Three-dimensional structural architecture and evolution of the Eocene pull-apart basin, central Maracaibo basin, Venezuela

Abstract

Three-dimensional seismic mapping of interpretative sub-surface time slice sections, incorporating age data and detailed structural observations places constraints on the structural architecture and stratigraphic evolution of the Icotea pull-apart basin in the central Maracaibo basin, Venezuela. All four fault-bounded sides of the Icotea basin, its ∼3-km-thick Eocene basin fill of clastic sediments and faults pre-dating the opening of the basin can be mapped in three dimensions. The development of the Icotea basin provides an excellent observational basis for understanding the structural history of three sets of regionally extensive faults and testing two models for the formation of pull-apart basins in general. Three main fault trends produced at different periods in the formation of the Cretaceous–Recent Maracaibo basin are mapped using 3D seismic data in the central part of the basin: (1) N–NE-striking normal faults, including the Icotea fault; these faults formed originally during Late Jurassic–Early Cretaceous rifting and reactivated as left-lateral strike–slip faults during late Paleocene–Eocene convergent deformation between the Caribbean and South American plates; (2) NW striking faults formed by late Paleocene–Eocene overthrusting of the Caribbean plate and downward flexure of the South American plate to create a major foreland basin depocenter; and (3) NE-striking normal faults, of pre-Cretaceous age, were reactivated during late Paleocene–Eocene plate convergence. Three-dimensional architecture of the Icotea basin interpreted from five time slices through the basin and its flank areas supports the simple pull-apart model for the Eocene opening of the Icotea basin. The amount of extension across the suite of normal faults ranges between 0.8 and 2.25 km. This range of offset is consistent with some previous estimates of minor left-lateral displacement along the Icotea fault but is inconsistent with either low-angle or high-angle thrusting during Eocene time, as inferred from previous interpretations of widely spaced two-dimensional seismic lines. The normal faults that formed the pull-apart basin reactivated pre-existing faults due to plate flexure.