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