Paleocean Events During Paleocene/Eocene Boundary At Gamba Basin, In Southern Tibet

With the development of DSDP and ODP, a lot of important results have beenachieved in palaeoceanography. One of them is the geologic event at thePaleocene/Eocene boundary (P/E). A marine boundary succession is well preserved inthe Gamba region of southern Tibet. The research on micro-fauna and carbon, oxygen,strontium isotopes and magnetic susceptibility reveals that the signals of globalPaleocene/Eocene boundary event are well recorded in the Gamba region. Thebenthic foraminifera were extinguished stepwise toward the top of the PaleoceneZongpu Formation, with a general extinction rate of 69%. Overturn of foraminiferaoccurs at the P/E boundary that is indicated by the extinction of genus Miscellanea.The recovery of the faunal happened gradually upward from the bottom of the EoceneZhepure Formation. Except 12 species were survived from the Paleocene, all other 56genera are new types of Eocene and present three recovery stages. According to theanalysis, PETM event caused seawater temperature rising and environment change.This event happened abruptly and lasted a short time, benthic foraminifera cannot fitfor it and begin to extinct. After that, the temperature return to normal, with newgenus appeared. A clear negative Carbon isotope shift of -4‰ occurs at the boundary.It is well correlated with standard isotopic shift in the world. The changes of the seaenvironment can help us to explain this kind of phenomenon. But the changes ofoxygen isotope are not consistent with event. The strontium isotopic shift is notobvious at the boundary, but an important peak appears above the boundary that ismatched with the 53ma level. Magnetic susceptibility change is obscure at theboundary but a sharp change of magnetic susceptibility clearly appears at two metersabove the boundary. All above significant changes imply that the Tethys-Himalayanarea was affected by the Paleocene/Eocene Thermal Maximum (PETM). Temperaturewarming in deep oceans also occurred in shallow marine sequence but with expandedduration.