Benthic foraminifers as indices of diversity and hyposalinity in a modern clastic shelf regime, off Bombay, India

Abstract

A tidally energized clastic shelf regime at 25-45 m depth off Bombay-Daman composed of silty sand, silty clay, and clay fractions is located between a sand bar and the coast. The sand bar, running parallel to the coast, has a variable height of 7-20 m at submerged depth. Sub-Recent foraminiferal populations and their diversity are noticeably low at stations near the sand bar while relatively high in the clay substrate. Miliolids are abundant in the sandy and silty substrates. @iAmmonia, Ammobaculites@@, and miliolids are the dominant species followed by @iNonion@@ in silty, @iNonionella in clay, and @iFlorilus@@ and @iElphidium@@ in silty clay substrates. In the living populations @iAmmonia@@ and @iAmmobaculites@@ are also abundant but @iSlphidium, Nonionella@@, and miliolids are rare, while @iNonion@@ is totally absent. The similarity index between the two populations is considerable. The ~a index and triangular plot representations of Murray (1973) indicate hyposalinity. This may be attributed to freshwater influx from the rivers. Nonionidae and Miliolidae are found to be negatively affected (inversely proportional) by the organic carbon content in the sediment. Reworked Paleogene fauna from the nearby Surat-Broach area are also observed in this region