Sonograph Patterns of the Central Western Continental Shelf of India

P.S Rao


Side scan sonar and bathymetric surveys were conducted on the central western continental shelf of India. The sonographs portray a smooth, relatively featureless inner shelf, up to a depth less than 40-50 m, which is covered with fine grained sediments. The sonographs of the outer shelf, from beyond 60 m depth, to the shelf edge, exhibit bedforms such as reef outcrops (algal and oolitic ridges) and minor topographic undulations. Towards the shelf edge these give way to isolated colonies of algal knolls. A transition zone with tonal variations is present between 40 and 60 m water depth. Ground-truth data from sediment and rock distribution maps indicate depositional (inner shelf), nondepositional or erosional (outer shelf) environments and a combination of both in the transition zone. These match well with the sonographs.


Sonograph; sediment texture; algal ridges and algal knolls

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