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Examples include ripples and dunes on the bed of a river. Bedforms are often preserved in the rock record as a result of being present in a depositional setting. Bedforms are often characteristic to the flow parameters, [1] and may be used to infer flow depth and velocity, and therefore the Froude number.
Cross-bedding is formed by the downstream migration of bedforms such as ripples or dunes [3] in a flowing fluid. The fluid flow causes sand grains to saltate up the stoss (upstream) side of the bedform and collect at the peak until the angle of repose is reached. At this point, the crest of granular material has grown too large and will be ...
Flow regimes in single-direction (typically fluvial) flow, which at varying speeds and velocities produce different structures, are called bedforms. In the lower flow regime, the natural progression is from a flat bed, to some sediment movement (saltation etc.), to ripples, to slightly larger dunes. Dunes have a vortex in the lee side of the dune.
Sinuous-crested dunes exposed at low tide in the Cornwallis River near Wolfville, Nova Scotia Ancient channel deposit in the Stellarton Formation (Pennsylvanian), Coalburn Pit, near Thorburn, Nova Scotia. Sediment motion can create self-organized structures such as ripples, dunes, or antidunes on the river or stream bed. These bedforms are ...
Cross-beds, or "sets," are not layered horizontally and are formed by a combination of local deposition on the inclined surfaces of ripples or dunes, and local erosion. Graded beds show a gradual change in grain or clast sizes from one side of the bed to the other. A normal grading occurs where there are larger grain sizes on the older side ...
The Great Sand Dunes National Park has the highest sand dunes in North America. There are 30 square miles of dune field with five massive dunes – the tallest being 750 feet.
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Unlike low flow regime bedforms like dunes and ripples which generally produce downstream dipping cross stratification, antidunes produce a mixture of low-angle downstream and upstream dipping strata. While antidunes migrate upstream, upstream dipping cross-stratification is not indicative of antidunes or upper flow regime conditions.