To assess the conditions of carbonate rocks formation on the Karelian craton in the paleoproterozoic based on geochemical data

We present a comparative analysis of the carbonate sedimentation conditions in two Paleoproterozoic basins located in the south-east and north of the Late Archean Karelian craton in the North Onega and Pana-Kuolayarvi synclinories. The carbonate accumulation began in both paleobasins during the Late Jatulian. Carbonate rocks in the Onega sequence are predominantly dolostones, including stromatolite varieties, whereas in the Pan Kuolayarvi succession, they comprise both dolostones and limestones. During the Late Jatulian, cyanobacteria thrive in the coastal marine settings of the Onega basin. Some portions of the basin may have been disconnected from the open sean at this time, facilitating the development of evaporite processes. There was no such diversity of cyanobacterial communities in the Pana-Kuolayarvi basin, and there was no evaporitization. According to geological and lithological data, shallow, lagoon, playa lake and sabha environments existed in the Onega paleobasin in the Late Jatulian time. In the Pana-Kuolayarvi paleobasin, the conditions are shallow, at times with increased water input from the continent, and open marine settings. The geochemical characteristics of the carbonate rocks we obtained lead to the same facies conclusions. The stromatolites in the Onega pleobasin were formed mainly in the intertidal zone, at times the connection of the basin with the open sea was reduced and the conditions approached the lagoon. The oxic conditions existed for a limited time during Jatulian only in the Onega basin. Basically, in the both sedimentation basins the oxygen content was close to the boundary of the transition from disoxic to oxic conditions. Fluctuations in the magnitude of the Ce anomaly in stromatolite laminae reflect changes in the oxygen content in water directly in contact with the stromatolite buildup, which creates the possibility of the existence of oxygen “oases” in the paleobasin with disoxic and oxygen-deficient conditions. Conclusions about redox conditions existing in the paleobasin, based only on geochemical markers, are not sufficient. Conclusions regarding the conditions prevailing in a paleobasin with carbonate sedimentation agree maximally with geological and lithological data based on a set of geochemical characteristics, including REE spectra, values of Ce and Eu anomalies, and ratios of individual lanthanides. These conclusions are supplemented by an analysis of paired correlations between redox-sensitive elements.