New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/44 Dissolution of Permian Salado salt during Salado time in the Wink area, Winkler County, Texas Kenneth S. Johnson, 1993, pp. 211-218 in: Carlsbad Region (New Mexico and West Texas), Love, D. W.; Hawley, J. W.; Kues, B. S.; Austin, G. S.; Lucas, S. G.; [eds.], New Mexico Geological Society 44th Annual Fall Field Conference Guidebook, 357 p. This is one of many related papers that were included in the 1993 NMGS Fall Field Conference Guidebook. Annual NMGS Fall Field Conference Guidebooks Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed geoscience papers. 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No material from the NMGS website, or printed and electronic publications, may be reprinted or redistributed without NMGS permission. Contact us for permission to reprint portions of any of our publications. One printed copy of any materials from the NMGS website or our print and electronic publications may be made for individual use without our permission. Teachers and students may make unlimited copies for educational use. Any other use of these materials requires explicit permission. This page is intentionally left blank to maintain order of facing pages. New Mexico Geological Society Guidebook, 44th Field Conference, Carlsbad Region, New Mexico and West Texas, 1993 211 DISSOLUTION OF PERMIAN SALADO SALT DURING SALADO TIME IN THE WINK AREA, WINKLER COUNTY, TEXAS KENNETH S. JOHNSON Oklahoma Geological Survey, University of Oklahoma, Norman, Oklahoma 73019 Abstract—The Wink area, on the east edge of the Delaware Basin, was the site of dissolution of Permian Salado salts during Salado time. The Wink area is above the crest of the deepl y buried Capitan Reef and is just 2 mi east of a major dissolution trough that contains anomalously thick Late Permian, Triassic and Cenozoic sediments. Salado-age dissolution had not been recognized previously because of the obvious dissolution, collapse and infilling of the nearby dissolution trough during post-Salado time. The Salado Formation is informally divided into eight units, based upon examination of geophysical logs of 47 wells drilled in the four-section study area in Winkler County, Texas. Anomalous local thinning of Salado salt units, accompanied by anomalous thickening of overlying Salado rock units at the same site, is the major evidence of this Salado-age dissolution; anomalously thick local accumulations result from sedimentary filling of depressions created by dissolution and subsidence of underlying salts. Each of the Salado units thins anomalously by 15 -50 ft at one or several sites in the area, whereas five of the younger units thicken anomalously by 10 -45 ft above the sites of thinning. These thickness anomalies typically occur within horizontal distances of 1000 ft or less. INTRODUCTION AND GEOLOGIC SETTING age and consist mainly of evaporites of the Castile, Salado and Rustler Winkler County and the Wink area are located astride the boundary Formations, overlain by red-bed shales and siltstones of the Dewey between the Delaware Basin on the west and the Central Basin Platform Lake Formation. Above the Permian are the Late Triassic Tecovas and on the east (Fig. 1). These major structural provinces are part of the Santa Rosa Formations (Dockum Group), which in turn are overlain greater Permian Basin of west Texas and southeast New Mexico and by Cenozoic alluvium deposited across a large area of the Delaware each is characterized by a different sequence of Permian strata (Fig. Basin and Central Basin Platform. 2). The provinces are separated by the Capitan Reef, a massive lime- Natural dissolution of salt beds of the Salado Formation in western stone and dolomite reef that fringed the Delaware Basin during Guad- Winkler County began during Late Permian time and still may be going alupian time. Permian strata younger than the Capitan are Ochoan in on today (Baumgardner et al., 1982). Abnormal thinning and thickening of individual salt units in the Salado, as well as local thickening of each of the overlying formations of Permian, Triassic and Cenozoic age, indicate that this process of dissolution and subsidence has occurred intermittently in the Wink area and began even before the end of Salado deposition. 