FRONT COVER-Index map of southeastern New Mexico and western Texas showing approximate position of Capitan Limestone (reef) and area discussed in this report. Circular 184 New Mexico Bureau of Mines & Mineral Resources A DIVISION OF NEW MEXICO INSTITUTE OF MINING & TECHNOLOGY Regional geology of Ochoan evaporites, northern part of Delaware Basin GO ERNYENT by ~etB@@$$~@&man Star Rte Box 1028, Corrales, New Mextco-87048 SOCORRO 1984 NEW MEXICO INSTITUTE OF MINING & TECHNOLOGY Laurence H. Lattman, Preridenr NEW MEXICO BUREAU OF MINES & MINERAL RESOURCES Frank E. Kottlowski, Director George S. Austin, Depuq Director BOARD OF REGENTS Ex Officio Toney Anaya, Governor of New Mexico Leonard DeLayo, Suprrinrendrnr of Public instruction Appointed Judy Floyd, President, 1977-1987, Las Cruces William G. Abbott, Secretq-Treasurer. 1961-1985. Hobbs Donald W. Morris, 1983-1989, Los Alamos Roben Lee Sanchez. 1983-1989. Albuuu~ruue Steve Tomes, 1967-1985, Socorro Original Prinfing, 1984 Published by Authority of State of New Mexico, NMSA 1953 Sec. 63-1-4 Printed by University of New Mexico Printing Plant. May 1984 Available from New Mexico Bureau of Mines & Mineral Resources, Socorro, NM 87801 Contents ABSTRACT 5 INTRODUCTION 5 STRATIGRAPHY 6 OCHOANSERIES 6 Castile Formation 6 Castile-Salado contact 8 Salado Formation 11 Rustler Formation 11 Dewey Lake Red Beds 13 MESOZOICROCKS OVERLYING THE OCIIOANSERIES 13 Rocks of Triassic age 14 Rocks of Cretaceous age 14 CENOZOICROCKS 14 Ogallala Formation 14 Gatuna Formation 14 SOILS 14 DISSOLUTION OF EVAPORITES 14 KARSTI'ROCESSES IN EVAPORlTES 16 THE ANCESTRALPECOS RIVER 17 DISSOLUTIONALONG THE EASTERN MARGIN OF THE DELAWAREBASIN 20 CONCLUSIONS 21 REFERENCES 22 Figures I-Index map of southeastern New Mexico and western Texas. 6 2-Nomenclature and stratigraphic relations of Guadalupian and Ochoan rocks, Delaware Basin. 7 3Llsopach map of Castile Formation. 9 4-Isopach map of Halite 111 and Halite IV. 10 5-(in pocket)-Cross section showing local interfingering of anhydrite-halite facies. 6-(in pocket)-Cross section showing lenticular bodies of halite in upper part of Castile Formation. 7-Correlation of marker beds. 12 8-Collapse breccia in Salado Formation. 13 9-Collapse sink in Rustler gypsum. 17 10-Index map showing position of Ancestral Pecos River and isopachs of Cenozoic fill. 18 11-Collapsed channel gravel in upper part of Gatuna Formation. 19 12-Close-up of gravel shown in Figure 11. 19 13-(in pocket)-Stratigraphic cross sections showing relationship of dissolution to course of Ancestral Pecos River. Tables 1-Marker beds in Salado Formation. 13 Abstract The Ochoan Series (Permian) in the northern part of the Delaware Basin, southeastern New Mexico, includes in ascending order the Castile, Salado, and Rustler Formations, and the Dewey Lake Red Beds. The Castile and Salado Formations comprise a seouence of eva~oriteswhich include anhydrite, gypsum, halite, and associated potash salts. The Rustler Formation contains some halite and minor amounts of potash minerals. These evaporites were de~ositedwithin the~ basin~ formed~~~~~~-~~ by the Capitan barrier ;eef, as well as across the rbef The evapotkes, as wull as the Capitan reef, are all subject to dissolution with resulting karst features analogous to those formed in limestone regions. An Ancestral Pecos River was the major drainage system in the western part of the Delaware Basin, New Mexico, during late Cenozoic time. That ancient river system was responsible for the formation of an extensive karst terrain along the east side of the present Pccos River in New Mexico and southward into Texas. During late Cenozoic time extensive dissolution occurred in the Salado Formation within the karst area as a result of the ground-water regime. The dissolutiun front was perched on the upper anhydrite member of the Castile Formation. On the eastern side of the Delaware Basin in New Mexico, a large collapse sink-San Simon sink-overlies the Capitan reef which is a prominent aquifer system in that area. So-called "breccia pipes" are ancient sinks which collapsed into the caverns in the reef on the northern margin of the basin. These have since been partially exhumed. The San Simon sink is presumed to be a mudern analog of these breccia pipes. Introduction Numerous studies of the Delaware Basin have been been expressed by critics of the WIPP site that soluble undertaken with various objectives. The earliest com- rocks in the Castile might be dissolved to provide an prehensive studies were the result of exploration for unstable base for the site. For these reasons, most petroleum. Drill holes penetrated Ochoan and older effort during the present study concentrated on the Permian rocks, providing control points for correla- regional setting of the Castile. tion of stratigraphic units. Potash minerals were dis- The Salado and Rustler Formations, the other salt- covered east of Carlsbad in 1925. Development of these bearing units in the Ochoan Series, receive less at- deposits included