Detailed Magnetostratigraphy of the Ordovician Sections of Leningrad Region: On the Presence of Fine Structure in the Moyero Ordovician Geomagnetic Superchron

Abstract—By the mid-2000s, a large body of magnetostratigraphic evidence had been accumulated, suggesting the existence of a geomagnetic superchron of reversed polarity in the Early to Middle Ordovician (the Moyero Reversed Polarity Superchron). The subsequent studies generally supported this hypothesis. However, there were also isolated reports that could either indicate the presence of a fine structure in the superchron, i.e., the existence of several short intervals of normal polarity within the superchron, or significantly limit its duration. Meanwhile, study of geomagnetic superchrons, further substantiation of the very existence of the Ordovician superchron and establishing its time limits is crucial for the development of the physical theory of geomagnetism, geological correlation, etc. Therefore, any information related to this issue should be carefully considered and verified. This paper presents the results of the detailed magnetostratigraphic study of some intervals from several Ordovician Ladoga sections. These intervals are coeval to those from the Ordovician of the northwestern Russia, Baltic region, and Scandinavia whose age corresponds to the Moyero reversed polarity superchron but which were previously reported to contain separate levels of normal polarity. Combined with the recent data on the Mishina Gora section of the Pskov region, these results provide yet another significant argument supporting the existence of the Moyero Ordovician geomagnetic superchron and its lack of fine structure.