Ocean Drilling Program (ODP) Leg 164 drilled 16 holes at seven sites in the northwestern Atlantic off the coast of the southeastern United States. Four cores recovered from the Carolina Ridge are short (50-60 m), and the presence of unconformities and condensed sections makes these cores unsuitable for paleontological study.
Eight long holes were drilled at three sites (Sites, 994, 995, and 997) on the Blake Ridge to recover the upper 700-750 m of sediments (Fig. 1). Four holes were for the spot sampling to obtain gas hydrates, and continuous sequences were recovered only from a single hole each at Sites 994 and 995, and from the combination of two adjacent holes at Site 997. In addition to the presence of unconformities and condensed sections at Sites 995 and 997, the poor recovery of pre-Quaternary sediments caused by the expansion of interstitial gas made high-resolution stratigraphic studies impossible for the Pliocene to Miocene sequences at these sites. Moreover, the relatively slow sedimentation rate and large coring gaps prevent a high-resolution paleoceanographic study for the Quaternary cores. Minor reworking of Cretaceous and Paleogene nannofossils is persistent in most of the cores studied, but as Gartner and Shyu (1996) had observed at Site 905 (Chesapeake Drift) penecontemporaneous reworking is not too severe in the drift that built the Blake Ridge. Redeposited Ascidian spicules (Okada, 1992) are common in many intervals.
Calcareous nannofossils biostratigraphy was studied for all the cores recovered from Holes, 994C, 995A, 997A, and 997B. The oldest sediments recovered from these sites belong to the latest Miocene Subzone CN9c of Okada and Bukry (1980). Although the sedimentary history and upward decrease in sedimentation rate are similar, the presence and duration of hiatuses and/or condensed sections differ significantly between the sites. Because Hole 994C has the most continuous sediment record and the least reworking, stratigraphic change in the total flora was analyzed for the entire 700 m sequence recovered from this hole. The record represents the floral history of the last 6 m.y.