Distribution of grain size and clay minerals in sediments from the INDEX area, Central Indian Basin

The granulometry of 21 box core sediments from five selected sites in the C entral Indian Basin (CIB) have been studied to understand the sediment size characteristics in the Pioneer area before the benthic disturbance experim ent. The sediments are predominantly clayey silt. Statistical parameters we re determined to understand the control and variations in the grain size. T he mean grain size (M(z)phi) ranged from 7.0 to 8.6 for the surface and fro m 6.6 to 8.6 for the subsurface sediments, indicating deposition of very fi ne fractions during the Neogene period. The sediments were pool ly sorted a s revealed from the higher a, values (2.7 to 2.9). Higher and negative valu es of skewness (SKI indicated a winnowing action of prevailing currents in the area. Average kurtosis (K-G) values for the surface (0.4 to 0.8) and su bsurface (0.5 to 1.2) showed that sediments were very platykurtic and lepto kurtic. Clay mineralogical studies showed that smectite had a wider range ( from 6% to 55%) and decreased southward because of its terrigenous origin. The terigenous influence of the sediments could be documented as far as 12 degrees S. Smectite and kaolinite increased eastward and chlorite decreased southward. This observation positively con-elated with the mean current di rection in the area. However the influence of Antarctic Bottom Water (AABW) in the area could be predicted from the southward increase in chlorite con tent.