CONTROLS ON SEDIMENT FLUX THROUGH THE INDUS SUBMARINE CANYON DURING THE LAST GLACIAL CYCLE

Transport of sediment through canyons on continental margins is one of the primary processes responsible for building submarine fans in many deep-sea basins. These fans are not only of economic interest as hydrocarbon reservoirs but also are potentially high-resolution archives of changing environmental conditions in the onshore drainage basins. Earlier models for sediment transport through canyons indicated a dominant role for sea level in controlling this flux, but this largely ignored the role of climatically modulated sediment delivery. We focus on evaluating the roles played by sea level variations and sediment supply in feeding sediment through the submarine canyon to the deep-sea basin and to assess the continuity of sandy channel fills.

Classic sequence stratigraphic models argue that submarine canyons and their associated deep-sea fans should become inactive during periods of rising and high sealevel as accommodation space is generated on the continental shelf. New cores from the canyon now show that sediment has been propagating deep through the shelf canyon during the entire Holocene. Sediment accumulation is known to be very rapid in recent times at the head of the canyon, but new ¹⁴C ages from foraminifera show that sandy sedimentation was ongoing in much deeper water in what is now an ox-bow cut-off at ~7 ka. A core in the mid shelf canyon shows that sedimentation there has been rapid since at least 1000 yrs ago, and may have involved significant recycling, possibly from the depocenter at the canyon head. Nd and Sr isotopes allow us to see that sediment in the canyon is of the same composition as that in the river mouth at the time of sedimentation. This raises the possibility that the river was directly supplying sediment to the canyon since at least 5 ka, shortly after eustatic sealevel stopped rising. Our data indicate that despite sealevel rise sediment supply to the canyon was not cut-off during the deglaciation, although the volume of the flux was reduced. We suggest that enhanced sediment supply, driven by strong monsoon rains onshore compensated for the rising sealevel and allowed the connection between river and canyon to be maintained.