A shallow seismic reflection study of the Gulf of Kutch, northwest India — Observations on its structural evolution

Abstract

A study of echosounding (678 line km) and shallow seismic reflection (180 line km) records of the E-W trending Gulf of Kutch, India showed the following features: The gulf margins in the east, and partly in the southeast and northwest are covered with 2–5m thick acoustically transparent clays. A U-shaped ENE-WSW or E-W channel of 25 km maximum width characterised by uneven topography occurs in the centre of the gulf, this channel being flanked by steep scarps about 10–14 m high. Additionally, about 40 m of thick dead-coral rocks dated at 10,000–13,000 yrs B.P. occur as currently submerged high standing blocks in the axial part of the gulf, and finally, three subbottom reflectors were located at depths of 4–10 m, 10–18 m and 18–20 m. The uneven topography of the U-shaped channel and the even topography of the gulf margins characterise the different energy regimes of the seabed. The correlation of steep scarps with a known fault helped in identifying two ENE-WSW or E-W trending parallel faults along the gulf. Correlation of onshore well-log lithology (near Kadach 75 km from the study area) with subbottom reflectors revealed a comparable sequence, this sequence consisting of sandstone, brown clays and limestones. The relict corals are submerged due to subsidence of the bedrock between the faults on which the corals grew. A regional fault across the margin, connecting the Saraswati Valley of the continental slope with the relict Saraswati River onshore through E-W faults downthrowing towards the north of the shelf and the gulf is proposed. The signatures of the tectonics are imprinted in the coastal morphology of the gulf. The channel scarps and the coral rocks are interpreted to be the result of faulting and subsidence of the bedrock between the two ENE-WSW or E-W trending faults.