Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

K. Pandarinath ¹, K. R. Subrahmanya ², M. G. Yadava ³, Surendra P. Verma ¹

Affiliations
1 Centro de Investigacion en Energia, UNAM, Priv. Xochicalco s/no., Col Centro, Apartado Postal 34, Temixco, Mor. 62580, MX
2 0cean Science and Technology Cell, Mangalore University, Mangalagangotri 574199, IN
3 Earth Science Division, Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, IN

Abstract

Organic matter in sediment layers of two sediment cores from the continental slope off southwest coast of India was dated by radiocarbon method and sedimentation rates were estimated. The age data show lateral and temporal variations in sediment accumulation rates. Sedimentation rates decrease gradually from the inner shelf to the deep-sea in the study area, with an exception at 332 m water depth. The sediment accumulation rates on the shallower continental slope (332 m water depth; 0.003-0.013 mm/yr) are lower than on the deeper slope (776 m water depth; 0.071-0.190 mm/ yr) during the entire period of core deposition (32.8 ka BP to present). The unusually lower sedimentation rates on the shallower slope region may be the result of prevailing adverse depositional conditions. The sedimentation rates were lower during 32.80-18.98 ka BP and 16.04-8.69 ka BP and higher during 18.98- 16.04 ka BP and 8.69 ka BP to present day. The temporal variations in sedimentation rates reflect the changes in detrital input to the sea as a result of variations in intensity of paleomonsoonal conditions.

Keywords

Sedimentation record, Paleomonsoon, Continental slope, Southwest coast.

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M. G. Yadava ¹, R. Ramesh ¹

Affiliations
1 Physical Research Laboratory, Navrangpura, Ahmedabad - 380 009, IN

Abstract

Stable carbon and oxygen isotope vanations in speleothems collected from four locations in India, viz , Gupteswar (Orissa), Dandak (Chhattisgarh), Sota (Uttar Pradesh), and Akalagavi (Karnataka), and spanning various periods within the last ˜3400 years with different growth rates (0 09 to 1 34 mm/yr), have been compared In this paper we investigate the causative mechanisms for the observed variations and the spatial coherence in the isotope signals, and discuss their similarities and differences with other sirmiar high-resolution monsoon proxy records We note that (I) monsoon rainfall, and not the cave temperature, exerts a dominant control over both the carbon and oxygen stable isotope variations, (11) the oxygen isotoprc trend during 1500 400 years ago in the Indian and Omanian speleothems are in phase, and (111) dilution due to dead carbon is limited to less than 15 %.

Keywords

Speleothems, Southwest monsoon, Rainfall, Stable isotopes, Radiocarbon, Varves, Paleomonsoon.

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