Trace fossils and ichnofabrics across the Ordovician depositional sequences of St. Petersburg region, Russia

The Ordovician sedimentary sequences in the St Petersburg Region represent a unique sequence of condensed sedimentation, dominated by bioclastic carbonates of temperate zone. The study of ichnofabric of these sediments can answer the following questions:l, to decipher individual episodes of sedimentation, erosion and diagenetic alterations of the Ordovician rocks in the St. Petersburg Region and in all the Baltica; 2, provided a conspicuous symmetry of ichnotaxa and ichnofabrics occurrences across the individual sedimentary sequences will be demonstrated, both local and global eustatic curves for the Early and Middle Ordovician will be precised; moreover, paradigms on the influence of the sea level to the ichnobabric might be upgraded; 3, previous studies in the area have ascertained intensive deep bioturbation and bioerosion of the strata, which are biostratigraphically equivalent to the Lower Ordovician. Such an intensity of deep bioturbation have not been presumed yet for the Early Ordovician.