Indus Delta Project

The Indus Fan is the second largest sediment body in the modern oceans. Its stratigraphy records the history of continental erosion during the uplift of the Himalaya and Karakoram, as well as following strengthening of the monsoon. The erosional record in the Arabian Sea is at the center of debates concerning the nature of continent-ocean interactions, and how climate, tectonic activity and erosion inter-relate. However, in order to interpret this record it is essential to understand what sediment the modern Indus River delivers to the coast and how this is transported to the deep sea fan. Pilot geochemical work has established that the modern river-fan system cannot be in state of equilibrium. While material in the main Indus River that reaches the foreland has a similar isotopic fingerprint to the material in the Pleistocene (and older) Indus Fan, the material in the modern river close to the coast is too radiogenic (i.e. of Himalayan provenance) to be representative of what has been historically delivered to the fan. Conversely sediment on the Pakistan Shelf is too unradiogenic to be typical of material delivered by the Indus now or in the past. These data indicate sediment bypassing and disequilibrium, possibly related to damming of the Indus over the last decades. Alternative theories to explain the apparent sediment distribution pattern include seasonal variability of the Indus bedload, large-scale sediment sequestering in the delta and major changes in the Indus drainage system since the Pleistocene.

Comparison of 2000 Landsat image of the delta with the mapped shoreline (red lines) and tidal sand bars (yellow lines) in 1950, showing moderate coastal retreat in the NW of the delta, progradation in the region of the Indus Mouth. Note the tidal inlets that characterize the Rann of Kutch area in the SE are much wider and deeper now than in 1950.

In this project we are characterizing the sediment in the river, delta, shelf, submarine canyon and deep-sea fan in order to constrain sediment distribution pathways and thus test these competing hypotheses for sediment flux. In doing so we shall quantify how quickly sediment is washed through the system and if it is sequestered in different parts of the system en route to the deep sea fan. We shall apply bulk sediment Nd and single grain Pb isotope provenance techniques to sediment samples largely already collected by earlier cruises, supplementing these with shallow core samples to be taken along the coast and on the subaerial delta, in collaboration with scientists from the Pakistani National Institute for Oceanography and the University of Karachi. We shall employ proven isotopic fingerprinting methods to constrain sediment source, using both bulk sediment Nd isotope and single grain Pb isotope analyses measured by ion microprobe (SIMS). The SIMS method is preferred because it allows very small grains to be analyzed that are below the resolution of the conventional TIMS approach. Cores recovered in the delta will be dated using AMS 14C , 210Pb, and 37Cs techniques in order to determine recent sedimentation rates along the coast, which together with satellite images, aerial photographs and older marine charts can be used to constrain the degree of sediment sequestering in the delta during Holocene sea-level rise, i.e. at a time when there is little evidence for active sedimentation on the deep-sea fan. A basic question that needs to be answered is whether sediment is being fed straight from the river into the Indus Canyon and to the deep sea fan despite the Holocene sea-level rise, as has been proposed for the Bengal Fan, or if sediment is all being trapped in the delta or reworked westward along the coast by current and wave activity. Our proposed research will also provide the first stratigraphic development model for Indus delta, the largest, least studied delta in the world. In addition, we will assess the consequences that the geo-engineering-scale experiment of damming the Indus have had on deltaic sedimentation during the last decades.

A few images from the first stages of the work

	Reconnaisance trip to the Indus Delta during January 2004. Trenching activities in the sediments deposited on the shores of a dhand, a temporary lake, located north of the Rann of Kutch resulted in a lot of interest and help from the local population.
Fishing boat on the shores of the Khobar Creek, the main outlet of the Indus River. The eroded banks expose semi-lithifed muds and abundant evidence of mangrove swamp growth, now all gone. Increased incursion of salt water through tidal creeks, driven by reduced flux from the river due to damming, has resulted in significant loss of agricultural land in the delta.
	Soft sediment deformation in river sands in the main Indus channel near Thatta. These sediment represent flood deposits laid down during monsoonal flood events, but left dry and >20 m above the river during the dry season.

Related Links

Peter Clift's Arabian Sea homepage

Learn about scientific drilling plans for the Indian Ocean Submarine Fans

Peter Clift
Woods Hole Oceanographic Institution
Department of Geology and Geophysics
Mail Stop 22
Woods Hole, MA 02543-1047
USA

tel: (508) 289-3437,
fax: (508) 457-2187,
email: pclift@whoi.edu