Bulk Mineralogy of Pleistocene Mediterranean Outflow Water Contourites at IODP Site 1387
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Date
2015-05
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The Ohio State University
Abstract
Expedition 339 of the Integrated Ocean Drilling Program collected ocean sediment cores at seven localities in the Gulf of Cadiz and on the West Iberian margin, a contourite deposition system (CDS) influenced by the Mediterranean Outflow Water (MOW). The cores provide an insight into circulation and climate patterns at the time of sediment deposition, and the rapid sedimentation rate from MOW allows for a detailed look at this sedimentary record. Sediment at Site U1387 is Pleistocene in age, as calculated by a shipboard age/depth model, and bulk mineralogy has been analyzed on the portion of core 256-280 meters below seafloor, representing sediment deposition 1.014-1.236 million years ago. Samples were powdered and x-ray diffraction patterns were acquired from the randomly oriented grains. Relative intensity ratios of a distinctive diffraction peak for each mineral phase compared to quartz were used as semi-quantitative indicators of mineral abundance. Changes in these ratios over time were examined 1) to define covarying mineral assemblages and 2) to identify any consistent compositional changes during glacial/interglacial cycles. Quartz and dolomite relative abundances covary, and illite and 7Å clays covary, but calcite does not covary with any other minerals. No definite correlation to glacial/interglacial cycles could be made, but the covariation of minerals is hypothesized to be a result of changes in grain size. Quartz and dolomite indicate the presence of larger grain size, while illite and the 7Å clays indicate smaller grain size.
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sedimentology, paleoclimatology, oceanography