Granulometric Analysis of the Exotic Sandstones in and around Moreh and Chandel, Chandel District, Manipur

Abstract

Chaotic assemblage of conglomerate, gritstone, sandstone, shale, limestone, chert and ophiolitic derivatives occurs along the western contact of Nagaland-Manipur ophiolite belt in N-S to NNE-SSW trending direction. This assemblage is known as sedimentary melange and extends for about 200 km from north-east of Chokla in Nagaland to the south of Moreh in Manipur. Sandstones being the dominant litho-unit among the sedimentary mélange have been selected for the present study. These sandstones occur as floating bodies intermingling with both Disangs and ophiolite, hence the term exotic sandstone is used. Analysis of grain size data of these exotic sandstones in and around Moreh and Chandel, Chandel district reveals that all the samples show unimodal distribution. Cumulative curves suggest saltation and suspension are the major mode of transportation of these sediments. Mean values ranging from 1.40 ? to 3.29 ? suggest medium to very fine sand size. Standard deviation values (0.20 to 1.10) suggest that these sediments are very well sorted to moderately sorted and indicate fluctuating energy conditions during the time of deposition. The values of skewness range from -0.88 to 0.19 and 76.31% of the samples are negatively skewed, indicating high energy condition during the time of deposition of the sediments. Bivariate plots suggest that sediments were deposited both in fluvial and near shore environments. Discriminant function analysis reveals that exotic sandstones of the present study area were deposited under diverse conditions