Seismic Facies Analysis of Fluvial-Deltaic Lacustrine Systems—Upper Fort Union Formation (Paleocene), Wind River Basin, Wyoming
Louis M. Liro, Yvonna C. Pardus, 1990. "Seismic Facies Analysis of Fluvial-Deltaic Lacustrine Systems—Upper Fort Union Formation (Paleocene), Wind River Basin, Wyoming", Lacustrine Basin Exploration: Case Studies and Modern Analogs, Barry J. Katz
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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 homogeneous 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 lithologie 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.
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Lacustrine Basin Exploration: Case Studies and Modern Analogs
Lacustrine environments are a major contributor of petroleum source rocks. Lacustrine source rock prediction is, however, influenced by numerous, complex variables governing lake sedimentation. Current predictive capability can be improved by attempting to map essential climatic variables to limit in space and time the area of lacustrine source rock exploration. Climatic characteristics that govern lake occurrence and the potential for stratification have been investigated with a General Circulation Model of the atmosphere for the present and for the mid-Cretaceous. In this analysis, the distribution of areas with a positive water balance first is used as an indicator of the distribution of areas conducive to lake formation. Second, the distribution of areas that experience large annual climatic variations is used as an indicator of the distribution of lakes that are less likely to be stratified and, hence, less likely to be sites of high organic-carbon preservation. Four factors used to define large climatic variations include (1) seasonal temperature cycle in excess of 40°C; (2) seasonal temperature extreme of less than 4C°; (3) average seasonal differences in precipitation minus evaporation balance in excess of 5 mm/ day; and (4) distribution of mid-latitude winter storms. Evidence is presented to support the capability of climate models that add insight into lacustrine source rock prediction by simulating geographic regions conducive to lake development and to stratification and organic-carbon preservation