Eocene siliceous and calcareous phytoplankton, Deep Sea Drilling Project Holes 95-612 and 95-613

Eocene siliceous and calcareous phytoplankton, with emphasis on silicoflagellates, were studied in 62 samples from DSDP Sites 612 and 613 on the continental slope and rise off New Jersey. The mid-latitude assemblages correlate well with assemblages from California, Peru, and offshore of southern Brazil, but are distinctly different from high-latitude cold-water assemblages of the Falkland Plateau off southern Argentina. Coccoliths and silicoflagellates provide evidence for the presence of a fairly complete middle and upper Eocene sequence, represented by a composite of Sites 612 and 613. A major unconformity occurs at the middle Eocene to upper Eocene contact at Site 612. The genus Bachmannocena Locker is emended and proposed as a replacement for genus Mesocena Ehrenberg for ring silicoflagellates. Six new silicoflagellates and one new diatom are described: Bachmannocena apiculata monolineata Bukry, n. subsp., Corbisema amicula Bukry, n. sp., C. bimucronata elegans Bukry, n. subsp., C. hastata incohata Bukry, n. subsp., C. jerseyensis Bukry, n. sp., Dictyocha acuta Bukry, n. sp., and Coscinodiscus eomonoculus Bukry, n. sp. Also, one new replacement name, B. paulschulzn Bukry, nom. nov., and 24 new combinations are proposed for genus Bachmannocena.

Physical properties and neutron texture measuerments of deep-sea carbonates of DSDP Holes 62-463 and 62-465A

In weakly indurated, nannofossil-rich, deep-sea carbonates compressional wave velocity is up to twice as fast parallel to bedding than normal to it. It has been suggested that this anisotropy is due to alignment of calcite c-axes perpendicular to the shields of coccoliths and shield deposition parallel to bedding. This hypothesis was tested by measuring the preferred orientation (fabric) of calcite c-axes in acoustic anisotropic, calcareous DSDP sediment samples by X-ray goniometry, and it was found that the maximum c-axis concentrations are by far too low to explain the anisotropies. The X-ray method is subject to a number of uncertainties due to preparatory and technical shortcomings in weakly indurated rocks. The most serious weaknesses are: sample preparation, volume of measured sample (fraction of a mm3), beam defocusing and background intensity corrections, combination of incomplete pole figures, and necessity of recalculation of the c-axis orientations from other crystallographic directions. Goniometry using thermal neutrons overcomes most of these difficulties, but it is time consuming. We test the interferences made about velocity anisotropy by X-ray studies about the concentration of c-axes in deep-sea carbonates by employing neutron texture goniometry to eight DSDP samples comprising mostly nannofossil material. Fabric and sonic velocity were determined directly on the core specimens, thus from the same rock volume and requiring no preparation. The c-axis orientation is obtained directly from the [0006] calcite diffraction peak without corrections. The fabrics are clearly defined, but weak (1.1 to 1.86 times uniform) with the maximum about normal to bedding. They have crudely orthorhombic symmetry, but are not axisymmetric around the bedding normal. The observed c-axis intensities, although higher than determined by the X-ray method on other samples, are by far too low to explain the observed acoustic anisotropies.

Distribution of abundance of planktic foraminifera and calcareous nannofossils at DSDP Sites 17-167 and 62-463

New paleomagnetic and paleontologic data from Pacific DSDP Sites 463 and 167 define the magnetic reversals that predate the Cretaceous Normal Polarity Superchron (K-N). Data from Mid-Pacific Mountain Site 463 provide the first definition of polarity chron M0 in the Pacific deep-sea sedimentary record. Foraminiferal biostratigraphy suggests that polarity chron M0 is contained entirely within the lower Aptian Hedbergella similis Zone, in agreement with foraminiferal data from the Italian Southern Alps and Atlantic Ocean. Nannofossil assemblages also suggest an early Aptian age for polarity chron M0, contrary to results from the Italian Umbrian Apennines and Southern Alps, which place polarity chron M0 on the Barremian-Aptian boundary. Biostratigraphic dating discrepancies caused by the time-transgressive, preservational, or provincial nature of paleontological species might be reconciled by the use of magnetostratigraphy, specifically polarity chron M0 which lies close to the Barremian-Aptian boundary. At Magellan Rise Site 167, five reversed polarity zones are recorded in Hauterivian to Aptian sediments. Correlation with M-anomalies is complicated by synsedimentary and postsedimentary sliding about 25 m.y. after basement formation, producing gaps in, and duplications of, the stratigraphic sequence. The magnitude and timing of such sliding must be addressed when evaluating the stratigraphy of these oceanic-rise environments.

(Table 1) Distribution of ichthyolith subtypes at DSDP Hole 62-464

At Site 464, a 308-meter-deep hole was drilled on the Hess Rise (39°51.64'N, 173°53.33'E; water depth 4637 m). The upper strata consist of siliceous clay and oozes of Pleistocene, Pliocene, and possibly latest Miocene ages (36 m) and the lower strata are Albian chert, chalk, and marlstone (219 m). The middle part of the stratigraphic section is pelagic brown clay (53 m) which is essentially barren of microfossils except for ichthyoliths. At the base of this middle unit in Core 10 is a recrystallized Cretaceous radiolarian assemblage and an impoverished late Miocene nannofossil assemblage. Fifteen samples from Cores 6 through 10 in the middle unit and three samples from the overlying siliceous clay were examined for ichthyoliths.