Coarse-grained fluvial lithofacies associated with the Paleocene/Eocene boundary in the Huerfano Basin, Colorado, USA.

Abstract:

The Paleocene–Eocene Thermal Maximum (PETM) is a rapid interval of global warming that occurred ~56 Ma. The PETM is characterized by an abrupt increase in mean annual temperature and decreased latitudinal temperature gradient. Resulting circulation changes likely modified the hydrologic cycle impacting spatiotemporal distribution of rainfall, fluvial sedimentation, and continental runoff. The goal of this study is to evaluate PETM global warming as an allogenic forcing on fluvial systems in the Huerfano Basin in southern Colorado as a point of comparison to other Laramide basins.

Huerfano Basin is a Laramide structural basin comprising the northernmost extension of the Raton Basin. Huerfano Basin is located to the south and east of previously identified PETM records in the Bighorn, Axehandle, and Piceance basins. Alluvial deposits of the Poison Canyon and Cuchara formations are exposed along the western basin margin and are of known Paleocene–Eocene age. Depauperate biostratigraphic data place the Paleocene–Eocene boundary near the contact between the two formations. Globally, the PETM is identifiable by a distinctive negative carbon isotope excursion in terrestrial and marine strata. In the Huerfano Basin, initial bulk organic carbon isotope analyses presented herein yield isotope ratios suggestive of other terrestrial records.

A prominent basal conglomerate in the Cuchara Formation is approximately coeval with the isotope excursion values. These observations suggest sedimentation in Huerfano Basin responded similarly to Bighorn and Piceance basins as the PETM generated pulses of coarse-grained alluvial lithofacies. However, the grain-sizes mobilized in Huerfano Basin are significantly coarser. Potentially this reflects the proximity to the Mississippi Embayment, the primary moisture source at the time. Overall this southern locality will allow systematic geographic comparisons in the hydrologic cycle response to the PETM in North America.