【作者】 王曦；

【导师】 万晓樵；

【作者基本信息】 中国地质大学（北京） ， 海洋地质， 2010， 博士

【摘要】 在古新世与始新世界线(P/E)时期的短时间内发生了一件全球性增温事件,被称为古新世/始新世最大热事件(PETM)。该时期的底栖大有孔虫的绝灭(BEE)以及演替(LFT)在古近纪底栖大有孔虫演化过程中起着非常重要的作用。西藏南部岗巴地区发育有良好的海相界线地层,在宗浦Ⅰ宗浦Ⅱ剖面中,对底栖大有孔虫动物群及碳、氧稳定同位素,锶同位素,磁化率的研究显示全球界线事件对该地区造成明显影响。在界线附近,底栖大有孔虫出现大量灭绝,平均总灭绝率达73%。据分析,PETM事件的发生造成海水温度的快速上升,底栖大有孔虫不能适应新的环境,从而发生灭绝。界线之上开始出现复苏,底栖大有孔虫的平均新生率为75%。事件过后,底栖大有孔虫SBZ4动物群被SBZ5~SBZ13动物群代替,以古新统宗浦组的Miscellanea miscella,Lockhartia haimei,Glomalveolina Primaeva的灭绝和Operculina一属的消失及始新统遮普惹组Nummulites willcox, Alveolina ellipsoidalis和Orbitolites complanatus出现为特征。在该时期,底栖大有孔虫也在进行着不同的进化并存在不同的古地理分布。在古新世界线顶部,碳稳定同位素值出现明显负偏,宗浦Ⅰ剖面的碳稳定同位素出现3期负向偏移,在界线处的低峰值为-4‰;宗浦Ⅱ剖面的碳稳定同位素低峰值为-7.9‰,然后迅速返回。两剖面在界线处的碳稳定同位素与全球同一时期碳稳定同位素事件表现一致;氧稳定同位素表现则与全球事件不太相同,这可能是由于成岩作用的影响。宗浦Ⅰ剖面中P/E界线处的锶同位素的变化趋势与全球P/E事件出现的时间—55Ma时锶同位素变化趋势相一致。在样品32即P/E界线以上2m处,磁化率值开始出现急剧的增加。造成这种突然变化的原因可降水或气候的改变。西藏南部岗巴地区宗浦Ⅰ和宗浦Ⅱ剖面古新世/始新世界线附近底栖大有孔虫、同位素、磁化率参数的有显著的变化,表明古新世/始新世地质事件对该地区有很大影响,也说明古新世/始新世界线全球地质事件同样发生在东特提斯低纬度浅海地区,只是在浅海地区影响时间更长。更多还原

【Abstract】 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.更多还原