SPECTRAL ANALYSIS OF PALEOGENE RED BEDS TO REVEAL THE LOCATION OF THE PALEOCENE-EOCENE THERMAL MAXIMUM AND THE TIMING OF LARAMIDE DEFORMATION, NORTHWESTERN WYOMING

Along the western edge of the Bighorn Basin in northwestern Wyoming, spectral analysis of undeformed L. Paleocene-Eocene Willwood Formation has previously been used to determine the location of the Paleocene-Eocene Thermal Maximum (PETM) near the Polecat Bench area (Aziz et al., 2008). Using a digital camera and ENVI software (method by Levin et al., 2007), we performed spectral analyses of two sections of Willwood in the Kimball Bench area of northwestern Wyoming with focus on constraining the location of the PETM and the timing of deformation in this area. The lower section was 111 m thick. The second section was 320 m thick, located one km northeast of the lower section.

North of the Kimball Bench area, previous mapping by Pierce (1965) shows a strong angular unconformity where tilted Cretaceous rocks are overlain by gently dipping Paleogene sediments. Our mapping has shown that the basal contact of the Paleogene rocks is nearly conformable with the underlying Cretaceous strata. In the Kimball Bench area, the Willwood Formation varies from gently dipping to locally overturned, suggesting that deformation occurred after deposition of the lower Willwood.

During field reconnaissance in the Kimball Bench area, we observed a section of thick, well-developed, densely spaced red paleosols in the Willwood Formation which we suspected to be the PETM. Our analyses revealed the location of the PETM within the lower section of deformed Willwood. There are ~1200 meters of folded Willwood above the 55 meter-long section containing the PETM. The PETM lasted between 100,000 and 200,000 years, and from our work, there is another 1200 meters of deformed Willwood above the PETM. This 1200 meter section was deposited over a time interval ranging between ~2.2 and 4.4 million years, therefore, deformation in the Kimball Bench area began at least 2.2 million years into the Eocene, 3.5 million years later than previously thought (Pierce, 1965).