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A large dune complex is called a dune field, [7] while broad, flat regions covered with wind-swept sand or dunes, with little or no vegetation, are called ergs or sand seas. [ 8 ] [ 9 ] [ 10 ] Dunes occur in different shapes and sizes, but most kinds of dunes are longer on the stoss (upflow) side, where the sand is pushed up the dune, and have ...
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. As the upper flow regime forms, the dunes become flattened out, and then produce antidunes. At higher still velocity, the antidunes are flattened ...
Sand dune cross-beds can be large, such as in the Jurassic-age erg deposits of Navajo Sandstone in Canyonlands National Park. Aztec Butte shown here Formation of cross-stratification Schematic of eolian cross-bedding Close up of cross-bedding and scour, Logan Formation, Ohio Tabular cross-bedding in the Navajo Sandstone in Zion National Park Tabular cross-bedding in the South Bar Formation in ...
A diagram of various depositional environments. In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be formed after lithification, if the sediment is preserved in the rock record.
Schematic QFL diagram showing tectonic provinces and sandstone provenance. A QFL chart is a representation of the framework grains and matrix that is present in a sandstone. This chart is similar to those used in igneous petrology. When plotted correctly, this model of analysis creates a meaningful quantitative classification of sandstones. [24]
Nugget Sandstone near Red Fleet Reservoir, Uintah County, Utah. Uniform grain size and these large cross-stratification are indicative of an ancient sand dune. Nugget Sandstone showing a bounding surface between two sets of ancient sand dunes, where wind scour eroded the top of the lower dune before the second dune advanced over it.
A type of dune that forms as a result of low sediment supply in regions where wind blows in one primary direction. This causes the dune to have a concave shape, with the tails facing downwind. [8] Transverse dunes and Seif dunes are some alternative examples of the effect of unidirectional air flow on dune formation. Barchan dune schematic ...
Such a particle may be a grain of sand, a pebble, cobble or boulder. Although roundness can be numerically quantified, for practical reasons geologists typically use a simple visual chart with up to six categories of roundness: Very angular: corners sharp and jagged; Angular; Sub-angular; Sub-rounded; Rounded; Well-rounded: corners completely ...