Depositional Processes and Carbon Burial on a Turonian Prodelta at the Margin of the Western Interior Seaway
Elana L. Leithold, Walter E. Dean, 1998. "Depositional Processes and Carbon Burial on a Turonian Prodelta at the Margin of the Western Interior Seaway", Stratigraphy and Paleoenvironments of the Cretaceous Western Interior Seaway, USA, Walter E. Dean, Michael A. Arthur
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Lower-middle Turonian strata of the Tropic Shale and correlative Tununk Shale Member of the Mancos Shale accumulated in muddy prodeltaic environments near the western margin of the Cretaceous Western Interior Seaway. These fine-grained rocks are well exposed in outcrops along the southern margin of the Kaiparowits Plateau and in the Henry Mountains region in southern Utah, and they have been sampled in a core drilled by the United States Geological Survey near the town of Escalante, Utah. The rocks consist of bottomset, foreset, and topset facies that accumulated at progressively increasing rates during the eastward progradation of subaqueous deltaic clinoforms. Bottomset facies accumulated in relatively distal settings where sedimentation was dominated by deposition of both terrigenous and biogenic particles from suspension. In these strata, the shapes of fecal pellets, thicknesses of event layers, and intensity of bioturbation point to relatively slow rates of sediment accumulation. Foreset and distal topset beds, in contrast, suggest more rapid sediment accumulation, primarily as the result of episodic turbidity currents and storm processes.
Within the progradational succession, upward increasing organic carbon content and hydrogen indices and decreasing values suggest that the amount of marine organic carbon buried increased over time and with proximity to the shoreline. These trends parallel evidence for both increasing rates of sediment accumulation and decreasing levels of bottom water oxygenation and are interpreted to reflect increasing preservation of labile marine carbon. Studies of the Tropic and Tununk shales suggest that along the western margin of the seaway, proximal foreset facies are major repositories of marine organic carbon.
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This volume presents the results of a coordinated, multidisciplinary study of Cretaceous carbonate and clastic rocks in cores collected along a transect across the old Cretaceous seaway that extended from the Gulf Coast to the Arctic by a team of academic, industry and U.S. Geological Survey scientists. The overall goal was to construct a subsurface transect of mid-Cretaceous strata that were deposited in the U.S. Western Interior Seaway. In particular, the papers in this volume focus on the Graneros Shale, Greenhorn Formation, Carlile Shale, and Niobrara Formation and equivalents in cores from six drillholes from western Kansas, southeastern Colorado and eastern Utah.