Evolution of the Bahia Basin: Evidence for Vertical-Axis Block Rotation and Basin Inversion at the Caribbean Plate Margin Offshore Northern Colombia

Galindo, Pedro A.¹ and Lonergan, Lidia
¹[email protected]

The Bahia Basin is located in the NW corner of South America where a complex history of subduction, accretion and transpression is on-going since Cretaceous times. The Bahia Basin is located just offshore from major strike-slip fault systems that affect northern Colombia and lies behind the toe of the modern accretionary wedge, where the Caribbean Plate is being subducted obliquely beneath South America.

This study uses a high quality 3D-PSTM seismic volume, regional 2D seismic reflection lines, together with borehole data from one exploratory well drilled within the area of the 3D seismic volume. The mapping of the Upper Miocene Unconformity (UMU) highlights the presence of a young, deep, narrow basin trending NE-SW which is bounded to the NW by a major fault: the Bahia Fault. This fault shows an initial phase of normal displacement with later inversion along some segments. Its footwall appears to be formed by three separate blocks. Structural maps above and below the unconformity were constructed to identify the changes in structural style through the evolution of the basin. Structures below the UMU show high-density, low-displacement, domino-style normal faults within the blocks of the footwall of the Bahia Fault. The strike of the normal faults varies from block to block; from SW to NE: NW-SE in the first block, NNE-SSW in the second block and WNW-ESE in the third block. The change in orientation of the normal faults between the different blocks is explained as a possible result of vertical-axis block rotation linked to the opening of the young depocentre. Subsequently the Bahia fault has been inverted and SW-NE trending folds have formed in rocks above the UMU as a result of the latest stage of shortening related to subduction at the Caribbean Plate margin. The evolution of the inverted structures is analysed by thickness maps of the syntectonic packages.

This study shows the structural styles associated with the evolution of the Bahia Basin which helps to understand the complex array of structures observed in a transpressive setting, and highlights the use of 3D seismic reflection data to test models of vertical-axis block rotation and basin inversion. This has a direct implication in the hydrocarbon exploration of basins along this type of plate boundary, and particularly in the understanding of basin evolution along the margin between the Caribbean and South American Plates.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013