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Cross-beds are layers of sediment that are inclined relative to the base and top of the bed they are associated with. Cross-beds can tell modern geologists many things about ancient environments such as- depositional environment, the direction of sediment transport (paleocurrent) and even environmental conditions at the time of deposition.
These structures are within sedimentary bedding and can help with the interpretation of depositional environment and paleocurrent directions. They are formed when the sediment is deposited. Cross-bedding Cross-bedding is the layering of beds deposited by wind or water inclined at an angle as much as 35° from the horizontal. [1]
Types of beds include cross-beds and graded beds. 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 ...
Hummocky cross-stratification from the Book Cliffs, Utah. Hummocky cross-stratification from the Arisag Formation (Silurian), Nova Scotia. Hummocky cross-stratification is a type of sedimentary structure found in sandstones. It is a form of cross-bedding usually formed by the action of large storms, such as hurricanes. It takes the form of a ...
Cross-bedding in Zion National Park, Utah.Both the tangential bases on the cross beds and the truncations of overlying layers can be used as a way up indicator. A dinosaur footprint preserved in positive relief is a trace fossil indicating the bottom (or sole) of the bed (Lower Jurassic Moenave Formation, southwestern Utah).
Cross-bedding – the axis of a trough cross bed or the down-dip direction of a tabular cross bed point the direction of paleo flow. Current ripple marks – will have the short side of the ripple pointing down stream. Sole markings/flute casts – the short, steep side will point up stream, and the long, tapered side points down stream.
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Very small cross-lamination means that the ripple height is roughly one centimeter. It is lenticular, wavy and flaser lamination. Small Small cross-bedding are ripples set at a height less than ten centimeters, while the thickness is only a few millimeters. Some ripples that may fit this category are wind ripples, wave ripples, and current ripples.