Redox Conditions and Metal-Organic Carbon Relations of Eocene Bituminous Shales (Veliler/Mengen-Bolu/Turkey)

Abstract

The proposed bituminous shale sequences in the Eocene sediments are located at the vicinity of Veliler (Mengen/Bolu) in northwest Turkey. The total section is 11.87 m thick, consisting mainly of organic carbon-rich marl and shale, which is 8.17 m thick. Organic-carbon rich sediments are enriched in several redox-sensitive and stable sulfide-forming trace elements. Bituminous shales were geochemically analyzed in order to find total organic carbon (1.07–15.17 wt%), major elements (Si, Al, Fe, Mg, Mn, Ca, Ti, Na, K, P), and trace elements (V, Ni, Co, Cr, Cu, and Zn) of the whole rock. The results are discussed based on the organic and inorganic association of trace elements and their use as redox conditions of sedimentation. Whole rock concentrations are indicative of changes in the dysoxic sedimentation conditions according to V/V+Ni ratio (0.46) and authigenic U (10.19) to suboxic-anoxic conditions according to U/Th ratio (6.46). The most important sediment sources of the trace elements are authigenic (Mo, Ni, Co, As, U, Sr, Cr, and Mg) and detrital (Ba, V, Pb, Fe, Cu, Si, and Ti) content. Enrichment factors of Corg, Mo, Cu, Pb, Zn, Ni, Co, Mn, Fe, As, U, Th, Sr, V, P, Cr, Mg, Ba, Na, and K are calculated with recpect to their abundance of average shale, black shale, recent and ancient upwelling sediments, and sapropels, such as Mediterranean sapropels, Monterey Formation, Namibian mud lens, Gulf of California and Peru margin.