古新世/始新世全球增温在西藏岗巴地区的表现

随着深海钻探计划(DSDP)和大洋钻探计划(ODP)的开展,在古海洋学领域取得了许多重大发现。古近纪古新世与始新世(P/E)界线间的地质事件的发现便是其重要成果之一。西藏南部岗巴地区发育有良好的海相界线地层。对生物群、碳、氧、锶稳定同位素以及磁化率的研究显示,全球界线事件在西藏南部岗巴地区具有明显的影响。古新统宗浦组顶部底栖有孔虫动物群阶段性绝灭,总灭绝率为69%。始新统遮普惹组底部有孔虫逐渐复苏,除12种为古新世的残存类型外,始新世生物组合全为新的属种,并呈现三个复苏阶段。碳稳定同位素表现为三期负向偏移,在界线处出现-4‰的异常。这一异常与全球碳稳定同位素事件表现一致。锶同位素在界线位置没有明显的变化,而明显的峰值出现在界线之上,并与全球53Ma出现的锶同位素变化相对应。磁化率在界线之上2m处出现一个很明显的波动,与第3期碳同位素异常吻合。所有研究结果表明,西藏南部(特提斯-喜马拉雅低纬度浅海环境)在古新世与始新世界线时期出现明显的气候变化,说明全球深海温度增高在浅海环境具有相同表现,只是影响时间较长。

The global Paleocene/Eocene Thermal Maximum event in the Gamba area, Tibet

With the development of DSDP and ODP, several important results have been achieved in palaeoceanography. One of these is the Paleocene/Eocene boundary (P/E) event. A marine boundary succession is well preserved in the Gamba region of southern Tibet. Research on micro-fauna, carbon, oxygen, strontium isotopes and magnetic susceptibility reveals that the signals of global Paleocene/Eocene boundary event are well recorded in the Gamba region. The benthic foraminifera were extinguished in stepwise fashion toward the top of the Paleocene Zongpu formation, with a general extinction rate of 69%. An overturn of foraminifera occurred at the P/E boundary as indicated by the extinction of genus Miscellanea. Faunal recovery occurred gradually upward from the bottom of the Eocene Zhepure formation. Except for 12 species, which survived from the Paleocene, all other 56 genera are new in the Eocene and present three recovery stages. A clear negative Carbon isotope shift of -4‰ is recorded at the boundary and is well correlated with other standard isotopic events. The strontium isotopic shift is not obvious at the boundary, but an important peak appears above the boundary that is matched with the 53 Ma level. A sharp change of magnetic susceptibility is also clearly located two meters above the boundary. All the above features indicate significant changes, implying that the Tethys-Himalayan area was affected by the Paleocene/Eocene Thermal Maximum (PETM). The temperature warming in deep oceans also occurred in shallow marine sequence but with expanded duration.