Geosyncline is a geological concept which was developed in the late 19th and early 20th centuries before the concept of plate tectonics was developed. A geosyncline was described as a subsiding linear trough that was caused by the accumulation of sedimentary rock strata deposited in a basin and subsequently compressed, deformed, and uplifted into a mountain range, with attendant volcanism and plutonism. The filling of a geosyncline with sediment is accompanied in the late stages of deposition by folding, crumpling, and faulting of the deposits. Intrusion of crystalline igneous rock and regional uplift along the axis of the trough generally complete the history of a particular geosyncline. It is then transformed into a belt of folded mountains. Thick volcanic sequences, together with greywackes (sandstones rich in rock fragments with a muddy matrix), cherts, and various sediments reflecting deepwater deposition or processes, were considered eugeosynclinal deposits of the outer deepwater segment of geosynclines.

The geosyncline hypothesis is an obsolete concept involving vertical crustal movement that has been replaced by plate tectonics to explain crustal movement and geologic features.

Geosynclines were divided into miogeosynclines and eugeosynclines, depending on the types of discernible rock strata of the mountain system.

A miogeosyncline develops along a passive margin of a continent and is composed of sediments with limestones, sandstones and shales. The occurrences of limestones and well-sorted quartz sandstones indicate a shallow-water formation.

A eugeosyncline consists of rocks from deep marine environments. Eugeosynclinal rocks include thick sequences of greywackes, cherts, slates, tuffs and submarine lavas. The eugeosynclinal deposits are typically more deformed, metamorphosed, and intruded by small to large igneous plutons. Eugeosynclines often contain flysch typical of a continental-continental convergent boundary.

An orthogeosyncline is a linear geosynclinal belt lying between continental and oceanic terranes, and having internal volcanic belts (eugeosynclinal) and external nonvolcanic belts (miogeosynclinal). Also known as geosynclinal couple or primary geosyncline. A miogeosyncline is the nonvolcanic portion of an orthogeosyncline, located adjacent a craton. A zeugogeosyncline is a geosyncline in a craton or stable area within which is also an uplifted area, receiving clastic sediments, also known as yoked basin. A parageosyncline is an epeirogenic geosynclinal basin located within a craton area. An exogeosyncline is a parageosyncline that lies along the cratonal border and obtains its clastic sediments from erosion of the adjacent orthogeosynclinal belt outside the craton. Also known as delta geosyncline; foredeep; or transverse basin.

This page was last edited on 24 February 2018, at 13:27.
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