Living benthonic foraminifera in a tidal environment: Gulf of Khambhat (India)

Abstract

Living benthonic foraminifera from the top one centimeter layer from 23 surface sediment samples have been studied. Samples were collected from the tidally affected inner shelf off the Daman Bombay sector of the Arabian Sea. The northern half of the study area is a high energy environment, it is deep and it is bounded by a narrow, long shallow (at a submerged depth of 7-20 m) sand bar (Eastern Bank) which rises from 40-43 m depth and is separated from the coast by the parallel Sutherland Channel. The southern half of the study area has a smooth topography and low-energy environment. A total of 60 species, of which 16 were living, were recorded in the study area. The diversity index (alpha) of the living assemblages is less than 3 and on the triangular diagram there is a greater concentration of points in the Rotaliina corner with some Textulariina and a general absence of Miliolina. Ammobaculites persicus, Ammonia annectens, A. papillosus, Asterorotalia dentata and Pararotalia nipponica are abundant in the living assemblage. The eastern flank of the Eastern Bank is marked by extensive sand waves and an almost total absence of living individuals. There is a concentration of reworked Paleogene foraminifera derived from the nearby Surat-Broach outcrops. These two features are indicative of a possibly mobile substrate. The high tidal range and the high concentration of suspended matter and thus low penetration of light might also be the cause for the absence of living individuals in the samples from the eastern flank of the sand bar