渐新世初大冰期事件: 南大西洋ODP1265站的记录

始新世—渐新世(EO) 过渡期间, 地球由两极无冰的“温室地球”进入到南极有冰的“冰室地球”, 其中以发生在早渐新世初的大冰期事件尤为意义重大.南大西洋ODP1265站氧碳稳定同位素在EO过渡期间发生重大变化, 表明早渐新世全球气温迅速下降, 南极大陆东部首次出现大规模永久性冰盖, 同时全球碳储库发生重大改组, 这一结果与全球其他地区的记录一致.碳酸盐含量、粗组分、浮游有孔虫碎壳率以及碳酸钙软泥的粒度在EO界线附近都发生了突变, 指示了海洋表层生产力的升高、碳酸盐补偿深度(CCD) 的突然加深以及气候快速变冷对生物和碳酸盐沉积的影响. 

The Earliest Oligocene Glacial Maxmum: Records from ODP Site 1265, South Atlantic

The most prominent cooling event of the Cenozoic earth surface during the long-term transition from a non-glaciated planet, or "green-house world", to a polar glaciated planet, or "ice-house world", is the earliest Oligocene glacial maximum (EOGM), immediately following the Eocene-Oligocene (E/O) boundary at about 33.7 Ma. This study analyzed benthic foraminiferal oxygen and carbon isotopes, carbonate content, coarse fraction, planktonic foraminiferal fragmentation, benthic foraminiferal percentage, and carbonate ooze grain size in samples from deep-water Site 1265, Ocean Drilling Program (ODP) Leg 208 on the Walvis Ridge, South Atlantic. The results show that the earliest Oligocene δ18O values represent the magnitude of continental ice sheets on east Antarctica and indicate a large decrease in both surface and deep water temperatures of worldwide oceans during the Eocene-Oligocene transition. Carbonate content, coarse fraction, planktonic foraminiferal fragmentation, benthic foraminiferal percentage and grain size of ODP Site 1265 indicate that carbonate content increases rapidly across the E/O boundary, reflecting the increasing of ocean paleo-productivity, the abrupt deepening in the carbonate compensation depth (CCD) and their impacts on faunas and carbonate deposition.