Lithology and Structures of Quaternary Sediments of Indus Fan: ABSTRACT

Abstract

The surface sediments of the Indus fan are primarily chalks, marls, and brown clays. Massive terrigenous sediment dilutions occur only in the areas within 100 km from the Indus River confluence. Throughout most of the fan, underlying the sediments, are gray-green muds and turbidites of Pleistocene age. However, the details of lithology and structures of Pleistocene sediments vary from region to region in the fan. The sediments of the upper fan region are primarily fine-grained muds (with several, small silt beds, Td-e), except on the valley floors where coarse-grained turbidites (Ta-e), are commonly present. Two main valley systems, one eastern and the other western, exist on the upper fan. Bioclastic turbidites are common in the eastern valley syste , and are derived from the sediment slumps of the Indian margin. Most of the terrigenous, coarse-grained sediments have bypassed the upper fan and reached the End_Page 734------------------------------ distal areas extending to the Carlsberg Ridge. The percent sand is higher and the number of thick sand beds is more common in the distal areas of the fan; Bouma turbidite sequences, Ta-e, are common. Two main sand lobes are distinguished in the distal fan--an extensive western lobe, derived through channels resulting from the branching of the western valley system, and a restricted, eastern lobe, derived from the eastern valley system. The distributions of these lobes coincide with areas of thick sediments as seen on seismic profile records, implying that sediment dispersal similar to that in the Pleistocene occurred in earlier times. End_of_Article - Last_Page 735------------