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Seventeen sites were drilled on Leg VI of the Deep Sea Drilling Project in 5 contrasting areas of the Pacific: (1) Pacific basin floor, (2) Shatsky Rise, (3) Horizon Ridge, (4) Caroline Ridge, and (5) Philippine Sea.
Sediments of the Pacific basin floor are characteristically Tertiary brown clays overlying Cretaceous nannoplankton oozes containing chert and lithified ash. Tertiary chert-bearing nannoplankton oozes were found on Horizon Ridge. On the Shatsky Rise, Neogene nannoplankton oozes unconformably overlie Eocene and Upper Cretaceous nannoplankton oozes; Lower Cretaceous and Jurassic(?) carbonate oozes there have abundant chert. These Jurassic(?) to Lower Cretaceous sediments are the oldest reported from the Pacific. The sequence on the Caroline Ridge is Pleistocene to Oligocene nannoplankton ooze and volcanic ash lying on a very smooth "basement" of olivine dolerite. In the Philippine Sea, Miocene to Oligocene brown clay, thick volcanic ash, and red metamorphosed limestone lie on an irregul r "basement" of olivine basalt.
Shipboard measurements of 6 physical properties were made on the sediments recovered: natural gamma radiation, sound velocity, wet-bulk density, porosity, thermal conductivity, and penetrability. These correlate chiefly with lithology and show no systematic variation with age or depth of burial. Gamma radiation is typically highest in zeolitic clays, intermediate in ash and brown clay, and low in microfossil ooze. Clayey sediments and microfossil ooze have low sound velocities (about 1.5 km/sec), sand-silt size ashes and microfossil ooze intermediate values (about 1.6-2.2 km/sec), and limestone and basalt the highest values (3.19-6.02 km/sec).
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