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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)

Abstract


Journal of Sedimentary Petrology
Vol. 57 (1987)No. 1. (January), Pages 30-38

A Depositional Model of the Antelope Coal Field, Powder River Basin, Wyoming

Christine M. Budai, Michael L. Cummings

ABSTRACT

The Anderson and Canyon coal seams are the main seams at the Antelope coal field in the south-central Powder River Basin. Each Previous HitseamNext Hit splits into multiple and thinner coal seams to the southwest in the study area. The strata underlying the Canyon coal Previous HitseamNext Hit suggest that the area of the Antelope coal field was a poorly drained swamp that developed into a well-drained swamp with minor small channels. The area further changed to a poorly drained swamp which initiated peat accumulation in the Canyon coal swamp. The lithologies, sedimentary structures, and isopach maps of the Canyon Previous HitseamNext Hit partings indicate that crevasse splaying, lacustrine conditions, and small crevasse-channel development produced the observed splits in the Canyon coal Previous HitseamNext Hit. Distal overbank deposits occur at the top of the C nyon Previous HitseamNext Hit and at the base of the Anderson Previous HitseamNext Hit; well-drained swamp deposits and crevasse splay, lake, lacustrine delta, and small channel-fill deposits occur between the coal seams. The Anderson coal Previous HitseamNext Hit represents another development of a poorly drained swamp where peat accumulation was significant. The rocks overlying the Anderson Previous HitseamNext Hit represent a combination of the environments mentioned above, with deposits from lakes and well-drained swamp environments dominating.

The coal-beating sediments were deposited in paludal and tributary subsystems along the northern margin of the Wright delta. Deposition of the Canyon and Anderson coal seams and associated parting lithologies may have occurred when a river system or parts of that system underwent anastomosis. The coal swamp in which the Anderson Previous HitseamTop was deposited was destroyed when the anastomosed character of the river system ended or the anastomosed river system shifted westward. This may reflect a relative change in the rate of subsidence within the basin.


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