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From a sedimentologic study of the Emery Sandstone Member of the Mancos Shale (Upper Cretaceous) in southern Castle Valley, Utah, it is possible to determine depositional environments, paleogeography, textural and mineralogical characteristics, and possible sediment sources.
Tidal-flat deposits are dominant in the Emery, but subtidal (shoreface) and offshore deposits also occur. The paleotidal range is estimated to have been 1.3-1.7 m (4.3-5.6 ft). Many asymmetric, transgressive-regressive cycles of two different magnitudes and periods are present. They formed in response to minor fluctuations in sea level combined with slight variations in the subsidence rate.
The Emery Sandstone was deposited in the foreland of the Sevier orogenic belt. The average orientation of the paleoshoreline, as determined by paleocurrent analysis, was N9°W. Sediment was probably transported southward from the Utah-Idaho-Wyoming border area by longshore currents.
Well-sorted, subrounded to subangular, very fine-grained subarkose is the dominant rock type in the Emery. Dolomite and calcite are the major cements. Average porosities, based on thin section analysis, are less than 2%.
Abundant chert grains and reworked authigenic quartz overgrowths suggest a sedimentary source terrane. The observed amounts of feldspar could have been derived from Mesozoic sedimentary rocks exposed in the Sevier orogenic belt.
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