Climatic vs. Eustatic Controls on Sediment Flux to the Indus Submarine Fan, Indian Ocean
The Indus submarine fan is formed by the erosion of the western Himalayas and associated ranges of Southwest Asia. Sediment flux into the deep water is driven by rock uplift in the mountains but on a variety of timescales the rate of transport is modulated both by sea level (i.e., accommodation space) and climatically modulated erosion and storage of sediment onshore. New, shallow high-resolution seismic and coring data from the Pakistani shelf now shows that large amounts of sediment are stored on the shelf during sealevel highstand periods and that there are significant degrees of reworking from older shelf sediments, as well as longshore drift, so that the sediment in the shelf clinoforms is not closely coupled to the composition of sediment in the river discharge at any one time. The river itself has primarily been fed since 10 ka by incision and erosion of older fluvial terraces rather than by new erosion of the bedrock. Regional-scale landsliding in the early Holocene, triggered by strong summer monsoon rain may be responsible for storage of large amounts of sediment in the big river valleys. Around 20% of flux is derived from incision of the floodplains. This introduces a lag of 10 ky in the transport of sediment from source to the coast. There is an additional lag of at least 10 ka on the shelf for the sediment to be reworked into the submarine canyon and hence into the fan. Sediment reaching the submarine fan is heavily decoupled from the erosion processes in the mountains, at least on the scale of a glacial cycle.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013