Geochemical indicators for origins and sedimentary environments of marine sediments and siliceous sedimentary rocks are reviewed. Al
2O
3/TiO
2 and Zr/TiO
2 values are useful indicators for sources of detrital materials in sediments, because these values in igneous rocks change systematically (acidic > intermediate > mafic). MnO/TiO
2 and Co/TiO
2 values and Co-Ni-Zn diagram, on the other hand, are useful for discrimination between pelagic sediments and hemipelagic ones. Pelagic sediments deposited under oxic environment are characterized by high MnO/TiO
2 and Co/TiO
2 values and enrichment of Co and Ni relative to Zn, compared with hemipelagic sedmiments. In addition to these indicators, stratigraphic variation of MnO and CO
2 (derived from carbonate minerals) concentrations can discriminate between pelagic sediments and hemipelagic ones. In hemipelagic sediments where diagenetic remobilization of manganese is active, MnO and CO
2 concentrations often show covariation and manganese carbonate bands (rhodochrosite-concentrated layers) are found at depths. It should be also noted that these geochemical indicators are, in some cases, modified by diagenesis and subaerial alteration. Careful application of these indicators to analyses of sedimentary paleoenvironments is required.
抄録全体を表示