Abstract

Recent studies in the central Andean areas of Bolivia, northern Chile, and southern Peru have organized stratigraphic, paleontologic, and possible depositional settings for these rocks. In Bolivia, correlation is made between the Sierras Subandinas, Cordillera Oriental, and altiplano. In the Cordillera Oriental are the Icla (600 m), Humampampampa (1000 m, with seven members), and Cha-kjeri (500 m) Formations, in ascending order. For the altiplano there are the Belen (2000 m, lowest), Sicasica (700 m, with two distinctive members), and Collpacuchu (600 m, highest) formations. Still not clearly understood is the eastern Bolivian Devonian stratigraphy, which consists of the Los Monos (1000 m +) and Iquiri (800 m) formations. The bulk of the Devonian sequence, fine to coarse sandstones, siltstones, and shales was deposited during early Emsian through late Eifelian time, with the possibility of younger beds being present in the northwest and subandean regions. Stratigraphy in adjacent Cabanillas, Peru, shows a development similar to Bolivia’s altiplano sections. All the above sequences record Malvinokaffric Realm brachiopods, which have been re-described in the last decade. In southwest Peru are two sequences, at Aplao (approximately 1500 m) and Cocachacra (200 m), that diverge significantly from the Cabanillas section. No diagnostic faunas have been recovered at Aplao. In lutites at the Cocachacra section are Eastern Americas Realm brachiopods, whose affinities appear similar to faunas from Floresta, Colombia. The most recent information comes from northern Chile, in the Sierra de Almeida, where at least 1000 m of coarse grained sandstones and volcanic cobble bearing conglomerates contain Tropidoleptus carinatus, a brachiopod indicative of the upper part of the Bolivian sequence, that was deposited in an extremely shallow, west facing marine setting. The Precambrian Arequipa Massif and Late Ordovician Puna Terrane formed a western land source for most of the Bolivian intracratonic basinal sequence. The Brazilian Shield formed an eastern margin to this basin. West of the Puna Terrane lay a possible Chilean fore-arc basin, which may have connected to a later “successor” basin that extended into Peru.