonate nodules (e.g., unit 4). Although charcoal clasts occur sparingly in other Tornillo Group sandstones (Lehman, personal communication), these are unusually common constituents throughout all of the conglomeratic and sandy intervals of the ‘odd conglomerate.’ The charcoal clasts are rounded, and must have been transported some distance prior to deposition, but they are soft and disintegrate quickly when exposed, and would not have survived prolonged transport. It seems likely that they were derived from trees burned a short time before deposition of the ‘odd conglomerate’ in the immediate vicinity of the Rough Run area. The sandstone clasts are also generally

104

Texas Tech University, Jacob Cobb, August2016 well rounded, which indicates that they were subject to some transport prior to deposition; however, the sandstone is weakly indurated with clay and calcite cement, the clasts may have rounded after a short time, and also would not have survived prolonged transport. The size, composition, and rounding of the clasts in the ‘odd conglomerate’ therefore indicate that flow conditions during transport were strong enough to move and round large cobbles and boulders, but short enough in duration so that soft sandstone, mudstone, and charcoal clasts were not destroyed by abrasion.

The fault that cuts the ‘odd conglomerate’ (between sites K and L) appears to have been active during sedimentation, because the conglomerate thickens dramatically on the downthrown side (i.e., this is a syndepositional or ‘growth’ fault; see chapter 2). On the upthrown side of the fault, the conglomerate is very thin, but includes the largest boulders observed in the area. Both to the northeast and southwest of the fault, the sandstone intervals within ‘odd conglomerate’ thicken, and the separate depositional units are more distinct. The detailed geometry and extent of the fault were not studied, and so its origin is uncertain.

No other syndepositional faults are known in the Black Peaks Formation, although several have been described in the overlying early Eocene Hannold Hill Formation

(see Lehman and Busbey, 2007; their figure 10) – these are high- angle reverse faults interpreted as due to Laramide tectonism. The Rough Run fault appears to be a normal fault, although it might be interpreted instead as the head scarp of a large slump (e.g., due to mass wasting rather than tectonism). The fault itself is unlikely to have been the actual source of the ‘odd conglomerate,’ because the

105

Texas Tech University, Jacob Cobb, August2016 conglomerate accumulated on both upthrown and downthrown sides of the fault, and is comprised of rounded clasts that must have been transported some distance

(i.e., not fault-related breccia or angular clasts derived directly from the fault scarp). However, Smit et al. (1996) stated that seismic shaking of the Chicxulub impact casued local faulting and slumbing. Therefore, it is possible that this syndepositional fault was caused by the Chicxulub impact, but this is still uncertain.

In summary, the basic features of the ‘odd conglomerate’ indicate that it records an unusual event. It was deposited during or shortly after motion on a local fault that was buried during sedimentation. At least three brief episodes of sedimentation occurred in short succession, under rapid (upper flow regime) conditions, and transported coarse materials from the local area, including burned wood, for a relatively short distance prior to deposition. A period of tranquil lacustrine sedimentation occurred after a period of fluvial depsotion, during which mudstone with unionid bivalves accumulated (unit 9).

Significance of Charcoal

The abundant charcoal grains present within the “odd conglomerate” may be significant. No charcoal was observed in underlying units, and so it is unlikely that these grains were derived through erosion of older sediments. If the charcoal was produced by fires that occurred at or around the time of deposition of the “odd conglomerate,” these could have been due to local forest fires, nearby volcanic activity, or fires produced by the Chicxulub bolide impact. If the charcoal resulted 106

Texas Tech University, Jacob Cobb, August2016 from normal and usual events such as forest fires ignited by lightning strikes or volcanic activity, then charcoal grains might be expected as a common constituent of the sediments, since the Tornillo Group floodplains were densely forested (see

Wheeler and Lehman, 2000), and Tornillo sediments include abundant volcanic debris (Lehman, 1991). But, instead the abundance of charcoal is another unusual aspect of the “odd conglomerate” and suggests a more unusual origin.

Kring (2007) summarized evidence for impact-generated ‘wildfires’ found at K/Pg boundary sequences at various sites around the world. Such evidence includes the presence of fusinite (Tschudy et al., 1984), soot, pyrolitic polycyclic aromatic hydrocarbons, carbonized plant debris, and charcoal. The deep-water

K/Pg boundary tsunami deposit at Arroyo el Mimbral (Tamaulipas, Mexico) includes abundant fossil charcoal, including semifusinite and pyrofusinite (Kruge,

1994). The charcoal in this deep-water tsunami deposit is believed to have been a result of fires in nearby regions due to extreme heating from the Chicxulub bolide impact. The extreme heating could have been due to irradiation produced during passage of the bolide through the atmosphere, later rise of the resulting impact fireball, and reentry of ejecta droplets following that (Melosh et al., 1990; Kruge et al., 1994). Heating is thought to have produced widespread fires as the bolide neared earth’s surface moments prior to impact. This initial thermal pulse induced a firestorm that charred proximal terrestrial vegetation, and the subsequent impact produced a mega-wave that quenched the firestorm at least in coastal areas (Kruge et al., 1994). If these interpretations are correct, then firestorms preceded the tsunami by some significant time interval, the temperatures were high enough,

107

Texas Tech University, Jacob Cobb, August2016 and the fires progressed rapidly enough to completely incinerate vegetation prior to arrival of the tsunami at sites in northern Mexico. It is possible, therefore that the charcoal present throughout unit 8 could be a result of the Chicxulub impact, and would support interpretation of the “odd conglomerate” as the K/Pg boundary tsunami bed.

Sand Grain Morphology

Of the 122 sand grains extracted from the “odd conglomerate” and examined using scanning electron microscopy, most have shapes and surface microtextures considered typical for detrital quartz grains transported by normal fluvial processes (see chapter 4). Most of the grains display anhedral forms and evidence for abrasion such as rounded edges and v-shaped percussion fractures – a trait often considered diagnostic of fluvial transport processes (Mahaney, 2002).

This is compatible with derivation of most of the quartz from older sedimentary and volcanic rocks, and deposition of the ‘odd conglomerate’ by fluvial processes.

A few of the quartz grains have euhedral bipyramidal forms subject to varied degree of rounding due to abrasion, and these could also have been derived from erosion of volcanic rocks or crystal-rich ash beds deposited nearby.

A few quartz grains (four), however, show intersecting sets of planar cleavage or planar fractures (see chapter 4). These planar deformation features have been shown to result from both tectonism as well as ‘shock’ metamorphism associated with bolide impacts. Both processes generate similar microtextures; however, the spacing between lamellae and nature of the intersection between sets 108

Texas Tech University, Jacob Cobb, August2016 of lamellae differ (Boggs et al., 2001). The few grains extracted from the ‘odd conglomerate’ exhibit spacing and intersections more compatible with shock metamorphism, but a conclusive determination is not possible. These grains show very little evidence for abrasion, which suggests they had been subject to limited transport – an observation that may also be compatible with their origin by shock metamorphism and for example, direct deposition from fall-out after the Chicxulub bolide impact. If the grains had been reworked from older tectonites, they would be expected to show evidence for more prolonged transport.

Similarly, a few grains (six) show unusually smooth ‘saucer’ and ‘dumbbell’ shapes similar to those found in microtecktites and glass spherules generated by bolide impacts (see chapter 4). Grains when examined by energy dispersion spectrometry so high concentrations of silicon (determined using EDS under

SEM), and so their composition may not be compatible with typical microtektites.

The grains do, however, exhibit forms typical for two of the three major classes of microtektites – ‘splash’ forms and ‘ablated’ forms (Glass, 1990). Splash forms include sphere, disk, dumbbell, and teardrop shapes. Ablated forms are those that underwent a second period of melting that resulted in formation of an external

‘flange.’ The resemblance of these grains to microtektites may indicate that they originated in the same way, as melted glass generated from a bolide impact and shaped aerodynamically, but that in this case the target rock composition was higher in silicon than in other cases. It is generally believed that the Chicxulub impact target rock was dominated by carbonates and evaporates, however, it has been stated by Christian Koeberl (1993) that a revision to the target rocks needs to

109

Texas Tech University, Jacob Cobb, August2016 be done to allow for the presence of silica rick rocks near the surface. The presence of silica rich rock at the surface would be more supportive of the microtektite like quartz grains being generated from the Chicxulub impact. More detailed study of the chemistry and crystallography of the Rough Run spherules are necessary to determine their origin.

