36. HIGH-RESOLUTION SILICA PORE-WATER PROFILES IN SEDIMENTS OF THE MADEIRA ABYSSAL PLAIN, EASTERN NORTH ATLANTIC 1Gert J. De Lange 2 |
ABSTRACTHigh-resolution pore-water sampling has been undertaken to define the pore-water silica profile vs. depth for Holes 950A and 952A in the Madeira Abyssal Plain, eastern North Atlantic. The silica pore-water concentration in the upper 50 meters below seafloor (mbsf) faithfully records the presence of biogenic silica in organic-rich turbidites. Between 50 and 250 mbsf, that is, between 1 and 6.5 Ma, however, the silica pore-water concentration is low and stable, pointing to the absence of biogenic silica in the organic-rich turbidites in this interval. Such absence could indicate a change in source area, or in the north-west African upwelling system during that period. Near 280 mbsf in Hole 950A, and below 290 mbsf in Hole 952A, enhanced levels of silica are again observed in the pore waters, which indicates that biogenic silica is present in the deep organic-rich turbidites. For Hole 952A, this coincides with the interval where enhanced levels of diatoms have been reported. The high-resolution pore-water sampling in Holes 950A and 952A has resulted in the identification of potential intervals where authigenic silica phases are likely to have formed, thus enabling future studies on the diagenetic redistribution of silica in marine sediments. |
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