Transient drying during the Paleocene–Eocene Thermal Maximum (PETM): Analysis of paleosols in the bighorn basin, Wyoming

Abstract

The Paleocene Eocene Thermal Maximum (PETM) was a transient episode of global warming that occurred at the Paleocene/Eocene boundary. The event is marked by a sharp decline in carbon isotope values that is globally recognized from marine and continental sections. The negative isotope excursion has been attributed to the release of methane hydrates from oceanic sediments. Although studies concur that temperatures rose during the PETM, changes in precipitation are not well understood. Alluvial paleosols in the Bighorn Basin that span the PETM interval contain a continuous and highly resolved record of climate including information on precipitation. They show a significant but transient decrease in precipitation at the onset of the PETM but a gradual return to pre-PETM levels by the end of the interval. The paleosols also show additional, although less dramatic, wet/dry cycles within the PETM interval that may correspond to precessional cycles that have been identified in the marine record of the PETM. This study counters interpretations of increased precipitation for Wyoming at this time and shows the importance of detailed case studies of continental strata to test climatic generalizations and models that have been developed for PETM precipitation patterns.