The Mediterranean Ridge is an arcuate ridge of deformed sediment caught up in the convergent plate margin between the African plate and the Aegean. An intensive campaign of SeaMARC I and SeaBeam surveys followed by piston coring has been conducted along the contact between undeformed turbidites of the Sirte Abyssal Plain and folded and faulted sediments of the Mediterranean Ridge. Along the outer edge of the Ridge, surficial sediments have been deformed into sinusoidal ridges and troughs (wavelengths 0.5–2 km, amplitude 20–150 m), which we interpret as folds. In plan view, the ridge and the trough fabric parallels the NW-SE trending regional contours, suggesting that the folds formed in response to compression orthogonal to the Mediterranean Ridge. The outermost ridge is shedding a debris apron out onto the abyssal plain, implying that uplift and deformation are ongoing. We show that the geometry of the outermost folds can be produced by elastic bending of a packet of 5–10 relatively strong layers, each 10–20 m thick, interbedded between weaker layers; we equate the strong layers with gypsum beds in the Messinian upper evaporites. Folding the seafloor from a flat layer into the observed ridge and trough topography would shorten the layer by less than 2%. Two percent shortening (equals two percent thickening) is insufficient to create the observed relief of the Mediterranean Ridge even if the entire sediment column down to basement were involved; we infer that additional shortening/thickening is accommodated by thrust faulting above a decollement at the top of the Messinian salt layer. At distances > 15 km from the deformation front and more than 500 m from the abyssal plain, sharp-edged, fine-grained side-scan lineations with very little vertical relief cut across the kilometer-scale ridge and trough topography. These fine-grained lineations fall in two groups trending N/S to NNE/SSW and ~ENE. We interpret these lineaments as traces of conjugate strike-slip faults formed in the same compressional regime which formed the NW/SE trending folds. The onset of strike-slip faulting may coincide with the cessation of imbricate thrust fan development above the initial salt-controlled decollement surface. The following characteristics of the Mediterranean Ridge are attributed to the presence of evaporites in the incoming sedimentary section: (1) initial deformation by folding rather than thrust faulting; (2) narrow taper; (3) rapid rate of outward growth; (4) karstification.

The southeast Bahama banks have been colliding with the island of Hispaniola along a restraining bend within the northern Caribbean plate boundary zone since the late Miocene. A SeaMARC II/seismic reflection investigation was conducted along the deep-water flanks of Mouchoir Bank, Silver Bank, and Navidad Bank to evaluate the response of these carbonate platforms to active plate tectonic collision. Overall, our data provide evidence of large-scale platform margin retreat which contrasts sharply with the prograding platform margins in the tectonically passive northwest Bahamas.North of Silver Bank there is a large (approximately 5,000 km2), deep-water (3,000-4,000 m) plateau that records the drowning and step-back (approximately 50 km) of an Early Cretaceous carbonate platform margin. Intact (uneroded) segments of this Cretaceous platform margin may occur along the seaward edge of the deep-water plateau (Bahama Escarpment) separated by large (20 km across) erosional reentrants. A coalescing system of broad (up to 10 km), shallow (< 200 m relief) canyons, akin to mountainous avalanche chutes, funnel debris into the reentrants from the flank of Silver Bank. The reentrants are interpreted as zones of structural weakness produced by passage of the Atlantic spreading center along a transform plate boundary during the Late Jurassic-Early Cretaceous. Drowning and step-back appear to be part of a global response of carbonate platforms to a mid-Cretaceous tectonic pulse of ocean crust formation, and relative sea-level rise.The southern margin of Mouchoir Bank has also been drowned and has stepped-back by about 30 km. This event occurred during the Late Tertiary prior to the mid-Pliocene and is attributed to tectonic tilting and subsidence resulting from oblique underthrusting of the southeast Bahamas beneath Hispaniola. The southern margin of Mouchoir Bank is also characterized by large (approximately 20 km across) amphitheater-shaped "scallops" that expose Tertiary shallow-water limestones along their deep-water flanks. Seaward of one scallop is a large (25 km wide, 50 km long) mass movement with flow lines preserved on the seafloor. We interpret these scallops as catastrophic collapse structures triggered by large earthquakes generated along the collision zone since the Late Tertiary.South of Navidad and Silver banks is a very complex seafloor morphology resulting in part from the accretion of a portion of the Bahamas onto Hispaniola. There is also a series of E-W oriented down-to-basin normal faults that have caused the platform margin to retreat. Extensional stress along this predominantly transpressive plate boundary may be a consequence of rotation of the nearby Puerto Rico block or lithospheric bending during oblique subduction.This study provides an initial framework within which to view the actualistic response of carbonate platforms to plate tectonic collision.

A SeaMARC II and seismic reflection investigation of the deep-water margins of carbonate banks in the southeast Bahamas has documented the retreat of these isolated platforms since mid-Cretaceous time. This retreat is in sharp contrast to prograding carbonate platforms in the passive northwest Bahamas and provides an initial framework within which to view the response of carbonate platforms to tectonic processes. Processes of retreat include large-scale (50-60 km) step-back of platform margins during the mid-Cretaceous; tectonic subsidence and downfaulting during the late Tertiary; and large-scale collapse of platform margins, which may be an active process. Step-back during the mid-Cretaceous correlates with a global tectonic pulse of ocean formation and relative sea-level rise; downfaulting may be a response to either late Tertiary lithospheric bending during subduction and/or block rotation along the North American-Caribbean plate boundary; and collapse may be related to earthquake shocks generated by active plate-tectonic collision between the southeast Bahamas and Hispaniola.