Textural characteristics and distribution of ostracoda in core sediments from the Gadilam river estuary, Cuddalore, Tamil Nadu, southeast coast of India

To know the distribution of brackish water Ostracoda and to investigate the sediment characteristics, a core (105 cm) has been collected from the Gadilam river estuary and it was sub-sampled into 21 samples at 5 cm width regular interval. All the sediment samples were analyzed as per standard micropaleontological techniques in order to investigate the distribution and occurrence of ostracod fauna. A total of 27 ostracod taxa belonging to 16 genera, 12 families, 3 superfamilies and 2 sub-order of the order Podocopida, have been identified based on published articles Throughout the core (from top to bottom) the calcareous forms were noticed. The ostracod species Kalingella mckenziei and Jankeijcythere mckenziei are widely distributed in the core and they outnumbered the rest of the species. The faunal assemblages recorded are tropical, brackish to neritic (shallow marine) and benthic in nature (Hemicytheridea paiki, Hemicytheridea bhatiai, Jankeijcythere mckenziei, Kalingella mckenziei, Neosinocythere dekrooni, Paijenborchellina sp., Stigmatocythere indica and Tanella gracilis). In the analyzed core, there is no faunal assemblage at the depth between 80-85 and 95-105 cm. The sediment characteristics such as calcium carbonate, organic matter and sand-silt-clay ratio also determined and correlated with the observed ostracod populations. Based on the detailed study, it is noticed that high calcium carbonate and low organic matter of the sediment are congenial for population abundance. From the overall distribution of Ostracoda in all the subsamples, siltysand is found to an accommodative substrate for the prosperity of Ostracoda. The statistical aspect of ostracod carapace-valve ratio has been studied to identify the rate of sedimentation which infers a faster rate of deposition of sediments in the Gadilam River estuary.