Tectonics and sequence stratigraphy of the Venezuelan Basin, Caribbean Sea
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The central core of the Caribbean plate is the 3-4-km-deep Venezuelan Basin that is underlain by late Cretaceous oceanic plateau and oceanic crust. The Venezuelan Basin is obliquely subducted to the east-southeast beneath the continental South American plate at the east-west-trending South Caribbean deformed belt (SCDB), a 50-100-km-wide wedge of accreted sedimentary rocks. I have mapped the structure and sequence stratigraphy of five late Cretaceous to recent sedimentary sequences overlying a 230,000 km² area of the Venezuelan Basin. The dataset includes ~5900 km of 2D seismic reflection data acquired during five separate surveys from 1974-2004; these seismic data are tied to DSDP drill sites 146/149 and 150 which provide age and lithologic control on the interpreted sequences. I use these data to document older Cretaceous faults formed soon after the formation of the plateau and oceanic crust; to explain the along-strike variations in structural style of the actively subducting Caribbean plate; and to constrain the age and tectonic mechanism for the initiation of subduction along the SCDB. The earliest set of faults are normal faults, only affect rocks of Late Cretaceous age, and approximately parallel a set of seafloor-spreading magnetic anomalies described by previous workers. These normal faults are widely spaced in the area of smooth-topped lava flows making up the 15-km-thick oceanic plateau, but they are much more densely distributed in the area of abnormally thin (3-5-km-thick), rough-surfaced, oceanic crust in the eastern Venezuelan Basin. The faults are interpreted as the result of back-arc extension behind the Aves volcanic arc during the late Early to Late Cretaceous. Selective reactivation of inherited faults and new bending-related faults affecting late Cretaceous to recent sedimentary sequences strike east-west and parallel the trend of the SCDB. The age of the initiation of subduction at the SCDB has been determined based on the age of onlapping, wedge-shaped, sedimentary sequences in the Venezuelan Basin. Subduction began in the western Venezuelan Basin in the middle Eocene in the western study area, in the early Miocene in the central study area, and in the post-early Miocene-Recent in the eastern study area. The ages of subduction agree with a similar eastward younging in the age of folding and thrusting in northern South America. From this observation I infer that subduction of the Caribbean plate beneath the SCDB initiated as a backthrust response to collision between the Caribbean arc and the South American continent that began in the early Eocene and youngs in an eastward direction.