A model of alluvial megafan sedimentation: Ganga Megafan

Ganga Megafan is one of several megafans, developed in the northern and cen tral part of the Ganga Plain, that formed during the middle Late Pleistocen e under conditions of higher sediment-water discharge and higher regional s lopes than today. Incision by the Ganga River exposes 15-30 m. thick megafa n deposits in the valley walls and cliffs. Ganga Megafan deposits can be se parated into four zones: Zone I - Gravelly braided streams; Zone II - Sandy braid plain; Zone III - Anastomosing channel plain; and Zone W - Meanderin g channels with broad interfluve areas. Deposits of each zone show distinct facies associations. Palaeocurrents fan from SW to SE and E, while the gra in size decreases from proximal to distal fan. At present, fan-building act ivity is highly subdued and is restricted only to the northernmost 5-10 km wide belt of Piedmont plain. (C) 2001 Elsevier Science BN. All rights reser ved.