Within-plate deformations in the Maracaibo and East Zulia basins, western Venezuela

• Published in: Marine and petroleum geology 1997-03, Vol.14 (2), p.139-163
• Main Authors: Roure, François, Colletta, Bernard, De Toni, Bruno, Loureiro, Daniel, Passalacqua, Herminio, Gou, Yves
• Format: Article
• Language: English
• Subjects: Andean orogeny; Caribbean orogeny; Earth sciences; Earth, ocean, space; Exact sciences and technology; Maracaibo; Stratigraphy; tectonic inversion; Tectonics. Structural geology. Plate tectonics; Venezuela
• ISSN: 0264-8172; 1873-4073
• DOI: 10.1016/S0264-8172(96)00063-3

Subsurface data help in understanding the complex geometry of major structures of the Maracaibo basin and surrounding areas. During extensional and compressional phases, decoupling levels were activated in the Upper Cretaceous black shales and the Paleogene flysch sequences, thus inducing frequent disharmony between a rigid basement and thin-skinned cover structures. Two main extensional episodes are widespread across the Maracaibo basin: the first episode, late Jurassic in age, accounts for the development of north-northeast-trending basement horsts and asymmetrical grabens. The second episode, more probably a transtensive one, occurred during Paleogene times. It reactivated older north- and northwest-trending basement-involving faults (i.e. the Ceuta and Pueblo Viejo faults), but also generated listric normal faults and negative flower structures in the sedimentary cover. By contrast, compressional deformations are localized and reactivate older basement faults, inducing the frequent inversion of former Jurassic or Lower to Middle Eocene grabens, shortcuts in the basement and coeval wedging or fishtails in the sedimentary cover. Thus, the major inversion episode in the Maracaibo basin is Upper Eocene in age, and probably relates to the emplacement of the Caribbean nappes further to the northeast. It was followed by an episode of tectonic quiescence and erosion during the Oligocene. Neogene deformations have a limited extent beneath Lake Maracaibo, but become widespread in the west towards the Perija foothills or in the southeast near the North Andean thrust front, where they account for the development of frontal triangle zones. East of the lake, the East Zulia basin is characterized by extremely thick Paleogene flysch and a post-Middle Eocene continental molasse. Superimposed on late Jurassic or early Paleogene troughs and normal vertical offsets of the basement, the Upper Eocene to Oligocene basin fill is largely detached from its substratum along a regional detachment in the Eocene mud pile. Thus, these thin-skinned extensional structures display a piggyback attitude, with progressive migration of depocenters overtime and gentle gliding of the sedimentary cover over underlying basement blocks. The faulted borders of these late Eocene-Oligocene basins were subsequently reactivated transpressively during late Neogene times, accounting for the frequent inversion of former Oligocene depocenters.