【作者】 张振芳；

【导师】 方念乔；

【作者基本信息】 中国地质大学（北京） ， 古生物学与地层学， 2003， 博士

【摘要】 东北印度洋孟加拉湾位于世界屋脊—喜马拉雅山之南，是喜马拉雅山和青藏高原剥蚀物的主要承载区，因此二者之间在物质的剥蚀、输送和沉积过程中存在密切的关联。孟加拉扇的沉积以浊流作用为主，沉积速率相对较高，可对其进行短尺度、高精度古气候变化研究；东经90°海岭的沉积以远洋—半远洋沉积为主，沉积速率较低，但雄踞扇底的海岭较少受浊流、等深流活动的改造，保存了沉积过程的原始信息，是进行长尺度古海洋学研究的理想场所。 本文通过对孟加拉湾扇区的MD77190和MD81345以及岭区的DSDP217、DSDP216、OPD758和MD813496支岩芯上新世以来长短两个尺度的稳定同位素地层、碳酸盐地层、磁化率地层、陆源物质粒度等的深入研究，探讨了该区沉积记录对5.2MaB.P.来喜马拉雅山加速隆升的响应以及与“中更新世转型”、“中布容溶解”事件和末次冰期中的D-O旋回、海应事件等全球性或区域性古海洋、古气候变化之间的耦合关系。也对研究区30万年来印度季风的演化、表层海水古生产力、海水古化学、陆源物质输入量和沉积速率等的变化做了深入细致的研究，探讨了这些变化之间的联系及相互作用，并与高纬度冰川—气候旋回及低纬度日照量的变化做了对比分析。通过海陆气候对比和远程气候对比揭示出高纬度地区不稳定快速气候变化在该区存在积极响应，二者之间存在气候变化的遥相关说明该区气候变化具有全球性。另外，该区气候变化与低纬度日照量变化的一致性说明该区气候变化也具有区域性。 通过对各指标的理论分析和相互对比印证，探明其气候环境指代意义后对研究区上新世以来的古气候、古环境变化进行了探讨。从ODP758磁化率、碳酸钙沉积通量和非碳酸钙沉积通量变化反映出研究区在5.1、3.9-3.4、1.7和0.8MaB.P.附近陆源物质的输入量增加，这可同现有资料表明的喜马拉雅山上新世以来的隆升历史。其中后两次隆升较为强烈，表现在三项指标同期快速增加且增幅较大。后三次隆升分别与青藏高原隆升过程的青藏运动A幕(3.6MaB.P.)、青藏运动C幕(1.7MaB.P.)和昆仑—黄河运动(1.2-0.6MaB.P.)的时间一致。对印度季风和轨道变化的相位关系分析发现2.6、1.7、1.2-0.6MaB.P.是印度季风的重要转型时期，后两次转型与该区沉积记录反映的喜马拉雅山和青藏高原隆升完全对应，说明研究区沉积记录和古气候演化对高原隆升信号的响应是存在的，可作为高原隆升的远程监视器。 ODP758的碳酸钙含量、＞150μm的粗组分含量以及浮游有孔虫生物地层揭示出在0.55-0.4MaB.P.研究区深海碳酸盐遭受强烈溶解。碳酸钙含量明显降低；＞150μm的粗组分减少；浮游有孔虫中易溶种比例减少，抗溶种比例增加。此事件与大西洋、太平洋、印度洋其他海区及南沙海区沉积记录中的“中布容溶解”事件一致，反映了其存东北印度洋中霎带i山以来沉积记录及古气候淡化 张报并 在的广泛性。对＞150 p m 的粗组分含量进一步分析发现，深海碳酸盐的溶解存在 0．6－0．4M。的长周期震荡，“中布容溶解”事件是其中最后一次，可能与人洋长期CaZ十 通量变化和／或深水碳循环有关。 ODP758浮游和底栖有孔虫氧同位素曲线记录了发生在中更新世0．85MaB．厂附近 的主导周期转型事件。对二者进行 100ha滤波分析发现偏心率周期在 1．ZMaB里突显， 之后在1．10．gMaBP．这一周期一度减弱，在0．85MaBP再度增强并趋于主导周期。转 型事件发生的时间与最后一次高原强烈隆升的时间一致，推测二者之间可能有某种关 w。 对海岭L的三支岩芯 DSDPZ16、DSDP27和 ODP758陆源物质粒度分析发现，菲 南面的 ZI6的中值粒径和平均粒径均人于靠北面的 2 7，这与海岭上陆原物质的原厂。 搬运的水动力条件及海岭与扇底的相对高程矛盾，由此推测有另外的非碳酸盐物质来 源。进一步分析发现这个来源是Sunda岛弧的火山灰物质，虽然这部分物质的景相对 极少，但其粒度较粗，从而使整体粒度出现卜述反粒序。由于控制两个物源亚区供应 量的因素不同，据此可判别古气候变化。 对孟加拉湾30万年来多岩芯、多指标综合研究发现研究区气候变化既受冰川一气 候旋问的控制又受低纬度日照量变化的影响。冰期时陆源物质沉积通量增加、碳酸钙 含量减少、磁化率升高、＞150Vm 的粗组分含量增加、底栖有孔虫6门C降低，说明 冰期时由于海平面下降，岸线向海推进，陆源物质输入量增加，一方面导致磁化率升 高，另一方面刺激表层生物生产力增加。陆源物质输入量和表层生物生产力增加共同 作用使冰期时沉积速率增大，相对较高的沉积速率和陆源物质的稀释作用使深海碳酸 盐的保存增加，问冰期情况相反。另外在扇区的＊＊7刀叨岩芯中发现了一套颜色深浅 相间的韵律层沉积，对其进行多指标研究发现它反映了末次冰期以来的快速气候变化， 可与阿拉伯海区、圣巴巴拉盆地以及格陵兰冰芯记录的rO旋回和海应事件对比，反 映了研究区气候变化与高纬度气候不稳定的遥相关。从孟加拉扇区沉积的粘土矿物组 合及盐度变化说明低纬度日照量变化对研究区古气候变化有?更多还原

