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    Marine geology

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    Glimpses_Geoscience_Res_India_80.pdf (145.7Kb)
    Date
    2004
    Author
    Rao, V.P.
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    Abstract
    Marine geological investigations for the last four years extend from water column to sedimentary records. The sediment trap experiments in the Arabian Sea showed strong correlation between seasonal variations of pteropod/planktic foraminiferal ratios and fluxes of CaCO sub(3), organic carbon and biogenic opal. Ba sub(excess) strongly correlates with biogenic opal indicating biogenic origin of Ba. Several proxies have been used for understanding the palaeoclimate/palaeooceanography from the marine sedimentary records. The proxies include organic carbon, stable isotopes of planktic and benthic foraminifers, delta Sup(13) C and delta sup(15) N of the sediments, alkenones, Mg/Ca ratio in Globigerinoides ruber, rock-magnetic properties, artificial neural networks (ANN) based on quantitative analyses of planktic foraminifers. The results suggest arid climatic conditions and increased productivity during the Last Glacial Maximum (LGM). The sea surface temperature was 2.1 degrees C cooler during LGM than at present. Early monsoon intensification occurred in two abrupt steps, at 9500 yrs and 9100 years BP. The mean sea level rise estimated from the tide-guage data was less than 1 mm/yr. Investigations on the relic carbonates along the western continental margin of India indicate evidences of late Quaternary neo-tectonic activity in the Gulf of Kachchh and carbonate platform. Provenance studies have been carried out on the Ayeyarwady continental shelf, Andaman Sea and western margin of India, using suspended particulate matter and Sr-Nd isotopes of sediments, respectively. Investigations on the onshore and offshore phosphorites and dolomites indicate microbial mediation in their formation. Episodes of hydrothermal activity in the Central Indian Basin were reported at 10 ka and 425 to 650 ka, based on the occurrence of volcanic spherules. Studies on Gas-hydrates and methane-derived carbonates were reported from the identification of Bottom Simulating Reflections and computed gas hydrate stability thickness map and, authigenic carbonates in the form of high-magnesium calcites and aragonite.
    URI
    http://drs.nio.org/drs/handle/2264/7564
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