Clay minerals in SW Indian continental shelf sediment cores as indicators of provenance and palaeomonsoonal conditions: a statistical approach

Two sediment cores from the inner continental shelf of SW India, SK-148/13 (4.66m long; from 50m water depth) and SK-148/14 (5.37m long; from 22m water depth), were studied for provenance and palaeomonsoonal implications. Sediment layers at different depth intervals in these cores were estimated for clay minerals and organic matter content. Five surface sediment samples from the nearby Kali River estuary of the adjacent hinterland were also analysed for clay mineral contents. In both cores and Kali River sediments, smectite is the dominant clay followed by illite, and kaolinite or chlorite. Based on the similarities of the abundances of clay minerals and their relative wt-% in the inner shelf sediment cores and in surface sediments of the estuary as demonstrated by significance tests, Al-rich illite, and negligible contribution of clay from the deep-sea and aeolian sources, it can be inferred that the sediments of the two inner continental shelf cores were derived from the adjacent hinterland. Application of statistical discordancy and significance tests on the down-core variations in the crystallinity index (CI) of illite and organic matter content in the sediment cores indicates intense monsoonal (high rainfall) conditions at the adjacent hinterland during about 4300-6200 and 9300-10,400 years BP. These inferences are comparable to those from other well-established palaeomonsoonal indicators such as sedimentation rates and mineral magnetic properties. The CI of illite, an easily determinable and climatically sensitive parameter, can thus be a reliable palaemonsoonal indicator for inner shelf sediment cores. The statistical methodology used in this work highlights the advantages of a quantitative interpretation of the data instead of the conventional qualitative visual examination.