Significance of Shocked Quartz

Quartz grains with planar deformation features (PDF’s) have been reported at K/Pg boundary sites worldwide, but the size and abundance of quartz grains with PDF’s varies among sites. Comparisons between sites are limited, however, due to differing research goals and analytical procedures. Most of the studies that report shocked quartz grain abundances have been conducted at marine depositional sites, and are not generally comparable to the continental “odd conglomerate” site at Rough Run. Botswick and Kyte (1996) found that the abundance and concentration of shocked quartz also varies with preservation of the fallout layer itself, and is a function of the size-fractions sampled, and the absolute concentration of shocked quartz relative to total quartz at any locality.

Shocked quartz grains reported from sites in Europe and New Zealand are generally smaller (maximum of c.190 microns), and are less abundant than in

North America (e.g., Bohor, 1990). The largest quartz grains displaying PDF’s

(500 to 1250 microns; Bostwick and Kyte., 1996) are found in and around the

Gulf of Mexico and Caribbean (e.g., Haiti). According to Artemieva and Morgan

(2009), the mean size for shocked quartz grains found at distances less than 3000 110

Texas Tech University, Jacob Cobb, August2016 km from the Chicxulub impact site is 60 to 80 microns. Generally, larger shocked quartz grains are not as common, but they are more abundant in North America, and in areas close to the Chicxulub impact site, than in more distant areas.

The four grains from the “odd conglomerate” that appear to show planar deformation features are all larger than 200 microns. However, the sample was sieved prior to analysis to remove fine grains, and so for the most part grains under about 65 microns were not even examined. Instead, coarser grains were quickly scanned through a binocular scope to detect those with more obvious planar features or possible PDF’s. As a result, the larger grains were selected for examination, because planar features were easier to recognize among loose grains viewed through a binocular scope. Although only 4 quartz grains with apparent

PDFs were found in 122 grains from the “odd conglomerate,” it appears that the actual fallout layer itself may not be preserved here, grains were not examined in a systematic fashion, and many of the grains selected were not quartz (i.e., spherules or feldspar grains that only appeared to be quartz under initial examination with a binocular scope). The overall abundance and size distribution of quartz grains with

PDF’s in the “odd conglomerate” is therefore uncertain.

Interpretation of the ‘odd conglomerate’

Several of the possible origins for the ‘odd conglomerate’ (outlined in chapter 1) seem unlikely in light of the observations described above. For example, striking differences in its thickness, sedimentary structure, grainsize, and

111

Texas Tech University, Jacob Cobb, August2016 composition make it unlikely that the ‘odd conglomerate’ is a ‘normal’ fluvial channel deposit. Deposition of the conglomerate on both upthrown and downthrown sides of the fault at Rough Run East, rounding of the gravel clasts, and their unique composition make it unlikely that the ‘odd conglomerate’ was derived from that local fault scarp. No extra-basinal clast types are found in the

‘odd conglomerate’, as might be expected during a major episode of down-cutting due to base-level change or regional tectonism – for example, as is observed in the base of the underlying Javelina Formation, and in the overlying Hannold Hill

Formation (attributed to episodes of tectonism by Lehman, 1991). The unusual features of the ‘odd conglomerate,’ its stratigraphic position at or around the K/Pg boundary, and its general similarity to beds interpreted as impact-generated tsunami deposits at the K/Pg boundary in marine strata of northern Mexico (e.g., Lawton et al., 2005) suggest that it may have a similar origin.

Comparison with modern tsunami deposits

Studies of modern tsunami deposits, as well as ancient sediments that have been interpreted as results of tsunami, are based on coastal or shallow marine depositional environments. The Rough Run East area was an inland fluvial floodplain several hundred kilometers landward of the shoreline at the time of the

K/Pg boundary, and so there may be no modern (or ancient?) analogs that might serve as a model for effects that would be expected if a tsunami were propagated upstream inland from the coast that far.

Peters and Jaffe (2010) identified several characteristics of modern tsunami 112

Texas Tech University, Jacob Cobb, August2016 deposits: a sharp erosional basal contact, a geometry that forms landward-thinning sand sheets, deposit thickness of 1 to 30 cm, few depositional layers (typically 1 to

4), normal grading, mud cap, rip-up clasts, boulders, soft sediment deformation features (flame structures), and a coastal sediment source. It is typical for thin layers of fine sand, silt, or clay to separate individual layers (Jaffe et al., 2003;

Razzhigaera et al., 2006). Rip-up clasts (composed of cohesive mud and soil eroded from the underlying surface, transported and deposited by the tsunami) are a common feature of recent tsunami deposits (Shi et al., 1995; Nanayama et al.,

2000; Gelfenbaum and Jaffe 2003: Jaffe et al., 2003; Fritz et al., 2007; Hawkes et al., 2007; Morton et al., 2007; Choowong et al., 2008; Matsumoto et al., 2008;

Nichol and Kench, 2008; Paris et al., 2009; Srinivasaluet al., 2009; Srisutam and

Wagner, 2009), and these are particularly common in the lower part of the tsunami deposit or in the mud cap (Goff et al., 2004).

Not all of these features may be preserved in every tsunami deposit, depending on environment and varied intensity of erosional processes. In the case of the ‘odd conglomerate’ some of these features are apparent (erosional base, multiple depositional units, normal grading, rip-up clasts, and boulders) but all of these might result from other depositional processes, and are not particularly diagnostic for tsunami. The landward- thinning depositional sand sheet geometry cannot be assessed due to the limited nature of the outcrop at Rough Run East. A coastal sediment source can be ruled out given the results of petrographic study of the ‘odd conglomerate’ (see chapter 4), but this might be expected given its location at such great distance from the shoreline. Although there is not a distinct

113

Texas Tech University, Jacob Cobb, August2016 mud cap over the ‘odd conglomerate’ it does fine upward to the overlying unionid- bearing sandy lacustrine mudstone (unit 9).

The multiple layers of a tsunami deposits are formed by multiple tsunami waves. Tsunami deposits have been noted by Hori et al. (2007) to alternating layers coarse-grained and fine-grained deposits that overlay each other. The alternating layers is generated by the incoming and outgoing of tsunami waves, and the multiple sets of tsunami waves allows for multiple layers to form. Also, it is believed that the source of the coarse-grained sediments are generated from the up-flow.

At one location (site P) the ‘odd conglomerate’ exhibits a truncated flame structure (figure 2.23). Matsumoto et al. (2008) documented similar structures in modern tsunami deposits of Thailand. This type of structure is typically interpreted as a result of dewatering following a strong unidirectional current, and associated with multilayer deposits created by successive waves of a tsunami (Peters and

Jaffe, 2010). The truncated flame structure is characterized by protrusion of the fine-grained upper portion of an underlying layer into the coarse-grained lower portion of the overlying layer. The tops of the protrusions are inclined in the downstream direction and have flat truncated tops. This structure forms when sediment accumulates during a stagnant period between tsunami waves, and contains a high concentration of mud that allows for ductile deformation induced by the following wave. Similar structures have been documented in other depositional settings, however, and are not diagnostic of tsunami activity.

Syndepositional faults, such as the one that affected deposition of the ‘odd

114

Texas Tech University, Jacob Cobb, August2016 conglomerate’ at Rough Run East, have been attributed to seismic activity resulting from bolide impacts, such as the Chicxulub impact. Smit et al. (1996) and Denne et al. (2013) concluded that seismic activity due to the Chicxulub impact caused faulting and large- scale slumping in areas within and surrounding the Gulf of Mexico (e.g., at Moscow Landing, La Lajilla, and Mimbral) and triggered large mass-flows (e.g., at Bochil, in Mexico, and Guatemala). All of these sites are in shallow to deep marine environments, but they indicate that faults were generated over a wide area due to the bolide impact at Chicxulub. The fault at Rough Run East may have a similar origin.

