Outcrop
 | This articleneeds additional citations forverification.(September 2011) |
Anoutcroporrocky outcropis a visible exposure ofbedrockor ancientsuperficial depositson the surface of the Earth and otherterrestrial planets.[1]
Features
[edit]Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered bysoiland vegetation and cannot be seen or examined closely. However, in places where the overlying cover is removed througherosionortectonic uplift,the rock may be exposed, orcrop out.Such exposure will happen most frequently in areas whereerosionis rapid and exceeds theweatheringrate such as on steep hillsides, mountain ridges and tops, river banks, andtectonically activeareas. InFinland,glacialerosion during the last glacial maximum (ca. 11000 BC), followed by scouring by sea waves, followed byisostatic uplifthas 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.
Study
[edit]Outcrops allow direct observation and sampling of thebedrockin situforgeologicanalysis and creatinggeologic maps.In situ measurements are critical for proper analysis ofgeological historyand outcrops are therefore extremely important for understanding thegeologic time scaleof earth history. Some of the types of information that cannot be obtained except from bedrock outcrops or by precise drilling and coring operations, arestructural geologyfeatures orientations (e.g. bedding planes,foldaxes,foliation), depositional features orientations (e.g. paleo-current directions, grading,facieschanges),paleomagneticorientations. 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.
Examples
[edit]OnOrdnance Surveymaps 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 inCaliforniais theVasquez Rocks,familiar fromlocation shootinguse in manyfilms,composed of upliftedsandstone.[2][3]Yanais another example of outcrops, located inUttara Kannadadistrict inKarnataka,India.
-
-
Precambrianoutcrop in Finland -
-
Outcrop nearYana, India -
-
Outcrop in theVasquez Rocks Natural Area Parkof southernCalifornia -
Valley of Desolation in theCamdeboo National Park
See also
[edit]
References
[edit]- ^Howell, J. V., 1960,Glossary of Geology and Related Sciences.Washington, DC: American Geological Institute, pp. 207-208
- ^"oxy.edu. Vazquez Rocks. access date:5/22/2010".Archived fromthe originalon 2011-06-08.Retrieved2010-05-24.
- ^"parks.lacounty.gov. Vazquez Rocks Natural Area and Nature Center. access date:5/22/2010".Archived fromthe originalon 2012-09-20.Retrieved2010-05-24.
