Diagenesis: Sulfate & Halide Cements and Authigenic Precipitates
2015. "Diagenesis: Sulfate & Halide Cements and Authigenic Precipitates", A Color Guide to the Petrography of Sandstones, Siltstones, Shales and Associated Rocks, Dana S. Ulmer-Scholle, Peter A. Scholle, Juergen Schieber, Robert J. Raine
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Sulfates and halides can form significant cements in sandstones but typically only in very specific settings. Early formed gypsum, anhydrite and halite are common in arid, highly evaporitic settings and form not only cements but also bedded deposits and displacive or replacive precipitates. Additional sulfates and halides, such as glauberite (a sodium calcium sulfate), barite (BaSO4), celestine (SrSO4), sylvite (KCl) and many others, can form in surficial settings, but most such minerals are rare and may not survive subsequent diagenetic alterations because of their generally high solubility. Eogenetic sulfates and halides are especially common precipitates in arid-region playa lakes, dunes and interdune flats, as well as continental and coastal sabkhas (e.g., Kinsman, 1969; Benison and Goldstein, 2000; Warren, 2006). Gypsum is the most common of these minerals, and extensive gypsum cementation, mostly within 10 m (33 ft) of the ground surface, can produce gypsiferous soils, gypsum crusts and fully cemented gypcretes (Watson, 1985; Nettleton, 1991; Hartley and May, 1998). Gypsum cements in terrigenous strata can consist of coarsely poikilotopic crystals (encompassing numerous detrital sand grains), isolated lenticular crystals or crystal clusters (desert roses), gypsarenites with graded cement sizes and alabastrine gypsum with individual crystallites that average less than 50 μm in diameter (Watson, 1985). Although gypsum is the major precipitate in such surficial deposits, in settings with especially hot, arid, evaporitic and low humidity conditions, anhydrite (anhydrous calcium sulfate)andevenhalitecanbefoundcementingsurficial and near-surficial sands and muds, especially in sabkhas and saline pans (Kinsman, 1969; Casas and Lowenstein, 1989; Warren, 2006).
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AAPG Memoir 109 is designed as a practical guide for students and professionals to learn the fundamentals of microscopic examination of sandstones, mudrocks, and associated rocks. With more than 1100 color illustrations, it covers the identification of grains, textures, and structures of clastic terrigenous rocks as well as their diagenetic alteration (compaction, cementation, dissolution, and replacement) and porosity reduction or enhancement. It also provides classification diagrams for formal description of those rocks and their porosity. Although the majority of the outcrop and subsurface examples come from the United States (35 states and Puerto Rico), there are representative photographs from 32 other countries, including many from the offshore areas. The foldout birefringence chart and an included DVD with Powerpoint files of all of the petrographic images provide additional aids for instructors and students.