Present-day Venezuela may be divided into the following major structural provinces—Perijá Mountains Goajira-Paraguaná arch, Maracaibo basin, Falcon, Venezuelan Andes, Caribbean ranges, Barinas-Apure basin, Eastern Venezuela basin, and Guayana shield.
The pre-Cretaceous history is little known. A Paleozoic geosyncline may have existed in Western Venezuela, but any important regional metamorphism there was pre-Devonian. ? Mid-Ordovician, Late Devonian or early Carboniferous, and Permian to Triassic deformations may be postulated, but their trends cannot be evaluated at present. Toward the end of the Paleozoic widespread uplift, accompanied by faulting and volcanism, raised the whole country above sea level.
The Perijá, Maracaibo, Andes, and Barinas-Apure provinces owe their character as distinct units to the Tertiary Andean deformation, with the basins sinking as the mountains arose. The Cretaceous and Eocene oil fields of Western Venezuela owe their existence to the Andean orogeny; the middle to late Tertiary fields are less directly linked to it. There is some indication that movements began first in the northwest (Sierra de Perijá) during the Eocene, progressed southeastward across the more-or-less stable Maracaibo platform, reached the Andes at the close of the Eocene, and culminated in the Mio-Pliocene. The mountains, with dominant trend of N. 35° E. for the Perijá and N. 50° E. for the Andes, are essentially complexly folded and faulted structural arches with high angle reverse, normal, and wrench faults. Mountainward-dipping reverse faults are thought to bound their flanks. Both the Maracaibo and Barinas-Apure basins have asymmetrical cross sections with deepest zones close to the flanks of the Andes.
The displacement on a large northeast Bocono fault trend may have to be taken into account in reconstructing the deformation of the Andes.
Beginning in the Late Jurassic, the Caribbean sea began an extensive transgression of northern and western Venezuela. An east-west trending Caribbean geosyncline developed in the extreme north.
Volcanism and major deformation of the Caribbean geosyncline began about Middle Cretaceous time, leading to the folding, faulting, and metamorphism of the previously deposited Mesozoic rocks. However, sedimentation, volcanism, deformation, and metamorphism, although on decreasing scale, continued throughout Late Cretaceous and Paleocene time and perhaps into the early Eocene. Dominant structural features in the Caribbean ranges trend N. 60°---80° E.; wrench (strike-slip) faulting is common.
To many geologists, an outstanding tectonic feature of northern Venezuela is a series of long east-west trending, right-lateral wrench faults, that are located close, and roughly parallel, to the coast. Best known of these are the Oca fault in the west and the Pilar fault in the east. It is possible that these faults are at least as old as Cretaceous, that they are related to the tectonic history of the general Caribbean area, as suggested by Bucher and others, and that they have played a major role in the deformation of all of Venezuela. The importance of these faults as dominant features has yet to be proved and caution is advised in evaluating their significance in the tectonic history of Venezuela.
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.