Oxygen isotopic compositions of end-members in a multicomponent mixture: Ediacaran weathering material from the East European Craton

The aim of the present study was to investigate the oxygen isotopic composition of the Ediacaran weathering material from the western margin of the East European Craton. This area presents a unique opportunity to investigate the Ediacaran strata with a minimum diagenetic overprint. Paleosol intervals, containing material formed during the most advanced weathering stages, rich in kaolinite and iron (hydr)oxides, and corresponding sedimentary rocks were investigated. Bulk material and separated clay fractions were subjected to reactions with hot dithionite-citrate-bicarbonate solution in order to remove free iron (hydr)oxides. The obtained material was characterized by X-ray diffraction, chemical analysis, thermogravimetric analysis, and the measurement of oxygen isotope composition. Comparison of the isotopic compositions of iron (hydr)oxides and phyllosilicates, extracted from the natural and dithionite-citrate-bicarbonate treated samples, bulk, and clay fractions, leads to the conclusion that these compounds are in isotopic disequilibrium in the investigated samples. Disequilibrium is caused by the presence of diagenetic illite, originating from the Caledonian and Variscan hydrothermal pulses. The average isotopic composition of kaolinite was extracted from the phyllosilicate data by extrapolation. The temperature estimate, based on the average isotopic composition of iron (hydr)oxide and kaolinite, depends strongly on the hematite-water fractionation factor used in the calculation but qualitatively agrees with the expected tropical weathering conditions. The complex approach needed to extract these data from multicomponent mineral mixtures results in large analytical error if precise error propagation analysis is applied. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The study aimed to investigate the oxygen isotopic composition of the Ediacaran weathering material from the western margin of the East European Craton. Results showed isotopic disequilibrium caused by diagenetic illite in the investigated samples.