--> Abstract of 2006 AAPG/GSTT Hedberg Conference

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Mobile Shale Basins – Genesis, Evolution and Hydrocarbon Systems”

June 4-7, 2006 – Port of Spain, Trinidad & Tobago



Tectonically-driven Plio-Pleistocene structural development of the Columbus Basin, offshore Trinidad, West Indies


R. Gibson1, K. Meisling1 and J. Bhajan2

1BP America, Houston, Texas

2BP Trinidad & Tobago, Port of Spain, Trinidad



The late Tertiary Columbus Basin is situated along the transpressional plate margin between the South American and Caribbean plates, immediately west of the subduction boundary between the Caribbean and Atlantic plates (Barbados accretionary prism).  Previous structural models for this basin have emphasized movement of mobile shale as a primary control on the observed structural geometries. In this paper, we present an alternative model in which the observed structures are products of large-scale tectonic driving forces within a zone of dextral displacement transfer from the Caribbean-South American plate boundary into the Caribbean-Atlantic subduction complex. In this model, shale mobilization is only a minor phenomenon, largely reflecting dewatering of rapidly deposited fine-grained slope deposits.

Major structures within the 35000+’ thick, Miocene-Pleistocene siliciclastic section of the Columbus Basin are regionally detached from an underlying north-dipping Cretaceous-Paleogene passive margin succession. Although the detachment does not necessarily stay at the same stratigraphic level everywhere in the basin, there appears to be linkage of the detachment from the thrust system that bounds the NW side of the basin, through a zone of extension on the shelf, and basin-ward to the Barbados accretionary prism.

Structures in the western, shelfal part of the basin include a NW-SE striking extensional fault system and NE-SW trending contractional folds.  2D restoration of the extensional fault system shows that in excess of 35km extension occurred, much of it accommodated on a counter-regional fault system situated near the depositional shelf edge as it prograded northeastward since middle Pliocene time.  Triangular domains of relatively poor seismic imaging, previously interpreted as masses of mobile shale, are interpreted as rafted blocks of slope mudstones bounded by (1) relatively young basin-ward dipping normal faults and (2) faulted segments of older counter-regional normal faults. Some of the normal faults in this system are folded and rollover anticlines in the NW part of the basin are locally inverted due to Pleistocene NW-SE shortening.

Farther NE, on the present-day slope, E-W oriented dextral strike-slip zones are the dominant structures and were active during shelf extension. These are spatially associated with and gradually give way down-slope into NE-SW trending contractional folds of the Barbados prism. The folds trend at nearly right angles to the shelf extensional faults and, thus, cannot be contractional features at the toe of a gravitationally driven system. 3D restoration illustrates that the strike-slip fault zones in the slope domain partitioned the counter-regional footwall into large blocks, thus accommodating the large-scale extension on the shelf and transferring displacement basin-ward into contractional structures of the Barbados accretionary prism. 

We interpret the Plio-Pleistocene Columbus basin as a thin-skinned pull-apart basin formed during southeastward stepping of dextral displacement from the Caribbean-South American plate boundary into the Caribbean-Atlantic subduction complex. Extensional, strike-slip, and contractional structures in various parts of the Columbus Basin are genetically associated with one another and accommodate 3D strain in this complex plate corner. Although small-scale features related to mobile shale (mud volcanoes) are well documented in the basin, large-scale shale mobility is not required to produce the observed structural patterns.

AAPG Search and Discovery Article #90057©2006 AAPG/GSTT Hedberg Conference, Port of Spain, Trinidad & Tobago