Seismic and stratigraphic interpretation of the Morichito Subbasin, eastern Venezuelan basin

Salazar, Migdalys Beatriz
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The Morichito Subbasin is a southwest-northeast oriented depocenter that is located in the Eastern Venezuelan Foreland Basin (EVFB). The Morichito Subbasin covers an approximate area of 1,000 km² between the Serranía del Interior fold and thrust belt and the Pirital High. This basin was formed during the Neogene as the result of complex transpressional interactions between the Caribbean and South-American plates. Previous studies have tried to address the tectonostratigraphic significance of the Morichito Subbasin but about 1,800 km² recently acquired 3D seismic volumes allowed us to expand our understanding of this subbasin. The relevance of the Morichito Subbasin lies in the fact that it provides a valuable stratigraphic record that can be used to unveil the timing of the main deformational events that took place in this portion of the EVFB. This work presents the tectonostratigraphic evolution of the Morichito Subbasin by defining four sequences (Units I to IV). These units were defined based on the integration of well logs and biostratigraphic information with geomorphological interpretations that were performed using 3D seismic data. Unit I (E. Miocene to M. Miocene) was deposited in shallow marine environments (the Carapita Formation) and its areal coverage extends to the south, beyond the boundaries of the Morichito Subbasin suggesting that Unit I pre-dates the formation of the Pirital High. Unit II (M. Miocene) is composed of alluvial fan deposits (the Morichito Formation) that were derived from the Serranía del Interior fold and thrust belt; pinch-out relationships against the Pirital High indicates that Unit II was contemporaneous with the Pirital thrusting event. Units III (L. Miocene to E. Pliocene) and IV (E. Pliocene to Recent) are composed of shallow marine and fluvial deposits (Las Piedras and Mesa Formations). These two units represent the final phases of basin infilling when tectonic activity and subsidence were at lower rates