Main morphostructural elements in Bolivia from west to east are—
The Cordillera Occidental which exposes Tertiary and younger extrusives.
The Altiplano depression with thick Tertiary and Quaternary sediments and extrusives in a probably downthrown block.
The Cordillera Real, “backbone of the Bolivian Andes,” with Tertiary or Mesozoic granitic and quartz monzonite intrusives forming peaks exceeding 21,000 feet and containing the rich tin mining districts of Bolivia.
The Cordillera Oriental consisting mainly of Ordovician and Devonian sediments. Carboniferous, Cretaceous, and Tertiary sediments are preserved in synclinal cores.
The Subandean zone or Andean foothills generally consisting of marine Devonian and continental post-Devonian sediments. The producing oil fields of southern Bolivia are located within this zone.
The open country called the Beni plain and Chaco plain in the north and south of Bolivia, respectively, present site of oil exploration activity.
The Brazilian shield exposing Precambrian basement.
The Paleozoic section in Bolivia includes rocks from all periods and has a maximum thickness on the order of 50,000 feet. Cambrian, Ordovician, Silurian, and Devonian, dominantly shallow marine shales and sands, were deposited throughout the Andean and Pampa areas and along the Brazilian shield.
The Permo-Carboniferous sediments consist of alternating glacial and interglacial deposits of continental origin in southern Bolivia. These become increasingly more marine toward the northwest. Lower Permian limestones, known in Peru, extend into Bolivia as far as the Subandean zone.
Post-Permian continental type deposition follows. A large gap in sedimentation probably exists between Permo-Triassic and Upper Cretaceous.
Thick continental Tertiary deposits fill parts of the Subandean zone and the Chaco and Beni plains, and are known in the synclines in the southern part of the eastern Cordillera.
The conspicuous elbow of the Andes in the Arica-Santa Cruz corner possibly had its origin in Precambrian time and has guided the tectonics ever since.
A transcurrent fault zone is believed to have influenced Bolivian tectonics between Corumbá-Santa Cruz and probably continuing through the Cochabamba-Oruro areas to the Chilean coast near Arica.
The present Bolivian Andes are the product of a late Tertiary orogeny. By comparison, the earlier orogenies of the Mesozoic and Paleozoic exerted a mild effect on the structure of Bolivia.
Although lateral compression is generally believed responsible for the folding and faulting of the Andes and of their eastern foothills, some geologists now strongly postulate that mostly vertical uplift created the present picture of this impressive mountain system in Bolivia.
Figures & Tables
The first article in this book is the address that introduced the technical program of the 46th Annual Meeting of the AAPG. The organization and presentation of this symposium volume was developed in an orderly geographic continuity. Modern concepts of structural form and the sequence of tectonic events are carefully reported all along the mountainous western margins of the American continents. The relationship of this structural knowledge to the accumulation of oil and gas is constantly emphasized in the 26 papers contained herein.