 | This articleneeds additional citations forverification. Please helpimprove this article byadding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Outcrop" – news ·newspapers ·books ·scholar ·JSTOR(September 2011) (Learn how and when to remove this message) |
Anoutcrop orrocky outcrop is a visible exposure ofbedrock or ancientsuperficial deposits on the surface of the Earth and otherterrestrial planets.[1]
Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered bysoil and vegetation and cannot be seen or examined closely. However, in places where the overlying cover is removed througherosion ortectonic uplift, the rock may be exposed, orcrop out. Such exposure will happen most frequently in areas whereerosion is rapid and exceeds theweathering rate such as on steep hillsides, mountain ridges and tops, river banks, andtectonically active areas. InFinland,glacial erosion during the last glacial maximum (ca. 11000 BC), followed by scouring by sea waves, followed byisostatic uplift has produced many smooth coastal and littoral outcrops.
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.
Outcrops allow direct observation and sampling of thebedrockin situ forgeologic analysis and creatinggeologic maps. In situ measurements are critical for proper analysis ofgeological history and outcrops are therefore extremely important for understanding thegeologic time scale of earth history. Some of the types of information that cannot be obtained except from bedrock outcrops or by precise drilling and coring operations, arestructural 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 very important for understanding fossil assemblages, and paleo-environment, and evolution as they provide a record of relative changes within geologicstrata.
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 thelaw of superposition, theprinciple of original horizontality,principle of lateral continuity, and theprinciple of faunal succession.
Outcrops occur in numerous forms, including, but not limited to:[2]
OnOrdnance Survey maps inGreat 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 inCalifornia is theVasquez Rocks, familiar fromlocation shooting use in manyfilms, composed of upliftedsandstone.[3][4]Yana is another example of outcrops, located inUttara Kannada district inKarnataka,India.
