ROGER Y. ANDERSON Department of Geology, the University of New Mexico, Albuquerque, New Mexico 87106 WALTER E
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ROGER Y. ANDERSON Department of Geology, The University of New Mexico, Albuquerque, New Mexico 87106 WALTER E. DEAN, JR. Department of Geology, Syracuse University, Syracuse, New Yor\ 13210 DOUGLAS W. KIRKLAND Mobil Research and Development Corporation, Dallas, Texas 75221 HENRY I. SNIDER Department of Physical Sciences, Eastern Connecticut State College, Willimantic, Connecticut 06226 Permian Castile Varved Evaporite Sequence, West Texas and New Mexico ABSTRACT is a change from thinner undisturbed anhy- drite laminae to thicker anhydrite laminae that Laminations in the Upper Permian evaporite generally show a secondary or penecontem- sequence in the Delaware Basin appear in the poraneous nodular character, with about 1,000 preevaporite phase of the uppermost Bell to 3,000 units between major oscillations or Canyon Formation as alternations of siltstone nodular beds. These nodular zones are correla- and organic layers. The laminations then change tive throughout the area of study and underly character and composition upward to organi- halite when it is present. The halite layers cally laminated claystone, organically laminated alternate with anhydrite laminae, are generally calcite, the calcite-laminated anhydrite typical recrystallized, and have an average thickness of the Castile Formation, and finally to the of about 3 cm. The halite beds were once west anhydrite-laminated halite of the Castile and of their present occurrence in the basin but Salado. were dissolved, leaving beds of anhydrite Laminae are correlative for distances up to breccia. The onset and cessation of halite depo- 113 km (70.2 mi) and probably throughout sition in the basin was nearly synchronous. most of the basin. Each lamina is synchronous, The Anhydrite I and II Members thicken and each couplet of two laminated components gradually across the basin from west to east, is interpreted as representing an annual layer of whereas the Halite I, II, and III Members are sedimentation—a varve. thickest in the eastern and northeastern part of The thickness of each couplet in the 260,000- the basin and thicken from southeast to north- varve sequence (a total thickness of 447.2 m, west. This distribution and the synchroneity 1467 ft) has been measured individually and indicate a departure from the classical model of recorded and provides the basis for subdividing evaporite zonation. and correlating major stratigraphic units within the basin. The uppermost 9.2 m (30.3 ft) of the INTRODUCTION Bell Canyon Formation contains about 50,850 The Castile Formation (Upper Permian) in varve couplets; the Basal Limestone Member the Delaware Basin of Texas and New Mexico of the Castile about 600; the lowermost anhy- is often cited as perhaps the best example of a drite member of the Castile (Anhydrite I) con- large deep-water evaporite deposit for which tains 38,397; Halite I, 1,063; Anhydrite II, there are no modern analogs. In addition, the 14,414; Halite II, 1,758; Anhydrite III, 46,592; Castile is well known for its remarkably dis- Halite III, 17,879; and Anhydrite IV, 54,187. tinct laminations of calcite and anhydrite, The part of the Salado collected (126.6 m) con- which are assumed by many to reflect annual tains 35,422 varve couplets. The Bell Canyon- sedimentation. Castile sequence in the cores studied is appar- The regular interlamination of salts of dif- ently continuous, with no recognizable uncon- ferent solubilities (calcite and anhydrite; anhy- formities. drite and halite) implies that depositional con- The dominant petrologic oscillation in the trols must have fluctuated in response to some Castile and Salado, other than the laminations, periodic process or event. Udden (1924) sug- Geological Society of America Bulletin, v. 83, p. 59-86, 18 figs., January 1972 59 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/83/1/59/3428556/i0016-7606-83-1-59.pdf by guest on 25 September 2021 O 100 200 300 KILOMETERS Figure 1. Index maps showing location of the cores and P. R. R. Co. UNM-Pokorney no. 1, Blk. 61, T. studied and their general relationship to features of the and P. R. R. Co. UNM-Phillips no. 1, Sec. 3, Blk. 110, Delaware Basin. Well locations as follows: UNM- PSL. David Flood no. 1 Grisham and McAlpine, Sec. Cowden no. 2, Sec. 34, Twp. 1, Blk. 62, T. and P. R. R. 42, Blk. 54, PSL. Union Oil Co.-University "37" no. Co. UNM-Cowden no. 4, Sec. 33, Twp. 2, Blk. 62, T. 4, Sec. 37, Blk. 20, Univ. Lands Survey. