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Multichannel seismic data suggest that the Indus Canyon off the Indus River and at least 3 other canyons that existed in the past on the Pakistan-India shelf fed sediments to several channel-levee systems on the adjacent upper Indus fan since Oligocene-Miocene uplift of the Himalayas. The canyons on the shelf, when they were active, were primarily erosional. However, the channels were erosional-depositional on the continental slope and primarily depositional on the upper fan. The channels of the upper fan are as much as 10 km (6 mi) wide, and may be V- or U-shaped in cross section. The channels in the upper fan as well as the feeder canyons on the shelf migrated extensively in space and time. On one multichannel seismic line parallel to depositional strike, 15 events of c annel activity on the upper fan have been observed. There were 2 types of channel migration. In one type, the channels were abandoned, and new ones were opened at entirely different locations. In another type, the channels gradually moved as the banks on one side receded owing to erosion, and the banks on the other side advanced in the same direction because of sediment deposition. The uplift of the Murray Ridge, tectonics in the Indus River drainage basin, changes in sediment-input rates and sea level changes, and complete plugging of channels by slumped sediment masses probably caused the first type of migration. Coriolis force and channel meander, among other things, might have caused the gradual migration.
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