RICE UNIVERSITY PROVENANCE AND PALEOTECTONIC SETTING OF CONGLOMERATES IN THE VIRGILIAN HOLDER FORMATION, NORTHERN SACRAMENTO MOUNTAINS, NEW MEXICO BY CHARLES PRESTON DUNNING A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS Thesis Director's Signature: ABSTRACT PROVENANCE AND PALEOTECTONIC SETTING OF CONGLOMERATES IN THE VIRGILIAN HOLDER FORMATION, NORTHERN SACRAMENTO MOUNTAINS, NEW MEXICO Charles Preston Dunning The Late Pennsylvanian (Virgilian) Holder Formation of the Sacramento Mountains, south central New Mexico, is composed of clastic and carbonate rocks cyclically deposited on the narrow Sacramento Shelf. Coarse channel fill con¬ glomerates are often found in the lower terrigenous member of the cycles. The cycle thicknesses, coarse terrigenous clastic thicknesses and the trend of the conglomerate chan¬ nels respond to both the pre-cycle topography and the growth of topographic structures during deposition of the cycle. The prominence of the tectonic structures appear to have increased during the early Virgilian to a maximum during cycle 6. The relatively thin and uniform thicknesses during cycle 7 indicates that growth of shelf structures was at a minimum. Growth was renewed during cycles 8 and 9, documented by the rejuvenation of the La Luz Anticline and the Dry Canyon Syncline. Paleotransport directions from the lower 9 cycles generally indicate southwesterly transport, away from the Pedernal Uplift and into the Orogrande Basin. Where channels are recognized, there is good correlation between channel trends and transport directions. During the height of the transgressive phase of the cycle, the Paleozoic detritus derived from the Pedernal Uplift was involved in high energy coastal processes at the base of the escarpment. It was in this environment that Paleozoic chert and Cambro-Ordovician Bliss Formation quartz¬ ite clasts were rounded, and whatever feldspars and Pre- Pennsylvanian limestones that has not been reduced insitu on the uplift or in transport, were destroyed. High energy runoff from the uplift spread the cherts, quartzites and quartz sand across the shelf as clastic flows. These flows cut the channels, incorporating shelf linestones of Virgilian age into the Virgilian conglomerate deposits. Acknowledgments I would like to gratefully acknowledge the New Mexico Bureau of Mines and Mineral Resources and its director, Frank Kottlowski, for funds supporting field and laboratory work, and the Sigma Xi organization for additional financial assistance. Dr. James Lee Wilson deserves much credit for comple¬ tion of this thesis. He suggested the study, helped obtain funding, spent time in the field and was involved in all stages of lab work and writing. His support, encouragement and constructive criticism are certainly appreciated. Thanks also go to the other members of my committee, Drs. John B. Anderson and John E. Warme, for their help in the field and for critically reading the thesis. Mr. Ben Donegan, Leonard Resources, Albuquerque, New Mexico, was very helpful in sharing his knowledge of previous work in the area. I benefited from the assistance of and discussions with many students in the field, particularly John Van Wagoner, Dennis Kurtz, Joan Mussler Spaw, Ann Leavesley, Camille Hueni, and Jerry Kennedy. Mr. and Mrs. John Anderson of Roswell, New Mexico, and their daughter, Jenna, made the field season more enjoyable by opening their home to me on numerous occasions. I wish to acknowledge the help of many people at Rice University: Bill Lambert for his ongoing encouragement; Keith Shanley for drafting and other assistance; Ken Hahn for help with photography, for reading the text, and for his invaluable assistance in preparing for the thesis defense; John Van Wagoner, Dennis Kurtz and Roy Adams for many hours discussing the various geologic aspects of the thesis and reading the text; and Mary Bogert for typing and for her constant encouragement. Appreciation is expressed to Mrs. James Lee Wilson for the use of her office and typewriter in preparing the rough copy, and to Charlena Williams for her fast and expert typing of the final copy. Appreciation is extended to Mr. James Bogert, Garland, Texas, for my "home away from home" and to my own parents and family for their financial and moral support during the past three years. And a very special acknowledgment goes to two individuals who have been most important to me these diffi¬ cult past two years; Cane, my field assistant--and my dog— and of course Mary--the little things make all the difference. TABLE OF CONTENTS Page INTRODUCTION 1 LOCATION 2 REGIONAL MORPHOLOGY 5 STRUCTURAL SETTING 6 Pre-Pennsylvanian 6 Pennsylvanian-Permian 6 Post Permian 9 PENNSYLVANIAN HOLDER FORMATION 10 TOPOGRAPHIC AND TECTONIC CONTROLS ON DEPOSITION OF VIRGILIAN CYCLES 15 Previous Work . 