Abstract

Pebbles in stream deposits may be oriented with their long axes parallel, transverse, or unrelated to direction of current movement. Pebbles in top-set and bottom-set beds tend to lie longitudinally to the flow direction. Those which move by jumping instead of rolling have random orientations and may, in being deposited, disturb the preferred orientation of pebbles that move by rolling. Imbrication of flat pebbles results from removal of sediment supporting the upstream end of a pebble and deposition of sediment under the downstream end, resulting in an upstream dip of the flat pebble surface.

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