Rocky Mountain Section - 64th Annual Meeting (9–11 May 2012)

Paper No. 3
Presentation Time: 9:15 AM


RASMUSSEN, Dirk and FRICKE, Henry, Geology, Colorado College, Colorado Springs, CO 80903,

The Paleocene Eocene Thermal Maximum (PETM), a rapidly occurring and global interval of climate change, yielded the highest temperatures of the last ~80 My. In addition to a global change in temperature, the PETM is thought to have impacted fluvial sedimentation and, by extension, hydrology in terrestrial basins. The goal of this study is to investigate whether such a PETM-sedimentation link exists in the Wind River Basin (WRB) of Wyoming.

It is possible to identify the PETM in the rock record because it is coincident with a 2-6‰ negative carbon isotope excursion (CIE) in terrestrial records. Preliminary carbon isotope data from bulk sedimentary organic matter from the early Cenozoic Indian Meadows and Fort Union formations in the southeastern part of the WRB identify a ~4-5‰ negative CIE. Both the magnitude of this excursion and the absolute carbon isotope ratios of organic matter are consistent with other terrestrial records of the PETM CIE, thus indicating that the PETM is preserved in the WRB.

The PETM section in the WRB is associated with a sedimentological transition from organic-rich mudstones to channel sands. Onset of the coarser beds, interpreted as fluvial channel deposits, occur stratigraphically below the CIE onset. One possible explanation for this onset is that this represents sedimentological response driven by climatic change prior to main phase PETM. Alternatively, the CIE onset may be coincident with sedimentological changes observed but effectively masked in the isotope record due to a higher influx of recycled carbon from Mesozoic sedimentary rocks in channel sands. In either case, it seems apparent that the climate change at/near the PETM had a pronounced influence on sedimentology in the Wind River Basin.