渐新世初大冰期事件:南大西洋ODP1265站的记录

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

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 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 δ^18O 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.