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31295002537222.Pdf (4.834Mb) PALEONTOLOGY AND PALEOENVIRONMEXT OF TME JAXES GRAVEL QUARRY, CROSBY COUNTY, TEXAS by DAVID D. PROCTOR A THESIS IN GEOSCIENCES Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirei ients for the Degree of MASTER OF SCIENCE Approved Decei iber, 1980 f /i— 'r' I ^ÎCO TABLE OF CONTENTS LIST OF FIGURES iv LIST OF PLATES v • I. INTRODUCTION 1 Setting 1 Scope of Study 2 Objective and Statement of Problems 3 Methods of Study 3 II. PREVIOUS INVESTIGATIONS 6 Taphonoray 6 Geology 12 Paleontology 15 Stratigraphic Position 19 Age 24 III. GEOLOGY OF THE JANES QUARRY 28 Physical Stratigraphy 28 Environment of Deposition 33 IV. PALEONTOLOGY OF THE JANES QUARRY 35 Faunal Content •. 35 Faunal Interpretations 42 V. BIOSTRATIGRAPHY AND AGE OF THE JANES QUARRY 44 Biostratigraphy 44 Age 44 VI. TAPHONOMY OF THE JANES QU.\RRY 46 Taphonomic Observations and Interpretations 46 Evaluation of Taphonomic Procedures 49 ii VII. RECONSTRUCTION OF PALEOENVIRONMENT AND CONDITIONS OF INTERMENT 52 VIII. CONCLUSIONS 54 LIST OF REFERENCES CITED 56 PLATES 62 111 LIST OF FIGURES Figure 1. Voorhies Dispersal Groups 11 2. Composite Stratigraphic Section of the Pliocene Formations on the Southeastern Llano Estacado 14 3. Wood Committee Provincial Ages 21 4. Stratigraphic Sections 30 5. Fauna of the Janes Gravel Quarry 36 IV LIST OF PLATES Plate 1. Map of the Janes Gravel Quarry 64 2. View showing modem quarry wall 66 3. Stratigraphic Section 1 66 4. Stratigraphic Section 2 68 5. Stratigraphic Section 3 68 6. Clay drapes on braid bar islands 70 7. Close up of sand filled dessication cracks in the clay drapes of the braid bar island 70 8. Overview of right maxillary of Osteoborus validus frora the collection of Mr. Robert Morrow 72 9. Gomphotheriura raandible frora the collection of Mr. Robert Morrow 72 10. Crushed skull of Goraphotheriura (TTU-P-9500) 74 11. Upper and lower cheek teeth of Pliohippus sp. (TTU-P-9502-9507) 74 12. Upper cheek teeth of Neohipparion sp. (TTU-P-9508-9511) ... 76 13. Right upper cheek teeth of Neohipparion sp. frora the collection of Mr. Robert Morrow 76 14. Diagrara of u.pper horse tooth 78 15. Isolated upper tooth of Nannippus sp. (TTU-P-9512) 80 16. Mandibular fragment of an unidentified rhinocerotid (TTU-P-9513) 80 17. Partial left ramus of Megatylopus sp. (TTU-P-9514) 82 18. Canon bone frora a large camel cf. Megatylopus sp. from the collection of Mr. Robert Morrow 82 V CHAPTER I INTRODUCTION In the spring of 1974, the Division of Vertebrate Paleontology of the Museum of Texas Tech University was alerted to an extremely large concentration of bones at a local gravel quarry. At the request of the operators of the Janes Gravel Quarry, a group of students inspected the deposit. At this time it was noted that the faunal remains consisted mainly of proboscidean and equid fossils occurring in a coarse sand and gravel sequence. In the fall of 1974, another team of students, under the direction of Dr. Pat Rich, revisited the locality. As the locality represented an ideal taphonomic occurrence, it was decided that the writer should pursue such a study as part of his Master's prograra. Setting The Janes Gravel Quarry is located nine and one quarter miles east of Slaton, Texas in the southwest portion of Crosby County. Lying 150 feet below the flat plain on an erosional bench, the quarry site occurs on the southwest side of the headward eroding canyon of Yellowhouse Draw. This erosional bench, which represents the resistant basal section of the Bridwell Formation, can be traced for railes along the eastern edge of the escarpment (Frye and Leonard 1957) . Within the quarry, the bone bearing gravels occurred approximately 21 feet below the surface. Quarry operators encountered the bones while clearing overburden above their paying gravels located between approximately 26 and 50 feet below the original ground surface. The fauna seemingly was Pliocene in age, but whether it belonged in the Clarendonian or Hemphillian land raararaal ages was not immediately apparent. From discussions with heavy machinery operators it was possible to reconstruct an original probable extent of some 31 acres (Plate 1). These inforraants, among whom were a number of araateur collectors, also indicated that the nature and content of the bone bed had been similar throughout its entire extent (i.e. large quantities of 'elephant' and horse bones). Tnis in itself was a cause for considerable wonder because the norraal habits of modem elephants seeraed to preclude the possibility of such a large concentration of individuals in one place. Scope of Study The original questions posed for this study were based on the assuraption that the biostratigraphic relationships and paleoenvironment of the Pliocene Ogallala Forraation were reasonably well understood, and that the only unique problera for study was the taphonomic history of the bone bed itself. After the initial fieldwork, however, a scan of the local