Abstract: Ancient Submarine Canyon and Channel Morphology, Indus Cone, Offshore Pakistan

T. R. McHargue, J. E. Webb, L. G. Kessler

Continuous multichannel seismic investigation of a part of the Indus cone, offshore Pakistan, shows the presence of over 3,000 m of Miocene deep-sea fan deposits. The excellent resolution of these data affords recognition of channel and canyon features not common in such studies. The ancient outer shelf and upper slope are characterized by at least three large, closely spaced, deep erosional-canyon systems from 25 to 30 km wide. These systems show several stages of canyon development and are filled with layered sediment up to 1,200 m thick. The lower slope and upper rise are characterized by numerous smaller erosional canyons which extend laterally for about 100 km and represent two and possibly three periods of development. Both the upper and lower continental rises are haracterized by aggradational and laterally migrating channels with well-developed levees. These channels are commonly 8 km wide with levees extending 10 to 12 km on each side. Such individual systems are up to 30 km wide. Individual levee deposits attain a thickness of 500 m. Discontinuous reflectors within individual channels may be analogous to the sand bodies in modern braided-fluvial systems.

The ancient Indus cone is envisioned as a multiple submarine canyon-channel fan complex where one or more canyons and/or channels were in dynamic equilibrium and supplied by widely fluctuating volumes of sediment. These fluctuations in sediment supply probably were controlled by tectonic pulses of the Himalayas during the middle Miocene.

AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma