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In geology, a clastic wedge is a thick accumulation of sediments or sedimentary rocks eroded and deposited landward of a mountain chain. They begin at the mountain front, thicken considerably landwards of it to a peak depth, and progressively thin with increasing distance inland. As they are often lens-shaped in profile, the process by which these sedimentary wedges are shaped is due to the regressive and transgressive movement from bodies of water.[1] Perhaps the best examples of clastic wedges in the United States are the Catskill Delta in Appalachia and the sequence of Jurassic and Cretaceous sediments deposited in the Cordilleran foreland basin in the Rocky Mountains.[2]
Not all clastic wedges are associated with mountains. They are also a characteristic of passive continental margins such as the Gulf Coast; these are quiescent environments, where sediments have accumulated to great thickness over a long period of time.[3] In addition to prehistoric clastic wedges that have grown over time, the presence of microfossils and organic materials shown to be more abundant.[4] These passive margin continental shelf sediment sequences are termed miogeoclines.[5]
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Clastic wedges are often separated into one of two distinct types: flysch, mostly dark shales that originate from moderate to deep marine water; and molasse, which is composed mainly of red sandstones, conglomerates, and shales that were deposited in terrestrial or shallow marine environments.[6]
Sedimentary Cycles
editThe conceptual geology of a clastic wedge can be referred to sedimentary cycles; in which is the reoccurring sequence of geological events upon stratigraphic surfaces.
See also
editReferences
edit- ^ Zecchin, Massimo; Catuneanu, Octavian (2015-04-01). "High-resolution sequence stratigraphy of clastic shelves III: Applications to reservoir geology". Marine and Petroleum Geology. 62: 161–175. doi:10.1016/j.marpetgeo.2014.08.025. ISSN 0264-8172.
- ^ Stanley, Steven M. Earth System History. New York: W.H. Freeman and Company, 1999. ISBN 0-7167-2882-6 pp. 243, 489
- ^ Stanley, p. 516
- ^ Zecchin, Massimo; Catuneanu, Octavian (2013-01-01). "High-resolution sequence stratigraphy of clastic shelves I: Units and bounding surfaces". Marine and Petroleum Geology. 39 (1): 1–25. doi:10.1016/j.marpetgeo.2012.08.015. ISSN 0264-8172.
- ^ Dietz, Robert S. and John C. Holden, 1966, Miogeoclines (Miogeosynclines) in Space and Time, Journal of Geology, Vol. 74, No. 5, Part 1 (Sep., 1966), pp. 566-583
- ^ Stanley, Steven M. Earth System History. New York: W.H. Freeman and Company, 1999. ISBN 0-7167-2882-6