ANTARCTIC SUBTROPICAL HUMID EPISODE AT THE PALEOCENE-EOCENE BOUNDARY - CLAY-MINERAL EVIDENCE

Clay-mineral assemblages from East Antarctica have been analyzed at hi gh stratigraphic resolution (20 to 1 ka) throughout the interval from 55.6 to 55.0 Ma, which includes the terminal Paleocene isotopic excurs ion in Ocean Drilling Program Site 690B on Maud Rise (lat 65-degrees-S ) in the Weddell Sea region. Changes in the clay associations reflect a major increase in chemical weathering caused by increased temperatur e and/or rainfall in at least this sector of East Antarctica for a bri ef (270 ka) interval in the latest Paleocene. This represents the most intense warming known for the Cenozoic. This high-latitude climatic e pisode is recorded synchronously by stable isotopes and clay minerals. A progression is evident in the clay assemblages during the latest Pa leocene that apparently reflects changing relations between temperatur e and precipitation. This sequence began with the inter-val of rapid t emperature increase that marks the beginning of the oxygen isotopic ex cursion. A brief increase in kaolinite at the inception of the excursi on suggests a temporary increase in year-round precipitation in Antarc tica, in response to an increased continent-to-ocean temperature gradi ent. This kaolinite spike was followed by almost total dominance by sm ectite for the remainder of the isotopic excursion (approximately 120 ka), suggesting that warmer Southern Ocean surface temperatures of 18 to 22-degrees-C were associated with seasonal precipitation (alternati ng wet and dry seasons). Clay-mineral variations on Antarctica during the isotopic excursion reflect a tight coupling between oceanic and co ntinental climate change. Immediately following the excursion at appro ximately 55.22 Ma, kaolinite percentages increased to values similar t o modern subtropical-tropical areas for approximately 150 ka, a remark able event for the Antarctic. Abundant kaolinite suggests perennial ra infall and minimum soil temperatures of 15-degrees-C during at least p art of the year. The kaolinite increased during a time of lower Southe rn Ocean surface-water temperatures, suggesting increased atmospheric heat transport toward the poles. A temporary change in atmospheric cir culation is suggested from dominantly zonal to meridional.