The most prominent cooling event of the Earth surface during Cenozoic in 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 Ol...The most prominent cooling event of the Earth surface during Cenozoic in 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 Oligo-cene Glacial Maximum (EOGM) above the Eocene/Oligocene boundary at about 33.7 Ma. Planktonic and benthic fo-raminiferal oxygen and carbon isotopes, carbonate content, and coarse fraction, along with high-resolution color reflec-tance and magnetic susceptibility records during 3530 Ma, from deep-water Sites 1262 and 1265, Ocean Drilling Pro-gram (ODP) Leg 208 in South Atlantic, reveal the global cooling event occurring in both surface and deep oceans. The results show that the earliest Oligocene d 18O values during 33.533.1 Ma represent the magnitude of continental ice sheets on east Antarctica and indicate the large decrease in both surface and deep water temperatures of worldwide oceans. The d 13C records show the large excursion during the period of EOGM event and indicate some types of shift in global carbon reservoir, probably demonstrating the sudden increase in organic carbon burial rates and the changes in the distribution and timing of production. At the same time, lithologic composition, carbonate content, color reflectance, and coarse fraction brought about significant changes close to the Eocene/Oligocene boundary, reflecting the abrupt deepening in the carbonate compensation depth (CCD). Changes in carbonate content were revealed from the color reflectance identify periodicities associated with eccentricity of the Earths orbit (100 and 400 ka), further indicating or-bitally forced global climate variations in the Early Oligo-cene.展开更多
文摘The most prominent cooling event of the Earth surface during Cenozoic in 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 Oligo-cene Glacial Maximum (EOGM) above the Eocene/Oligocene boundary at about 33.7 Ma. Planktonic and benthic fo-raminiferal oxygen and carbon isotopes, carbonate content, and coarse fraction, along with high-resolution color reflec-tance and magnetic susceptibility records during 3530 Ma, from deep-water Sites 1262 and 1265, Ocean Drilling Pro-gram (ODP) Leg 208 in South Atlantic, reveal the global cooling event occurring in both surface and deep oceans. The results show that the earliest Oligocene d 18O values during 33.533.1 Ma represent the magnitude of continental ice sheets on east Antarctica and indicate the large decrease in both surface and deep water temperatures of worldwide oceans. The d 13C records show the large excursion during the period of EOGM event and indicate some types of shift in global carbon reservoir, probably demonstrating the sudden increase in organic carbon burial rates and the changes in the distribution and timing of production. At the same time, lithologic composition, carbonate content, color reflectance, and coarse fraction brought about significant changes close to the Eocene/Oligocene boundary, reflecting the abrupt deepening in the carbonate compensation depth (CCD). Changes in carbonate content were revealed from the color reflectance identify periodicities associated with eccentricity of the Earths orbit (100 and 400 ka), further indicating or-bitally forced global climate variations in the Early Oligo-cene.
