Planktonic foraminifers recovered from Leg 166 drilling exhibited a progression from well-preserved to poorly preserved specimens with increasing depth. The high carbonate production and shedding from Great Bahama Bank diluted the pelagic biogenic sediment components to the extent that planktonic foraminifers show scattered occurrences, particularly in the lower Pliocene and/or uppermost Miocene in Sites 1003-1005 and Site 1007. However, a reasonable biostratigraphic framework could be constructed for these sites because thin layers dominated by terrigenous sedimentation contained moderately well preserved specimens throughout the lower Pliocene to Miocene interval. Because of the rarity of some age-diagnostic species, it was not always possible to place the zonal boundaries with certainty; however, the timing of foraminiferal biohorizons was consistent with the nannofossil biostratigraphy.
Most of the indicator species were found in sufficient number to render a more reliable biostratigraphic framework for the more distal sites (Sites 1006 and 1007). These sites also contained better preserved planktonic foraminifers and more complete Neogene sequences. For example, Sites 1003 and 1007 were drilled ~5 km apart and recovered similar sedimentary sequences. However, where Site 1003 recorded unconformities indicated by the juxtaposition of zonal taxa, Site 1007 recorded an apparently continuous section but with a reduced rate of sedimentation instead of hiatuses (Eberli, Swart, Malone, et al., 1997). Sedimentation rates at the most distal Site 1006 were the most constant, recording substantially higher rates in only the lower Pliocene.