Copyright by Nysha Chaderton 2009 - The University of Texas at ...

1994). The origin of the Oceanic Formation has been debated for more than two
decades, and two distinct hypotheses persist that offer opposing explanations.
The first hypothesis, introduced by Speed (1982), puts forward an Oceanic
Formation that was deposited within the proto-Tobago Forearc Basin and that has
subsequently been thrust more than 20 km eastward to its present position (Figure
4.9). This hypothesis seeks to reconcile the potential age overlap of the Oceanic
and Scotland Formations, the latter of which has been dated as young as
Oligocene in age (Baldwin, 1986). Speed interpreted the Oceanic Formation as
having a lower section that exhibited nappe geometries as a result of eastward
transport of the lower section and an upper section that was a single, undisrupted
sheet The timing of the emplacement of this upper sheet is said to be late Miocene
or Pliocene, when the sheet was thought to have fully covered the underlying
Scotland Formation. Speed (1982) used erosion prior to deposition of the
Pleistocene reef to explain thinning of the sheet of the Oceanic Formation that
occurs over the island of Barbados.
The second hypothesis, proposed by Pudsey (1982), suggests that the
Oceanic Formation is an in situ deposit that has been tectonically uplifted along
with the Barbados Ridge. Poole and Barker’s (1980) geological map of Barbados
features a generalized vertical section in which the Oceanic Formation
conformably overlies the Scotland Formation of Barbados. These researchers
postulated that the Oceanic Formation formed in situ after the rapid submergence
of the island and surrounding areas. The Oceanic Formation has been constrained
to deposition in 2,000 to 4,000 m of water (Saunders et al., 1984). To
accommodate this depth of deposition, Poole and Barker (1982) invoked a
subsidence and re-submergence of the island of at least 2,000 m, to allow for
deposition of the sediments, followed by a reemergence.
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