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Calcareous nannofossils are sufficiently numerous in the upper 900 m of the Neogene sediment drift cored beneath the lower continental rise at DSDP Site 603 to permit delineation of zones, correlations with the paleomagnetic data (Pliocene-Pleistocene only), and the detection of major Miocene hiatuses and their correlation with seismic stratigraphy. Holes 603, 603B, and 6O3C were spudded in lower Pleistocene sediments just east of the crest of the Hatteras Outer Ridge, and all nannofossil zones and subzones are accounted for down to a hiatus within the middle Tortonian (late Miocene) Zone CN8. This hiatus lies some 30 m above a more extensive disconformity between 661 and 672 m where sediments of Subzone CN7a and a portion of Zone CN6 have been removed. The resulting hiatus is correlated with local reflection Horizon M2, which is considered equivalent to the regional Reflector Merlin. The hiatus between 661 and 672 m dates Merlin at this site between about 9.6 and 10.4 Ma. A strong, parallel, unnamed reflector is correlated with the superjacent hiatus within CN8, and is dated between 8.5 and 9 Ma. These disconformities help delineate a "condensed" interval, which falls within the Vail et al. (1980) cycle TM3.1. This eustatic event has been characterized as the sharpest and most profound sea-level drop of the late Miocene. The lower Tortonian "condensed" interval at Site 603 is closely correlative with spectacular debris flows cored in presumed canyon fill deposits immediately above reflection Horizon M2/Merlin at DSDP Site 604 on the upper rise off New Jersey. We suggest that the erosion along the lower rise at Site 603 and the synchronous canyon cutting evidenced by the debris flows on the upper rise at Site 604, both associated with the regional Reflector Merlin, are linked closely to Southern Hemisphere glacial activity which led to the formation of the West Antarctic Ice Sheet. Apart from the lower Tortonian "condensed" interval, the drift sediments of the Hatteras Outer Ridge are primarily muddy contourites, augmented to some extent by fine turbidites in the lower portion. Most were deposited at a rate of about 87 m/Ma. Just after the late Miocene erosional events, sedimentation rates during nannofossil Zone CN8b time were 192 m/Ma, about double that for the overlying section. This suggests that the site was then the locus of deposition for material eroded during canyon-cutting events along the slope and shelf. The lowest sample dated (911 m) is assigned to Subzone CN5b (not older than 13.1 Ma). A rare glauconitic silty sand turbidite at 834.8 m contains upper Eocene coccoliths, probably eroded from submarine outcrops along the slope, perhaps during a brief middle Miocene canyon-cutting episode.

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Neogene Calcareous Nannofossils from Deep Sea Drilling Project Site 603, Lower Continental Rise, Western North Atlantic: Biostratigraphy and Correlations with Magnetic and Seismic Stratigraphy