Depositional Environments and Diagenesis of the Tensleep Sandstone, Eastern Big Horn Basin, Wyoming
David Mankiewicz, James R. Steidtmann, 1979. "Depositional Environments and Diagenesis of the Tensleep Sandstone, Eastern Big Horn Basin, Wyoming", Aspects of Diagenesis, Peter A. Scholle, Paul R. Schluger
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Study of lithologies and sedimentary structures in seven surface sections and five cores indicates that the Tensleep Sandstone in the eastern Big Horn Basin was deposited in a coastal environment. The lower part of the Tensleep formed in a siliciclastic sabkha whereas the upper part represents deposition in a coastal eolian dune complex. Previous paleomagnetic and paleowind studies by others indicate that during deposition of the Tensleep Sandstone, the area lay in a trade wind belt, a setting similar to many of the major coastal sabkhas today.
Diagenesis of the Tensleep Sandstone was a function of both depositional environment and tectonic history. Early cements (anhydrite and dolomite) were, for the most part, related to the chemistry of subsurface waters in the sabkha and associated environments. However, later pre- and post-hydrocarbon entrapment cements (quartz and feldspar overgrowths and rhombic dolomite) appear to be related to episodes of tectonism (Jurassic arching and Laramide folding and faulting). Analyses of surface and subsurface waters show that calcite cement presently is stable at the surface and in the subsurface to the south. To the north, anhydrite is now stable in the subsurface.
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Aspects of Diagenesis
There are a number of gaping holes in accumulated knowledge within the discipline of sedimentology. Perhaps one of the largest holes has been the general subject of diagenesis in clastic rocks. It was therefore fortuitous that two symposia covering various aspects of diagenesis (mainly in clastics) were presented a year apart in different parts of the country but with the same motivation – to contribute to the closing of that knowledge gap. Sedimentologists now have a fairly good idea of the what and the how of sediment deposition. What happens after the sediments are lithified has frequently been ignored. It was the aim of both editors of this publication to approach the subject from two different viewpoints. Schluger directed a symposium which looked mainly at clastic reservoirs, and Scholle presented a symposium which examined various aspects of paleotemperature control of diagenesis.