STEADY PALEOCLIMATIC CONDITIONS ACROSS THE EOCENE-OLIGOCENE TRANSITION INDICATED BY PALEOSOLS ON TWO CONTINENTS

The marine oxygen isotopic record indicates precipitous cooling and/or ice sheet growth across the Eocene-Oligocene transition. Traditionally, it has been assumed that this climatic step will also be recorded by terrestrial paleoclimate proxies. However, previous paleoprecipitation and paleotemperature estimates based on paleosols in North American (Oregon, Nebraska, and Montana) suggest instead that changes associated with the Eocene-Oligocene transition are a small part of a long, steady decline rather than a sudden shift from one steady state to another (Nebraska, Oregon), or essentially nil when compared to the whole of the Cenozoic (Montana). New paleoprecipitation and paleotemperature results from paleosols on the Isle of Wight (UK) yield a similar result, even though the paleogeographic setting is totally different. Whereas the North American sites all represent fluvial-lacustrine depositional settings with at least some forest cover, the most appropriate modern analogue for the Isle of Wight succession is the Florida Everglades and the resulting vegetation shows evidence of rooted and floating aquatics and of saline incursions. The sequence also includes growth-banded fossils that indicate minimal change in terms of paleotemperatures, a result consistent with the new paleosol findings. Taken together with the North American paleosol results, this suggests relatively steady annual climatic conditions across the Eocene-Oligocene transition, and that other climatic variables such as seasonality may have driven the observed faunal and floral turnover events.