Meredith K. Rhodes¹, Alan R. Carroll¹

(1) UW-Madison, Madison, WI

ABSTRACT: Nonmarine Sequence Stratigraphic Interpretation of the Laney Member, Eocene Green River Formation, Washakie Basin, Wyoming

The Laney Member of the Green River Formation is exposed for ~ 100 km along the Delaney and Kinney Rims in the Washakie Basin of SW Wyoming. Detailed stratigraphic correlation is based on outcrop and core measured sections and was facilitated by regional field observations, electric logs, and outcrop gamma ray measurements. In the Washakie basin, the Laney Member is divided into three distinct units based on lithology and stratigraphic architecture. 1) The Lower LaClede Bed is characterized by meter scale aggradational cycles containing basal ooid/ostracode grainstones and stromatolites overlain by calcareous and dolomitic microlaminated mudstone. Mudcracks at the top of these cycles suggest periods of subaerial exposure. Laterally equivalent strata at the basin margin are alluvial and fluvial in nature. These cycles are interpreted to represent transgression and regression in a balanced-fill lake. The top of the Lower LaClede Bed is a regionally extensive sequence boundary marked by 1-2 m deep sand-filled cracks. 2) The overlying Buff Marker Bed consists of wavy-bedded calcareous and dolomitic silt to fine-grained sand with low angle and trough cross beds, asymmetrical ripples and intraclasts horizons. The unit thickens toward the basin center, thins and fines upward, and is interpreted as fluvial or deltaic deposits that were reworked during a major transgression. 3) The Buff Marker Bed grades conformably into the Upper LaClede Bed, a thick interval of ostracode rich, microlaminated calcareous and dolomitic mudstone with minor marginal lacustrine facies. This final lake facies is interpreted as a transition to an overfilled lake basin and records a shift in basin depocenter to the south.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado