Abstract

Detailed facies analysis and morphotectonic investigations of the Malin River's alluvial fan in the western Ganga Plain, India, reveal that the morphology of the fan is largely tectonically controlled whereas the sedimentary processes are mainly climatically controlled. The sedimentation occurred in two distinct evolutionary cycles which are separated by a time gap. The older cycle deposited thick gravelly units up to the distal-fan area, whereas the sediment fill of the younger cycle is gavel-dominated in the proximal-fan area, gravel–sand dominated in the middle-fan area and sand–mud dominated in the distal-fan area. The gravels of the older cycle were emplaced by intense sediment gravity flows during periods of strengthened monsoon and steeper regional gradient. During the younger cycle, the proximal to distal parts of the fan were dominated by different sedimentary processes. This was a time of relatively weaker monsoon and gentler regional slopes, when gravels could travel only up to the middle-fan area. The gravels in the proximal-fan area have mainly been deposited by sediment gravity flows and channel processes; in the middle-fan area channel processes, sheetfloods and sediment gravity flows have been the main sedimentary processes; and in the distal-fan area fluvial processes of channel migration and overbank deposition have been the main sedimentary processes.

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