1 resultado para Crystalline regions

em Publishing Network for Geoscientific


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Elevated regions in the central parts of ocean basins are excellent for study of accumulation of eolian material. The mass-accumulation rates of this sediment component appear to reflect changes in the influx of volcanic materials through the Early Cretaceous to Recent history of Deep Sea Drilling Project Site 463, on the Mid-Pacific Mountains. Four distinct episodes of eolian accumulation occurred during the Cretaceous: two periods of moderate accumulation, averaging about 0.2 to 0.3 g/cm**2/10**3 yr, 67 to 70.5 m.y. ago and 91 to 108 m.y. ago; a period of low accumulation, approximately 0.03 g/cm**2/10**3 yr, 70.5 to 90 m.y. ago; and a period of high accumulation, about 0.9 g/cm**2/10**3 yr, 109 to 117 m.y. ago (bottom of the hole). Much of the Cenozoic section is missing from Site 463. Upper Miocene to Recent sediments record an upward increase in accumulation rates, from less than 0.01 to about 0.044 g/cm**2/10**3 yr. The late Pliocene-Pleistocene peak may reflect the change to glacial-wind regimes, as well as an increase in volcanic source materials.