EARLY EOCENE RECORDS OF PALEOPRECIPITATION WITH INSIGHT INTO THE AMALGAMATION OF ALASKA

In many paleoclimatic reconstructions, the late Paleocene-early Eocene is considered to have been one of the warmest episodes of the Cenozoic, and is perhaps second only to the middle Cretaceous greenhouse episode as a period of extreme global warmth during the past 100 m.y. The late Paleocene-early Eocene has been characterized as having globally-averaged surface temperatures 2-4ºC greater than today, and ice-free poles inhabited by mammals, reptiles and deciduous forests. Although some worst-case climate model scenarios predict future temperatures similar to temperatures hind cast for the middle Cretaceous greenhouse state, the overall greater paleogeographic similarity of the late Paleocene-early Eocene to the modern world may provide the most meaningful potential worst-case analog to Earth’s near-term climate future.

This study presents oxygen isotopic records of paleoprecipitation derived from early Eocene paleosol siderite spherules obtained along a paleolatitudinal transect from Arkansas to Alaska. The oxygen isotopic values display a pronounced south to north gradient toward more depleted values, an observation that is very similar to those observed along a transect of middle Cretaceous paleosols. These results support early Eocene reconstructions with paleotemperatures as warm as those determined for the middle Cretaceous, and provide evidence for an accelerated early Eocene atmospheric hydrologic cycle.

In the Samovar Hills near Mount Saint Elias, Alaska, less depleted values interrupt the overall smooth south to north gradient in oxygen isotope depletion. The less depleted oxygen isotope values support paleotectonic models of the Yakutat Terrain as a far-traveled continental block derived from the south, and provides further evidence for the reliability of oxygen isotope data from paleosol siderites for use in paleoenvironmental applications.