Geochemical and Isotopic Signatures of Surficial Sediments from the Western Continental Shelf of India: Inferring Provenance, Weathering, and the Nature of Organic Matter

Abstract

suggested that the sediments are moderately weathered despite the intense orographic rainfall in the source area. Variability in degree of chemical weathering is seen with the change in provenance. In general, the sediments north of Goa with a provenance of Deccan basalts show higher chemical weathering index. C org /N molar ratios (range = 6.9 and 14) are mostly between 10 and 12 which are closer to marine organic matter values. This is corroborated by marine δ 13 C values (-18.2 to-21.6‰). While, they broadly fall within the marine values, heavier values are seen in northern transects off Porbandar and Dwaraka where the sediments have a provenance different from those in the south. This could be due to a higher contribution from C-4 type vegetation in the north, consistent with heavier δ 13 C values in terrestrial plants in source regions. Comparatively heavier δ 15 N values are observed for the northern transects (north of Ratnagiri) which is supported by the intense denitrification in the northern Arabian Sea.

Lead distribution in coastal and estuarine sediments around India

“…Table 1 Concentration of Pb in different lithologies (Wedepohl, 1978 Smectite and kaolinite-rich assemblage, illite, chlorite and gibbsite derived from the Gneissic Province occur both on the central to southern part of west coast of India. A geochemical study by Kurian et al (2013) along the western continental shelf has shown distinct north-south differences consistent with the source signatures. The Deccan Trap basalt characterizes the sediments in the north (from coastal Gujarat to Goa) and gneisses and granulites in the south (from Goa to southern most part of Kerala).…”

Perspectives on the Terrestrial Organic Matter Transport and Burial along the Land-Deep Sea Continuum: Caveats in Our Understanding of Biogeochemical Processes and Future Needs

“…Substrates may also slow the process of carbon remineralization if they are adsorbed onto particles (e.g., clays) or form complexes with macromolecules (e.g., humic substances) (Mayer et al, 2004;Burdige, 2007;Arnosti, 2011). The smectite-bearing shelf sediments derived from Deccan Trap shown to contain enriched carbon isotope values, even richer than marine organic matter (Kurian et al, 2013). It is also known that most OC is rapidly metabolized and/or photolysed and returned to the atmosphere as CO 2 (Cole et al, 2007), when they are not adsorbed onto mineral particles.…”

Sources and distribution of organic matter in thirty five tropical estuaries along the west coast of India-a preliminary assessment

“…The sediments from south group estuaries are dominated by OM sourced from plant due to the combined effect of littering in the Western Ghats as well as soil erosion. The Narmada and Sabarmati estuaries contain mainly C 4 plant and soil derived OM because of the intense impact of C 4 agriculture (Kurian et al, 2013). Terrestrial OM from C 3 and C 4 plant detritus is dominant (57%) in the near shore and coastal sediments of the Bay of Bengal (Krishna et al, 2013), which contain 47% of marine OM.…”