Which process causes coarser sediment fractions to deposit proximally within an alluvial fan?

💡 Explanation

When flow leaves a confined channel onto an alluvial fan, decreased slope causes a reduction in shear stress, because shear stress is proportional to the slope, resulting in the settling of coarser, heavier sediments first. Therefore, proximal deposition of coarse sediment occurs due decrease in slope, rather than infiltration, winnowing, or precipitation which don't separate sediments by grain size.

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