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Stratigraphic relations between the shallow, generally open-marine deposits of the Triassic miogeosyncline in eastern Idaho (Thaynes Formation) and shelf deposits in Wyoming (Red Peak and Crow Mountain Formations) have been uncertain. The principal marker bed in the Wyoming sequence, the Alcova Limestone Member, has been correlated variously with many different parts of the Thaynes, and even has been considered to be younger than the Thaynes. The writers demonstrate that the Alcova is an eastward-extending, marine tongue of a limestone in the upper part of the Thaynes, the "sandstone and limestone unit." This resolution of the problem is possible only by the combined use of surface and subsurface stratigraphic sections, sedimentary petrography, paleontology, bedding types and sedimentary structures.
Red Peak-Thaynes correlations lead to the reconstruction of an average paleogeography for western and central Wyoming and adjacent Idaho. In eastern Idaho and westernmost Wyoming, carbonate mounds and oolite shoals lined the shelf edge. Restricted, shallow-marine conditions existed from the banks into western Wyoming. Throughout western and central Wyoming, shallow open-marine conditions prevailed.
Despite differences in age and tectonic setting, the facies relations and the reconstructed paleogeography resemble the Permian shelf-basin sequence of West Texas. This suggests the possibility that oil and gas accumulations are present along the shelf edge, although subsequent deformation may have allowed the hydrocarbons to escape.
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