Abstract

Laboratory experiments and examination of core samples from Holocene sand bodies demonstrate that vadose infiltration of muddy water through sand is an effective mechanism by which clay can be emplaced into sand. Infiltrated clays form coatings on, and bridges between, sand-sized framework grains. Clay particles are mostly oriented parallel to grain surfaces in coatings and perpendicular to grain surfaces in bridges. The amount of clay emplaced as coatings and bridges is determined by complexly interacting variables that include sand grain size, clay particle size, clay particle shape, concentration of suspended sediment, and clay composition. Of these, relatively coarse sand sizes and high concentrations of suspended sediment appear to promote the emplacement of the most infiltrated clay. In Holocene sands, the formation of grain coatings and bridges is facies dependent. Infiltrated clays are most effectively emplaced in environments characterized by high suspended sediment concentrations, fluctuating water levels, and minimal sediment reworking (e.g., point bar and delta plain). In contrast, virtually no infiltrated clay is emplaced in environments characterized by low suspended sediment concentration and continuous reworking (e.g., beach and tidal delta).

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