Section 3 Environments of Subaqueous Gypsum Deposition
Published:January 01, 1987
B. Charlotte Schreiber, 1987. "Section 3 Environments of Subaqueous Gypsum Deposition", Marine Evaporites, Walter E. Dean, B. Charlotte Schreiber, Walter E. Dean, Gerald M. Friedman, Robert J. Hite, Roy D. Nurmi, Omer B. Raup, B. Charlotte Schreiber, Douglas J. Shearman
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It has just been within the past 15 years that intensive studies of in situ evaporite deposits have been carried out and the first working models formulated for the origin of such deposits. These studies have focused on deposition along supratidal margins of normal marine basins. However, examination of evidence from the geologic record has long suggested that many evaporite bodies were also deposited within previously existing, open marine basins. These basins apparently had become constricted and developed hypersaline conditions within the water which they enclosed. Recently, data obtained from the latest Miocene (Messinian) sediments of the Mediterranean Basin and from modern salinas have shown that specific submarine evaporites do indeed exist and their facies are demonstrable. The primary composition, texture, and form that comprise these subaqueous deposits are only partly understood. Incomplete understanding arises, in part, because there are so few hypersaline water bodies existing in the world today in which environments may be observed that serve as an analogy to those which formed evaporites. It seems that another problem in interpretation of any marine evaporite, whether modern or ancient, lies within the materials themselves because they are exceedingly prone to alteration both while on the surface and after burial. Because of this ease of alteration, the ancient record left to us can be totally misleading.
The range of environments under which evaporites can form and accumulate is as diverse as that for carbonates, and, in a general way, for every type of carbonate sediment, there is an equivalent evaporite.
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Evaporites were classified on the basis of their environmental relationships, particularly with respect to the under- and over-lying sedimentary sequences. The scope of knowledge that went into establishing this classification was limited to deposits developed in cratonic (continental crust) areas of the world. The advent of the concept of sea-floor spreading, together with new data collected by the Deep Sea Drilling Project and extensive submarine seismic surveys, both on the continental margins and in the deep-sea, enables us to classify evaporitic sediments on the basis of tectonic settings as well as sediment affinities. The various divisions are in a sense artificial; the one classification readily overlaps with the other, and each of the groupings may grade through time and space.