Regional geomorphology of the continental slope of NW India: Delineation of the signatures of deep-seated structures

Abstract

Geomorphological features (derived from 16,000 lkm of echo-sounding and bathymetric data) and deep-seated tectonic tectonic structures of the continental margin off NW India are presented. The shelf break over the entire region occurs between 80 to 154 m water depth, and adjacent to Saurashtra and Bombay High the depth and orientation of the shelf edge show marked variations. The boundary of the slope is shallower in the northern portion (about 1450 m in the vicinity of the Indus) than in the southern region (2900 m off Bombay). The steep slope off the Gulf of Kachchh has relatively smooth physiography due to higher input of fluvial sediment and burial of structures. The gentler slope off Saurashtra and the Bombay High area has numerous complex features, the most prominent among them being benches at depths of 180-230 m (width 2-10 km) and 650-780 m and a series of bathymetric highs and lows. Slope breaks are also observed between 400 and 600 m off Bombay and between 560 and 960 m off Saurashtra. These features are surface manifestations of the anticlinal features extending along the shelf in this region. Unevenness (order of 100-300 m) due to slumping is also observed at the base of the slope. Based on the correlation between tectonic structures of this area and these subphysiographic features, extension of the Saurashtra Anticline onto the slope, a new strike slip fault (the southern boundary fault of Narmada graben) and an along-shelf anticlinal structure off Saurashtra are delineated