Paleolatitude estimation and premises for geomagnetic field instability from the Proterozoic drilling core material of the south-western part of the East European Craton

Abstract

This study addresses new paleomagnetic, geochemical, mineralogical, and rock-magnetic data from four drill cores of the western part of the East European Craton, representing mainly siliciclastics supplemented by volcaniclastics and a few basaltic rock samples. The cores comprise Mesoproterozoic samples of 1400–1030 Ma and Neoproterozoic (Ediacaran) samples of 588–541 Ma. According to the magnetic data, the dominant magnetic carrier in basalts is magnetite, while two genetic types of hematite (detrital and syngenetic/early diagenetic) carry magnetization in sedimentary rocks. The characteristic components of the natural remanent magnetization (NRM), carried by the fine-grained hematite (intermediate temperature component [CM]) and the coarse-grained hematite (high-temperature component [CH]), were identified during thermal cleaning. Mineralogical and geochemical studies provided evidence for detrital and synsedimentary/early post-sedimentary origin of fine-grained hematite and suggested hot and humid environmental conditions on the western part of Baltica during Meso- and Neoproterozoic time. Because of a low-temperature diagenetic history, which affected the Mesoproterozoic and Ediacaran rocks of Pinsk 26, Ochrymy IG-1, and Šaškai 2 boreholes, no post-Ediacaran paleomagnetic overprint is expected there. On the basis of these findings, the CM component in these profiles was classified as nearly primary (synsedimentary/early post-sedimentary) in origin. The CH component in these profiles and the Ediacaran sandstones of the Kaplonosy IG-1 section is also considered primary and acquired as detrital NRM (DRM). Paleomagnetic results yielded a reliable record with the domination of shallow-to-moderate inclinations, showing both polarities. The calculated paleolatitudes for 550–541 Ma time span, regardless of correction for the inclination error, fall within the subequatorial zone. Steeper inclinations, suggesting subpolar paleolatitudes, were observed in the volcaniclastics and basalts interlayering with sedimentary rocks and, sporadically, in the Ediacaran sedimentary successions. The origin of this steep component, however, was attributed to the anomalous behavior of the geomagnetic field, as a consistently warm environmental facies pattern did not support a fast and far-distance, cross-latitudinal, poleward movement of Baltica during the Ediacaran time and then back to the equator. These results complement previous studies that sought to resolve uncertainty of the paleogeographic position of Baltica in the Proterozoic time.