Channel-levee System - the Major Controlling Mechanism for the Sediment Deposition on the Indus Fan

The Indus fan is the most pronounced and extensive physiographic and sedimentary feature of the Arabian Sea as well as it is the second largest submarine fan in the world. It has developed off the passive continental margin of Pakistan and India, covering an area of about 1.1 x10 km which makes it one of the largest sediment bodies in the ocean basins, totalling ~5 x 10 km in volume. The present Indus fan owes its evolution and development mainly to the Himalayan orogeny, the Indus River and its submarine canyon and the resulting channel-levee system, greatly influenced by the sealevel fluctuations, since late Oligocene/Miocene times. The turbidity currents are the dominating controlling process, along with the pelagic sedimentation and mass wasting deposition, in the formation of the Indus fan. The intensity and frequency of the turbidity currents varied in response to the sea-level changes. Turbidity currents, mainly during the late Tertiary sea-level low stands, transported sediments to the fan from the Indus delta, through the Indus canyon and into an extensive, complex, meandering and braided network of fan valleys. Silt and sand were deposited within the channels whereas, clay and sand-size mica were deposited from over bank flows on the levees. During the high sea-level stands the terrigenous sediments were generally trapped within the Indus delta and thus the fan became the site of predominantly pelagic/hemipelagic sedimentation; this is represented by the draping of foraminiferal-nannoplankton ooze over most of the channel-levee system. Besides indicating increased