Comparison with proximal K/Pg boundary Sites

Most K/Pg boundary sites that are very distant from the Chicxulub impact site consist of a thin ‘boundary clay’ in most cases no more than a centimeter or so in thickness, containing spherules and shocked minerals within a clay matrix, and in many cases exhibiting an iridium abundance anomaly (Artemieva and Morgan,

2009). In contrast, “proximal” K/Pg boundary sites in and around the Gulf of

Mexico are much thicker and coarser grained, with evidence for mass wasting or tsunami deposition. Sites around the Gulf of Mexico are entirely within marine deposits, however, making comparison with the ‘odd conglomerate’ unit at Rough

Run difficult.

K/Pg boundary deposits found in and around the Gulf of Mexico region differ from site to site, but according to Smit et al. (1996) there appears to be a consistent depositional sequence that can be subdivided into four basic 115

Texas Tech University, Jacob Cobb, August2016 lithological units.

Unit 1) is a basal unit that consists of poorly sorted, coarse-grained sediments, usually pebbly sandstones, filling irregular scours and channels cut within underlying uppermost Cretaceous strata. This unit generally includes spherules (interpreted as chilled melt droplets) that typically have an internal bubbly texture. There may be several sublayers within this unit, each of which is laminated, and may contain spherules, small limestone clasts, rip-up clasts, and boulders eroded from underlying units. Planktic and benthic foraminifera, and in some cases phosphatic and glauconitic grains are also present.

Unit 2) is in most cases composed of fining-upward medium- to fine-grained sandstones lenses that have filled in shallow scours or blanketed over unit 1. These lenses can display a wide variety of structures such as ripple cross-lamination and parallel- lamination. Current orientations determined from sequential lenses often display 180- degree changes in direction in successive sublayers. The sandstone layers vary in composition, but typically include foraminifera, lithic grains, and minor plant debris. ‘Armored mud balls’ may occur at the base of this unit, and are in some cases covered with spherules and limestone clasts.

Unit 3) consists of thinning- and fining-upward fine sandstone layers with small- scale cross-lamination, and alternating thin layers of siltstone or mudstone draping over the sandstone layers. The thin siltstone layers may contain grains of

Ni-rich spinel, and iridium concentrations above background level. Burrows are also generally present within the top layers of unit 3.

Unit 4) is composed of alternating layers of millimeter-scale fine sandstone

116

Texas Tech University, Jacob Cobb, August2016 and siltstone laminations. A 5 to 10 cm thick calcareous siltstone or mudstone layer is present over most K/Pg outcrops in northeastern Mexico, and at the Brazos River site in Texas.

Although the “odd conglomerate” on Rough Run Creek was deposited in a non- marine environment, its basic subdivisions show some similarity with units 1 and 2 found in the Gulf of Mexico K/Pg boundary tsunami deposits. It has a basal unit composed of poorly sorted pebble conglomerate with large boulders, rip-up clasts, and scattered spherules. It has an overlying unit that includes multiple fining-upward intervals with finer grained sandstone layers between conglomerate beds. The sandstone layers also contain some mudstone rip-up clasts, charophytes, charcoal, altered quartz grains, and spherules. Beds comparable to units 3 and 4 found in typical Gulf of Mexico K/Pg boundary deposits could be within the base of the gray mudstone overlying the “odd conglomerate,” but have yet to be studied carefully.

The “odd conglomerate” in the Rough Run Creek area may be the only example of a “proximal” non-marine K/Pg boundary site so far discovered. This may account for the differences with coastal, shallow marine, and deep marine deposits thus far documented around the Gulf of Mexico region close to the

Chixulub impact site. The distinct, thin, “distal” fall-out deposit found in the

‘boundary clay’ further inland at other non-marine sites in North America has not been identified in the Rough Run Creek section, and it may be obscure or absent here as at some other “proximal” sites.

117

Texas Tech University, Jacob Cobb, August2016

Future work

A variety of future studies could be conducted to determine conclusively whether the “odd conglomerate” actually represents the K/Pg impact horizon. For example, isotopic age determinations, even for detrital zircons in units immediately above and below the “odd conglomerate” may help further constrain its age. It would also be useful to sample systematically through the “odd conglomerate” and overlying strata to determine whether an iridium abundance anomaly may be present here. Significant anomalies have not been detected at all or even many

K/Pg boundary sites. Iridium can be easily mobilized and concentrated at redox boundaries (e.g., Colodner et al., 1992; Miller et al., 2010; Gertsch et al., 2011a,

2011b; Keller, 2014). Therefore, small (<1- 1.5ppb) Ir anomalies are thought to be unreliable impact markers. Of 345 K/Pg boundary sections identified worldwide,

85 have iridium-rich anomalies, and only 5 have large anomalies (Keller, 2014).

Nevertheless, if present, a significant Ir-abundance anomaly would help confirm the origin of the “odd conglomerate.”

A systematic study of the abundance and concentration of shocked quartz grains and spherules within the unit, and detailed single-grain chemistry, or TEM

(crystallographic method) analyses of the spherules would be useful to determine their origin. Sampling through silt and fine sand grains for quartz textures and examination of quartz grains that are between 60-80 microns for shocked quartz would also be useful. If future analyses confirm correlation of the “odd conglomerate” with the K/Pg boundary event, then more detailed studies of the

118

Texas Tech University, Jacob Cobb, August2016 sedimentary processes responsible for its deposition would also be warranted, as the theoretical predictions for flow dynamics in tsunami transmitted inland several hundred kilometers have yet to be tested.

119

Texas Tech University, Jacob Cobb, August2016

Figure 6.1. Correlation of Dawson Creek, Rough Run Amphitheater, and Rough Run East. Modified images from Lehman and Busby (2007).

120

Texas Tech University, Jacob Cobb, August2016

CHAPTER 7 CONCLUSIONS

In the Big Bend region of Texas, Upper Cretaceous and Paleocene strata are found in the Javelina and Black Peaks formations of the Tornillo Group. Whether or not the K/Pg boundary event horizon itself is actually preserved here, however, has been debated because of poor fossil preservation and lack of other age constraints in the appropriate stratigraphic interval, and a lack of mineralogical or geochemical evidence typically associated with the impact horizon elsewhere. In the present study, an exposure of the K/Pg boundary interval at a recently discovered site, referred to here as “Rough Run East,” is described in detail.

Mapping of the Rough Run East area shows that the K/Pg boundary interval here is well exposed, with minimal alluvial cover and limited structural complexity, in contrast to other sites at Dawson Creek and Rough Run Amphitheater described in earlier studies. The “odd conglomerate” bed, found previously at the Rough Run

Amphitheater site farther west, is much better exposed here over a distance of about a kilometer, and its significance is more apparent. Vertebrate fossils found above and below the “odd conglomerate,” and charophyte oogonia found in the bed itself, indicate that it was deposited at or around the time of the K/Pg boundary.

The boundary interval can also be broadly constrained with U/Pb isotopic ages – one of 69.0 ± 0.9 Ma for a tuff bed well below the boundary that had been reported previously, and a second age determination of 63.70 ± 0.47 Ma reported in the present study for zircons in a bed found well above the boundary.

121

Texas Tech University, Jacob Cobb, August2016

The “odd conglomerate” as well as an overlying lacustrine mudstone unit at Rough Run East are lenticular, and appear to occupy a broad paleo-valley incised into underlying strata. The conglomerate bed is thinner, includes very large boulders, and is generally much coarser grained than conglomerates found in typical fluvial channel deposits in the Tornillo Group. Its composition is also unusual and homogeneous, consisting of rounded sandstone clasts, abraded pedogenic carbonate nodules, mudstone ‘rip-up’ clasts, and charcoal.

Petrographic study of the common sandstone pebbles within the conglomerate indicates that the clasts were derived locally, probably from underlying or nearby weakly consolidated sandstone beds. The ‘odd conglomerate’ was deposited during or shortly after motion on a small local fault that was buried during sedimentation. At least three successive episodes of deposition are recorded in the conglomerate – each resulting in a thin fining-upward conglomerate-sandstone interval. Sediment transport took place under rapid (upper flow regime) conditions, and clasts were transported only a relatively short distance prior to deposition. A period of calm lacustrine sedimentation occurred afterward, during which mudstone with unionid bivalves accumulated.

