Although sea-level fluctuations are known to have occurred throughout Earth's history, their controls, global synchrony, amplitudes, rates, and effects are still largely unknown. The reason for the uncertainty in assessing each of these parameters is the complex interaction between eustasy, subsidence, and sediment supply. Different methods and approaches have been used to separate each parameter, producing a variety of results that are often controversial (e.g., Miller et al., 1998). Much of the controversy is caused by the conflicting results of the methods used. For example, estimates on the amplitudes of sea-level changes based on the sedimentary record usually yield much higher values than those relying on the stable isotope proxy (Pitman and Golovchenko, 1983; Haq et al., 1987; Miller et al., 1985). There is no doubt that the changing sea level leaves its record in the sedimentary bodies of continental margins. The sequence stratigraphic concept postulates that each global sea-level change creates a characteristic sequence of sediments that can be correlated with sedimentary basins around the world (Vail et al., 1977). In addition, the concept proposes that a predictable facies succession would develop within each sequence. The sequence stratigraphic concept relies on the following assumptions:
The sequence stratigraphic concept and its facies models have been controversial ever since they were proposed (Pitman and Golovchenko, 1983; Miall, 1986; Summerhayes, 1986; Cloetingh, 1986; Cathles and Hallam, 1991). The controversies surrounding sequence stratigraphy reflect the unresolved problems of the sea-level issue. Two main problems are (1) the difficulty in separating the role of tectonic subsidence from eustasy in creating unconformity bounded sequences and (2) the difficulty in assessing the synchrony of sea-level changes in different ocean basins. Also, few data sets exist that test the assumptions of the concept. The Ocean Drilling Program (ODP) has set a priority to address such key questions surrounding sea-level changes by using a variety of approaches (COSOD II, 1987; Sea-Level Working Group (SL-WG) Report, 1992). The SL-WG (1992) recommended drilling transects of holes across several continental margins as a potentially best strategy.
ODP Leg 166 is one of
these transects. The seven drilling sites of the Bahamas Transect along the
western margin of the Great Bahama Bank (Fig.
1) also offered the unique opportunity to apply three independent ways
of addressing problems of sea-level changes. First, the modern Great Bahama Bank
is a flat-topped platform on a passive continental margin, and its flat top
records sea level as a dipstick. Second, cores from the proximal portion of the
transect indicate that the prograding sequences record sea-level changes in
their facies and stratigraphic architecture (Eberli et al., 1997; in press).
Third, the correlative deep-water deposits in the Straits of Florida encode the 
18O
proxy of sea-level changes in their foraminiferal assemblages. The combination
of these three methods could potentially evaluate with a much higher confidence
the relationships between depositional patterns vs. seismic reflection geometry
and the frequency of glacio-eustasy as recorded in the oxygen isotope record vs.
the cyclo- and sequence stratigraphic depositional units.
The Bahamas Transect was designed to address four main sea-level objectives. The aim of this synthesis chapter is to briefly outline each of these objectives and describe the results that were obtained on board the JOIDES Resolution during Leg 166 and the postcruise scientific research related to Leg 166. The drilling along the Bahamas Transect has generated a wealth of data regarding the sedimentary record of carbonates with respect to sea-level changes—in particular concerning the question of highstand and lowstand shedding of carbonates. Results from biostratigraphic dating document the chronostratigraphic significance of seismic sequence boundaries, corroborating one of the fundamental assumptions of seismic sequence stratigraphy that stratal surfaces are essentially time synchronous (Vail et al., 1980). Ages of the sequence boundaries in the Bahamas will be compared with those at the New Jersey margin (Miller et al., 1996) and the global sea-level chart (Haq et al., 1987). An interesting discrepancy in the frequency of high-frequency sea-level changes between the sedimentary record and the oxygen isotope record will be discussed.
The amplitude of sea-level change in the Neogene is not considered here. The Leg 166 transect sites are all in deep water and thus are not suitable for such an analysis.
