CONTROLS ON SEDIMENT FLUX THROUGH THE INDUS SUBMARINE CANYON SINCE THE LAST DEGLACIAL

Transport of sediment through canyons on continental margins is one of the primary processes responsible for building submarine fans. These fans are not only of economic interest as possible hydrocarbon reservoirs but are potentially archives of changing environmental conditions in the drainage basins. Such sedimentary records may allow the relationships between climate, tectonics, erosion, and weathering to be investigated if the sediment transport process can be understood. In particular, we target the degree of reworking and “signal shredding”. Earlier models for sediment transport through such canyons indicated a dominant role for sea level in controlling this flux, which largely ignored the role played by climatically modulated sediment delivery.

Classic sequence stratigraphic models argue that submarine canyons and associated deep-sea fans become inactive during periods of rising and high sealevel. Cores from the Indus Canyon now show that sedimentation continued throughout the Holocene. We present new age and provenance data from a variety of cores covering the last ~20 ka that show continuous deep-water sedimentation through the Indus Canyon since at least ~11 ka. Large volume turbidite flows mantled terraces >200 m above the thalweg throughout the Holocene and their deposits show trends in lithology and geochemistry which coincide both with rising sea level and times of strong summer monsoon in the Early-Mid Holocene. We use Nd-Sr isotope compositions to show that canyon sediments are similar to the Holocene river mouth, suggesting direct supply from the river into the deep water system, with no more than ~8 k.y. of possible buffering, and likely much less from 5.5 to 12 ka. Significant reworking of older sediments during sea level rise can be excluded so that deep-water sediment in the canyon contains a direct record of the Indus River sediment load. Thus signal shredding within the canyon appears to be limited, at least since ~11 ka, suggesting that climatically modulated sediment supply dominates over sea level in controlling canyon sedimentation in high sediment supply settings. Our study allows the difference between reworking within the canyon and direct supply from the river to be resolved for the first time in a major submarine canyon.