The southeastern Caribbean subduction to strikeslip transition zone: a study of the effects on lithospheric structures and overlying clastic basin evolution and fill
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The formation and evolution of sedimentary basins are best understood within the context of prevailing tectonic conditions. This dissertation presents an integrated geologic and geophysical study of the southeast Caribbean–northeast South American margin which is characterized by a 300-km-long curved transition from subduction to strike-slip plate boundary interaction. Tomography models are generated to image the geometry and orientation of the subducting slab and associated upper mantle structures, and integrated with observations made from gravity, magnetic and seismicity data. The plate boundary interaction changes laterally from: (1) direct subduction where oceanic South American lithosphere dips towards the west at up to 65° beneath the Caribbean plate; to (2) collision where South American transitional-continental type lithosphere dips 44°–24° beneath the Caribbean plate; to (3) east-west oriented strike-slip interaction where the slab is detached from the South American continent. A tectonostratigraphic framework based on the interpretation of ~10,000 km of 2-D seismic and abundant well data is used to study the evolution of the structures and basin fill of the margin. The basins are characterized by composite and superimposed structural styles which differ from basins formed in pure strike-slip or convergent margins. A NW–SE oriented tear fault aligned with the South American continent-ocean-boundary defines the boundary between different contractional styles in the sedimentary succession of the subduction and collision provinces. An examination of bathymetric conditions and the upper Pleistocene succession of the continental shelf suggest a bimodal sediment transport process, linked to shoreline changes. Current-driven, strike-parallel sediment distribution systems dominate during highstand, generating unique shelf-bound channels and fills. Lowstand across the area is characterized by dip-directed, sediment distribution systems with SW–NE oriented channels that direct sediments to the shelf edge and deep basin environments. The results of this study illustrate that plate boundary conditions and associated lithospheric arrangement at depth, play a significant role in influencing the form of shallow structures, basins and surface geomorphology. Crustal-scale structures; influenced by deeper lithospheric-scale configuration, act over longer time-scales to create and deform depocenters; while sea-level stand exerts significant control on the timing and location of sedimentation over shorter time periods.