Abstract: An investigation to record spatial and seasonal distribution of recent benthic ostracoda was carried out along two transects (East and Northeast) off Rameswaram island of Tamil Nadu coast, India. Thirty sediment and bottom water samples were collected during January 2011 and April 2011 and analysed for various physico-chemical and sediment characteristics using standard procedures. The top 4 cm sediment was preserved in 10% formaldehyde and later in the laboratory the live and total population of Ostracoda was determined using the rose Bengal stain technique. Faunal frequencies for benthic ostracods were computed and correlated with physico-chemical and sediment characteristics. The correlation reveals that ostracod frequency has a positive correlation with sandy substrate and negative correlation with clay substrate and OM%. Faunal frequencies increased by 3 times during summer (April 2011) although values of physico-chemical and sediment characteristics do not show considerable variation from January 2011. The east transect is proximal to the coral reef and characterized by sandy substrate in both seasons, supports high populations and therefore is more congenial for ostracod proliferation. Finally, environmental variables have been correlated with those measured three decades ago to understand the causes for variations.

Abstract This study reviews the morphology, hydrodynamics and sedimentology of 33 modern straits, including examples from diverse tectonic and climatic settings. Strait morphology ranges from short, simple straits to long, tortuous passages many hundreds of kilometres long; depths range from 10 m to >1 km. The morphological building block of strait sedimentation is a constriction flanked by open basins; a single strait can contain one or several of these. Currents accelerate through the constrictions and decelerate in the basins, leading to a spatial alternation of high- and low-energy conditions. Currents in a strait can be classified as either ‘persistent’ (oceanic currents or density-driven circulation) or ‘intermittent’ (tidally or meteorologically generated currents). Constrictions tend to be bedload partings, with the development of transport paths that diverge outward. Deposition occurs where the flow decelerates, generating paired subaqueous ‘constriction-related deltas’ that can be of unequal size. Cross-bedding predominates in high-energy settings; muddy sediment waves and contourite drifts are present in some straits. In shallow straits that were exposed during the sea-level lowstand, strait deposits typically occur near or at the maximum flooding surface, and can overlie estuarine and fluvial deposits. The most energetic deposits need not occur at the time of maximum inundation.