Abstract
The Santaren Channel separates Cuba and Cay Sal Bank, the westernmost platform of the Bahamian archipelago, from Great Bahama Bank. Multichannel seismic data from the southern Santaren Channel reveal that the outer edge of the Cuban Fold and Thrust Belt is situated within the channel. Newly acquired 2D high-resolution multichannel seismic data east and north of Cay Sal Bank reveal that the bank itself is part of the Cuban Fold and Thrust Belt. In addition, seafloor displacements, observed in the seismic data, the multibeam-bathymetry, and sub-bottom (parasound) profiles, document neotectonic activity in the area. The data sets acquired during the M95 cruise on the R/V Meteor in 2013 are combined with the old regional seismic profiles and tied to the borehole information from ODP LEG 166 and the deep industrial Great Isaac-1 well on the northwestern tip of Great Bahama Bank. These combined data sets allow the tectono-stratigraphic evolution of Cay Sal Bank and its adjacent seaway to be delineated. Careful processing that included migration of the newly acquired seismic data produced high-quality seismic images that improve the imaging of the various structural elements and the stratigraphic correlation of facies and tectonic changes in the study area. The Santaren Channel is a long-lived, deep-water re-entrant into the shallow-water platform area that formed after Jurassic rifting but it experienced morphologic alterations from the Cretaceous to the recent time. The horizon map of the top Albian reflection illustrates a wide and deep channel that was bordered on both sides by the steep slopes of the adjacent platforms. In the Turonian, compressional forces fold part of the deep-water sediments into a NNW-SSE trending anticline that remains a high until the Early Miocene. With the onset of the Florida Current and the concomitant onset of drift deposition in the Santaren Channel, the anticline is buried. The increased sedimentation rate from the drift deposition results in a shoaling of the seaway and the transformation into a V-shaped form. Seven depositional systems are identified in the seismic facies analysis in the region. Most pronounced is the near vertical juxtaposition of the chaotic-transparent seismic facies of shallow-water carbonates with the more continuous seismic reflections of the deep-water sediments. Within the deep-water facies, high-amplitude reflections (turbidites), chaotic-transparent intervals (slump units) and down-cutting channels are seismic expressions of mass-gravity flow processes. Wavy seismic facies and large mounded sedimentary bodies are the result of current processes such as sand waves and drift deposits. Acoustic pipes are detected within the deep-water sediments associated with pockmarks and coral mounds, and are interpreted as fluid escape features. The structural analysis reveals two types of fault systems; deep-rooted fault systems and strata-bound faults. The latter are the dominant structural feature in the southern profiles and the most dominant type in this system are polygonal faults that are interpreted as having formed by fluid escape. They are detected mostly in the drift deposits. The polygonal faults are associated with acoustic pipes and some end, like the acoustic pipes, underneath pockmarks, indicating that they are also pathways for migrating fluid and hydrocarbons. The deep-rooted fault systems are reminiscent of wrench faults but also display characteristics of thrust faults. These reactivated deep-rooted faults and growth anticlines on the eastern side of the Cay Sal Bank clearly place the edge of the Cuban Fold and Thrust Belt east of Cay Sal Bank into the Santaren Channel. An anticline protruding from Cay Sal Bank to the NE is the northeastern tip of the deformation. The position of these tectonic elements confirms that Cay Sal Bank is part of the Cuban Fold and Thrust Belt. A sea-floor break that is around 40 km in length and 50 m in depth at the northeastern portion of the Cay Sal Bank document neotectonic activity along the outer fringe of the fold belt. Five earthquakes in early 2014 at the eastern edge of the Nortecubana Fault further south within the Fold and Thrust Belt document that present-day tectonism is occurring in the region. Based on all of these findings, a new structural model is proposed as a final product of this study. This model relocates the Cuban Fold and Thrust Belt further east and north and confirms continuous shortening between Cuba and the Bahamas.