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Beds of lava flows exposed on the island of La Gomera. Bed thickness is a basic and important characteristic of beds. Besides mapping stratigraphic units and interpreting sedimentary facies, the analysis of bed thickness can be used to recognize breaks in sedimentation, cyclic sedimentation patterns, and gradual environmental changes. [10]
Normally graded beds generally represent depositional environments which decrease in transport energy (rate of flow) as time passes, but these beds can also form during rapid depositional events. They are perhaps best represented in turbidite strata , where they indicate a sudden strong current that deposits heavy, coarse sediments first, with ...
These beds range from millimeters to centimeters thick and can even go to meters or multiple meters thick. Sedimentary structures such as cross-bedding, graded bedding, and ripple marks are utilized in stratigraphic studies. They help indicate the original position of strata in geologically complex terrains.
A bedform is a geological feature that develops at the interface of fluid and a moveable bed, the result of bed material being moved by fluid flow. 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.
Marker horizons (also referred to as chronohorizons, key beds or marker beds) are stratigraphic units of the same age and of such distinctive composition and appearance, that, despite their presence in separate geographic locations, there is no doubt about their being of equivalent age (isochronous) and of common origin.
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 ...
The Dakota is a sedimentary geologic unit name of formation and group rank in Midwestern North America. The Dakota units are generally composed of sandstones, mudstones, clays, and shales deposited in the Mid-Cretaceous opening of the Western Interior Seaway. [7]
Armour of basalt blocks. In hydrology and geography, armor is the association of surface pebbles, rocks or boulders with stream beds or beaches.Most commonly hydrological armor occurs naturally; however, a man-made form is usually called riprap, when shorelines or stream banks are fortified for erosion protection with large boulders or sizable manufactured concrete objects.