SECULAR CHANGES IN SEDIMENTARY GEOCHEMISTRY ACROSS THE ARCHEAN–PROTEROZOIC BOUNDARY IN THE FARDEEP CORE OF FENNOSCANDIA

The Archean–Proterozoic boundary represents a period of substantial changes in the atmospheric, geologic, paleoclimate, and paleoenvironmental conditions on Earth. The oxygenation of the atmosphere, widely known as the Great Oxidation Event, is an example of one significant shift that occurred across this boundary from 2.5 to 2.3 Ga. The increase of free-oxygen in the atmosphere is commonly associated with the earliest global Huronian Glaciation, disappearance of the S-MIF signal, emergence of continents above sea level, and the decrease of Δ17O in shales. In this study we investigate geochemical proxies in the sedimentary and magmatic rocks of the Immandra-Varzuga, Pechenga and Onega basins, located in Fennoscandia, Russia. Whole rock compositional data from shales suggest different tectonic settings, varying from arc, rift and collisional environments. Whole rock compositional data from basalts indicate a predominantly mid-ocean ridge basalts (MORB) source, with associated within-plate lava, and minor island arc lava contributions. X-Ray Diffraction (XRD) analysis of shales shows that the primary and secondary mineralogy compositions remain similar through time, suggesting the predominance of quartz, albite, illite, biotite, and clinochlore. The environmental depositional conditions in these settings are being complemented by nitrogen and carbon analyses. In this ongoing work, we will evaluate the presence of absence of significant geochemical changes in the Archean-Paleoproterozoic boundary with respect to potential secular changes in weathering conditions, depositional environments, and tectonic shifts.