Late Quaternary seismic sequence stratigraphy of the Gulf of Kachchh, northwest of India

Abstract

High-resolution seismic reflection and bathymetric data in 10 to 50 m water depth in the Gulf of Kachchh, northwest of India, have been analysed together with earlier results from the area. They have revealed geomorphic features and Late Quaternary seismic sequence stratigraphy of 25-m-thick sediments. Seabed topography is uneven except in the east, carpeted by thick acoustically transparent to semitransparent sediment clays and stratified limestone beds. The sediments consist of (1) the transparent unit `A` up to 12 m thick, (2) thick 8 to 10 m diffuse seismic reflection free unit `D,` and (3) 4 to 5 m thick hummocky reflections unit `K`. The geomorphic/subsurface features are pinnacles (1 to 2 m high) and mounds (4 to 5 m high) on the seafloor and subsurface in the south and west, valleys (1 to 3 m) on the seafloor in the south and subsurface in the north and onlap of reflectors in the north. They mark corals, seafloor incisions, and sediment influx. Spatial shifts of valleys that mark a high energy tidal regime incising the seafloor in paleo and present times appear to be due to neotectonics: subsidence and uplift. Based on the seismic images and on correlation with the sea level curve published by other authors, the pinnacles, mounds, and the hummocky reflectors are interpreted as corals (live and relict) formed in subaqueous conditions. The reflection-free sediments are coral debris, sands mostly derived during the interglacial period of late Pleistocene and Holocene when the gulf was exposed to arid climates during lowered sea levels, around Last Glacial Maximum (centered approx. 18 ka). Access to unique sedimentary records of the Late Quaternary climates/sea level changes even of decadal scale can be retrieved by collecting sediments/corals from shallow drill wells in the gulf.