outcrop

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An outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. ^[1]

View of a bedrock outcrop near San Carlos Water, Falklands Islands. As exemplified in the picture an outcrop has to be immersed in soil and sediments.

Granite outcrops at Silesian Stones Mountain in southwestern Poland.

Roadside outcrop of Ordovician limestones and shales in southeastern Indiana.

Roadside outcrop of a pegmatite lens (light-colored mass) in an amphibolite gneiss in Norway.

Features

Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be seen or examined closely. However in places where the overlying cover is removed through erosion or tectonic uplift, the rock may be exposed, or crop out. Such exposure will happen most frequently in areas where erosion is rapid and exceeds the weathering rate such as on steep hillsides, mountain ridges and tops, river banks, and tectonically active areas. Bedrock and superficial deposits may also be exposed at the Earth's surface due to human excavations such as quarrying and building of transport routes.

Study

Outcrops allow direct observation and sampling of the bedrock in situ for geologic analysis and creating geologic maps. In situ measurements are critical for proper analysis of geological history and outcrops are therefore extremely important for understanding the geologic time scale of earth history. Some of the types of information that can only be obtained from bedrock outcrops, or through precise drilling and coring operations, are; structural geology features orientations (e.g. bedding planes, fold axes, foliation), depositional features orientations (e.g. paleo-current directions, grading, facies changes), paleomagnetic orientations. Outcrops are also critically important for understanding fossil assemblages, paleo-environment, and evolution as they provide a record of relative changes within geologic strata.

Accurate description, mapping, and sampling for laboratory analysis of outcrops made possible all of the geologic sciences and the development of fundamental geologic laws such as: law of superposition, principle of original horizontality, principle of lateral continuity, and principle of faunal succession. Outcrops can therefore be considered the fundamental element of geologic science.

Examples

On Ordnance Survey maps in Great Britain, cliffs are distinguished from outcrops: cliffs have a continuous line along the top edge with lines protruding down, outcrops have a continuous line around each area of bare rock. An outcrop example in California is the Vasquez Rocks, familiar from location shooting use in many films, composed of uplifted sandstone.^[2][3]

See also

Earth sciences portal

• Bedrock
• Geologic time scale

References

External links

Media related to Outcrops at Wikimedia Commons

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