296
c. G. ST. C. Kendall· A. Sen
Seismic profiles of the northwestern Great Bahamas Bank have been interpreted to document the lateral growth potential of isolated platforms that were
welded together by margin progradation to form larger banks (Eberli and Ginsburg 1987, 1989). The mechanism responsible for an evolution from aggradation
to progradation was thought to be sediment overproduction on the platform
(Hine et al. 1981, Willer et al. 1990). Excess sediment was transported offbank
and caused a decrease in accommodation space on the marginal slope. Progradation occurred in pulses that are interpreted to result from third-order sea-level fluctuations (Eberli and Ginsburg 1987, 1989). Limited well control has prevented confirmation of these hypotheses, but sedimentary simulation can be
used to demonstrate the proposed theory for platform evolution is reasonable,
and matches the sea-level events on the Haq et al. (1987) charts (Eberli et al.
1994).
3.2
Seismic Stratigraphic Interpretation
Eberli and Ginsburg (1987) had previously correlated sequence boundaries on
the seismic section across the Andros Channel to the Haq et al. (1987) chart. In
the present study, the line was re-interpreted. Initially second-order unconformities were identified on the basis of their very extensive erosional character and
their correlation to the second-order sea-level events of the Haq et al.1987 chart
(Fig. 5). Third-order unconformities were then identified enclosing their equivalent seismic sequences. The ages of these latter sequences were bracketed with
the ages determined from the second-order type 1 unconformities, and correlated with the third-order, type 1, unconformities of the Haq et al. (1987) chart
(Fig. 5). As can be seen from the interpretation of the seismic, the major events
on the Haq curve have produced distinct stratigraphic signals (Fig. 3). For instance, following the sea-level fall at 30 Ma in early Oligocene times, a major unconformity was created. This separates the Upper Neogene carbonate accumulation from the rest of the Tertiary and the Cretaceous. Similarly, a major fall in
sea level occurred at 10.5 Ma and this also has a distinct seismic expression as a
major unconformity. It is apparent that the sea level fell below the shelf margin
with the resulting unconformity bracketing the series of third-order sea-level
events between 10.5 and 30.0 Ma. While examining the geometric position of
these latter sequences with respect to the shelf margin, and counting them, it can
be seen that more unconformities can be identified than there are sea-level
events on the Haq et al. (1987) chart. It is suspected that some of these interpreted sequences may be a result of separating the products of both low and high
stand cycles of sea level as sequences. Despite these additional sequences, there
appears to be a general match of the onlapping relationship of the different sequences on the seismic (Fig. 2) and the extent of basinward retreat of shorelines,
with the amplitude of the sea-level events (Fig. 5). Having made the sequence
stratigraphic interpretation, a simulation was developed.
c. G. ST. C. Kendall· A. Sen
Seismic profiles of the northwestern Great Bahamas Bank have been interpreted to document the lateral growth potential of isolated platforms that were
welded together by margin progradation to form larger banks (Eberli and Ginsburg 1987, 1989). The mechanism responsible for an evolution from aggradation
to progradation was thought to be sediment overproduction on the platform
(Hine et al. 1981, Willer et al. 1990). Excess sediment was transported offbank
and caused a decrease in accommodation space on the marginal slope. Progradation occurred in pulses that are interpreted to result from third-order sea-level fluctuations (Eberli and Ginsburg 1987, 1989). Limited well control has prevented confirmation of these hypotheses, but sedimentary simulation can be
used to demonstrate the proposed theory for platform evolution is reasonable,
and matches the sea-level events on the Haq et al. (1987) charts (Eberli et al.
1994).
3.2
Seismic Stratigraphic Interpretation
Eberli and Ginsburg (1987) had previously correlated sequence boundaries on
the seismic section across the Andros Channel to the Haq et al. (1987) chart. In
the present study, the line was re-interpreted. Initially second-order unconformities were identified on the basis of their very extensive erosional character and
their correlation to the second-order sea-level events of the Haq et al.1987 chart
(Fig. 5). Third-order unconformities were then identified enclosing their equivalent seismic sequences. The ages of these latter sequences were bracketed with
the ages determined from the second-order type 1 unconformities, and correlated with the third-order, type 1, unconformities of the Haq et al. (1987) chart
(Fig. 5). As can be seen from the interpretation of the seismic, the major events
on the Haq curve have produced distinct stratigraphic signals (Fig. 3). For instance, following the sea-level fall at 30 Ma in early Oligocene times, a major unconformity was created. This separates the Upper Neogene carbonate accumulation from the rest of the Tertiary and the Cretaceous. Similarly, a major fall in
sea level occurred at 10.5 Ma and this also has a distinct seismic expression as a
major unconformity. It is apparent that the sea level fell below the shelf margin
with the resulting unconformity bracketing the series of third-order sea-level
events between 10.5 and 30.0 Ma. While examining the geometric position of
these latter sequences with respect to the shelf margin, and counting them, it can
be seen that more unconformities can be identified than there are sea-level
events on the Haq et al. (1987) chart. It is suspected that some of these interpreted sequences may be a result of separating the products of both low and high
stand cycles of sea level as sequences. Despite these additional sequences, there
appears to be a general match of the onlapping relationship of the different sequences on the seismic (Fig. 2) and the extent of basinward retreat of shorelines,
with the amplitude of the sea-level events (Fig. 5). Having made the sequence
stratigraphic interpretation, a simulation was developed.