--> Abstract: Temporal Self-Organization of Lacustrine Sedimentary Facies, Eocene Green River Formation, Wyoming, by Alan R. Carroll, Jeffrey T. Pietras, Meredith K. Rhodes, L. Ashley Hubbard, and Kevin M. Bohacs; #90039 (2005)
[First Hit]

Datapages, Inc.Print this page

Temporal Self-Organization of Lacustrine Sedimentary Facies, Eocene Green River Formation, Wyoming

Alan R. Carroll1, Jeffrey T. Pietras2, Meredith K. Rhodes1, L. Ashley Hubbard1, and Kevin M. Bohacs3
1 University of Wisconsin-Madison, Madison, WI
2 BP Exploration (Alaska) Inc, Anchorage, AK
3 ExxonMobil Upstream Research Company, Houston, TX

The three lacustrine facies associations that define the Green River Formation represent discrete and persistent stratigraphic patterns, rather than end-members in a genetic continuum. They are physically separated by basinwide stratigraphic surfaces that denote irreversible, long-term changes in the dominant mode of sedimentation. These surfaces are hierarchically similar to marine transgressive or maximum flooding-downlap surfaces, but have origins related to changes in regional drainage networks. The first surface is a regional unconformity that separates Previous HitbalancedNext Hit-fill facies from underfilled facies above. It is termed a “drainage isolation surface” because it marks a transition to internal basin drainage. Flooding over a “drainage recapture surface” occurs at the contact between underfilled and overlying Previous HitbalancedNext Hit-fill facies. This surface corresponds to an abrupt reappearance of fossil fish, and to a dramatic and nearly instantaneous rise of 87Sr/86Sr in lacustrine carbonate. These phenomena both reflect the capture of a new and distinct freshwater drainage underlain by relatively radiogenic rocks. Finally, a “fill to spill” flooding surface marks the transition from Previous HitbalancedNext Hit-fill to overfilled facies. The presence of distinctly different stratigraphic intervals separated by discrete surfaces implies emergent behavior of a complex system that is resistant to short-lived external perturbations. For example, during deposition of the Previous HitbalancedNext Hit-fill lower LaClede Bed a giant volcanic debris avalanche diverted drainage away from Lake Gosiute, causing basin desiccation. However, the basin quickly re-flooded as normal drainage was reestablished, and subsequently returned to Previous HitbalancedTop-fill conditions. The interpretation of stratal stacking patterns as the emergent behavior of a complex system represents a new paradigm in stratigraphy, with practical implications that reach beyond lacustrine strata.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005