We might hope that the deep-water sedimentary record reflects processes on land in the region where the sediments are sourced, giving us insight into a combination of tectonic activity and climatic changes. A study looking at the Indus Shelf and Canyon offshore Pakistan led by Peter Clift and including Tim Henstock from G&G suggests this isn’t the case, even though at different stages in the glacial cycle we expect very different sources and volumes of sediments.
We found significant storage and re-working of sediments over periods much longer than 10000 years (the time of the last sea level low) in large clinoforms on the shelf and in the upper section of the canyon before there is transport further down the canyon to the deep sea. Although the top of the canyon has accumulated recent sediment at a rate of 1m every 10 years, with sandy layers that may represent the product of annual monsoon floods, the last similar material reached the mid canyon around 7000 years ago. The mid canyon itself has a number of terraces with near-seabed sediments dated as long ago as 49000 years, suggesting that the canyon itself may also act as a region where sediments are alternately stored and then reworked before they are transported out into the deep Arabian Sea. This buffering means that there is no simple relationship between the onshore processes of erosion and the offshore deposition of sediments.
The study was funded by the NERC and was published in Basin Research