292
C. G. ST. C. Kendall· A. Sen
strandline position (which additionally assume a continental relief and/or tectonic behavior), paleobathymetry, seismic sequence onlap, stacked subsidence
curves, and the matching of sequence geometries with graphical simulations
(Burton et al.I988). Despite the fact that sea-level amplitudes cannot be measured independently, stratigraphic predictions based on sea-level curves or tectonic models of behavior are reproducible and verifiable away from areas of interest. This is because the onlapping or downlapping of the sediments involved
is dependent on the rates of sedimentation, the tectonic movement and sealevel position. Hence, if rates of subsidence and of carbonate accumulation are
constant for several cycles of eustatic sea level, then the frequency and amplitude of the onlapping sequence geometries will be the product of the frequency and amplitude of the changes in eustatic sea level. The hypothesis presented
here is that if the sequence geometries of a sedimentary simulation generated
with the Haq et al. (1987) chart match the interpreted sequence on the seismic,
then the ages of these latter sequences can be assumed to match those of the
simulation. The shallow water carbonate platforms of Bahamas provides a perfect opportunity to test the hypothesis.
2
The Assumptions
To build reasonable simulations of stratigraphic interpretations that capture
sea-level events, geologic sections are required for which it can be assumed that
there was a low rate of uniform subsidence and a high rate of constant sediment
accumulation for several sea-level cycles ofthe Haq et al. (1987) curve. Examples
of the response to this kind of stratigraphic signal can be seen on the seismic sections of the Lower Cretaceous of offshore South Africa (Fig. 1) and the onshore
seismic of the National Petroleum Reserve of Alaska (Fig. 8 in Bird et al. 1992).
It can also be recognized on the seismic record for the Neogene of the Bahamas
platform (Fig. 2) and the Neogene section displayed in the cliffs of the island of
Mallorca, offshore eastern Spain (Fig. 3). In all these locations, the rates of subsidence appear to be low while the sedimentation rates are high. The result is
that the changing onlapping position of the sequence geometries of these areas
are assumed to be produced by sea-level changes.
With the absence of absolute sea-level positions for a paleoshore, it was assumed that should the rate of sedimentation be sufficiently high, then any shoreward accommodation was filled to sea level. When this happens the shelf margin
can then be used as a proxy of the sea-level position. This assumption is not unreasonable for most carbonate shelves, but when it is applied to clastics confirmatory paleobathymetric markers are needed. In the case of carbonates the reasonableness of this assumption can be seen expressed in the seismic sections of
the Neogene of the Bahamas (Fig. 2) and the cliffs of Neogene sediments exposed in the cliffs of the island of Mallorca (Fig. 3). The sedimentary sections developed in both these locations are the product of carbonate accumulation ,rates
which were high enough to fill the accommodation space up to sea level during
C. G. ST. C. Kendall· A. Sen
strandline position (which additionally assume a continental relief and/or tectonic behavior), paleobathymetry, seismic sequence onlap, stacked subsidence
curves, and the matching of sequence geometries with graphical simulations
(Burton et al.I988). Despite the fact that sea-level amplitudes cannot be measured independently, stratigraphic predictions based on sea-level curves or tectonic models of behavior are reproducible and verifiable away from areas of interest. This is because the onlapping or downlapping of the sediments involved
is dependent on the rates of sedimentation, the tectonic movement and sealevel position. Hence, if rates of subsidence and of carbonate accumulation are
constant for several cycles of eustatic sea level, then the frequency and amplitude of the onlapping sequence geometries will be the product of the frequency and amplitude of the changes in eustatic sea level. The hypothesis presented
here is that if the sequence geometries of a sedimentary simulation generated
with the Haq et al. (1987) chart match the interpreted sequence on the seismic,
then the ages of these latter sequences can be assumed to match those of the
simulation. The shallow water carbonate platforms of Bahamas provides a perfect opportunity to test the hypothesis.
2
The Assumptions
To build reasonable simulations of stratigraphic interpretations that capture
sea-level events, geologic sections are required for which it can be assumed that
there was a low rate of uniform subsidence and a high rate of constant sediment
accumulation for several sea-level cycles ofthe Haq et al. (1987) curve. Examples
of the response to this kind of stratigraphic signal can be seen on the seismic sections of the Lower Cretaceous of offshore South Africa (Fig. 1) and the onshore
seismic of the National Petroleum Reserve of Alaska (Fig. 8 in Bird et al. 1992).
It can also be recognized on the seismic record for the Neogene of the Bahamas
platform (Fig. 2) and the Neogene section displayed in the cliffs of the island of
Mallorca, offshore eastern Spain (Fig. 3). In all these locations, the rates of subsidence appear to be low while the sedimentation rates are high. The result is
that the changing onlapping position of the sequence geometries of these areas
are assumed to be produced by sea-level changes.
With the absence of absolute sea-level positions for a paleoshore, it was assumed that should the rate of sedimentation be sufficiently high, then any shoreward accommodation was filled to sea level. When this happens the shelf margin
can then be used as a proxy of the sea-level position. This assumption is not unreasonable for most carbonate shelves, but when it is applied to clastics confirmatory paleobathymetric markers are needed. In the case of carbonates the reasonableness of this assumption can be seen expressed in the seismic sections of
the Neogene of the Bahamas (Fig. 2) and the cliffs of Neogene sediments exposed in the cliffs of the island of Mallorca (Fig. 3). The sedimentary sections developed in both these locations are the product of carbonate accumulation ,rates
which were high enough to fill the accommodation space up to sea level during