Sand grains from the matrix of the “odd conglomerate” and from the sandstone layer at its top include a few quartz grains with planar deformation features, and spherules with ‘splash’ and ‘ablated’ morphologies. These, together with the other unusual aspects of the “odd conglomerate” suggest that this bed may record the Chicxulub impact event – the syndepositional fault triggered by

122

Texas Tech University, Jacob Cobb, August2016 the impact itself, abundant charcoal grains resulting from the ensuing firestorm, and the very coarse conglomerate generated by a high velocity flow event – perhaps the transit of tsunami waves upstream several hundred kilometers from the coastline at that time. If this interpretation is correct, then the “odd conglomerate” may provide the first documentation of this event in a proximal non-marine setting. Other well studied proximal K/Pg boundary sites around the

Gulf of Mexico and Caribbean are exclusively in coastal, shallow marine, and deep marine deposits. In contrast, other known continental K/Pg boundary sites are in distal settings where only a thin atmospheric fall- out layer is recorded.

Further detailed studies of the chemistry, mineralogy, and precise age of the “odd conglomerate” are necessary to determine whether it is actually records the K/Pg boundary event.

123

Texas Tech University, Jacob Cobb, August2016

BIBLIOGRAPHY

Alasstair G. Dawson and Iain Stewart, 2007. Tsunami deposits in the geological record. Sedimentary Geology 200, 166-183 Alvarez, L.W., Alvarez, W., Asaro, F., and Michel, H.V., 1980. Extraterrestrial cause for the Cretaceous/Tertiary extinction. Science, v. 208, p. 1095- 1108. Alvarez, W., Smit, J., Lowrie, W., Asaro, F., Margolis, S.V., Claeys, P., Kastner, M., and Hildebrand, A.R., 1992. Proximal impact deposits at the Cretaceous-Tertiary boundary in the Gulf of Mexico: A restudy of DSDP Leg 77 Sites 536 and 540: Geology, v. 20, p. 697–700, doi:10.1130/0091- 7613(1992)020<0697: PIDATC>2.3.CO;2. Alvarez, W., Claeys, P. and Kieffer, S.W., 1995. Emplacement of Cretaceous- Tertiary boundary shocked quartz from Chicxulub crater. Science, 269(5226), pp.930-935. Artemieva, N. and Morgan, J., 2009. Modeling the formation of the K–Pg boundary layer. Icarus, 201(2), pp.768-780. Bohor, B.F., 1990. Shocked quartz and more; impact signatures in Cretaceous/Tertiary boundary clays, in Sharpton, V.L., and Ward, P.D., eds., Global catastrophes in Earth history: Geological Society of America Special Paper 247, p. 335-342. Bohor, B. F., and Betterton, W. J., 1993. Arroyo el Mimbral, Mexico, K/T unit: Origin as debrisflow/turbidite, not a tsunami deposit: Proceedings, Lunar and Planetary Science Conference, v. 23, p. 143–144. Boggs, S., Krinsley, D.H., Goles, G.G., Seyedolali, A. and Dypvik, H., 2001. Identification of shocked quartz by scanning cathodoluminescence imaging. Meteoritics & Planetary Science, 36(6), pp.783-791. Bostwick, J.A., Kyte, F.T., 1996. The size and abundance of shocked quartz in Cretaceous–Tertiary boundary sediments from the Pacific basin. In: Ryder, G., Gartner, S., Fastovsky, D. (Eds.), The Cretaceous–Tertiary Event and Other Catastrophies in Earth History. In: Special Papers, vol. 307. Geological Society of America, Boulder, Colorado, pp. 403–415. Bourgeois, J., Hansen, T. A., Wiberg, P. L., and Kauffman, E. G., 1988. A tsunami deposit at the Cretaceous-Tertiary boundary in Texas. Science, v. 241, p. 567– 570. Bralower, T.J., Paull, C.K., and Leckie, R.M., 1998. The Cretaceous-Tertiary

124

Texas Tech University, Jacob Cobb, August2016

boundary cocktail: Chicxulub impact triggers margin collapse and extensive sediment gravity flows: Geology, v. 26, p. 331–334, doi:10.1130/009- 7613(1998)026<0331:TCTBCC>2.3.CO;2

Byars. C., 1981. Mexican site may be link to dinosaurs disappearance. Houston Chronicle. December 13, p. 1, continued on p. 18. Chapin, C.E. and Cather, S.M., 1981. Eocene tectonics and sedimentation in the Colorado Plateau-Rocky Mountain area. In: W.R. Dickinson and W.D. Payne (Editors), Relations of Tectonics to Ore Deposits in the Southern Cordillera. Arizona Geological Society, Digest, 14: 173-198.

Chapin, C.E. and Cather, S.M., 1983. Eocene tectonics and sedimentation in the Colorado Plateau-Rocky Mountian area. In: J.D. Lowell (editor), Rocky Mountain Foreland Basins And Uplifts. Rocky Mountain Association Geology, Denver, Colorado, pp.33-56. Chen, K.Y., Yuan, H.L., Song, J.Y., Bao, Z.A., He, G.F. and Fan, C., 2011. Zircon U-Pb Dating and Trace Element Analyses Using Laser Ablation Quadrupole Inductively Coupled Plasma Mass Spectrometry in Small Volume (10 μm). Journal of Earth Science and Engineering, 1(3), pp.53- 67. Choowong, M., Murakoshi, N., Hisada, K., Charusiri, P., Charoentitirat, T., Chutakositkanon, V., Jankaew, K., Kanjanapayont, P., and Phantuwongraj, S., 2008. 2004 Indian Ocean tsunami inflow and outflow at Phuket, Thailand. Marine Geology, v. 248, p. 179–192. Cobb, R.C. and Poth, S., 1980. Superposed deformation in the Santiago and northern Del Carmen Mountains, Trans-Pecos Texas. In: P.W. Dickerson, J.M. Hoffer and J.F. Colodner, D.C., Boyle, E.A., Edmond, J.M., and Thomson, J., 1992. Postdepositional mobility of platinum, iridium, and rhenium in marine sediments. Nature, V. 358, p. 402-404, doi:10.1038/358402a0. Cornejo-Toledo. A., and Hernandez-Osuna, A., 1950. Las anomalias gravimetricas en la Cuenca salina del istmo, planicie costera de Tabasco. Campeche y Pensula de Yucatan: Boletin de la Asociacion Mexicana de Geologos Petroleros. V. 2. P. 453-460.

Denne, R.A., Scott, E.D., Eickhoff, D.P., Kaiser, J.S., Hill, R.J. and Spaw, J.M., 2013. Massive Cretaceous-Paleogene boundary deposit, deep-water Gulf of Mexico: New evidence for widespread Chicxulub-induced slope failure. Geology, 41(9), pp.983-986.

125

Texas Tech University, Jacob Cobb, August2016

Erdlac, R.J., Jr., 1990. A Laramide-age push-up block: the structures and formation of the Terlingua-Solitario structural block, Big Bend region, Texas. Geological Society of America Bulletin, 102: 1065-1076.

