Site 1006 is located in 658 m of water in the northern portion of the Santaren Channel ~30 km from the western platform edge of the Great Bahama Bank (Fig. 1). It is the most distal member of five transect sites drilled during Leg 166. Site 1006 was positioned on a thick, continuous sequence of Neogene-aged drift sediments. The sediment drifts interfinger with prograding carbonate bank deposits in the Florida Strait.
We attempted to date the sedimentary section as accurately as possible by using a combination of detailed biostratigraphy and cyclostratigraphy to document sedimentation rate changes at Site 1006. Cyclostratigraphy allows the use of the characteristics of variations in the Earth's orbital elements for producing a measure of time that results in a detailed chronostratigraphy. Recent studies have shown that orbitally induced time series can be obtained from Pliocene and Miocene sections (Hilgen, 1991; Hilgen et al., 1995; Shackleton et al., 1990). Here, we use the cyclostratigraphic technique to date the cyclic sequence of Site 1006. The Leg 166 shipboard party described the presence of pervasive cyclicity in the entire middle Miocene-lower Pliocene section (Eberli, Swart, Malone, et al., 1997). The cyclicity is attributed to sea-level changes that result in fluctuations in sediment production by the carbonate factory of the Great Bahama Bank (Eberli, Swart, Malone, et al., 1997). Delivery of neritic carbonate material to the basin during sea-level highstands results in expanded sections compared to erosion or starved sedimentation of pelagic and siliciclastic material during sea-level lowstands (Droxler and Schlager, 1985; Reijmer et al., 1988). This alternating pattern of deposition has dominated sedimentation near platforms and has also occurred at Site 1006 in the Pleistocene (Kroon et al., Chap. 2, this volume; Rendle et al., Chap. 6, this volume). There is no reason to assume that this pattern did not prevail in the Miocene-Pliocene period; thus, we assume that detailed sedimentation rate changes reflect fluctuations in carbonate platform productivity in relation to sea-level changes.
Whole-core measurement of magnetic susceptibility and downhole resistivity logs (SFLU and FMS) were used to sample the cyclic section. Unfortunately, only a single hole was drilled in the Miocene-lower Pliocene part of the section, but logging of the hole ensured a complete documentation of the cycles. The section is highly expanded, so that all the cycles can be resolved on the resistivity logs, and particularly in the FMS images. To calculate time, we mostly used the downhole logs rather than the whole-core magnetic susceptibility variations because of the possibility of core gaps. The sedimentation rates based on detailed biostratigraphy demonstrate that the dominant cycle present in the logs is compatible with the Earth's precessional cycle. In the unfortunate absence of magnetostratigraphy, time was calculated from the cycle record for the upper Miocene-lower Pliocene section of Site 1006, and this period of time was then anchored to a biostratigraphic event with a well-known absolute age.
In this paper, we show that the variability of platform production relates to precessionally induced sea-level changes. Moreover, we show that the thickness rather than the amplitude of the precessional sediment cycles is modulated at longer periods, which are very similar to known cycles of orbital eccentricity, at periods of ~125 k.y. ~400 k.y., and ~2000 k.y. Hence, we infer that eccentricity plays an important role in modulating the amplitude of sea-level change in the middle-late Miocene period.