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Atlantic |
Department of Geology and Mineralogy, Oxford OX1 3PR, U.K.
The lower to middle Eocene Scotland Group is about 1700 m thick at outcrop and can be divided into: (A) The Lower Scotland Formation consisting of (1) the Walkers Member (500 m): graded turbidite sands and clays, arranged in sand-dominated and clay-dominated packets; (2) the Morgan Lewis Member (200 m): almost all clay, with two sand intervals; (B) the Upper Scotland Formation consisting of (3) the Murphys Member (about 350 m): a thickening and coarsening upward sequence including slumped beds; (4) the Chalky Mount Member (0–250 m): coarse and conglomeratic sands with large slide blocks and minor interbedded muds; (5) the Mount All Member (about 500 m): coarse and fine turbidite sands and clays, much disturbed and displaying no overall sequence. The group was deposited by mass-flow processes in a deep marine environment, probably in a deep-sea trench or a submarine fan.
Current flow was from the SW and mineral composition supports derivation from South American metamorphic rocks. Clay mineralogy shows an upward trend from mainly smectite to mainly kaolinite.
An ENE structural trend is present throughout the island and is anomalous in the present plate-tectonic setting adjacent to a north-south trending island arc. Deformation increases in complexity up the succession; this may be due to sedimentary slumping, partly a result of increasing disturbance by rising mud diapirs. This locally culminated in extrusion of hydrocarbon-rich mud—the overlying Joes River Formation. The Barbados Ridge probably comprises clastic sediments deposited both in a trench and on the Atlantic Ocean floor.
