Depositional models for two Tertiary coal-bearing sequences in the Powder River Basin, Wyoming, USA

Depositional controls on peat-forming environments which produce thick (>10m) coal beds can be inferred from relationships between coal bed geometry, maceral composition and associated lithologies. Study of these relationships within sedimentary sequences associated with the Wyodak-Anderson (Palaeocene) and the Felix (Eocene) sub-bituminous coal beds in the Powder River Basin, Wyoming, USA suggests two modes of fluvially controlled peat accumulation. The Wyodak-Anderson peat is interpreted to have formed in restricted parts of the floodplain that were separated by deposits of contemporaneous, anastomosed channels. The channels and associated sediments maintained their position through time because they were confined by thick deposits of raised Wyodak-Anderson peat. In contrast, the Felix coal bed is interpreted to have formed as a raised but widespread peat on an abandoned platform of meander-belt sands.

The purpose of this paper is to compare and contrast two different fluvial depositional settings that produced anomalously thick (>10m) coal deposits in the intermontane Powder River Basin of Wyoming, USA. These models may be useful as predictive tools for coal exploration and production.