Fassett, J.E., Heizler, M.T. and McIntosh, W.C., 2010. Geologic implications of an 40Ar/39Ar single-crystal sanidine age for an altered volcanic ash bed in the Paleocene Nacimiento Formation in the southern San Juan Basin. In Geology of the Four Corners country: New Mexico Geological Society 61st Annual Field Conference Guidebook (pp. 147-156). Fouch, T.D., Hanley, J.H., Forester, R.M., Keighin, C.W., Pitman, J.K., and Nichols, D.J., 1987. Chart showing lithology, mineralogy, and paleontology of the nonmarine North Horn Formation and Flagstaff Member of the Green River Formation, Price Canyon, Central Utah: a principal reference section. U.S. Geological Survey, Miscellaneous Investigations Map I-1797-A. Fritz, H.M., Kongko, W., Moore, A., McAdoo, B., Goff, J., Harbitz, C., Uslu, B., Kalligeris, N., Suteja, D., Kalsum, K., Titov,V., Gusman, A., Latief, H. Santoso, E., Sujoko, S., Djulkarnaen, D., Sunendar, H., and Synolakis. C., 2007. Extreme runup from the 17 July 2006 Java tsunami: Geophysical Research Letters, v. 34, L12602, doi:10.1029/2007GL029404. Fronimos, J.A. and Lehman, T.M., 2014. New specimens of a titanosaur sauropod from the Maastrichtian of Big Bend National Park, Texas. Journal of Vertebrate Paleontology, 34(4), pp.883-899. Gault, D.E. and Sonett, C.P., 1982. Laboratory simulation of pelagic asteroidal impact: atmospheric injection, benthic topography, and the surface wave radiation field. In L.T. Silver and P.H. Schultz (eds.) Geological Implications of Impacts of Large Asteroids and Comets on the Earth. Geological Society of America, Special Paper 190, p. 69-92. Gilmore, C.W. 1919. Reptilian faunas of the Torrejon, Puerco, and underlying Upper Cretaceous formations of San Juan County, New Mexico. U.S. Geological Survey, Professional Paper 119, 68 p. Glass, B.P., 1990. Tektites and microtektites: key facts and inferences. Tectonophysics, 171(1), pp.393-404. Gelfenbaum, G., and Jaffe, B., 2003. Erosion and sedimentation from the 17 July, 1998 Papua New Guinea Tsunami: Pure and Applied Geophysics, v. 160, p. 1969– 1999, doi:10.1007/s00024-003- 2416-y. Goff, J., McFadgen, B.G., Chague-Goff, C., 2004. Sedimentary differences between the 2002 Easter storm and the 15th century Okoropunga tsunami,

126

Texas Tech University, Jacob Cobb, August2016

southeastern North Island, New Zealand. Marine Geology 204, 235-250.

Grambast, L., 1971. Remarques phylogenetiques et biochronologiques sur les Septorella du Cretace terminal de Provence et les charophytes associees. Paleobiologie Continentale, 2, p. 1-38. Gretsch, B., Keller, G., Adatte, T., Garg, R., Prasad, V., Fleitmann, D., and Berner, Z., 20011a. Environmental effects of Deccan volcanism across the Cretaceous- Tertiary transition in Meghalaya, India. Earth and Planetary Science Letter, v. 310, p. 272-285. Gretsch, B., Keller, G., Adatte, T., and Berner, Z., 2011b. Platinum group element (PGE) geochemistry of Brazos sections, Texas, in Keller, G., and Adatter, T., eds., End- Cretaceous Mass Extinction and the Chicxulub Impact in Texas: Society for Sedimentary Geology (SEPM) Special Publication 100, p. 228-249. Gries, J.C. and Haenggi, W.T., 1970. Structural evolution of the eastern Chihuahua Tectonic Belt. West Texas Geological Society Publication, 71- 59: 119-137.

Gulick, S.P.S., Christeson, G.L., Barton, P.J., Grieve, R.A.F., Morgan, J.V. and Urrutia‐Fucugauchi, J., 2013. Geophysical characterization of the Chicxulub impact crater. Reviews of Geophysics, 51(1), pp.31-52. Haenggi, W.T. and Gries, J.C., 1970. Structural evolution of the northeastern Chihuahua Tectonic Belt. SEPM Permian Basin Section, Publication., 70- 12: 55-69. Hansen, T., Farrand, R. B., Montgomery, H. A., Billman, H. G., and Blechschmidt, G., 1987. Sedimentology and extinction patterns across the Cretaceous- Tertiary boundary interval in East Texas. Cretaceous Research, v. 8, p. 229–252. Hart, M.B., Harries, P.J. and Cárdenas, A.L., 2013. The Cretaceous/Paleogene boundary events in the Gulf Coast: comparisons between Alabama and Texas. Gulf Coast Association of Geological Societies Transactions, p. 235-256. Hartnell, J.A., 1980. The Vertebrate Paleontology, Depositional Environment, and Sandstone Provenance of Early Eocene Rocks on Tornillo Flat, Big Bend National Park, Brewster County, Texas. Unpublished M.S. thesis, Louisiana State University, Baton Rouge, La., 74 pp. Hawkes, A.D., Bird, M., Cowie, S., Grundy-Warr, C., Horton, B.P., Hwai, A.T.S., Law,L., Macgregor, C., Nott, J., Ong, J.E., Rigg, J., Robinson, R., Tan- Mullins, M., Sa, T.T., Yasin, Z. and Aik, L.W., 2007. Sediments deposited

127

Texas Tech University, Jacob Cobb, August2016

by the 2004 Indian Ocean Tsunami along the Malaysia– Thailand Peninsula. Marine Geology, v. 242, p. 169–190. Heitmuller, F.T. and Hudson, P.F., 2009. Downstream trends in sediment size and composition of channel-bed, bar, and bank deposits related to hydrologic and lithologic controls in the Llano River watershed, central Texas, USA. Geomorphology, 112(3), pp.246-260. Hildebrand, A.R., and Boynton, W.V., 1988. Impact wave deposits provide new constraints on the location of the K/T boundary impact [abs.]: in Global catastrophes in Earth history: An interdisciplinary conference on impacts, volcanism, and mass mortality (Snowbird, Utah, October 20-23, 1988). Houston, Texas, Lunar and Planetary Institute, p. 76-77. Hildebrand, A.R., and Boynton, W.V., 1990. Proximal Cretaceous-Tertiary boundary impact deposits in the Caribbean. Science, v. 248, p. 843–847, doi:10.1126/science.248.4957.843. Iturralde-Vinent, M. A., 1992. Ashort note on the Cuban late Maastrichtian megaturbidite (an impact derived deposit?): Earth and Planetary Science Letters, v. 109, p. 225– 228. Izett, G.A., Maurrasse, F.J.-M.R., Lichte, F.E., Meeker, G.P., and Bates, R„ 1990. Tektites in Cretaceous-Tertiary boundary rocks on Haiti: U.S. Geological Survey Open-File Report 90-635, p. 1-31. Jaffe, B., Gelfenbaum, G., Rubin, D., Peters, R., Anima, R., Swensson, M., Olcese, D., Bernales L., Gomez, J., and Riega, P., 2003. Tsunami deposits: Identification and interpretation of tsunami deposits from the June 23, 2001 Perú tsunami: Coastal Sediments ’03 Proceedings, 13 p. Keller, G., MacLeod, N., Lyons, J. B., and Officer, C. B., 1993. Is there evidence for Cretaceous- Tertiary boundary age deep water deposits in the Caribbean and Gulf of Mexico?. Geology, v. 21, p. 776–780. Keller, G., 2014. Deccan volcanism, the Chicxulub impact, and the end-Cretaceous mass extinction: Coincidence? Cause and effect?. Geological Society of America Special Papers, 505, pp.57-89. Kellum, L. B., 1937. The geology and biology of the San Carlos mountains, Tamaulipas, Mexico: Ann Arbor, University of Michigan Press, 200 p. Koch, E., and Blissenbach, E., 1960. Die gefalteten oberkretazisch-tertiaren Rotschichten im Mittel-Ucayali-Gebiet, Ostperu. Beihefte zum Geologischen Jahrbuch 43, 103 p. Koeberl, C., 1993. Chicxulub crater, Yucatan: tektites, impact glasses, and the

128

Texas Tech University, Jacob Cobb, August2016

geochemistry of target rocks and breccias. Geology, 21(3), pp.211-214. Kring, D.A., 2007. The Chicxulub impact event and its environmental consequences at the Cretaceous–Tertiary boundary. Palaeogeography, Palaeoclimatology, Palaeoecology, 255(1), pp.4-21. Kruge, M.A., Stankiewicz, B.A., Crelling, J.C., Montanari, A., Bensley, D.F., 1994. Fossil charcoal in Cretaceous–Tertiary boundary strata: evidence for catastrophic firestorm and megawave. Geochim. Cosmochim. Acta 58, 1393–1397. Lawton, T.F., Shipley, K.W., Aschoff, J.L., Giles, K.A., and Vega, F.J., 2005. Basinward transport of Chixulub ejecta by tsunami-induced backflow, La Popa basin, northeastern Mexico, and its implications for distribution of impact-related deposits flanking the Gulf of Mexico. Geology 33(2):81-84. Lehman, T. M., 1985. Stratigraphy, Sedimentology, and Paleontology of Late Cretaceous (Campanian-Maastrichtian) Sedimentary Rocks in Trans-Pecos Texas. Unpubl. Ph.D. Dissertation, Univ. Texas at Austin, Texas, 310 pp.

