The island of Barbados represents the structural high of the Barbados ridge, which has risen above the sea level throughout the last million years or less (Speed et al 1991). An estimated 7/8 of the land mass is covered in a Pleistocene coral cap which was deposited in a series of terraces. Four major tectonostratigraphic units have been identified onshore below the coral cap, which are exposed at the surface throughout the Scotland District in the north-eastern region of the island. The four major units are; the Basal complex, Prism cover, Oceanic allochthon and diapirs.
Regional Geological Setting of Barbados
Barbados is located east of the southern Lesser Antilles arc system, which comprises of an active magmatic arc platform and an extensive forearc. The forearc consists of two principal elements, the Barbados accretionary prism, and the Tobago forearc basin (known locally as the Tobago Trough). The accretionary prism sits above the westward moving subducted Atlantic oceanic plate, separated by a basal detachment fault. It is confined to the east by an outer deformation front and transitions to the west where it is wedged by relatively undeformed strata within the forearc basin. The highly deformed transition zone is known as the Inner Forearc Deformation belt, where the prism has its thickest stratigraphic column. The Barbados Island, the structural high of the prism is located within the IFDB. The arcward side of the IFDB is marked by one or more major thrusted anticlines, with a westward vergence. This trend is referred to as the Inner Deformation Front.
The sediments of the accretionary prism which originated from terrigenous cratonic sources on the South American plate would have been eroded and transported into foredeep basins along a passive South American and Caribbean plate margin; by deep-sea fluvial systems during the early Eocene. These sediments accumulated well within the forearc basin(s) along the eastern margin of the Caribbean plate and were gradually scraped off as the American plate was subducted below the Caribbean plate, and accreted to form the prism. Imbricate stacked thrusts along the ODF on the most eastern section of the prism, along with back thrusting and folding along the IDF forearc basin illustrates a trapping of sediments and subsequent accretion. Tectonic activity during the mid-Miocene to late-Miocene led to the uplift of the southern Lesser Antilles arc platform, the northern range of Trinidad and the Barbados Ridge, which underwent erosion and led to the further deposition of sediments into the adjacent forearc Tobago basin. Further uplift and erosion throughout the Pliocene led to large volumes of sediments being deposited into the Barbados trough which is south east of the Barbados ridge.
Presently, there is a major deep sea submarine fluvial system depositing sediments within the subduction trench along the outer deformation front (ODF) of the prism. These quartz rich terrigenous sediments are being injected through the deltaic system of the Orinoco in the north east region of the South American continent.
The accretionary prism commonly referred to as the Barbados Accretionary Prism (BAP), has been the most studied prism worldwide. The BAP is unique in its own right for several reasons. It is the largest prism when one considers the volume of trapped sediment, with a width of approximately 250 km and estimated thickness of 20 km. The BAP has the slowest known plate convergence rate, estimated at 0.5 – 2.2 cm/year. It is also associated with a proven, oil-prone source rock (the Cretaceous La Luna) with a demonstrated petroleum system onshore Barbados, while most other prisms are highly gas-prone; and it has a high quartzose sediment content due to the proximal South American terrigenous sediment source.