ALBERT

Description: 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.

Description: Calcareous nannofossils were studied from Jurassic and Cretaceous sediments drilled in the western Pacific during Ocean Drilling Program Leg 129. Mesozoic sediments at Sites 800, 801, and 802 are dominated by volcaniclastic turbidites, claystones, porcellanites, and radiolarites. Pelagic limestones are limited to the middle Cretaceous, and a few calcareous claystones were recovered in the Upper Jurassic section at Site 801. We documented the distribution of nannofossils, their total abundance, preservation, and relative species abundance based on semiquantitative and qualitative studies. Preservation of the calcareous nannofloras is poor to moderate, and the total abundance fluctuates from rare to very abundant. Marker species proposed for the middle and Late Cretaceous were recognized, allowing the application of standard nannofossil biozonations. At Site 800 calcareous nannofloras are abundant and moderately preserved in the Aptian-Cenomanian, and nannofossil biostratigraphy constitutes the basic stratigraphic framework for this interval. Radiolarians are the most abundant and persistent group throughout the sequence drilled at Site 801. Long intervals are barren of nannofloras and assemblages are usually characterized by low abundance and poor preservation. Nannofossil biostratigraphy was applied to the upper Aptian-Cenomanian interval and a few marker species were recognized for the late Tithonian. At Site 802 Cretaceous biostratigraphy is mainly based on calcareous nannofossil biozones corroborated by radiolarian and palynomorph events in the late Aptian-Coniacian age interval. A hiatus was indicated between the Santonian and the late Campanian, and another is suspected in the interval between the Cenomanian and the Coniacian.

Description: Only Site 802 has recorded appreciable Cenozoic carbonate sediments during Ocean Drilling Program Leg 129 in the central Mariana Basin of the western Pacific Ocean. Calcareous nannofossils provide the best biostratigraphic information for the 360-m Tertiary section, which consists primarily of volcaniclastic turbidites interbedded with calcareous claystone and chalk. Many samples contain significant amounts of nannofossils reworked from older sediments. An unconformity appears to be present between Cores 129-802A-32R and -33R, with upper Oligocene-lower Miocene sediments above and lower Eocene-upper Paleocene sediments below the unconformity. The sediments below the unconformity contain abundant reworked Cretaceous nannofossils. Only one sample from Site 801 yielded nannofossils, and those consist of a mixture of Campanian-Maastrichtian and Paleogene forms.