Lehman, T.M., 1986. Late Cretaceous sedimentation in Trans-Pecos Texas. In: P.H. Pause and R.G. Spears (editors), Geology of Big Bend Area and Solitario Dome, Texas. West Texas Geological Society. Fieldtrip Guidebook, Published, 86-82: 105-110. Lehman, T.M., 1988. Stratigraphy of the Cretaceous-Tertiary and Paleocene- Eocene transition rocks of Big Bend: discussion. Journal of Geology, 96: 627-631 Lehman, T. M., 1990. Paleosols and the Cretaceous/Tertiary transition in the Big Bend region of Texas. Geology, 18: 362-364. Lehman, T. M., 1991. Sedimentation and tectonism in the Laramide Tornillo Basin of West Texas. Sedimentary Geology, 75: 9-28. Lehman, T. M., and A. B. Coulson. 2002. A juvenile specimen of the sauropod dinosaur Alamosaurus sanjuanensis from the Upper Cretaceous of Big Bend National Park, Texas. Journal of Paleontology 76:156–172. Lehman, T.M., 2004. Mapping of Upper Cretaceous and Paleogene strata in Big Bend National Park, Texas. Geological Society of America, Abstracts with Program, 36(3): A-10. Lehman, T.M., McDowell, F.W., and Connelly, J.N., 2006. First isotopic (U/Pb) age for the Late Cretaceous Alamosaurus vertebrate fauna of West Texas, and its significance as a link between two faunal provinces. Journal of Vertebrate Paleontology 26(4):922-928

129

Texas Tech University, Jacob Cobb, August2016

Lehman, T. M., and Busbey, A. B., 2007. Big Bend Field Trip Guidebook. Society of Vertebrate Paleontology, 67th Annual Meeting, Field Trip Guidebook, 69 p. Mack, G.H. and Clemons, R.E., 1988. Structural and stragraphic evidence for the Laramide (early Tertiary) Burro Uplift in southwestern New Mexico. New Mexico Geological Society, Guidebook, 39th Field Conference, pp. 59-66. MacLeod, N. and Keller, G., 1991a. Hiatus distributions and mass extinctions at the Cretaceous/Tertiary boundary. Geology, 19(5), pp.497-501. MacLeod, N. and Keller, G., 1991b. How complete are Cretaceous/Tertiary boundary sections? A chronostratigraphic estimate based on graphic correlation. Geological Society of America Bulletin, 103(11), pp.1439- 1457.

Mahaney, W.C., 2002. Atlas of sand grain surface textures and applications. Oxford University Press, USA. Mancini, E. A., and Tew, B. H., 1993. Eustasy versus subsidence: Lower Paleocene depositional sequences from southern Alabama, eastern Gulf Coastal plain: Geological Society of America Bulletin, v. 105, p. 3–17. Matsumoto, D., Naruse, H., Fujino, S., Surphawajruksakul, A., Jarupongsakul, T., Sakakura, N., and Murayama, M., 2008. Truncated flame structures within a deposit of the Indian Ocean Tsunami: evidence of syn-sedimentary deformation: Sedimentology, v. 55, p. 1559-1570. Maurrasse, F.J.-M.R., 1980. New data on the stratigraphy of the Southern Peninsula of Haiti, in Maurrasse, F.J.-M.R., ed., Premier colloque sur la géologie d'Haïti: Port- au-Prince, p. 184-198. Maurrasse, J.-M. R., and Sen, G., 1991. Impacts, tsunamis and the Haitian Cretaceous- Tertiary boundary layer. Science, v. 252, p. 1690–1693. Maxwell, RA., Lonsdale, J.T., Hazzard, R.T., and Wilson, J.A. 1967. Geology of Big Bend National Park, Brewster County, Texas: University of Texas at Austin, Bureau of Economic Geology Publication 6711, 320 p. Mebrouk, F., Tabuce, R., Cappetta, H., and Feist, M., 2009. Charophytes from the Cretaceoeus/Paleocene of Middle Atlas (Morocco): systematic and biochronologic implications. Revue de Micropaleontologie, 52:131-139. Melendez, A. and Molina, E. 2006. Secciones estratigráficas del límite Cretácico/Terciario. Informe final para el "Proyecto Global Geosites", IGME. (inédito).

130

Texas Tech University, Jacob Cobb, August2016

Melosh, H.J., Schneider, N.M., Zahnle, K.J., Latham, D., 1990. Ignition of global wildfires at the K/T boundary. Nature 343, 251–254. Miller, K.G., Sherrell, R.M., Browning, J.V., Field, M.P., Gallagher, W., Olsson, R.K., Sugarman, P.J., Tuorto, S., and Wahyudi, H., 2010. Relationship between mass extinction and iridium across the Cretaceous-Paleogene boundary in New Jersey: Geology, v. 38, p. 867-870, doi:10.1130/2014.2505(17). Molina, E., Alegret, L., Arenillas, I., Arz, J. A., Gallala, N., Hardenbol, J., von Salis, K., Steurbaut, E., Vandenberghe, N. and Zaghbibturki, D. 2006. The Global Boundary Stratotype Section and Point for the base of the Danian Stage (Paleocene, Paleogene, "Tertiary", Cenozoic) at El Kef, Tunisia: Original definition and revision: Episodes, 29 (4), 263-273.

Montanari, A., Claeys, P., Asaro, F., Bermudez, J., and Smit, J., 1994. Preliminary stratigraphy and iridium and other geochemical anomalies across the KT boundary in the Bochil Section (Chiapas, southeastern Mexico), in New developments regarding the K/T event and other catastrophes in Earth history: Lunar and Planetary Institute. Morgan, H. J., Jr., 1931. The Velasco-Mendez contact in the vicinity of the Ebano Field, Mexico: Journal of Paleontology, v. 5, p. 42–47. Morton, R., Jaffe, B., and Gelfenbaum, G., 2007. Physical criteria for distinguishing sandy tsunami and storm deposits using modern examples. Sedimentary Geology, v. 200, p. 184–207. Muehlberger, W.R., 1980. Texas lineament revisited. In: P.W. Dickerson, J.M. Hoffer and J.F. Callender (editors), N.M. Geol. Soc. Guidebook, 31st Field Conference, Trans- Pecos Region, pp. 113-121. Muir, J. M., 1936. Geology of the Tampico region, Mexico: Tulsa. American Association of Petroleum Geologists, 300 p. Musacchio, E.A., 2000. Biostratigraphy and biogeography of Cretaceous charophytes from South America. Cretaceous Research, 21:211-220. Nanayama, F., Shigeno, K., Satake, K., Shimokaka, K., Koitabashi, S., Miyasaka, S., and Ishii, M., 2000. Sedimentary differences between the 1993 Hokkaido-nansei-oki tsunami and the 1959 Miyakojima typhoon at Taisei, southwestern Hokkaido, northern Japan: Sedimentary Geology, v. 135, p. 255-264. Nichol, S.L., and Kench, P.S., 2008. Sedimentology and preservation potential of carbonate sand sheets deposited by the December 2004 Indian Ocean

131

Texas Tech University, Jacob Cobb, August2016

tsunami: South Baa Atoll, Maldives: Sedimentology, v. 55, p. 1173–1187. O’Campo, A. C., Pope, K. O., and Fischer, A. G., 1996. Ejecta blanket deposits of the Chicxulub Crater from Albion Island, Belize, in Ryder, G.,Fastovsky, D., and Gartner, S., eds., The Cretaceous-Tertiary event and other catastrophes in Earth history: Geological Society of America Special Paper 307, p. 75–88. Olsson, et al., 2002. Sequence stratigraphy and sea-level change across the Cretaceous- Tertiary boundary on the New Jersey passive margin. In: Koeberl, C., MacLeod, K.G. (eds.), Catastrophic Events and Mass Extinction: Impacts and Beyond. Geological Society of America Special Paper, vol. 356, pp. 97-108.

