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

Observations from Seismic Data
In seismic data, these Forearc Basin Sediments show simple onlap
relationships with the underlying crystalline basement of the Lesser Antilles
Island Arc (Figure 4.5). Time-equivalent units along the east flank of the Tobago
Basin show simple onlap relationships onto the accretionary prism sediments.
Although there is some deformation of Tobago Forearc Basin units, no nappe
geometries or duplex relationships as reported by previous workers (Torrini and
Speed, 1989; Speed and Torrini, 1989; Speed and Larue (1982) are observed in
the seismic data. The presence of channels, observed on seismic data, within the
TFB proper suggests episodes of clastic deposition occurred within the basin
(Figure 4.3).
Reconstruction of the Tobago Basin
The closure of the Tobago Basin, as recorded by the sedimentary fill,
shows that the basin has steadily decreased in size since the mid-Miocene (Figure
4.10a-e). The earliest stage of development was when Eocene- and possibly
Cretaceous-age sediments were deposited into the basin from a southern sediment
source, and in lesser amounts from the Lesser Antilles Island Arc (LAIA) (Figure
4.10a). The direction of influx from the LAIA is shown with arrows pointing
toward the Tobago Basin. These units fill the deepest part of the basin,
immediately west of the thrust front. Sediments are also delivered to the Atlantic
Abyssal Plain and are incorporated into the growing accretionary prism at the
Outer Deformation Front (ODF). Sediments are accreted adjacent to the basin
where the downgoing Atlantic plate (AP) is subducting beneath the Caribbean
plate (CCB).
57