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

Abstract

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.

Uranium in Source Rocks: Role of Redox Conditions and Correlation with Productivity in the Example of the Bazhenov Formation

“…The Upper Jurassic-Lower Cretaceous deposits of the Formation (J 3 -K 1 ) are distributed throughout the West Siberian oil and gas Basin, covering over 1 million km 2 . These deposits occur at depths of 2500-3000 meters between Upper Jurassic terrigenous rocks and Lower Cretaceous mudstones [16][17][18]. The thickness of the formation varies from 25 to 80 m, with an average of 30-40 m. The rocks are represented by siliceous, clayey-siliceous, carbonate, and clayey-carbonate-siliceous varieties with high organic matter (OM) content [19,20].…”

Upper Jurassic–Lower Cretaceous Source Rocks in the North of Western Siberia: Comprehensive Geochemical Characterization and Reconstruction of Paleo-Sedimentation Conditions

“…Differences in sedimentation conditions and initial organic matter type in the central and peripheral areas led to the formation of the Bazhenov deposits with different lithological characteristics, total organic carbon (TOC) distribution, composition, and petroleum generation potential. The results of the studies of the Bazhenov Formation rocks and organic matter are reported in numerous publications, including the marine sediments of the central part (distal areas of the paleo-sea) [1,[4][5][6][7][8][9] and sediments formed in the peripheral parts (proximal paleo-sea areas) [1,5,7,[10][11][12][13][14]. Although data have been extensively published, there is still a potential for deepening the knowledge via application of the scope of analytical methods and investigation of the least studied areas.…”

“…The interval investigated includes the Bazhenov Formation and upper part of the Abalak Formation deposits from the Oxfordian stage of the Upper Jurassic to the Berriasian of the Lower Cretaceous (Figure 1). [4]) and stratigraphy of Mesozoic deposits (modified after Afanasenkov [14]); the investigated stratigraphic interval is marked by frame.…”

“…Figure 1. Location of the studied area (modified after Zanin[4]) and stratigraphy of Mesozoic deposits (modified after Afanasenkov[14]); the investigated stratigraphic interval is marked by frame.…”