The Biological And Geochemical Records And The Response To The Global Event Transitional Paleocene/Eocene Thermal Maximum Event In Tibet

A rupid global warming occurred at the Paleocene and Eocene boundary (P/E), which is known as the Paleocene-Eocene Thermal Maximum event (PETM).The benthic extinction event (BEE) and larger foraminifera turnover (LFT) during the Paleocene-Eocene transition constitutes an important step in Paleogene larger-foraminifera evolution. A marine boundary succession is well preserved in the Gamba region of southern Tibet. Research on larger foraminifera fauna, carbon and oxygen stable isotopes, strontium isotopes and Magnetic susceptibility in the sections of ZongpuⅠand ZongpuⅡshow that the signals of global Palaeocene-Eocene boundary event are well recorded in the Gamba region. At the P/E boundary, the larger benthic foraminifera were extensive extinction with an average general extinction rate of 73%. According to the analysis, PETM event caused seawater temperature rising and environment change during a short time, larger benthic foraminifera cannot fit for it and begin to extinct. Following the event, larger benthic foraminifera began to recover with the average rate of 75%. The replacement of SBZ4 fauna by SBZ5~SBZ13 fauna, as characterized by the gradual extinction of Paleocene taxa such Miscellanea miscella,Lockhartia haimei,Glomalveolina primaeva and disappearance of Operculina in Zongpu formation and the rise of Eocene taxa Nummulites willcox, Alveolina ellipsoidalis and Orbitolites complanatus in Zhepure formation. In that period, large benthic foraminifera are also great for a different evolution and the existence of different palaeogeographic distribution. The carbon isotope appeared three negative shifts in ZongpuⅠsection with peak value is -4‰at the boundary. A clear negative Carbon isotope shift is recorded at the boundary with the peak value is -7.9‰in ZongpuⅡsection. The situation of carbon isotope is well correlated with other standard isotopic event. The change of oxygen isotope is different with global change, the probability caused by effects of the diagenesis. The strontium isotopic shift is not obvious at the boundary, but an important peak appears above the boundary that is matched with the 55Ma level. Magnetic susceptibility change is obscure at the boundary but a sharp change of magnetic susceptibility clearly appears at two meters above the boundary, the reason for this sudden change maybe is rainfall or climate change.All above significant change imply that the Tethys-Himalayan area was affected by the Paleocene/Eocene Thermal Maximum (PETM). This event also takes place in the East Tethyan low latitude shallow marine but with expanded duration.