The Lower Cretaceous Paluxy Sand in Central Texas WILLIAM A
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Bulletin No. 2 The Lower Cretaceous Paluxy Sand in Central Texas WILLIAM A. "Creative thinking is more important than elaborate Frank Carney, Ph.D. Professor of Geology Baylor University 1929-1934 Objectives of Geological Training at Baylor The training of a geologist in a university covers a few years ; his education continues throughout his active life. The purposes of training geologists at Baylor University are to provide a sound basis of un derstanding and to foster a truly geological point of view, both of which are essential for continued professional growth. The staff considers geology to be unique among sciences since it is primarily a field science. All geologic research including that done in laboratories must be firmly supported field observations. The student is encouraged to develop an inquiring objective attitude and to examine critically all geological concepts and principles. The development of a mature and professional attitude toward geology and geological research is a principal concern of the department. THE BAYLOR UNIVERSITY PRESS WACO, TEXAS BAYLOR GEOLOGICAL STUDIES BULLETIN NO. 2 The Lower Cretaceous Paluxy Sand in Central Texas WILLIAM A. BAYLOR UNIVERSITY Department of Geology Waco, Texas Spring, 1962 Baylor Geological Studies EDITORIAL STAFF F. Brown, Jr., Ph.D., Editor stratigraphy, paleontology O. T. Ph.D., Adviser stratigraphy-sedimentation, structure, geophysics-petroleum, groundwater R. L. Bronaugh, M. A., Business Manager archeology, geomorphology, vertebrate paleontology James Dixon, Jr.. Ph.D. stratigraphy, paleontology, structure Walter T. Huang, Ph.D. mineralogy, petrology, metallic minerals The Baylor Geological Studies Bulletin is published Spring and Fall, by the Department of Geology at Baylor University. The Bulletin is specifical ly dedicated to the dissemination of geologic knowledge for the benefit of the people of Central Texas. The pub lication is designed to the results of both pure and applied research which will ultimately be important in the economic and cultural growth of the Central Texas region. Additional copies of this bulletin can be obtained from the Department of Geology, Baylor University, Waco, Texas. $1.00 CONTENTS Page Abstract ............. Introduction 5 Purpose ............ 8 Location ............ 8 Procedures ........... 8 Previous work .......... 8 Acknowledgments . 10 ............. 10 Description ............ 10 distribution . Thickness ............ Paleontology ............ 14 Stratigraphy . : ' . Facies relationships . Depositional environments 18 Age assignment ... ....... 21 Economic geology . 21 General features ........... 21 Agriculture . ... 21 Water supply . 21 South Bosque oil field . ... 21 Conclusions . 22 References ............ 23 Appendix I Localities . 24 Appendix II Production from the South Bosque oil field, McLennan County, Texas Index . - . .26 ILLUSTRATIONS FIGURES Page 1. Index map ............ 6 2. Nomenclature chart, Comanchean series, central Texas ... 7 3. Outcrop, isopach and locality map, Paluxy sand, central Texas . 9 4. Cross sections, Paluxy sand and adjacent strata, central Texas . 11 A. Northwest-southeast cross section B. North-south cross section 5. Physiographic divisions, central Texas ...... 12 6. Diagrammatic fades cross Trinity and Fredericksburg groups, central Texas . 13 7. Fine grains of well sorted, frosted sand, Paluxy formation, southern Erath County . 15 8. Very fine grains of poorly sorted, frosted quartz Trinity group, northern Erath County 15 9. Cross-bedded Paluxy sand beneath Walnut formation, Somervell County 16 10. Cross-bedded Paluxy sand Walnut formation, Bosque County ........... 16 11. Cross-bedded channel sand, Paluxy Rough Creek, 5.5 miles northwest of Walnut Springs, Bosque County ... 19 12. Horizontal beds of Paluxy sand, County .... 20 13. Horizontal beds of Paluxy sand with thin indurated ledges, Bosque County ........... The Lower Cretaceous Paluxy Sand in Central Texas WILLIAM A. ATLEE ABSTRACT The Paluxy formation is composed predominantly of to non-marine. Non-marine environments include flu to very fine-grained quartz sand. The Paluxy sand vial and perhaps eolian dunes, characterized by steeply attains a maximum thickness of about 190 feet in north dipping beds. Marine environments include fluvio- western Erath County and pinches out southward in and shallow shelf deposition, typified thin, southern Hill, McLennan, and Coryell counties. The horizontal, evenly sand and typical marine formation is both vertically and laterally gradational cross-beds. with clay, marl, and limestone beds of the overlying Petrographic examination and comparison suggest a Walnut formation. Downdip thinning results from in- genetic