STRATIGRAPHIC EVIDENCE FOR ENHANCED TERRESTRIAL PRECIPITATION, RUNOFF, AND EROSION DURING EOCENE THERMAL MAXIMA IN THE ARCTIC ALASKA PROVINCE, NORTHWESTERN NORTH AMERICA

The Eocene was a time of several abrupt global warming events (Eocene thermal maxima, or ETMs), each lasting on the order of 10⁴-10⁶ years. These events are considered to be the closest geologic analogs for modern global warming and associated changes in the hydrologic cycle. In the Arctic, much of what is known about the ETMs is based on the sedimentary record from a core in the central Arctic Ocean. This record presumably integrates information from the various Arctic landmasses and indicates several degrees of warming as well as enhanced runoff during the most pronounced ETMs. Although there are growing numbers of complementary records from the Arctic shelves, few are from the western Arctic.

Past palynological studies indicate that the Franklin Bluffs section of Arctic Alaska (present latitude ~70°N, paleo-latitude ~80°N) is Early Eocene in age. Hundreds of meters of strata are well exposed at this site, making it the most promising potential outcrop to study the ETMs in the Arctic Alaska province. Here, detailed sedimentologic characterization along measured sections reveals a basal, delta plain section, overlain by a shallow marine section that is capped by a conglomeratic, non-marine section. We present a new carbon isotope stratigraphy for the lower ~200 m of the outcrop (n~1000, measured on bulk organic carbon and organic fragments). To date, the most distinctive features of the isotope stratigraphy are a negative excursion near the base of the section (magnitude of ~5 ‰) and a relatively prolonged negative shift (magnitude of ~1 ‰) in overlying strata. We correlate the basal 5 ‰ excursion to the preeminent Paleocene-Eocene Thermal Maximum. It occurs within the delta plain section, which is predominantly muddy and sandy. However, the negative excursion interval is associated with anomalous conglomeratic sediments. Although correlation of overlying portions of the carbon isotope stratigraphy to global records is ongoing, the 1 ‰ shift in carbon isotope values is associated with an anomalous coarse-grained interval with sedimentary structures indicative of rapid sedimentation. Collectively, the data are consistent with the enhancement of rainfall, runoff, and erosion over the Arctic Alaskan portion of the broader circum-Arctic during the most extreme Eocene greenhouse climates (ETMs).