Late Quaternary sea level and environmental changes from relic carbonate deposits of the western margin of India |
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| Authors: | V Purnachandra Rao G Rajagopalan K H Vora F Almeida |
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| Institution: | (1) National Institute of Oceanography, Dona Paula, 403 004 Goa, India;(2) Birbal Sahni Institute of Palaeobotany, 53 University Road, Lucknow, India |
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| Abstract: | Relic carbonate deposits along the western margin of India occur as dolomite crusts, aragonite sands (pelletal / oolitic)
and aragonite-cemented limestones, oyster shells, corals, encrusted coralline algal and foraminiferal-dominated nodules. The
petrology and mineralogy of the deposits indicate that except for aragonite sands and foraminiferal nodules, the others were
formed in shallow marine conditions and serve as sea level indicators. Radiocarbon dates were measured for 62 relic deposits
covering the entire margin. The age of these deposits on the continental shelf off Cape Comorin and Mangalore, between 110
and 18 m depth, ranges between 12, 61014C yr BP and 6,39014C yr BP. On the northwestern margin of India, especially on the carbonate platform (between 64 and 100 m), the age ranges
from 17,250 to 6,73014C yr BP. The relic deposits of the Gulf of Kachchh at depths between 35 and 25 m are dated at 12,550–9,63014C yr BP. The age vs. depth plot of the relic deposits further indicates that the Gulf of Kachchh was inundated much early,
atleast by 15 ka, after the Last Glacial Maximum, and was subjected to uplift and subsidence during the Holocene. The carbonate
platform subsided during the early Holocene. Some of the relic deposits between Cape Comorin and Mangalore plot on or, closely
follow the glacio-eustatic sea level curve. Despite abundant siliciclastic flux discharged by the Narmada and Tapti during
the early Holocene, the platform off these rivers is largely devoid of this flux and carbonate sedimentation continued until
6,70014C yr BP. We suggest that the river-derived sediment flux diverted southwards under the influence of the SW monsoon current
and, thereby, increased the turbidity on the shelf and slope southeast of the carbonate platform and facilitated the formation
of deeper water foraminiferal nodules off Vengurla-Goa. |
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| Keywords: | Late Quaternary sea level western margin of India subsidence uplift depositional environment |
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