Sediment storage and reworking on the shelf and in the Canyon of the Indus River‐Fan System since the last glacial maximum

Abstract

The transport of sediment from the mouth of the Indus River on to the deep-water submarine fan is complicated by temporary storage within large clinoforms on the shelf on either side of the submarine canyon, where most of the sedimentation since the start of the Holocene has occurred. In contrast, shelf edge clinoform deltas represent the products of forced regression and not the progradation of highstand clinoforms as far as the shelf edge. Clinoform sediments have a mixed provenance that involves significant reworking of older sediment deposited during or before the last glacial maximum. Recent sedimentation in the canyon head has been very rapid in the last few centuries (ca. 10 cm year À1 ), but has been starved of sand probably because of 20th century damming. Sandy layers appear to represent annual monsoonal floods with a particularly large flood every 50-70 years. This canyon head sediment is also reworked by currents flowing along the canyon axis before being deposited deeper into the canyon. The last sandy sediment to reach the mid-canyon (ca. 1300 m depth) was transported around 7000 year BP at a time of rising sea-levels, and might reflect reworking by the transgression, or local slumping from the walls of the canyon. Dating of the uppermost in a series of terraces in the mid-canyon area suggests that the canyon may have been partly filled and emptied of sediment at least three times since ca. 50 ka. We conclude from the Holocene record that sediment flux to the deep-water fan experiences major buffering, reworking and recycling both on the shelf and within the submarine canyon prior to its deposition, so that turbidite sands in the deep Arabian Sea cannot be used to correlate with climatic or tectonic events onshore over timescales of 10 3 -10 5 years.

Millennial and centennial variations in zircon U‐Pb ages in the quaternary indus submarine canyon

“…This record shows a lack of sandy sediments in the upper 5 m, which Clift et al. () interpreted to reflect reduced sand transport to the river mouth following 20th‐century damming of the upstream Indus. If that is correct, it implies an unbuffered signal at least in the uppermost canyon in the recent past because changing flux from the river is mirrored immediately by sedimentation in the canyon.…”

“…A series of cores were taken within and adjacent to the canyon (Table ). These materials were collected in 2008–2009, together with swath bathymetry and shallow‐penetrating, high‐resolution seismic reflection profiles during cruise 64PE300 of RV Pelagia (Clift et al., ). We sampled selected cores along the canyon for detrital zircon U‐Pb dating.…”

“…Coring locations are shown in Figure b,c with simplified sedimentary logs in Figure . We sampled both the canyon thalweg (Indus‐21, ‐25) and terraces (Indus‐29, ‐30, ‐31) raised above that level, as well as an abandoned meander cut‐off (Indus‐28), previously dated as mid‐Holocene (Clift et al., ), to provide a relatively continuous record of sedimentation during sea level rise and the subsequent highstand. These cores span water depths from ~300 to ~1,300 m.…”

“…The fan has been mantled by carbonate sediments since~10 ka, indicating a general lack of deep‐water clastic supply (Kolla & Coumes, ). However, sedimentation rates have been rapid at the head of the canyon in the past few hundred years (Clift et al., ) and both hemipelagic and turbidite sediment continued to accumulate in the shelf canyon during the Holocene (Li et al., ).…”

Connections Between Fluvial To Shallow Marine Environments and Submarine Canyons: Implications For Sediment Transfer To Deep Water

“…In contrast, the Indus and Ganges-Brahmaputra deltas have active, muddy, subaqueous clinoforms that reach the heads of their respective canyons (Currie et al 2002;Clift et al 2014;Rogers et al 2015), which have eroded headward and now penetrate 100 km or more into the shelf. Based on calculation of sediment flux, Goodbred (2003) estimated that two-thirds of the sediment load of the Holocene Ganges River is trapped in the delta and delta plain, and 1/3 passes down the ''Swatch of No Ground'' Canyon onto the Bengal Fan, which is known to have been active throughout the Holocene (Weber et al 1997).…”