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Abstract

The Eocene Thermal Maximum 2 (ETM2) and Hyperthermal 2 (H2) events are Paleogene hyperthermal events occurring ~53.7 mya and ~53.6 mya, respectively, and are characterized by increased global temperatures and an influx of isotopically light carbon to the exogenic carbon reservoir. Unlike the much better studied Paleocene Eocene Thermal Maximum (PETM), no descriptions of environmental change during these events have been published, and to date only one record of the ETM2 and H2 has been reported from terrestrial sections. In this study, carbon isotope chemostratigraphy is used to identify records of the ETM2 and H2 in the Piceance Basin of western Colorado, and relate them to known section in the Bighorn Basin of Wyoming. Oxygen isotope records, weathering indices from major element concentrations in paleosols, and sedimentological changes are then used to study environmental and sedimentation changes associated with those events in the Piceance Basin. In particular, it is suggested that hyperthermal events are associated with a noted decrease in weathering intensity, decrease in soil moisture, enhanced seasonal precipitation, and a drastic change in the nature of sedimentation. In the Piceance Basin, there is evidence for a decrease in weathering during the ETM2 event, a decrease in soil moisture, seasonal precipitation, and a drastic change in sedimentation flux. The importance of having a second terrestrial record of the ETM2 and H2 in the Piceance Basin is revealed through comparison with the Bighorn Basin records. There are obvious geochemical and sedimentological differences between the two basins. Consequently, careful consideration must be applied when extrapolating environmental impacts from one locality through time or space in order to characterize the nature of terrestrial environmental change during hyperthermal events.

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