Grain Surface Features of Alluvial Sediments of Upper PravaraBasin and their Environmental Implications

摘要

Quartz sand grains obtained from a deeply gullied topography along the banks of two tributaries of River Pravara in Godavari Basin, Maharashtra have been examined with a scanning electron microscope (SEM) in order to make the environmental interpretations of these deposits. The sediments reveal features resulting from mechanical grinding as well as from chemical alteration. Conchoidal fractures, cleavage planes, grooves, v-shaped indentations etc are the mechanical features documented on the grains whereas solution pits of varying sizes and intensity, precipitation surfaces, oriented v-pits, solution crevasses and etching are the features of diagenetic origin. Few sand grains show the evidence of wind transported sediments. Several evidence indicate that the samples have undergone digenetic changes. Few grains exhibit the features of intense chemical breakdown. The overall assemblages of the grain surface features suggest that the samples have been subjected to subaqueous transport for a considerable period of time. The chemical features such as etching, solution pits or semi circular arcuate steps that are found in abundance in these grains are due to the dissolution of the sediments in a low energy fluviatile environment, such as in floodplain region.