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

研究更新世-全新世印度河系统气候和海平面变化期间的沉积物输送过程

• 批准号: NE/G002029/1
• 负责人: Peter Clift
• 金额: $ 16.74万
• 依托单位: University of Aberdeen
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2008
• 资助国家: 英国
• 起止时间: 2008 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FG002029%2F1
• 关键词: Investigating; Sediment; Transport; Processes; During

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.

沉积在大陆边缘深水中的沉积物是从邻近大陆块侵蚀而来的，因此是该区域构造和气候历史的记录。然而，解码这一沉积记录并不简单，因为从喜马拉雅山顶峰侵蚀下来的一粒沙子有一条漫长而复杂的路径，最终到达印度洋的安息之地。尽管如此，了解这些沉积物记录的回报是巨大的，因为它们通常提供了山脉长期侵蚀行为的唯一证据。这一点在南亚尤其重要，有人认为，印度-亚洲碰撞后，山脉，特别是青藏高原的隆起造成了重大的气候变化，最明显的是亚洲季风的加强。然而，证明气候和构造运动之间的联系还不可能，尽管印度河流入大海的沉积物可能是重建导致当今状况的一系列构造和气候事件的最佳希望。鉴于季风现在维持着66%的人类，了解其原因必须是一个高度优先的科学问题。在这个项目中，科学家们以前一直致力于研究巴基斯坦印度河沿岸的河流和三角洲系统，现在他们提议跟踪沉积物在大陆架上的离岸运输。对陆架沉积物的初步研究表明，这些沉积物可能根本不是来自河流，而是从西部沿沿着搬运而来的。如果是这样的话，河流中的沉积物去了哪里？比较19世纪和更近的图表，以及几代卫星图像，表明三角洲一直在向深海峡谷的顶部扩展，该峡谷向深海提供沉积物。河流中的沉积物是否绕过大陆架直接流入峡谷？这似乎很难想象，当海岸最初被最后一个冰河时代结束造成的海平面上升所淹没时。海平面上升将导致沉积物在河口附近被捕获，并结束深水中的沉积。在这个项目中，我们建议绘制出沉积物在最近的过去积累，以了解从印度河到达海洋的沉积物沉积在哪里，海平面上升后深海开始再次接收沉积物的速度有多快，以及输送到深海的沉积物类型是否在冰川消退期间随气候而变化。如果海平面和气候变化导致深海沉积物存在很长的时间间隔，那么这将影响我们可以从这些沉积物中重建多少侵蚀历史。我们将调查巴基斯坦大陆架的内部，以前的调查是向陆地的，特别注意三角洲和印度河峡谷顶部之间的区域。我们将利用地震反射法绘制沉积体图，并观察三角洲在最初淹没后如何开始向峡谷顶部扩展。我们将使用两种类型的地震勘探，一种提供非常详细但较浅的记录，另一种提供更深入海底但细节较少的记录。在八个选定地点对沉积物进行取芯，将能够通过对贝壳碎片和其他有机材料进行碳定年或通过对放射性210 Pb进行分析来确定沉积物的年龄。此外，可以分析砂和粘土的Nd同位素以限制它们的来源（即，从印度河或沿着马克兰海岸），注意这是否在短时间内发生变化，以及大陆架上的变化是否与三角洲的已知变化相对应。粘土矿物的X射线分析将用于记录沉积物来源地区风化性质的变化，这可以与当时已知的季风历史相匹配。将对选定的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。