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Alejandro Escalona, Department of Geological Sciences, The University of Texas at Austin,
and Paul Mann, Institute for Geophysics, The University of Texas at Austin

Two different tectonic models are proposed for the thick Eocene depocenter located along the northeastern margin of the Maracaibo basin, Venezuela. The first model proposes that the depocenter is a foreland basin controlled by southwestward-directed overthrusting during late Paleocene-middle Eocene collision between the Caribbean and South American plates. This model is based on the wedge-like geometry of the basin, paleocurrents and clinoforms, indicating NE to SW progradation from the thrust front located northeast of the present-day lake Maracaibo. The second model proposes that the northeast sedimentary wedge was controlled by a large tear fault, or lateral ramp, separating SE-directed, but independently moving, thrust sheets.

Regional seismic lines reveal the structure of the Paleogene depocenter in the northeastern area of the basin. These lines show a NS-trending inverted basin bounded by partially inverted reverse or strike slip faults. Well data of this area suggest that early Eocene sediments are mainly shales, while middle and upper Eocene sediments are coarser, forming a southwestward wedge in the present day lake area. Chaotic reflections, separating younger sediments sub-basins, within the inverted basin suggest the presence of shale diapirs activated by Eocene convergence. The elongate depocenter and present-day configuration of the inverted basin are more supportive of the tear fault origin. However, the Eocene clastic wedge exhibits features of a foreland basin setting, with multiple unconformities lapping out onto a forebulge.