Chalcophile elements in black shales of the Bazhenov Formation, West Siberian sea basin

The contents and distribution of chalcophile elements in the Upper Jurassic-Lower Cretaceous Bazhenov Formation (black shales), West Siberian sea basin, are related to the composition of rocks, sedimentation rate, and redox conditions of sedimentation. The total content of chalcophile elements in the argillaceous-siliceous and argillaceous mudstones of normal sections (1360.7 and 498.4 ppm, respectively) is higher than the clarkes for black shales of this type, while that in the silty argillaceous mudstones of anomalous sections (186.7 ppm) corresponds to average contents for clays. On the other hand, the contents of Zn, Cu, As, Se, Cd, and In in the argillaceous-siliceous mudstones are above the clarkes, those of Pb, Ga, Ag, Hg, and Te are close to the clarkes, and the contents of Tl, Ge, Bi, and Sn are below the clarkes. In the argillaceous mudstones of normal sections, the first group of elements includes Zn, As, and Ga; the second, Cu, Pb, Sb, Tl, Ge, and Bi; and the third, Se, Ag, In, Sn, Hg, and Te. In the silty argillaceous mudstones of anomalous sections, the first group includes Ga, Ag, Ge, Bi, and Te (?); the second, Cu, As, Cd, Pb, and In; and the third, Zn, Se, Sb, and Hg. We have found that S, Cu, Zn, As, Ge, Se, Ag, Cd, In, Sb, and Hg are associated with pyrite and organic matter in the formation, whereas Ga, Sn, Pb, Bi, and Tl are mainly of terrigenous origin (which was earlier substantiated by Ya.E. Yudovich and M.P. Ketris for the first four elements) and are associated with clay material.