Clay mineral assemblages of the bottom sediments from the Arctic ocean as an indicators of paleoclimatic changes during Cenozoic time (IODP Leg 302 data)
Article type :
International Geological Congress,oslo 2008
Composition of the clay fraction was investigated by IR and XRD methods. The IR-spectrums were mathematically simulated and compared with the clay mineral assemblages ratio. Semiquantitative evaluations of the clay minerals were based on the Biscaye method [Biscaye, 1965]. Robustness of the method was checked by analysis of the 100 samples prepared by using two procedures: settling on the glass base [Moore and Reynolds, 1997], and rapid filtration of a clay suspension onto a membrane [McAlister and Smith, 1995]. Also, different XRD optical systems (fixed and automatic divergence slits) have been used. Calculations were carried out using the software "MacDiff" [Petschick et al., 1996]. The results show the good precision of the data (coefficient of the variation higher 95%) and identical trends of the illite, smectite, chlorite and kaolinite distributions.
Clay minerals together with heavy minerals (e.g. pyroxene, amphibole) can be used for identification of the source areas for the terrigenous material delivered to the Lomonosov Ridge. Peculiarities of the sedimentation in the Arctic for the last several tens of Ma are governed by the climate changes. Results of the heavy and clay minerals investigations shows that the onset of a perennial sea ice cover in the Arctic Ocean was established at about 13 Ma [Krylov et al., 2008]. Below this level, fraction less than 0.002 mm contains mainly the amorphous oxides and hydroxides of the Si and Al; the content of the clay minerals is less than 10%. Such changes in the sediment composition testify the probable prevalence of the warm stagnant environment and colloid settling in the freshwater conditions. At the level of 50 Ma, the environments were different and bentonite sediments were deposited (content of the Na-montmorilonite exceed 90%).
This work was supported by RFBR-06-05-65166a and German Academic Exchange Service (DAAD).
1Institute of Geology of Ore Deposits, Mineralogy, Petrography and Geochemistry, RAS, Russian Federation;2All-Russia Research Institute for Geology and Mineral Resources of the World Ocean (VNIIOkeangeologi, Russian Federation;3Crystallography, Geosciences, University of Bremen, Germany; 4Mendeleyev University of Chemical Technology of Russia, Russian Federation; 5Russian State Geological Prospecting University, Russian Federation; 6Institute of Geology of Ore Deposits, Mineralogy, Petrography and Geochemistry RAS (IGEM RAS), Russian Federation