Physical properties of a sediment core from the Central Indian Basin

Abstract

A box core of 7.5 m was collected from the Central Indian Basin for the purpose of geotechnical studies and depthwise variation of physical properties and clay mineralogy. Water content, Atterberg limits, specific gravity are measured at regular intervals and clay mineralogy of same samples is studied. In general, the core shows depthwise increase in shear strength, specific gravity and decrease in water content, and depicts lithological changes. At a depth of about 4.7m a drastic change in the physical properties and clay mineralogy indicating sedimentary hiatus is observed which coincides with the Plio-Pleistocene boundary. The shear strength increases from 10 to 13 kPa at this depth, and inspite of higher clay size (< 4 ~km) fraction and montmorillonite content, the water content and liquid limit reduce drastically showing same values. These indicate the highly compressed and consolidated nature of this layer which may be due to overburden presure of thick water and sediment column. Wet density increases from 1.2 to 1.5 gm/cm@u3@@ and porosity decreases from 87 to 71% at this layer. The layer is about 30 cm thick and devoid of any radiolarian fossils which may be attributed to either sudden change in climate or volcanic activity which precluded preservation of radiolarian fossils. Illite-rich sediments in the core are attributed to Ganges turbidity currents from north whereas montmorillonite-rich layer is due to local volcanism in the Indian Ocean