Shallow-Water Gypsum in the Castile Formation - Significance and Implications
Published:January 01, 1989
Alan C. Kendall, Gill M. Harwood, 1989. "Shallow-Water Gypsum in the Castile Formation - Significance and Implications", Subsurface and Outcrop Examination of the Capitan Shelf Margin, Northern Delaware Basin, Paul M. Harris, George A. Grover
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The predominantly anhydritic Castile Formation (Lower Ochoan, Permian) of the Delaware Basin (Fig. 1) is commonly used to illustrate the necessity for surface-reflux in marine evaporite basins and as a textbook example of deep-water evaporite sedimentation in a barred basin. The occurrence of basin-wide, mm-calcite/anhydrite laminae and of salinity cycles (laminar anhydrite at the base, passing upward gradationally into 'nodular' anhydrite and laminar halite) have generated depositional models involving a brine-filled basin (up to 600 m deep) that exhibited periodic fluctuations in salinity. Such models have been widely applied to other evaporite-filled basins.
Pseudomorphs of bottom-grown gypsum crystals have been found in 'nodular' anhydrite intervals within the lower parts of the Castile Formation in the Union University "37" No. 4 well (Anhydrite I Member) and the much visited New Mexico roadside outcrop (the "State Line Outcrop") along U.S. 62, 1.2 km north of the Texas-New Mexico boundary (which Anderson and Kirkland, 1987, attribute to the uppermost Anhydrite II Member) (Figs. 2 and 3). Complete gradation between well-preserved pseudomorphs and nodular anhydrite layers in the Union core suggest that nodular anhydrite intervals throughout the Castile Formation were also originally composed of bottom-grown gypsum crystals. This would better explain their lateral persistence and their stratigraphic restriction to certain horizons than their being a recrystallization of anhydrite laminae, as has previously been suggested.
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Subsurface and Outcrop Examination of the Capitan Shelf Margin, Northern Delaware Basin
Shelf sandstone reservoirs are becoming a more and more common exploration target. What they are, how they may be characterized, and how they differ from shoreline and deep-water deposits in the subject of this publication. Shelf sands and sandstone reservoirs are among the more poorly understood types of sandstones. Continental, shoreline and deep water sandstones have all been studied in much more depth than have shelf sands and sandstones. However, during the last fifteen years significant progress has been made in understanding shelf sands and sandstones. Studies of modern sediments have allowed us to understand many of the depositional processes active on the shelf. This book is intended to be an up-to-date summary of shelf processes and products. The papers are intended for those new to shelf sands and sandstones as well as the shelf specialist.