relationship between the quartz sands of the with basinward facies of the Walnut for upper Trinity group and the Paluxy formation. How mation. ever, both sand units represent several cycles of deposi Field and subsurface evidence indicates that the Pa tion. luxy formation is the basal formation of the Fredericks- The Paluxy formation has several economic aspects burg group. In the area studied the Paluxy sand is beneficial to the central Texas area. Arenaceous soils sharply separated from the limestone sequence of the developed upon the Paluxy formation are agriculturally underlying Glen Rose formation. Field observations important. Since 1902, oil has been produced from the and subsurface information suggest that the Glen Rose- Paluxy sand in the shallow South Bosque field, McLen Paluxy contact represents a hiatus of greater magnitude nan County. In the northern part of the area the Pa than the diastemal Paluxy-Walnut contact. The Paluxy- Walnut contact reflects the transgressive nature of the luxy sand is an important southward downdip Walnut formation. the Paluxy water becomes less Along the out Several environments controlled the deposition of the crop thick sections of homogeneous quartz sand are po Paluxy conditions ranged from shallow marine tential sources of material for glass manufacture. The Comanchean series of Lower Cretaceous age in allied beds of strata" (idem). As further surface and central Texas (fig. is divided into three in subsurface investigations shed light on the true strati- ascending order these are the Trinity, Fredericksburg, graphic relationships of the formations which constitute and Washita groups. One of the few major strati- these divisions, it apparent that many carto graphic problems which the noted geologist R. T. graphic units are both laterally and vertically grada left to later investigators of Comanchean stratigraphy tional. Recently, Lozo and Stricklin p. 68) re (fig. 2) in central Texas, was the precise boundary be vised Hill's (1901) original 'divisions" based on fossil tween the Trinity and Fredericksburg groups or divi assemblages and relationships to ". tectonic- sions. sedimentary lithogenetic entities of subseries rank here Hill (1901, p. 118) subdivided the Comanchean series after called divisions." These divisions continue to ful into "divisions." The term was ''. intended to in fill the stratigraphic requirements of the cartographically clude subgroups of paleontologically or lithologically and lithologically defined group. The formations of the Fredericksburg group (fig. 2), as used in this report, Modified from a thesis submitted in partial fulfillment of the requirements for the M.S. degree in Geology, Baylor University, consist of the Paluxy Walnut clay, Comanche 1960. Peak limestone, and Edwards limestone. 6 BAYLOR GEOLOGICAL STUDIES Fig. 1. Index map. UOISIAIQ 8 BAYLOR GEOLOGICAL STUDIES PURPOSE series as a distinctive Hthologic and faunal unit of the American Cretaceous (1852), though he incorrectly Various interpretations have postulated for the classified these rocks as Turonian or Senonian in age. lateral and vertical stratigraphic relationships of the In G. G. Shumard applied the name "AVashita Paluxy sand with the overlying clay and under group" to strata near Fort Washita, Oklahoma. Two lying Glen Rose limestone in central Texas (figs. 1, 2). years later, Jules Marcou (1856) confirmed the The purpose of this report is to combine information obtained from surface studies with subsurface electrical existence of Lower Cretaceous strata in North America log, drillers' log, and other well data to form a more when he correctly identified and dated as Neocomian a complete and coherent picture of the stratigraphic rela group of fossils collected by G. G. Shumard from Texas tionships of the Paluxy sand within the area. Also in and western Oklahoma. cluded is a discussion of the general geology of the for In 1860 B. F. Shumard described the Cretaceous mation and its economic importance to central Texas. formations recognized in Texas and assembled them into a stratigraphic section. Some of the formations described by Shumard were named for geographic LOCATION localities and others were named for faunal the paleontologic names have since been replaced with The area of this report includes all or portions of Mc geographic names. Lennan, Bosque, Erath, Hood, Somervell, Hill, Coryell, Little was known of the geology of the Paluxv sand and Hamilton counties (fig. in central Texas. prior to R. T. Hill's initial investigation of the Lower Cretaceous section which began in 1886. Hill (1887, PROCEDURES p. 303) provisionally divided the Comanchean strata into a lower Fredericksburg and an Washita di Field and laboratory work was completed during the vision following G. G. Shumard's (1854) use of latter part