Distribution and ecology of benthonic foraminifera in the sediments of the visakhapatnam shelf east coast of india
Rao, M.S.; Vedantam, D.; Rao, J.N.
Palaeogeography Palaeoclimatology Palaeoecology 27(3-4): 349-369
Of 124 benthonic foraminiferal species identified from the sediments of the Visakhapatnam shelf, east coast of India, only 17 spp. are abundant. Bolivina vadescens is cosmopolitan and abundant in the entire shelf. Ammonia beccarii, A. papillosa, Asterorotalia trispinosa, B. compacta, Cibicides lobatulus, Discorbis australis, Florilus grateloupi and Hanzawaia concentrica are abundant in the inner shelf; Amphistegina radiata, Heterolepa dutemplei and Uvigerina proboscidea in the middle shelf; B. robusta, Bulimina gibba, Cassidulina laevigata, U. bifurcata and U. peregrina occur in the outer shelf. The benthonic population sizes are larger in the outer shelf than in the inner shelf, but species diversity is higher in the middle shelf than elsewhere. The species are arranged in 10 bathymetric groups which show that 20 spp. are restricted to the outer shelf, 29 to the inner shelf and 10 to the middle shelf while 24 spp. occur over the entire shelf. The foraminifera are grouped into dominant, characteristic and accessory species and these groups allow recognition of 4 biofacies in the Visakhapatnam shelf, restricted, respectively, to the depth zones of 0-20 m, 20-55 m, 55-90 to 105 m and 90 to 105-190 m. Bottom water temperature and currents, rather than sediment attributes and water salinity, influence the distribution patterns of the species and their population densities in sediments of the Visakhapatnam shelf.