Andean Geosyncline

Andean Geosyncline, a linear trough in the Earth’s crust in which rocks of the Mesozoic Era (251 million to 65.5 million years ago) and Cenozoic Era (65.5 million years ago to the present) were deposited in South America. An intense orogenic (mountain-building) event affected the older sediments in the geosyncline in the Late Cretaceous Epoch (99.6 million to 65.5 million years ago) and, combined with later deformational episodes, produced a pattern of scattered marine deposition in basins along the western margin of the geosyncline. The total area of deposition was great enough for some geosynclinal segments to be separately named—e.g., the Venezuelan-Peruvian Geosyncline. The rising highland belts provided much coarse sediment, and thicknesses as great as 6,080 metres (20,000 feet) are known from early Cenozoic sequences. During middle Cenozoic time, another orogenic phase occurred, accompanied by widespread volcanism. A complex history of intermittent uplift, block faulting, and erosion in late Cenozoic time led to a series of extensive uplifted erosion surfaces in Peru, Bolivia, and elsewhere. Uplift continued through the Late Pleistocene (about 126,000 to 11,700 years ago), giving rise to the present configuration of the Andes. Elevations of 4,600 metres (15,200 feet) are widespread, and many peaks attain 6,000 metres (19,800 feet) or more.