Complex Imbricate Systems In The Southern Caribbean Basin, Offshore Northern Colombia: Advanced Structural And Stratigraphic Analysis, And Implications For Regional Oil Exploration

Imbricate thrust structures are common in deep-water environments of active margins worldwide, including the Southern Caribbean basin, offshore northern Colombia. The imbricate systems in this region are part of the accretionary prism that resulted from the transpressional collision between the Caribbean and South American plates during Tertiary times. The Southern Caribbean basin offers an extraordinary opportunity to study imbricate thrust systems, as these structures are extremely well imaged at deep levels in seismic reflection profiles and because they preserve growth strata that record fold kinematics. Using fold shape, fault plane reflections, and patterns of growth sedimentation, we model the geometry and kinematics of this imbricate system using combined fault-bend folding and shear fault-bend folding theories. This imbricate system is formed above an Oligocene (?) weak décollement layer of variable thickness at the base of fault ramps. Individual fault-related folds within this imbricate system are characterized by long planar backlimbs that dip less - or much less - than the associated fault ramps, with increasingly shallower dips to growth strata, suggesting a component of progressive limb rotation. Forelimbs are short compared to backlimbs, but growth strata show more consistent dips that suggest a component of folding by kink-band migration. Growth sediments are deposited in piggyback basins formed over the backlimbs of individual imbricates and as onlapping sequences against the forelimbs. The growth stratigraphy consists of distal marine, fine-grained sediments; turbidite deposits, and condense sections. We present forward models of both break-forward and break-backward imbricate shear faultbend fold systems with the correspondent patterns of growth sedimentation derived using high resolution seismic data from similar imbricate systems in the deepwater Niger Delta, West Africa. Unlike conventional imbricate fault-bend folds, break-forward imbricate shear fault-bend folds are characterized by decreasing ramp and dip angles in adjacent thrust sheets toward the hinterland. The decrease in ramp and dip angles, effectively produce an increase in accommodation space for growth sedimentation, and a decrease in the structural relief. We use these models and the resulting patterns of growth stratigraphy to solve the sequences of imbrication in the Southern Caribbean Basin, which are key in the assessment of the exploration potential in this region.