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

STRATIGRAPHIC FRAMEWORK ONSHORE TO OFFSHORE
The layered Tobago Forearc Basin units (Figure 4.2) are equivalent to the
Oceanic Formation recognized in outcrop on the island’s eastern side. Although within
the TFB it is believed that this unit ranges from Middle Eocene to Upper Miocene in age,
onshore units are at youngest Middle Miocene in age (Barker and Poole, 1982) and are
believed to have been deposited in water depths between 2000 to 4000 m based on
foraminiferal data (Saunders, 1984). The Middle Miocene marks the initiation of TFB
closure and the emergence of the Barbados Ridge. Based on onshore analyses, these
rocks are interpreted throughout the region as deep marine pelagic clays and marls which
are interbedded with volcanic ash deposits (Speed, 1989, 1994). The entire unit thins to
the west onto the Lesser Antilles Island Arc high and post Mid-Miocene unconformity
sediments thin onto the Barbados Ridge. Sediments below the Mid-Miocene
unconformity drape over the Barbados Ridge and extend into the zone of piggyback
basins. The seismic character of this unit is that of layered, continuous reflectors with
minimal deformation by small-scale normal faulting. This seismic character is expected
as the pelagic deposits are interbedded with volcanic ash layers and are locally cut by
normal faults in outcrop.
Scotland Formation
The Scotland Formation is dated in outcrop as Lower Eocene in age and includes
the oldest rocks exposed on the island. This unit thickens onshore into a thick, (up to
2800 m), succession of sands and clays comprised of very coarse grained turbidites and
leveed channels deposits, with a conglomerate lag at the base of some large channels
indicating a high energy erosive system. In seismic data, this formation has been equated
with the western portion of the Barbados Accretionary Prism sediments and shows up as
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