geologic and paleontologic literature indicated that much confusion exists. In fact the relationship between the two local forraations within the Ogallala Group, the Couch and the Bridwell, in areas other than their referenced type areas was poorly understood. The coincidence of the two majpr Pliocene faunal ages, the Clarendonian and the Hemphillian, with these two forraations could not be assumed, and the paleoenvironmental reconstructions were raerely untested assuraptions. These problems led to a rapid restatement of the study. Qbjective and Statement of Probleras The objective of this study is to derive and present a paleo- environraental reconstruction of the tirae at which the bone bed in the Janes Gravel Quarry was deposited. In order to do this, the following questions were posed: 1. What is the stratigraphic position of the fauna? 2. What is the content of the fauna? 3. Víhat is the actual age of the fauna? 4. How did the faunal elements become interred? 5. What was the idepositional environraent? An additional procedural problem was formulated during the planning of the research. 6. Can the taphonomic concept of investigating the relationship of the faunal elements to the sediments in which they occur be used as a procedural approach to paleoenvironraental reconstruction? Methods of Study With the above probleras in raind, the writer proposed that taphonomy be utilized as an approach to the fieldwork. Vertebrates and vertebrate associations can be highly reflective of local environ- ment, while clastic sediments are also indicative of both the local depositional environment and the general source area frora which they are derived. The taphonomic procedure provides data on both areas. The variety of observations and measurements which should be made during a careful taphonomic study have been sumraarized by Munthe and McLeod (1975) . In addition, Munthe and McLeod (l^T'S) developed a series of forms to be used to facilitate the making of observations both on recent and fossil specimens. Collection of this extended amount of data reflects an optiraum research situation, but there was not enough tirae to make all these observations at the Janes Quarry. In order to fit conditions at the quarry, a two stage field procedure was developed At two different times quarrying activities were shifted from promising fossiliferous areas to allow the writer to salvage as rauch raaterial as possible. Both periods occurred during regular seraesters and therefore fieldwork had to be conducted between classes or done on weekends. The action of the earth stripper resulted in almost total destruction of the faunal material, thus the initial goal was the excavation of specimens that would document the content and age of the bone bed for later workers. With a limited crew of two or three individuals, only sraall areas could be cleared and worked. In these . areas bone orientation was raapped on all pieces large enough to raeasure. Only identifiable specimens were collected. In addition approximately a ton of the sediment was collected and wet screened in an attempt to locate small animal remains. In order to recover data during norraal quarrying activities another approach was used. Two prominent points, that were a substan- tial distance apart, were used as stations from which bearings were taken in areas that were being stripped. As faunal material appeared, bearings to each of these points were taken with a Brunton Compass. The intersection of the two rays marked the location of the specimen. From the earlier, more intensive excavations it was known that most of the fauna consisted of proboscidean, equid, caraelid, and rhino- cerotid remains, and (where possible) faunal eleraents were identified in place and orientations were raeasured with a Brunton Compass. In addition, an observation on the stage of wear exhibited by the dental elements was raade. Using this technique it was found that one person could make notes on apprximately one quarter of the material exposed by the stripper, while two persons could record as much as three quarters of the material as it was exposed. These simple, rapid raethods were not designed to produce vast quantities of data on which to base hypotheses concerning the nature of the bone bed. Rather they were intended to produce data which would allow the testing of tentative hypotheses already developed from inforraation gathered during the first stage, intensive excavations. In addition to the collection of faunal inforraation, there was also an eraphasis on the collection of sediraentological data. A series of stratigraphic sections were measured and described. Observations and interpretations were raade where possible in the field. Samples of the sand and gravel were taken and later examined to determine mineralogical content. CHAPTER II PREVIOUS IN'VESTIGATIONS Taphonoray Many geologists and paleontologists are not familiar with the concepts of taphonoray.
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