16 Field Data 20 Transport Systems 23 Provenance 24 CHARACTER OF VIRGILIAN CYCLES 29 Cycle 3 32 Cycle 6 37 Cycle 7 53 Cycles 8 and 9 57 SUMMARY 63 DISCUSSION 65 Paleoclimatology 65 Pedernal Uplift 66 Coastal Processes 67 Depositional Setting 68 Clastic Deposition 69 Provenance 71 BIBLIOGRAPHY 76 APPENDIX I 79 APPENDIX II 92 APPENDIX III 109 ILLUSTRATIONS Figure Page 1 Field Area Location 3 2 Field Area 4 3 Pennsylvania Physiography 7 4 Generalized Holder Formation Cycle 11 5 Lower 9 Cycles, Holder Formation 12 6 North Field Area 17 7 South Field Area 18 8 North Field Area Cycle 3 Isopach Map 33 9 South Field Area Cycle 3 Isopach Map 34 10 North Field Area Cycle 3 Clastic Isopach Map 35 11 North Field Area Cycle 6 Isopach Map 38 12 South Field Area Cycle 6 Isopach Map 39 13 North Field Area Cycle 6 Clastic Isopach Map 41 14 South Field Area Cycle 6 Clastic Isopach Map 42 15 South Field Area Cycle 6 Channels 43 16 North Field Area Cycle 6 Size Distribution Map 51 17 South Field Area Cycle 6 Size Distribution Map 52 18 North Field Area Cycle 7 Isopach Map 54 19 South Field Area Cycle 7 Isopach Map 55 20 South Field Area Cycle 7 Clastic Thickness Map 56 21 North Field Area Cycles 8 and 9 Isopach Map 58 22 South Field Area Cycles 8 and 9 Isopach Map 59 23 North Field Area Cycles 8 and 9 Clastic Isopach Map 61 24 Composite Paleotransport Directions—Lower 9 Holder Formation Cycles 64 25 The Origin of Feldspars in Sandstones .... 73 PLATES Plate 1 Virgilian Triticites in limestone clast ... 25 2 Paleozoic shell debris 27 3 Late Paleozoic ramose Bryzoan 27 4 Bliss quartzite 28 5 Virgilian quartzite clast 28 6 Cycle 6 conglomerate cutting into the top of the AR limestone 46 FIELD MAP In Pocket BEEMAN CANYON CROSS SECTION In Pocket DRY CANYON CROSS SECTION In Pocket 1 Introduction The Late Pennsylvanian Holder Formation of the Sacra¬ mento Mountains, south central New Mexico, is composed of clastic and carbonate rocks cyclically deposited on the narrow Sacramento Shelf. The carbonate units of each cycle are shallow, marine deposits, while the terrigenous clastic units range in character from shales to coarse silts and sandstones derived from the Permo-Pennsylvanian Pedernal Uplift to the east and northeast. In places, the terrigenous clastic portion of each cycle contains very coarse-grained conglom¬ erates. The areal distribution of these conglomerates and in particular their occurrence in down-cutting channels, afford significant insight into the Late Pennsylvanian paleoslope and drainage patterns of the Sacramento Shelf as related to local and regional tectonics. In addition, the distribution of the conglomerates and their channels docu¬ ment the direction from which the coarse elastics were de¬ rived. The sedimentologic character of the terrigenous elastics is a key to understanding the processes and environ¬ ment of their deposition. The mineralogy of the conglomerate clasts indicates that they are genetically related to the Paleozoic sediments overlying the Pedernal Uplift to the northeast. 2 Location The Sacramento Mountains, located in south central New Mexico, trend north-south for almost 100 miles (Figure 1). The field area is in the northern part of the mountain range lying almost totally within the Lincoln National Forest, and the majority of work was done along the steep west and south facing escarpments. The field area is roughly separated into northern and southern halves by New Mexico Highway 83 running east-west through Dry Canyon, connecting the city of Alamogordo with the town of Cloudcroft (Figure 2). The topographic map for the field area is the U.S.G.S. 15 minute series, Alamogordo Quadrangle, New Mexico, Otero County. Figure 1 Field Area Location Figure 2 Field Area Boundary fault is shown by hatchered line Biohermal buildup shown by stippling 4 5 Regional Morphology The Sacramento Mountains separate the Great Plains to the east from the Basin and Range topography to the west. The Tularosa Basin lying to the west of the Sacramento Moun¬ tains is a bolson created by Basin and Range tectonics which is filled by Quaternary alluvium, a vast gypsum sand deposit (the White Sands) and basalt flows associated with the rift¬ ing of the Rio Grande trough. The Sacramento Mountains form a steep western escarpment along the north-south trending boundary fault (Figure 2). The mountains rise from 4500 feet in elevation in the basin to over 9000 feet at the crest, 7-13 miles to the east. The gentle (1°) eastern slope of the Sacramento Mountains extends 80 miles to the Pecos River. Four major west-northwest draining canyons cut the field area creating exposures normal to those created by the north trending boundary fault. These canyons are, from north to south, Fresnal Canyon, Dry Canyon, Beeman Canyon, and Indian Wells Canyon (Figure 2). Access roads are severely restrict¬ ed by terrain and essentially all work was done on foot from points accessed from New Mexico Highway 83. 6 Structural Setting Pre-Pennsylvanian Prior to Pennsylvanian time south central New Mexico was characterized by a broad, flat shelf across which a sea entering from the south deposited clastic and carbonate sediments from Cambrian through Mississippian time.