Seismic Facies Analysis of Fluvial-Deltaic Lacustrine Systems—Upper Fort Union Formation (Paleocene), Wind River Basin, Wyoming

Abstract

Progradation of deltaic systems into Paleocene Lake Waltman (Wind River basin, Wyoming) is interpreted from seismic reflection data from the upper Fort Union Formation. Subdivision of the interval into seismic sequences and interpretation of variations in seismic attributes (i.e., amplitude, continuity, and frequency) allow detailed reconstruction of the depositional history of this interval. Sequences that show distinct clinoform morphology from seismic data are interpreted as lobate deltas. Higher amplitude, continuous events within the clinoforms are interpreted as prograding delta-front facies. Seismic data clearly demonstrate the time-transgressive nature of this facies. Downdip of the clinoforms, low-amplitude, generally continuous seismic events correspond to homog neous shales that represent deposition in an areally extensive, low-energy lacustrine environment. The lacustrine facies is traceable laterally in the seismic data, which allows interpretation of changes in lake morphology through late Fort Union time. Overlying the upper Fort Union lacustrine strata are fluvial deposits interpreted from discontinuous, variable-amplitude seismic facies. Seismic facies interpretations are compared to lithologic interpretations from a series of closely spaced wells adjacent to seismic lines across the basin to test the accuracy of depositional environment prediction from seismic data.