extensive drilling programs to de- tention here. They are discussed only as background termine their extent and grade. As a result of this for the consideration of processes of subsurface dis- development, the details of the potash-bearing for- solution. mations are well understood within the potash min- Methods of study included examination of surface ing district in the north-central part of the Delaware exposures over much of the northern part of the Del- Basin. aware Basin. The relationship of Ochoan rocks to ad- More recently, intensive studies have been under- jacent deposits has been studied to evaluate the history taken in a limited area in the north-central part of the of those rocks since their deposition. Ancient drainage Delaware Basin to determine the feasibility of storing systems were studied both by field observations and radioactive waste in underground beds of salt. These examinations of well logs. More than 300 wire-line studies have provided background for the proposed logs of drill holes in the northern part of the Delaware construction of a Waste Isolation Pilot Plant (WIPP). Basin were examined. Cores were studied from drill Numerous drill holes have penetrated portions of the holes in the vicinity of the proposed WIPP site as well Ochoan Series, the salt-bearing rocks, during these as from other parts of the basin. background studies. J. W. Mercer and R. P. Snyder of the U.S. Geological The present work was undertaken to summarize Survey contributed generously their time and knowl- some of the knowledge derived from these studies edge of the Delaware Basin. J. W. Mussey of Duval and to examine the regional geology of part of the Mining Corporation provided core of the Castile For- salt-bearing Ochoan Series in a northern part of the mation for study. The manuscript was reviewed and Delaware Basin. The Castile Formation, the basal unit constructively criticized by John W. Hawley of the of the Ochoan Series, underlies the WIPP site. Minute New Mexico Bureau of Mines and Mineral Resources, details of some aspects of the Castile have been stud- and Lokesh Chaturvedi of the State of New Mexico ied in the past, but its regional stratigraphy and geo- Environmental Evaluation Group. logic setting have been neglected. Some concern has Stratigraphy Ochoan Series Ochoan rocks in the northern part of the Delaware Basin are shown in Figure 2. Rocks of Permian age in southeastern New Mexico and western Texas are divided, from oldest to young- Castile Formation est, into the Wolfcampian, Leonardian, Guadalupian, The Castile Formation, the basal unit of the Ochoan and Ochoan Series. They were deposited in marine Series, was named by Richardson (1904, p. 43) for environments in a tectonically negative area, the Del- Castile Spring in Culberson County, Texas, about 20 aware Basin (Fig. l). Rocks from Wolfcampian through mi south of the New MexiceTexas State line. For a Guadalupian age are mostly fine-grained sandstones, time the Castile was divided into a "lower" and "up- siltstones, shales, and various types of limestone. per" salt series. Lang (1935, pp. 265-267) separated During Guadalupian time, the Capitan reef was built the "upper salt series" from the Castile and named it as a massive limestone barrier which fringed the mar- the Salado Formation. gins of the Delaware Basin. As defined by the Capitan Later, an extensive bed of anhydrite, which rests rseef, the Delaware Basin was an elongate, bowl-shaped on the Capitan Limestone in places in the subsurface, dlepression. Most of early Ochoan deposition was was defined as the base of the Salado Formation (Lang, confined to this basin. Later, during Ochoan time 1939). This anhydrite was described in detail and named when the basin became filled with sediments, some the Fletcher Anhydrite Member of the Salado For- t~edslapped across the reef into adjacent areas. mation (Lang, 1942, pp. 75-78). This definition served Most of the rocks deposited during Ochoan time to restrict the Castile to the Delaware Basin. were evaporites such as anhydrite, halite, and potash However, Jones (1954, p. 109; 1973, p. 10) indicated minerals with only minor amounts of limestone, mud- that the upper part of the Castile includes a north- stone, and siltstone. The rocks of the Ochoan Series ward-thinning tongue of anhydrite which overlaps are subdivided into (ascending) Castile Formation, the Capitan and Tansill Formations outside the basin. Salado Formation, Rustler Formation, and Dewey Lake This tongue appears to include the Fletcher, which is Red Beds. Within the Delaware Basin, the Castile For- transitional with the upper part of the Castile in the mation rests on the Bell Canyon Formation of the Delaware Basin. The Fletcher is readily separated from (hdalupian Series. The stratigraphic relations of the main body of Castile anhydrite around the margin FIGURE I-Index map of southeastern New Mexico and western Texas showing approximate position of Capitan Limestone (reef) and area discussed in this report.