Microelement Composition of Boundary CenomanianTuronian Sediments of Mountain Crimea and Northern-Western Caucasus As The Evidence of Global Anoxic Event

Abstract

To study the origin of sedimentary rocks of Mountain Crimea and Northern-Western Caucasus, a composition of rock samples was studied and the geochemical ratios of the elements in them were determined. Analytical data were obtained on the basis of a comprehensive approach including determination of total and organic carbon by CHNS- analysis, as well as macro- and microcomponents by atomic emission spectrometry with inductively coupled plasma (ICP-AES) and electrothermal atomic absorption spectrometry (ETAAS) after microwave-assisted sample preparation. For low contents of rare earth elements (REEs) preliminary cation-exchange matrix separation on Dowex AG 50W-X8 was used. That, in combination with calculated interelement correction coefficients, permitted ICP-AES determination of all REEs, Y and Sc with good precision (RSD below 10%) and detection limits (DLs) varying from 0.025 µg g^-1 (Eu, Ho, La, Lu, Y, Yb, Sc) to 0.10 µg g^-1 (Dy, Er, Gd). Noble

metals were determined by ETAAS using slurry technique with DLs 2 ng g^-1 (Au, Pd) and 2.5 ngg^-1

(Pt) after preconcentration on a powdered chelating sorbent POLYORGS-IV.

The accuracy of data was confirmed by the analysis of standard reference materials (limestone KH and black shale SChS-1).

Data obtained for samples of black shales and host rocks from cross-sections of Mountain Crimea and Northern-Western Caucasus show the principal differences in accumulation conditions of sediments in these geological regions.