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Avulsive Response in the Fluvial Systems of the Willwood Formation (Paleocene-Eocene) to the Paleocene-Eocene Thermal Maximum, Polecat Bench, Bighorn Basin, Wyoming

Daniel Woody

University of Colorado at Boulder, Department of Geological Sciences

Boulder, Colorado

[email protected]

The Paleocene-Eocene Thermal Maximum (PETM) constitutes 42 m of interbedded sand and silty to sandy mudstone on Polecat Bench in the Bighorn Basin, Wyoming. To date, the study has described in detail all 42 m of the PETM section as well as the intervals to 13.7 m below the base of the PETM and to 18.1 m above the PETM. Additionally, nine smaller subsections ranging in thickness from approximately 1 to 5 m have been described to determine lateral variability. Based on field descriptions, no apparent trend in thickness of identifiable beds has been identified, especially when only individual successive beds are analyzed. However, some amount of variability is apparent in groupings of sandier (avulsion) deposits and paleosol profile thicknesses. Paleosol and avulsion deposit variations may be related to short-term paleoclimate regime. More quantitative assessment is ongoing and is required to determine the statistical viability of such hypotheses.

Over 400 samples are currently being processed for laser grain size analysis, TIC, TOC and geochemical analyses. Thin sections are being billeted for point count analysis looking for composition and textural trends. Quantitative assessment of the above elements and any possible large-scale and cyclical trends willcontinue.

AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid