Which process causes the stratification of grain sizes within an alluvial fan deposit?

💡 Explanation

When sediment laden water slows abruptly on an alluvial fan, density sorting occurs because heavier, coarser grains settle out first near the apex, while lighter, finer grains are carried further downslope. Therefore, density sorting results, rather than chemical precipitation, thermal convection or electrostatic attraction, which do not significantly contribute to grain size stratification.

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