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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 73 (1989)

Issue: 9. (September)

First Page: 1103

Last Page: 1116

Title: Depositional Mechanisms and Organic Matter in Mowry Shale (Cretaceous), Wyoming

Author(s): Hugh R. Davis (2), Charles W. Byers (3), Lisa M. Pratt (4)


Four lithofacies, which accumulated under different depositional conditions, can be distinguished in the Lower Cretaceous Mowry Shale of Wyoming. Type and amount of organic matter in these lithofacies are governed largely by sediment transport mechanisms. Nearshore silt and mud containing terrestrial organic matter were deposited in a prodelta environment by tractive processes and from suspension. These sediments, along with terrestrial organic matter, were redistributed by waning bottom flows over a dysaerobic slope; pelagically deposited muds containing marine-derived organic matter accumulated between flow events. Muds farthest offshore accumulated in dysaerobic and anaerobic water by pelagic settling in a region unaffected by bottom currents; these muds contain predom nantly marine-derived organic matter.

Petroleum source potential increases in a southeastward direction across west and central Wyoming. This trend results from differential input of marine and terrestrial organic matter, clastic dilution, and postdepositional biodegradation.

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