Do inverted depositional sequences and allochthonous foraminifers in sediments along the Coast of Kachchh, NW India, indicate palaeostorm and/or tsunami effects?
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.
KeywordsGreat Barrier Reef Benthic Foraminifer Differential Global Position System Differential Global Position System Small Foraminifer
The authors express their gratitude to Dr. E. Desa, ex-Director, and Dr. S.R. Shetye, Director, National Institute of Oceanography and Dr. P.C. Pandey, Director, National Centre for Antarctic and Ocean Research for encouragement and permission to publish this paper. We are also indebted to Dr. A.K. Chaubey, Mr. M.C. Pathak and Dr. N.H. Hashimi for their support and suggestions throughout the study. We are thankful to Mr. R. Sinha, Mr. A. Mazumder, Mr. R. Saraswat and Miss Rajani Panchang for helping in various ways, and to Sri. P.C. Srivastava, Deputy Director General of the Geological Survey of India, for giving us the opportunity to present this work in the National Seminar on Four Decades of Marine Geoscientific Studies in India - A Retrospective. The Department of Ocean Development, New Delhi is thanked for financial assistance. We are indebted to Dr. Hal Palmer and an anonymous reviewer for their critical comments which helped improve the manuscript.
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