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Abstract

The Indus River drains the Western Himalayas and is supplying sediment to the second largest submarine fan in the world in the Arabian Sea. Sediment flux represents erosion in the mountains, driven by tectonic and climatic processes, yet these are buffered over several time scales, spanning millions of years in the foreland basin and shorter time scales due to storage in terraces and on floodplains. Further recycling and buffering of the erosional signal is possible because of interactions with the dunes of the Thar Desert, whose volume exceeds the size of the Holocene Delta along the eastern edge of the drainage basin.

Volume calculations suggest significant storage and recycling of sediment on time scales of around 10–20 ka both in the valleys of the Karakoram and on the flood plains adjacent to the mountain front. Although much of the sediment is generated by glacial processes, the transport of that material appears to be controlled by the strength of the monsoon precipitation. Sediments that are delivered to the ocean are transported relatively quickly into the submarine canyon but with only limited buffering at least in the landward portions. Rising and high stand sea level conditions do not cut off sediment supply to the canyon. The composition of material in the thalweg and terraces indicate lag times of no more than around 8000 years and probably much less between the river mouth and the canyon, especially in the early Holocene. Sediment supply modulated by the monsoon appears to dominate over sea level in controlling delivery to the deep ocean. On longer time scales (~2 Ma) sediments recovered on the submarine fan by IODP have most similarity with the interglacial composition of the Indus River rather than the glacial, as defined by zircon U-Pb ages. This again implies that monsoon precipitation dominates in controlling sediment flux to the deep sea.

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