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Abstract: Within-Plate Deformations in the Maracaibo and East Zulia Basins, Western Venezuela

Francois Roure, Bernard Colletta, Bruno De Toni, Daniel Loureiro, Herminio Passalacqua, Yves Gou

As a whole, the Maracaibo and East Zulia basins constitute a stable foreland area relatively to the surrounding orogens (Caribbean, Andean and Perija orogens).

Major decoupling levels were activated either during extensional and/or compressional phases in the Lower Cretaceous blackshales or in the Paleocene flysch sequences, thus inducing a frequent disharmony between a rigid basement and thin-skinned cover structures.

Two main extensional episodes are widespread across the Maracaibo Lake. The first episode, late Jurassic in age, accounts for the development of north-northeast trending basement horsts and asymmetrical grabens, where thick late Jurassic (La Pica) or early Cretaceous (Rio Negro) red beds were deposited. The Urdaneta basement fault and part of the Icotea trend originated during this event. The second episode, more probably a transtensional one, occurred during the Paleocene. It reactivated older basement faults, but also generated listric normal faults or flower structures in the sedimentary cover.

Late Eocene compressive deformations are localised and mainly connect with older basement faults (i.e. Icotea or Urdaneta), inducing the frequent inversion of former grabens. On the contrary Andean (Neogene) deformations are widespread in the west, toward the Perija Foothills, or in the Southeast nearby the North Andean thrust front.

Between the Lake's eastern margin and the western front of the Lara nappes, the East Zulia basin is characterised by its extremely thick Paleocene flysch (foredeep of the Caribbean chain), and a post-Middle Eocene continental molasse. Superimposed on late Jurassic or early Paleocene normal offsets of the basement, the late Eocene to Oligocene basin fill displays a piggyback attitude. This thin-skinned architecture of extensional structures relates to the occurrence of a regional detachment in the Eocene mud-pile.

Most of the structures, especially the faulted borders of the late Eocene-Oligocene basins, have been subsequently reactivated by a transpressive event during the late Neogene (coeval with the Andean compressions), that accounts for the frequent inversion of Oligocene depocenters.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France