Abstract
Multichannel seismic reflection lines from the southern Great Bahama Bank (GBB), with a complete record down to 5 s (two way travel time), reveal the nature of basement and the evolution of the bank, which was strongly influenced by tectonic activity. The reflection seismic profiles display a fragmented internal anatomy of the bank that is tectonically controlled by deep basement faults of different ages. Three distinct episodes of deformation have shaped the architecture of the southern GBB. During the first episode high-amplitude reflections overlaying the acoustic basement are displaced by faults creating a fault-bounded topographic relief. The seismic facies of the basement with faint continuous, horizontal internal reflections overlain by a continuous high-amplitude reflection horizon is reminiscent of continental or transitional crust with a sedimentary cover. The episode of extensional tectonism that affected these two seismic facies probably corresponds to the rifting phase in the Jurassic. The GBB established on this faulted crust but subsequent growth of the bank immediately leveled the topographic relief. During the growth of the bank in the Cretaceous about 5 km of shallow-water platform carbonates were accommodated by passive-margin subsidence. The second deformational episode occurred probably in mid-Cretaceous and was characterized by the reactivation of some pre-existing structures which first segmented GBB. In southern GBB it created a WNW-ESE-trending margin towards the Tongue of the Ocean. We speculate that this tectonic phase is a consequence of the reorientation of the stress regime that caused the plate reorganization in the Caribbean realm. The third deformational episode occurred during the Late Cretaceous-Middle Eocene when Cuba collided with the southern edge of the Bahamas platform. As a result of the collision, the bank was dissected by WNW-striking oblique-slip faults forming long, narrow, symmetric depressions within the bank. The deepest depressions were produced by a long WNW-ESE straight master fault zone consisting of oblique-slip faults with both normal and left-lateral strike-slip components of displacement. The faults offset the entire bank and diverged upwards in convergent fault slices, forming negative flower structures. Activity of most faults ceased with the end of the collision in the Late Eocene. The subsequent infilling by the highly productive carbonate environment healed the depressions masking the scars produced by tectonism. Since the late Cenozoic the southern GBB is mostly a flat-topped aggrading carbonate bank.