Geosynclines are further classified into miogeosynclines, eugeosynclines, and orthogeosynclines; dependent on rock strata, location, and nature of the mountain system. The ‘Geosynclines’ are major structural and sedimentation all units of the earth crust. Ural geosyncline is quoted as the representative example. Dana also reinstated that the trend of the mountain range follows the deepest part of the geosyclinal trough (1). These stages would be elaborated during the discussion of geosynclinal theory of Kober. A Geosyncline (originally called a geosynclinal) is an obsolete geological concept to explain orogens, which was developed in the late 19th and early 20th centuries, before the theory of plate tectonics was envisaged. There are five basic kinds of mountains: 1. (2) These are characterized by gradual sedimen­tation and subsidence. Mesogeosynclines are similar to the geosynclines con­ceived by Haug. Types of Geosyncline. The five types above are formed due to wide-reaching shifts in tectonic plates or earth’s crust, also known as plate tectonics. Par geosyncline. [5] In Stille and Kober's view, geosynclines and orogens were the unstable parts of the Earth's crust, in stark contrast with the very stable kratogens. Concept of Geosynclines, Geology, Geosynclines. He defined, for the first time, geosynclines as long, narrow and shallow and sinking beds of seas. Focus of this lecture is to explain the formation and mechanism involved in geosynclines. A geosyncline may be narrow or wide. (c) Formation of geosynclines due to compres­sion: Some geosynclines are formed due to compres­sion and resultant subsidence of outer layer of the crust caused by convergent convective currents. Dana named such water bodies as geosynclines. [15], Media related to Geosyncline at Wikimedia Commons, Bulletin of the Geological Society of America, https://en.wikipedia.org/w/index.php?title=Geosyncline&oldid=996039617, Creative Commons Attribution-ShareAlike License, This page was last edited on 24 December 2020, at 05:24. Volcanic Mountains 5. According to this view, regular, episodic global revolutions caused geosynclines to collapse, forming orogens. Tasman Sea, Arafura Sea, Weddell Sea and Ross Sea have been quoted as typical examples of such geosyncline. Caribbean Sea, the western Mediterranean Sea and Banda Sea have been quoted as examples of this category of geosynclines. Residual Mountain. [4][5] Eduard Suess, a leading geologist of his time, disapproved the concept of geosyncline, and in 1909 he argued against its use due to its association with outdated theories. They originated in positions similar to those of monogeosynclines. (ii) Polygeosynclines were long and wide water bodies. Haug could not explain these and many more questions. Such geosynclines are situated either within a continent or along its borders. In the second type the trough develops at the boundary between oceanic and continental crust. This metamorphism increases the density of rocks, with the result the lower layer of the crust is subjected to subsidence and thus a geosyncline is formed. Stille has further classified the geosynclines on the basis of intermittent volcanic activ­ity during their infilling into: Eugeosynclines have relatively high amount of volcanic products (Greek prefix eu means high status of igneous activity) while miogeosynclines have low volcanic products (mio means low). Geotectonics deals with the earth's crust as the dynamic system, formed as a result of a rather slow process, which may be formally subdivided into three stages: pre-geosynclinal, geosynclinal and post-geosynclinal. See more. “These are considered to have experienced more than one phase of orogenesis, consequently they may have been diversified by the production of one or more parallel geanticlines arising from their floors in the squeezing process”. This concept of Holmes has been severely criticised because the trans­fer and displacement of magmas cannot cause subsid­ence to form geosynclines. By Schuchert Monogeosynclines. Types of Geosyncline. [12][13] Stille theorized that the contractional forces responsible for geosynclines also formed epeirogenic uplifts, resulting in a pattern of undulation in the Earth's crust. They are potential site of mountain building activity and fold mountains. Geosynclines, after long period of sedimentation, are squeezed and folded into moun­tain ranges. 11.3) of Mesozoic era depicted unbelievable larger extent of rigid masses (land areas) in comparison to geosynclines (oceanic areas). He located 4 geosynclines between these ancient rigid masses e.g. Applachian geosyncline is considered to be the best example of monogeosynclines. The littoral margins of the geosynclines are affected by transgressional and regressional phases of the seas. He further pointed out that the process of subsid­ence of the geosynclinal beds was not a sudden process rather it was a gradual process. Taphrogeosyncline. Kober explained the concept of geosynclines and mountain building based on the force of Contraction which is produced by the cooling of the earth. Hall elaborated the concept of geosynclines as advanced by Dana. According to Haug ‘geosynclines are relatively deep water areas and they are much longer than they are wide’. According to Evans all the geosynclines irrespective of their varying forms, shapes and loca­tions are characterized by twin processes of sedimen­tation and subsidence. Report a Violation 10. these are never isolated - group of parallel ranges. [14] Steinmann contributed this correlation to the distinction between Cordilleran and Alpine-type mountains. Appalachian geosyncline geosynclines. Rocky and Ural geosynclines are quoted as the representative exam­ples of polygeosynclines. [6][11], Dana and Stille supposed that the collapse of geosynclines into orogens was result of the Earth's contraction over time. He identified four geosynclines located between these rigid masses: (i) Rockies geosyncline (ii) Ural geosyncline (iii) Tethys geosyncline and (iv) Circum-Pacific geosyncline. His geosyclines as very deep oceanic tracts are also not acceptable because the marine fossils found in the folded mountains belong to the group of marine organisms of shallow seas.
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