(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.

(Table 1) Geochemistry of feldspars at DSDP Holes 62-464 and 62-465A

Labradorite is the principal feldspar in tholeiitic basalt from Deep Sea Drilling Project Site 464, on northern Hess Rise. Andesine and oligoclase constitute most primary feldspar in the reportedly trachytic rocks from southern Hess Rise at Site 465. Secondary sanidine(?) has replaced the primary phases at Site 465. The secondary potassium feldspar probably resulted from reaction of trachyte with potassium-bearing hydrothermal fluids or sea water.

Mass-accumulation rates for the non-authigenic, inorganic, crystalline, eolian component of sediments recovered at DSDP Sites 62-464 to 62-466

The mass-accumulation rate (MAR) of the non-authigenic, inorganic, crystalline component of deep-sea sediments from the Pacific aseismic rises apparently reflects influx of eolian sediment. The eolian sediment usually is dominated by volcanic material, except during glacial times. Sediments from Hess Rise provide a discontinuous record of eolian MARs. During Albian to Cenomanian time, the influx of volcanic material was fairly high (0.35-0.6 g/cm**2/10**3 yr), recording the latest stages of the Albian volcanism that formed Hess Rise. From the Campanian through the Paleocene, influx of eolian sediment was low, averaging 0.03 g/cm**2/10**3 yr. None of the four Hess Rise drill sites show evidence of the Late Cretaceous volcanic episode recorded at many sites now in the equatorial to subtropical Pacific. Pliocene to Pleistocene samples record a peak in volcanic influx about 4 to 5 m.y. ago, which has been well documented elsewhere. The several-fold increase in eolian accumulation rates elsewhere which are correlated with the onset of severe northernhemisphere glaciation 2.5 m.y. ago is not obvious in the Hess Rise data.

Geochemistry, mineralogy and isotopes at DSDP Hole 62-464

The relationships between mineralogical and geochemical data on the three successive sedimentary facies at Deep Sea Drilling Project Site 464 are studied. The evolution of siliceous biogenic sediments is derived from the analyses of one Fe-Ti smectite concretion, and of siliceous aggregates occurring in the pelagic "brown clays." Along the sedimentary section, the trace elements enriching the authigenic silicates and the Fe-Mn oxyhydroxides vary, depending on the marine environment. The proportion of clays and carbonates into the siliceous deposits controls the diagenetic evolution of silica making up the quartz aggregates from the "brown clay" or the cristobalite cherts.