Investigating Sediment Transport Processes During Climate and Sea-Level Change in the Pleistocene-Holocene Indus System

沉积在大陆边缘深水中的沉积物受到邻近陆块的侵蚀，因此代表了该地区构造和气候历史的记录。然而，破译这一沉积记录并不容易，因为从喜马拉雅山顶侵蚀下来的一粒沙子有一条漫长而复杂的路径，才能最终到达印度洋的安息之地。尽管如此，了解这种沉积物记录的回报是巨大的，因为它们往往提供了现在被长期侵蚀的山脉行为的唯一证据。这一点在南亚尤其重要，有人认为，印度-亚洲碰撞后山脉的抬升，特别是青藏高原的抬升，造成了重大的气候变化，最显著的是亚洲季风的加强。然而，目前还不可能证明气候和构造作用之间的联系，尽管印度河输送到海洋中的沉积物很可能为重建导致目前情况的一系列构造和气候事件带来了最大的希望。考虑到季风现在支撑着66%的人类，理解其原因必须是高度科学的优先事项。在这个项目中，科学家们以前一直在研究巴基斯坦境内印度河岸上的河流和三角洲系统，现在他们提议跟踪近海跨越大陆架的沉积物输送。对陆架沉积物的初步研究表明，这可能根本不是来自河流，而是可以从西部沿海岸输送。如果是这样的话，河流中的沉积物去了哪里？对19世纪和更近的海图以及几代卫星图像的比较表明，三角洲一直在向深海海底峡谷的顶部扩张，向深海提供沉积物。河流中的沉积物会绕过陆架直接流入峡谷吗？这似乎很难想象，当海岸最初被上一个冰河时代结束导致的海平面上升淹没时。海平面上升将导致沉积物在河口附近被捕获，并结束深水沉积。在这个项目中，我们建议绘制最近沉积在哪里的地图，以了解从印度河进入海洋的沉积物沉积在哪里，海平面上升后深海开始重新接收沉积物的速度有多快，以及在冰川消融期间输送到深海的沉积物类型是否随着气候变化而变化。如果海平面和气候变化导致深海沉积有很长一段时间的差距，那么这将影响我们能从这些沉积物中恢复多少侵蚀历史。我们将调查巴基斯坦内陆大陆架，与以前的调查一样，特别关注三角洲和印度河峡谷顶部之间的区域。我们将使用地震反射方法绘制出沉积体的地图，并观察三角洲在最初溺水后如何开始堆积到峡谷顶部。我们将使用两种类型的地震勘探，一种提供非常详细但很浅的记录，另一种提供更深入的海底，但细节较少。对八个选定地点的沉积物进行取芯，将允许通过贝壳碎片和其他有机物质的碳测年或通过对放射性210Pb的分析来确定沉积物的年龄。此外，可以分析沙子和粘土中的ND同位素，以限制它们的来源(即印度河或马克兰海岸)，注意这种变化是否在短时间内发生变化，以及陆架上的变化是否与三角洲已知的变化相对应。粘土矿物的X射线分析将被用来记录沉积物来源地区风化性质的变化，这可以与此时已知的季风历史相匹配。将对200个样品进行粒度分析，以限制沉积过程和大陆架上活跃电流的功率。

Sediment deposited in deep water on continental margins is eroded from the adjacent landmasses and thus represents a record of the tectonic and climate history of that region. Decoding this sedimentary record is however not simple because a grain of sand eroded from the peaks of the Himalayas has a long and complex pathway to its eventual resting place in the Indian Ocean. Nonetheless, the rewards for understanding this sediment record are great, as they often provide the only evidence of how mountains now long eroded behaved. This is especially important in South Asia where it has been suggested that uplift of mountains, and especially the Tibetan Plateau, after the India-Asia collision has caused major climate changes, most notably the intensification of the Asian monsoon. However, proving the link between climate and tectonism has not yet been possible, though the sediments delivered to the sea by the Indus River likely hold out the best hope of reconstructing the series of tectonic and climate events that lead to the present day situation. Given that the monsoon now sustains 66% of mankind understanding its causes must be a high scientific priority. In this project scientists who have previously been working on the river and delta systems of the Indus onshore in Pakistan now propose to follow the sediment transport offshore across the shelf. Initial studies of shelf sediment show that this may not be derived from the river at all, but could be transported along the coast from the west. If so, where does the sediment in the river go to? Comparisons of 19th century and more recent charts, as well as generations of satellite images, show that the delta has been building out towards the top of the deep submarine canyon that supplies sediment into the deep sea. Does the sediment in the river bypass the shelf and run straight into the canyon? This seems hard to imagine when the coast was initially drowned by rising sea level caused by the end of the last ice age. Rising sea level would result in sediment being captured close to the mouth and an end to sedimentation in deep water. In this project we propose to map out where sediment has been accumulating in the recent past in order to see where sediment reaching the ocean from the Indus has been deposited, how quickly the deep sea started to receive sediment again after sea-level rise, and whether the types of sediment delivered to the deep sea changed with climate during deglaciation. If there was a long time gap in sedimentation in the deep sea caused by sea-level and climate change then this will affect how much erosion history we can reconstruct from those sediments. We shall survey the inner Pakistan Shelf, landward of previous surveys, with special attention to the region between the delta and the top of the Indus Canyon. We shall use seismic reflection methods to map out sediment bodies and see how the delta began to build out to the top of the canyon after initial drowning. We shall use two styles of seismic survey, one providing a very detailed, but shallow record, and one providing greater penetration into the seafloor but with less detail. Coring of the sediments in eight chosen locations will allow the age of the sediment to be determined by carbon dating of shell debris and other organic material or through the analysis of radioactive 210Pb. Furthermore, the sands and clays can be analyzed for Nd isotopes to constrain their sources (i.e., from the Indus or along the Makran coast), noting if this changes over short time spans and whether changes on the shelf correspond to those known from the delta. X-Ray analysis of clay minerals will be used to record changes in the nature of weathering in the sediment source regions, which can be matched to the known history of the monsoon at this time. Particle size analysis will be performed on a selection of 200 samples in order to constrain the depositional processes and the power of the currents active on the shelf.