212 JOHNSON This report focuses on subsurface evidence of natural dissolution of (Fig. 5A), contoured on the base of the Tansill Formation, shows struc- Salado salt units in the Wink area during Salado time. The study area tures beneath the Salado salts. A structural high over the Capitan Reef 2 comprises four sections (4 mi ) of land about 2 mi north of the town separates an eastward dip of 25 ft/mi from a westward dip of about of Wink (secs. 34, 35, 40 and 41 in Block B-5 of the Public School 500 ft/mi. The steeper westward dip reflects the steeply sloping face Land Survey). Within the study area, which is part of the Hendrick oil of the reef (Fig. 6) and is not related to salt dissolution. field, 227 petroleum tests and other boreholes have been drilled, mostly The second structure map (Fig. 5B), contoured on top of the Rustler during the oil-boom years of 1926-1930. Oil production is mainly from Formation, represents structures above the Salado salts. The Rustler the Yates Formation, with some from the overlying Tansill Formation. dips westward across the Wink area, 200-300 ft/mi east of the reef Geophysical logs suitable for correlation of units within the Salado are crest, and 400-500 ft/mi west of the reef. Locally, in the north, the available for 47 of the 227 wells. Rustler dips about 1500 ft/mi. The steeper Rustler dips west of the reef This report therefore is based upon an abundance of data points in mainly resulted from dissolution of the underlying Salado salts (Garza a relatively small area. It summarizes data presented by Johnson (1986) and Wesselman, 1959; Hiss, 1976; Baumgardner et al., 1982); as salt in a study of a collapse feature, the Wink Sink, which formed in 1980 was dissolved during Late Permian and post-Permian times, the over- as a result of dissolution of Salado salt (Baumgardner et al., 1982; lying Rustler subsided or collapsed to fill available space. This general Johnson, 1987). westward dip extends another 2 mi west of the study area, to the axis of a major "dissolution trough" (Fig. 6). LOCAL STRATIGRAPHY AND STRUCTURE DISSOLUTION OF SALADO SALTS The stratigraphy and structure within the four-section study area are important in documenting local dissolution in the Salado Formation. There is overwhelming evidence that Salado salts have been partly The Salado is a thick sequence of interbedded salt (halite) and anhydrite. dissolved by natural processes in and near the Wink area and the prin- The formation ranges from about 1315 ft thick in the northeast to about cipal conclusion of the current study is that at least some of the dis- 575 ft thick in the northwest (Fig. 3). Individual anhydrites typically solution took place during Salado time. Abnormal and abrupt thinning are 10-50 ft thick, whereas the intervening salts commonly are 10- of salt units, with concurrent thickening of overlying rock units above 100 ft thick. Variations in thickness of the Salado Formation and of the same site, is the major proof for this natural dissolution. The dis- individual salt units are largely due to dissolution of one or more of solution has been episodic in various parts of the Wink area; it began the salt units during Salado and post-Salado times. The depth to the as early as Salado time and then recurred during later Permian, Triassic top of the Salado in the Wink area ranges from about 900 ft in the east and Cenozoic times. Some natural dissolution of Salado salts still may to about 1600 ft in the west. For this study, the Salado Formation was be occurring, but there is no evidence to confirm or refute this. informally subdivided into eight units (Fig. 4). This subdivision utilized The Salado Formation consists chiefly of salt, with lesser amounts the same anhydrite marker beds as shown in the cross sections of of anhydrite and minor amounts of dolomite and shale. Where salt Baumgardner et al. (1982). Structure-contour maps below and above the Salado Formation help to show that the causes and effects of some thickness anomalies in Salado units are restricted within the Salado Formation. The first map SALADO SALT DISSOLUTION 213 dissolution has occurred, the stratigraphic section equivalent to the original 1978; Mercer and Hiss, 1978; Powers et al., 1978, 1990; Anderson salt-bearing strata is thinner by an amount essentially equal to the thickness of and Kirkland, 1980; Johnson, 1981, 1987; Baumgardner et al., 1982; salt layers that have been removed.