A New Seismic Stratigraphy in the Indian-Atlantic Ocean Gateway Resembles Major Paleo-Oceanographic Changes of the Last 7 Ma
A New Seismic Stratigraphy in the Indian-Atlantic Ocean Gateway Resembles Major Paleo-Oceanographic Changes of the Last 7 Ma
复制标题
印度-大西洋门户的新地震地层类似于过去 7 Ma 的主要古海洋变化
DOI：
10.1029/2018gc007668
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Gruetzner J
中科院分区：
文献类型：
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作者：
Gruetzner J
印度洋和大西洋之间的水团交换构成了全球温盐环流中不可或缺的大洋间联系。利用地震反射剖面研究了深部水流的长期变化，但地震地层学对晚中新世以来的时间段约束较差，没有得到很好的分辨。在这里，我们介绍了国际海洋发现计划站点U1475(阿古拉斯高原)的结果，该站点位于北大西洋深水入海口附近进入南大洋和南印度洋的沉积物漂移上方。U1475遗址包括一个完整的富含碳酸盐的地层剖面，该剖面记录了过去7 Ma气候引起的海洋环流变化。首次在漂移上部300米处发现了6个标志物反射体。这些反射层的形成主要是由于密度的变化，而这些变化主要是由生物沉积与陆源沉积的变化引起的。合成地震图可以根据生物地层学和磁性地层学对层位进行年龄分配。突出的反射体与晚更新世冰川/间冰期变异性、中更新世和早更新世的过渡以及北半球冰川的开始有关。一个特殊的早上新世(~5.3-4.0 Ma)被两个反射体包围，其特征是沉积速率(>；10 cm/Kyr)增加了四倍，并出现了沉积波。我们认为，这种向阿古尔哈斯高原的沉积物输送增强是由于北大西洋深水的最大流入导致底流环流模式的重组所致。
The exchange of water masses between the Indian Ocean and the Atlantic constitutes an integral interocean link in the global thermohaline circulation. Long‐term changes in deep water flow have been studied using seismic reflection profiles but the seismic stratigraphy was poorly constrained and not resolved for the time period from the late Miocene onward. Here we present results from International Ocean Discovery Program Site U1475 (Agulhas Plateau) located over a sediment drift proximal to the entrance of North Atlantic Deep Water into the Southern Ocean and South Indian Ocean. Site U1475 comprises a complete carbonate‐rich stratigraphic section of the last ~7 Ma that provides an archive of climate‐induced variations in ocean circulation. Six marker reflectors occurring in the upper 300 m of the drift are identified here for the first time. The formation of these reflectors is mainly due to density changes that are mostly caused by changes in biogenic versus terrigenous sediment deposition. Synthetic seismograms allow age assignments for the horizons based on biostratigraphy and magnetostratigraphy. Prominent reflectors are related to late Pleistocene glacial/interglacial variability, the middle and early Pleistocene transitions, and the onset of the northern hemisphere glaciation. A peculiar early Pliocene interval (~5.3–4.0 Ma) bounded by two reflectors is characterized by fourfold elevated sedimentation rates (>10 cm/kyr) and the occurrence of sediment waves. We argue that this enhanced sediment transport to the Agulhas Plateau was caused by a reorganization of the bottom current circulation pattern due to maximized inflow of North Atlantic Deep Water.