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/83/1/59/3428556/i0016-7606-83-1-59.pdf by guest on 25 September 2021 PERMIAN CASTILE EVAPORITE SEQUENCE, WEST TEXAS AND NEW MEXICO 61 gested that each calcite-anhydrite couplet thors (Anderson and Kirkland, 1966; Kirkland represented an annual increment of sediment— and Anderson, 1970) revealed that the lamina- a varve. Most investigators who have discussed tions could be correlated with great precision the Castile agree with Udden's annual inter- over the entire basin (distances up to 113 km or pretation but have been unable to agree on a 70.2 mi). The laminations continue in an unin- periodic mechanism. Adams (1944) suggested terrupted sequence from the preevaporite that new sea water was introduced by seasonal phase below the Castile upward into the breaching and sealing of a barrier. Briggs Salado Formation in a series of some 260,000 (1957) suggested that freshening due to annual laminae couplets, and provide a reference scale maximum spring tides could produce the for determining the precise volume and distri- Castile laminations. Neither of these explana- bution relation of the various components in tions seems adequate to account for the great the system. The continuous time series of lateral continuity and synchroneity of deposi- laminations also provides a basis for examining tional conditions over an area the extent of the the behavior of such a basin over much of its Delaware Basin, as demonstrated by correlation life history. ol laminae. This report deals with the broader aspects of Organically rich layers are associated with the evaporite system and considers chiefly the calcite laminae in the Castile. Richter-Bern- petrology and stratigraphic relations of the burg (1964) explained a similar association in major units in the basin. These units have been calcite-anhydrite couplets in the Permian correlated within the basin on the basis of Zechstein Formation of Germany by assuming individual laminae and indexed to a master that organic matter represented mass killing of time series. The laminations themselves are an planktonic organisms. It seems likely, however, additional focal point in the study. Also, some that laminae concentrations of organic matter interpretations are made concerning basin are the result of a periodic (annual?) increase paleogeography, solution, and other problems. in plankton productivity (blooms). The inves- The study is based partly upon sonic, elec- tigations of Carpelan (1957) and Phleger (1969) tric, and sample logs, and field observations, but have shown that evaporite basins can have mainly on a number of cores collected from levels of primary productivity greater than Culberson County, Texas, in the west-central adjacent "normal marine" environments. If part of the basin and one core from Winkler such organisms were phytoplankton, then there County, Texas, in the east-central part (see Fig. is a mechanism for calcite deposition in the 1 for locations). One of these cores (University seasonal blooming process and the attendant of New Mexico-Phillips no. 1) includes part of removal of CC>2 from the water. the Salado Formation, all of the Castile, and Organically rich layers are also associated part of the underlying Bell Canyon Formation. with the anhydrite of anhydrite-halite couplets Each section of this 5 cm (2 in.) core was where seasonal evaporation can be invoked as marked as it was removed from the core barrel the mechanism for layered halite deposition. In in order to maintain proper sequence and fact, organic or organically rich layers are com- superposition. The core was slabbed, polished, mon to all the laminae types in the Bell Can- and marked off at 5.08-cm (2-in.) intervals. yon-Castile sequence, and form a basis for the Photographs of the core were enlarged three assumption that throughout the sequence the times, and printed on strips of photographic lamination process is in tune with, if not influ- paper. Each couplet (for example, calcite- enced by, seasonal and probably annual plank- anhydrite) was interpreted, marked, and ton productivity. measured on the photographs, and the core While it has never been conclusively demon- measurements were recorded on computer strated that laminae couplets such as those of cards. The result is a time series of approxi- the Castile are varves, no other hypothesis for mately 260,000 varve couplets beginning in the couplet timing in laminated evaporites has been Bell Canyon Formation, about 10.67 m (35 ft) given serious consideration, and this investiga- below the base of the Castile and continuing to tion is framed upon the assumption that each a basal limestone breccia, probably of the couplet (organic-siltstone, organic-calcite, cal- Rustler Formation, that rests on top of the cite-anhydrite, anhydrite-halite) represents an laminations in the lower part of the Salado annual cycle of sedimentation. Formation, a thickness of about 447.2 m Earlier investigations by several of the au- (1467 ft). Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/83/1/59/3428556/i0016-7606-83-1-59.pdf by guest on 25 September 2021 62 ANDERSON AND OTHERS REGIONAL SETTING calcite-anhydrite couplets of the Castile, and into the Castile halites. The arrangement and So much previous work has been done on the character of the laminations change in succes- regional aspects of evaporites in the Delaware sive lithologies and it is this change by the Basin that no attempt will be made here to addition or subtraction of individual laminae present a complete picture of the setting of types that results in the gross changes that are the basin.