Paris, R., Wassmer, P., Sartohadi, J., Lavigne, F., Barthomeuf, B., Desgages, E., Grancher, D., Baumert, P., Vautier, F., Brunstein, D. and Gomez, C., 2009. Tsunamis as geomorphic crises: Lessons from the December 26, 2004 tsunami in Lhok Nga, West Banda Aceh (Sumatra, Indonesia): Geomorphology, v. 104, p. 59–72. Paull, C.K., Caress, D.W., Gwiazda, R., Urrutia-Fucugauchi, J., Rebolledo-Vieyra, M., Lundsten, E., Anderson, K. and Sumner, E.J., 2014. Cretaceous– Paleogene boundary exposed: Campeche Escarpment, Gulf of Mexico. Marine Geology, 357, pp.392-400.

Peck, R.E., and Reker, C.C., 1948. Eocene Charophyta from North America. Journal of Paleontology, 22:85-90. Peck, R.E., and Forester, R.M., 1979. The genus Platychara from the Western Hemisphere. Review of Palaeobotany and Palynology, 28:223-236. Penfield. G. T., and Carmargo Z., A., 1981. Definition of a major igneous zone in the central Yucatan platform with aeromagnetics and gravity. In Technical Program. Abstracts and Bibliographies. Society of Exploration Geophysicists, 51st annual Meeting. Tulsa. Oklahoma. Society of Exploration Geophysicists. P. 37. Peters, R. and Jaffe, B., 2010. Identification of tsunami deposits in the geologic record; developing criteria using recent tsunami deposits (No. 2010- 1239). US Geological Survey. Pope, K. O., A. C. Ocampo, G. L. Kinsland, and R. Smith., 1996. Surface expression of the Chicxulub crater, Geology, 24, 527–530. Razzhigaeva, N.G., Ganzei, L.A., Grebennikova, T.A., Ivanova, E.D., and Kaistrenko, V.M., 2006. Sedimentation particularities during the tsunami

132

Texas Tech University, Jacob Cobb, August2016

of December 26, 2004 in Northern Indonesia: Simelue Island and the Medan Coast of Sumatra Island: Oceanology, v. 46, p. 875–890. Renne, P.R., Deino, A.L., Hilgen, F.J., Kuiper, K.F., Mark, D.F., Mitchell, W.S., Morgan, L.E., Mundil, R. and Smit, J., 2013. Time scales of critical events around the Cretaceous-Paleogene boundary. Science, 339(6120), pp.684- 687. Riveline, J., Berger, J.P., Feist, M., Martin-Closas, C., Schudack, M., and Soulie- Marsche, I., 1996. European Mesozoic-Cenozoic charophyte biozonation. Bulletin de la Societe Geologique de France, 167:453-468. Runkel, A.C., 1990. Lateral and temporal changes in volcanogenic sedimentation; analysis of two Eocene sedimentary aprons, Big Bend region, Texas. J. Sedimentary Petrology, 60: 747-760. Sambrook Smith, G.H., Ferguson, R.I., 1995. The gravel-sand transition along river channels. Journal of Sedimentary Research A65, 423–430.

Savrda, C. E., 1991. Ichnology in sequence stratigraphic studies: An example from the Lower Paleocene of Alabama. Palaios, v. 6, p. 39–53.

Schiebout, J.A., 1974. Vertebrate paleontology and paleoecology of Paleocene Black Peaks Formation, Big Bend National Park, Texas. Texas Memorial Museum, Bulletin 24, pp. 88. Schiebout, J.A., Rigsby, C.A., Rapp, S.D., Hartnell, J.A. and Standhardt, B.R., 1987. Stratigrapghy of the Cretaceous-Tertiary and Paleocene-Eocene transition rocks of Big Bend National Park, Texas. Journal of Geology, 95: 359-375. Schiebout, J.A., Rigsby, C.A., Rapp, S.D., Hartnell, J.A. and Standhardt, B.R., 1988. Stratigraphy of the Cretaceous-Tertiary and Paleocene-Eocene transition rocks of Big Bend National Park, Texas, a reply. Journal of Geology, v. 96, p. 631-634. Seyedolali, A., Krinsley, D.H., Boggs, S., O'Hara, P.F., Dypvik, H. and Goles, G.G., 1997. Provenance interpretation of quartz by scanning electron microscope– cathodoluminescence fabric analysis. Geology, 25(9), pp.787-790. Sharpton, V. L., and Ward, P.D., eds., 1990. Global catastrophes in Earth history: An interdisciplinary conference on impacts, volcanism, and mass mortality. Geological Society of America Special Paper 247. 631 p. Sharpton. V. L., Schuraytz, B. C., Burke. K., Murali, A. V., and Ryder, G., 1990a. Detritus in K/T boundary clays of western North America; Evidence against 133

Texas Tech University, Jacob Cobb, August2016

a single oceanic impact, in Sharpton. V. L., and Ward. P. D., eds., Global catastrophes in Earth history: An interdisciplinary conference on impacts, volcanism, and mass mortality. Geological Society of America Special Paper 247. P. 349-359. Sharpton. V. L., Schuraytz. B. C., and Jones. J., 1990b. Argments favoring a single continental impact at the KT boundary. Meteoritics, v. 25. P. 408-409. Sharpton, V.L., Dalrymple, G.B., Marín, L.E., Ryder, G., Schuraytz, B.C. and Urrutia- Fucugauchi, J., 1992. New links between the Chicxulub impact structure and the Cretaceous/Tertiary boundary. Nature, 359(6398), pp.819-821. Sharpton, V.L., Burke, K., Camargo-Zanoguera, A., Hall, S.A., Lee, D.S., Marin, L.E., Suáarez-Reynoso, G., Quezada-Muñeton, J.M., Spudis, P.D. and Urrutia- Fucugauchi, J., 1993. Chicxulub multiring impact basin: Size and other characteristics derived from gravity analysis. Science, 261(5128), pp.1564-1567. Sharpton, V.L., Marin, L.E., Carney, J.L., Lee, S., Ryder, G., Schuraytz, B.C., Sikora, P. and Spudis, P.D., 1996. A model of the Chicxulub impact basin based on evaluation of geophysical data, well logs, and drill core samples. The Cretaceous- Tertiary event and other catastrophes in Earth history, pp.55-74. Shi, S., Dawson, A.G., 1995. Coastal sedimentation associated with the December 12, 1992, tsunami in Flores, Indonesia. Pure and Applied Geophysics 144, 525-536.

Sigurdsson, H., D’Hondt, S., Arthur, M. A., Bralower,T. J., Zachos, J. C., van Fossen, M., and Channell,J. E. T., 1991. Glass from the Cretaceous/Tertiary boundary in Haiti: Nature, v. 349, p. 482–487.

Sky and Telescope, 1982. Possible Yucatan impact basin: Sky and Telescope, v. 63. P. 249-250. Sláma, J., Košler, J., Condon, D.J., Crowley, J.L., Gerdes, A., Hanchar, J.M., Horstwood, M.S., Morris, G.A., Nasdala, L., Norberg, N. and Schaltegger, U., 2008. Plešovice zircon—a new natural reference material for U–Pb and Hf isotopic microanalysis. Chemical Geology, 249(1), pp.1-35.

