A large-scale depression in the earth's crust containing very thick deposits.
- ‘Both Permian perrinitid ammonoid areas are located within the transitional belt between the active geosyncline and the adjacent stable platform.’
- ‘For several generations of geologists the name of J. D. Dana was associated with the concept of the geosyncline, an elongated downwarp in the Earth's crust in which a great volume of sediments accumulated.’
- ‘They are not found from Franklinian, Andean, Italian, and Tasmanian geosynclines and their adjacent shelves.’
- ‘All of these perrinitid-bearing ammonoid faunas are distributed along the active linear geosynclines and their adjacent areas, i.e., the ‘Open-Sea’ within basin and out shelf.’