TECTONO-STRATIGRAPHIC INTERPRETATION OF THE MONAGAS FORELAND THRUST BELT, EASTERN VENEZUELA

The Monagas Foreland Thrust Belt is the result of a Neogene compression related to the oblique collision between Caribbean and South-American plates. Located in Eastern Venezuela Basin, this thrust belt comprises three principal tectonic provinces: the outcropping ranges of the “Serrania del Interior”, the Monagas foothills and the Maturin foredeep. Three main thrust systems were identified and dated through the integration of a structural interpretation, sequence stratigraphy and biostratigraphic data, allowing the proposition of an evolutionary model for these mountain ranges.

The interpretation of the structural styles within the Monagas foothills and the Maturin foredeep was based on 2D seismic profiles and 3D seismic data, together with well control. The interpretation in the “Serrania del Interior” outcropping ranges was based on surface geology cross sections, as well as the study of numerous stratigraphic columns taken across the ranges.

The seismic stratigraphy, the well control and the biostratigraphic data allowed the documentation of four main unconformities, each of one date the emplacement of the thrust systems interpreted in this study. The oldest unconformity is dated Lower Miocene, and is interpreted to represent the first tectonic pulse. The upper section of the Middle Miocene rests in onlap over erosional truncations, providing evidence for the interpretation of the second and major unconformity. This section dip strongly north, showing apparent downlaps on the northern wedge of the basin, and giving the wrong impression of a restricted basin sourced from the south. However, the integration of different data sets in this study suggests a southward opened basin with the majority of sands on its northern wedge, indicating that the apparent downlaps are actually coastal onlaps. The third unconformity represents the emplacement of the last thrust system, the reactivation of the second, and the tilting of the Pirital High, forming the Morichito Basin. Finally, the fourth unconformity, dated within the Pliocene, not only reflects the last reactivations over the belt, but also a major growth phase of the deformation front.