Geosyncline

In geology, geosyncline is a term still occasionally used for 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 tons of 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, are deposited in eugeosynclines, the outer deepwater segment of geosynclines.