Sedimentary Structures and Lithofacies Found in a Channel Bar of Brahmaputra River in Panikhaiti, Kamrup District, Assam

Abstract

Accumulation of sediments in river channels often leads to the formation of sediment bars. They form prominent elevated regions during the non-flood period within the river channel, and contain characteristic bedform features and internal stratification. These features reflect the hydrodynamic conditions prevailing during the deposition of the sediments. The present study deals with the recognition and interpretation of various bedform features and lithofacies that had developed in a channel bar of the Brahmaputra River, in Panikhaiti near Guwahati, Kamrup district, Assam. The different bedform features that are identified are small and mega ripples, water level cut marks, mud cracks, worm track and trails and raindrop imprints. Internal stratification was identified in trenches of depth ranging between 1.80 m and 2.25 m. in which eight varieties of lithofacies were identified. These are Trough cross-bedded sand (St), Planar cross-bedded sand (Sp),                 Horizontally laminated sand (Sh), Climbing ripple lamination (Sr), Convolute bedding (Fc), Flaser bedding (Sf), Massive sand (Sm) and Massive Mud (Fm). The lithofacies associations indicate deposition of sediments under multiple episodes of flood, and characterized by multiple migrations from low flow regime conditions to high flow regime conditions.