【Abstract】 Situated in south of Himalayas-the loftiest mountain ranges in the world, Bay of Bengal hosted most of erosion products from Himalayan and Tibetan Plateau. As the result, an enormous submarine sedimentary fan, as so called "Bengal Fan" has been deposited in the floor of Bay of Bengal. There is a clear relationship between Bengal Fan and Himalayas-Tibetan Plateau in the cause of terrigenous deposits erosion, delivery and sedimentation. During the formation of Bengal Fan, the greatest turbidite body in the world, turbidity currents sedimentation is the main dynamics to build the sedimentary framework. So the sedimentation rate of the fan is relatively high and it can be regarded as an ideal subject to carry out short-term and high-resolution paleoclimatic research. Ninetyest (90°E) Ridge is a submarine mountains of the Bay of Bengal. It is mainly documented by pelagic and himipelagic sedimentation. So the sedimentation rate of the ridge area is relatively low. On the other hand, this area is minor reformed by turbidity and bottom currents activity, so it contains some initial information of the sedimentary process. As such, it can be served as an ideal situation to so some long-term research on paleoceanography.Many proxy records have been developed to define the change of paleoclimate and paleocanograpphy. Here we present the stable isotope, weight content of CaCO3, magnetic susceptibility and grain size records of MD77190, MD81345 from the Bengal deep sea fan and DSDP216, DSDP217, ODP758, MD81349 from the Ninetyest Ridge to discuss the response of the sedimentary records to the rapid uplift of Himalayas and Tibetan Plateau. The coupling relationship of the global or regional paleoclimatic and paleoceanographic changes, such as mid-Plestocene Transition, mid-Brunhes Dissolution Event and the rapid climate variability during the last glaciation have also been discussed. The results shoe that the sedimentary records of the studied region have well documented not only the rapid uplift of Himalayas and Tibetan Plateau over the past 5.2Ma, but also the mid-plestocene transition and mid-Brunhes dissolution event, The results also suggest that the climatic changes in the low latitudes have a good response not only to the glacial-interglacial cycles and climatic instability in the high latitudes, but also to insolation of summer in the low latitudes.Firstly, basted on the theory analysis and comparison, we make a discussion about the climatic implications that the proxy indicators bear and the regional evolution concerned. Then we argue the Paleoclimatic and paleoenvironmental changes of the studied region since Pliocene time. The changes of magnetic susceptibility, mass accumulation rate (MAR) of CaCO3 and non-CaCO3 MAR form ODP site758 indicate that the loaded terrigenous sediments increased at 5.1MaB.R, 3.9-3.4 MaB.R, 1.7MaB.P. and 0.8MaB. P. These accompanied the rapid uplift of Himalayas since Pliocene. Among the four changes, the last two changes were relatively obvious; they indicate that the two uplifts were relatively significant. The last three changes coincided with the uplifts of Tibetan Plateau, so called "Episode A of Qinghai-Tibet Movement (3.6MaB.P.)", "Episode A of Qinghai-Tibet Movement (1.7MaB.P.)" and "Kunlun-Huanghe Movement (1.2-0.6MaB.P.) and thelast two changes coincided with the main period transition of the Indian monsoon. These suggest that the sedimentary records of the studied area have response to the uplifts of Himalayas and Tibetan Plateau and changes of paleoclimate. It can be regarded as a "watch" of the uplift. The changes of the CaCO3 content, coarse fraction (>150nm) content and planktonic foraminifer faunal variations from ODP site758 show that the dissolution of CaCO3 was great during 0.55-0.4MaB.P.. Because the first two proxy indicators clearly decreased and the amount of dissolution-sensitive species reduced, in the same time, the amount of dissolution-resistant species increased in this period. The event has been found in Atlantic Ocean, Pacific Ocean, the oth更多还原