Texture, composition and provinance of innershelf sediments between Narakkal and Purakkad, Kerala with special reference to the formation of Mud Banks

The continental shelf of southwest coast of India (Kerala) is broader and . flatter compared to that of the east coast. The unique characteristic feature of the study area (innershelf between Narakkal and Purakkad) is the intermittent appearance of 'mud banks' at certain locations during southwest monsoon. The strong seasonality manifests significant changes in the wind, waves, currents, rainfall, drainage etc., along this area. Peculiar geomorphological variation with high, mid and lowlands in the narrow strip of the hinterland, the geological formations mainly consisting of rocks of metamorphic origin and the humid tropical weathering conditions play significant role in regulating the shelf sedimentation. A complementary pattern of distri bution is observed for clay that shows an abundance in the nearshore. Silt, to a major extent, depicts semblance with clay distribution . Summation of the total asymmetry of grain size distribution are inferred from the variation of skewness and kurtosis.Factor I implies a low energy regime where the transportation and deposition phases are controlled mostly by pelagic suspension process as the factor loadings are dominant on finer phi sizes. The second Factor is inferred to be the result of a high energy regime which gives higher loadings on coarser size fractions. The third Factor which might be a transition phase (medium energy regime) representing the resultant flux of coastal circulation of the re-suspension/deposition and an onshoreoffshore advection by reworking and co-deposition of relict and modern sediments. The spatial variations of the energy regime based on the three end-member factor model exhibits high energy zone in the seaward portion transcending to a low energy one towards the coast.From the combined analysis of granulometry and SEM studies, it is concluded that the sandy patches beyond 20 m depth are of relict nature. They are the resultant responses of beach activity during the lower stand of sea level in the Holocene. Re-crystallisation features on the quartz grains indicate that they were exposed to subaerial weathering process subsequent to thei r deposition

Source Characterization of Sedimentary Organic Matter in a Tropical Estuary, Southwest Coast of India: A Biomarker Approach

The source, fate and diagentic pathway of sedimentary organic matter in estuaries are difficult to delineate due to the complexity of organic matter sources, intensive physical mixing and biological processes. A combination of bulk organic matter techniques and molecular biomarkers are found to be successful in explaining organic matter dynamics in estuaries. The basic requirement for these multi-proxy approaches are (i) sources have significantly differing characteristics, (ii) there are a sufficient number of tracers to delineate all sources and (iii) organic matter degradation and processing have little, similar or predictable effects on end member characteristics. Although there have been abundant researches that have attempted to tackle difficulties related to the source and fate of organic matter in estuarine systems, our understanding remains limited or rather inconsistent regarding the Indian estuaries. Cochin estuary is the largest among many extensive estuarine systems along the southwest coast of India. It supports as much biological productivity and diversity as tropical rain forests. In this study, we have used a combination of bulk geochemical parameters and different group of molecular biomarkers to define organic matter sources and thereby identifying various biogeochemical processes acting along the salinity gradient of the Cochin estuary

Geochemical characteristics of surficial sediments in a tropical estuary, southwest India

Geochemical characteristics of surficial sediments in the Panangad region of Cochin estuary, the largest brackish-water humid ecosystem in the south-west coast of India, were analysed. Temporal variations in nutrient stoichiometry, seasonal characteristics of redox elements Fe and S, and the phosphorus geochemistry were employed for the purpose. The stoichiometric analysis pointed towards autochthonous origin of organic matter, possibility of nitrogen limitation, and allochthonous modification of redox conditions. Seasonal variations were not statistically significant for all the geochemical parameters, whereas significant spatial variations were observed with lower values at sandy stations, suggesting that the texture of the sediments is the main factor influencing the sediment geochemistry. Significant inter-relations between the geochemical parameters also suggest a common control mechanism. Based on these geochemical characteristics, the study region can be effectively categorized into two distinct zones, viz. (1) erosion and transportation and (2) deposition zones