Do inverted depositional sequences and allochthonous foraminifers in sediments along the Coast of Kachchh, NW India, indicate palaeostorm and/or tsunami effects?

Abstract

The study of 134 subsurface sediment samples from three cores collected along the Coast of Kachchh, off Gujarat Province, NW India, shows the presence of 151 foraminifer species. Q-mode cluster analysis on foraminifer data for each core and radiocarbon dating at ten different downcore depths reveal an inverted sequence, with fine-grained sediments and small foraminifers sandwiched between normal detrital sediments at water depths of 10-20 m. It is postulated that approx. 8,000 years B.P., sediments ranging in age from approx. 10,000 to approx. 12,000 years B.P. were eroded from deeper offshore deposits by storm/tsunami(s), and were subsequently transported and redeposited in shallow regions, resulting in an inverted sequence, followed by a normal detrital sequence deposited between approx. 8,000 and approx. 7,000 years B.P. A second, similar event resulted in the deposition of approx. 10,000 year old sediments over a normally deposited, approx. 7,000-year-old sequence. The second inverted sequence was subsequently overlain by a normal sequence. It is hypothesized that the erosion and transportation of fine-grained sediments from deeper water, and their deposition in shallower water against the rule of gravity, are the result of storm/tsunami influence.