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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Authors: | R Nigam S K Chaturvedi |
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Institution: | (1) National Institute of Oceanography, Dona Paula, Goa, 403 004, India;(2) National Centre for Antarctic and Ocean Research, Headland Sada, Vasco-da-Gama, Goa, 403 804, India |
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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 ∼8,000 years B.P., sediments ranging in
age from ∼10,000 to ∼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 ∼8,000 and ∼7,000 years B.P. A second, similar event resulted in the deposition of ∼10,000 year old sediments
over a normally deposited, ∼7,000 year old sequence. The second inverted sequence was subsequently overlain by a normal sequence.
It is hypothesised 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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