Carbonate Deposits of Eastern Sarmatia (Early Precambrian Ignateevo Formation, Kursk Block): Sedimentation Conditions and Paleocontinental Correlations

Abstract

The Neoarchean–Early Paleoproterozoic section of the Eastern Sarmatia Kursk Block contains different formations: terrigenous-carbonate (Ignateevo Formation), terrigenous (Stoilo Formation), and banded iron (Korobki Formation). The Kursk Block sequences have obvious similarities to the coeval terrigenous-carbonaceous-ferriferous formations of the Kaapvaal and Pilbara cratons. The Ignateevo Formation dolomites are correlated with the Campbellrand–Malmani and Wittenoom–Carawine carbonate platforms. Carbonate rocks of all three cratons are silicified and show no evidence of clastic contamination. They are characterized by low Sr concentrations and are enriched in Fe and Mn. The REE distribution in carbonate rocks is characteristic of Neoarchean marine sediments: flat profiles on spider diagrams, positive La anomalies, absence of Ce anomaly, and increased Y/Ho ratios relative to the chondrite value. The values of δ13C (0.3–0.9‰ PDB) and δ18O (–10.1 to –13.0‰ PDB) in the Ignateevo Formation dolomites fall within the range of the Late Archean and Early Paleoproterozoic marine carbonate sediments. The 87Sr/86Sr ratio in the Ignateevo Formation dolomites (0.7101–0.7195) is higher than that in the Neoarchean marine carbonates, which implies either isolation of the paleobasin or disturbance of the Rb–Sr isotope systems during metamorphism. The Ignateevo Formation dolomites and calc-silicate rocks (intensively silicified dolomites) are closest in their isotope-geochemical characteristics to shallow-water dolomites of the Campbellrand–Malmani Platform (South Africa). Probably, the Ignateevo Formation dolomites and partly the formations composing the Campbellrand–Malmani Platform formed in the most isolated part of the paleobasin, which facilitated to their complete dolomitization and partial silicification.