Smit, J., and Romein, A. J. T., 1985. A sequence of events across the Cretaceous- Tertiary boundary: Earth and Planetary Science Letters, v. 74, p. 155–170. Smit, J., Montanari, A., Swinburne, N.H., Alvarez, W., Hildebrand, A.R., Margolis, S.V., Claeys, P., Lowrie, W. and Asaro, F., 1992. Tektite-bearing, deep-

134

Texas Tech University, Jacob Cobb, August2016

water clastic unit at the Cretaceous-Tertiary boundary in northeastern Mexico. Geology, 20(2), pp.99-103. Smit, J., Roep, Th.B., Alvarez, W., Claeys, P., Grajales-Nishimura, J.M., Bermudez, J., 1996. Coarse grained, clastic sandstone complex at the K/T boundary around the Gulf of Mexico: deposition by tsunami waves induced by the Chicxulub impact? In: Ryder, G., Fastovsky, D., Gartner, S. (Eds.), CretaceouseTertiary Event and Other Catastrophes in Earth History. Geological Society of America, Special Paper 307, 151e182. Srinivasalu, S., Rajeshwara Rao, N., Thangadurai, N., Jonathan, M. P., Roy P. D., Ram Mohan V., and Saravanan, P., 2009. Characteristics of 2004 tsunami deposits of the northern Tamil Nadu coast, southeastern India: Boletín de la Sociedad Geológica Mexicana, v. 61, p. 111-118. Srisutam, C. and Wagner, J.F., 2009. Multiple layer identification and transportation pattern analysis for onshore tsunami deposit as the extending tsunami data–a case study from the Thai Andaman Coast. Science of tsunami hazards, 28(3), p.205. Standhardt, B.R., 1986. Vertebrate Paleontology of the Cretaceous/Tertiary transition of Big Bend National Park, Texas. Unpublished Ph.D. dissertation, Louisiana State Univ., Baton Rouge, La., 298 pp. Stinnesbeck, W., Barbarin, J.M., Keller, G., Lopez-Oliva, J.G., Pivnik, D.A., Lyons, J.B., Officer, C.B., Adatte, T., Graup, G. and Rocchia, R., 1993. Deposition of channel deposits near the Cretaceous-Tertiary boundary in northeastern Mexico: Catastrophic or" normal" sedimentary deposits?. Geology, 21(9), pp.797-800.

Stoeffler, D., and Langenhorst, F. 1994. Shock metamorphism of quartz in nature and experiment: 1. Basic observation and theory. Meteoritics, 29: 155-181. Tomlinson, S.L. 1997. Late Cretaceous and early Tertiary turtles from the Big Bend region, Brewster County, Texas. Texas Tech University, unpublished Ph.D. dissertation, 194 p. Tschudy, R.H., Pillmore, C.L., Orth, C.J., Gilmore, J.S., Knight, J.D., 1984. Disruption of the terrestrial plant ecosystemat the Cretaceous–Tertiary boundary, western interior. Science 225, 1030–1032. Turner, K. J., M. E. Berry, W. R. Page, T. M. Lehman, R. G. Bohannon, R. B. Scott, D. P. Miggins, J. R. Budahn, R. W. Cooper, B. J. Drenth, E. D. Anderson, and V. S. Williams. 2011. Geologic map of Big Bend National Park, Texas. U.S. Geological Survey Scientific Investigations Map 3142:1–84

135

Texas Tech University, Jacob Cobb, August2016

Wheeler, E.A., and Lehman, T.M., 2000. Late Cretaceous woody dicots from the Aguja and Javelina Formations, Big Bend National Park, Texas, USA. International Associateion of Wood Anatomists Journal, 21(1): 83-120. Williamson, T.E. 1996. The beginning of the age of mammals in the San Juan Basin, New Mexico: biostratigraphy and evolution of Paleocene mammals of the Nacimiento Formation. New Mexico Museum of Natural History and Science, Bulletin 8, 140 p. Lucas, S.G., Cather, S.M., Abbott, J.C. and Williamson, T.E., 1997. Stratigraphy and tectonic implications of Paleogene strata in the Laramide Galisteo Basin, north- central New Mexico. New Mexico Geology, 19(4), pp.89-95. Woodward H. N., 2005. Bone histology of the Sauropod dinosaur Alamosaurus sanjuanensis from the Javelina Formation, Big Bend National Park, Texas. Texas Tech University, unpublished M.S. thesis, 224 p.

136

Texas Tech University, Jacob Cobb, August2016

APPENDIX

Section A

Figure 2.9. Section A of ‘odd conglomerate’ at western side of Rough Run East outcrop. This section shows two distinct conglomeratic intervals separated by an intervening sandstone bed (image taken by Brian Cobb). Mean grain size of sand fraction (vf to vc), mean grainsize of gravel fraction (g to b), and maximum clast size (x) shown in columns on left side. See fig. 2.11 for explanation of clast composition.

137

Texas Tech University, Jacob Cobb, August2016

Section C

Figure 2.10. Section C of the ‘odd conglomerate’ showing a large indurated cobble. Adjacent outcrop surface is covered by younger colluvium (image taken by Brian Cobb).

138

Texas Tech University, Jacob Cobb, August2016

Section D

139

Texas Tech University, Jacob Cobb, August2016

Section E

Figure 2.12. Section E of the ‘odd conglomerate’ showing three distinct conglomeratic intervals; photos below show the lower grain-supported conglomerate bed with a large laminated indurated sandstone cobble (image taken by Brian Cobb).

140

Texas Tech University, Jacob Cobb, August2016

Section F

Figure 2.13. Section F of the ‘odd conglomerate’ showing three distinct conglomeratic intervals separated by laminated sandstone. This section has large ‘rip-up’ clasts of purple mudrock (under pencil in photo) and reworked charcoal clasts within each layer (images taken by Brian Cobb).

141

Texas Tech University, Jacob Cobb, August2016

Section G

Figure 2.14. Section G of the ‘odd conglomerate’ showing merger of two conglomeratic layers laterally into a composite bed (images taken by Brian Cobb).

142

Texas Tech University, Jacob Cobb, August2016

Section H

Figure 2.15. Section H of the ‘odd conglomerate’ showing single conglomeratic bed with indurated cobbles of laminated sandstone and mudrock (images taken by Brian Cobb).

143

Texas Tech University, Jacob Cobb, August2016

Section I

Figure 2.16. Section I of the ‘odd conglomerate’ showing single bed with three sparse conglomeratic sandstone layers composed mostly of mudstone clasts (images taken by Brian Cobb).

144

Texas Tech University, Jacob Cobb, August2016

Section J

Figure 2.17. Section J of the ‘odd conglomerate’ showing very thin bed with large cobbles and boulders of sandstone and mudrock (images taken by Brian Cobb).

145

Texas Tech University, Jacob Cobb, August2016

Section K

Figure 2.18. Section K of the ‘odd conglomerate’ showing the largest boulder observed in the Rough Run East outcrop, a large slab of laminated sandstone within and projecting above the finer conglomerate bed. To the right of the boulder, fine granule gravel is concentrated rather than more typical pebble gravel to the left. (images taken by Brian Cobb).

146

Texas Tech University, Jacob Cobb, August2016

Section L

Figure 2.19. Section L of the ‘odd conglomerate’ showing abrupt thickening of entire interval on downthrown side of fault, and large laminated sandstone cobbles at base (images taken by Brian Cobb).

147

Texas Tech University, Jacob Cobb, August2016

Section M

Figure 2.20. Section M of ‘odd conglomerate’ showing two depositional units, without intervening sandstone layer, and large sandstone and mudstone cobbles at two levels (images taken by Brian Cobb).

148

Texas Tech University, Jacob Cobb, August2016

Section N

Figure 2.21. Section N of the ‘odd conglomerate’ with single distinct bed, and thin secondary calcite veins present (images taken by Brian Cobb).

149

Texas Tech University, Jacob Cobb, August2016

Section O

Figure 2.22. Section O of the ‘odd conglomerate’ showing subdivision into different colored intervals - upper and lower gray zones, and middle yellow zone (images taken by Brian Cobb).

150

Texas Tech University, Jacob Cobb, August2016

Section P

Figure 2.23. Detailed view of middle of section P (above) showing soft sediment deformation (flame structure?) truncated at base of conglomerate bed. (images taken by Brian Cobb).

Figure 2.24. Abrupt termination of ‘odd conglomerate’ (below) at eastern end of outcrop near section P (images taken by Brian Cobb).

151