Gravel and sand flotation: a sediment dispersal process important in certain nearshore environments

• Small rafts of floating sediment, predominantly of granule and small pebble size, were observed along a tidewater coast on James Ross Island, Antarctica. The sediment was lifted from the beach by the advancing tidewater and kept afloat by surface tension. The current transported the rafts at least 100-150 m off the beach, where the rafts broke up due to wind agitation of the sea surface and the gravel sank. This process can transport considerable volumes of sediment from the beach: it is estimated that flotation at the Naze launch ea. 500 kg per kilometer of shoreline per tidal cycle during calm and dry weather conditions, which for one summer season might end up in a total of 0.022 tons of sediment per meter of shoreline. The resulting sediments and sedimentary structures are concluded to be similar to those resulting from iceberg-, sea ice-, and algae rafting, and sediment gravity flows. Floating can be an important way of rafting gravels into fine-grained sublittoral or shallow-marine facies, and should be included when dealing with processes related to sedimentation in the nearshore marine environment.

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NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geology (hsv//eng)

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