Chronology of Cenozoic tectonic events in western Venezuela and the Leeward Antilles based on integration of offshore seismic reflection data and on-land geology

Abstract

Newly acquired, deep-penetration Broadband Onshore-Offshore Lithospheric Investigation of Venezuela and the Antilles Arc Region seismic reflection data from offshore western Venezuela (Bonaire Basin) and around the Leeward Antilles are combined with existing geologic and geophysical data sets to examine the chronology of Late Cretaceous–Cenozoic tectonic events in this part of the Caribbean–South American plate boundary zone. These tectonic events have controlled the maturation and structural trapping of known hydrocarbons in the offshore Bonaire Basin and the adjacent onland Falcn Basin. We infer three tectonic phases that are constrained using these combined data sets. (1) The late Eocene–early Oligocene, north-south opening of the 3–6-km (1.8–3.7-mi)-thick Falcn-Bonaire Basin occurred along east-west–striking normal fault systems that have locally been inverted by later tectonic phases. These Paleogene normal faults rifted the Upper Cretaceous arc crust and Paleogene marine depositional sequences within the offshore Bonaire Basin. (2) Northwest-striking normal faults crosscut the older normal faults of the Bonaire Basin and Leeward Antilles and form deep, submarine rifts that contain up to 4 km (2.5 mi) of sedimentary fill and form deep-water channels between islands of the Leeward Antilles. Offshore well data and age of onshore sediments in the Falcn Basin indicate that this second phase of rifting occurred mainly during the late Oligocene to early Miocene and remains active to the present. (3) Inversion of the subaerial Falcn Basin commenced during the middle Miocene. This inversion phase is reflected in the present-day pattern of an east-northeast–trending fold-thrust belt that can be traced over 200 km (124 mi) along strike in the Falcn Basin. A second offshore fold-thrust belt (La Vela) can be traced over a distance of 175 km (108 mi) along strike and parallel to the northeast-trending Falcn Basin coast. Restoration of imbricate thrusts seen on seismic lines perpendicular to the La Vela fold-thrust belt indicates a minimum of 7 km (4.3 mi) of northeast-southwest–directed, thin-skinned shortening. Geochemical work indicates that source rocks for scattered occurrences of hydrocarbons in the Falcn Basin and its coastal zone are Paleogene and Miocene marine shale. Reservoir rocks are Tertiary marine sandstone and shale deposited in Paleogene rifts formed during the first tectonic phase in the late Eocene to early Oligocene. Structural traps were formed by thrusting during the second tectonic phase in the late Oligocene to early Miocene.