BIOSTRATIGRAPHY OF VENDIAN–CAMBRIAN BOUNDARY STRATA IN THE NORTHWEST OF THE EUROPEAN PART OF RUSSIA

We carried out palaeontological studies of the Vendian–Cambrian boundary strata from the Leningrad Region in the north of the East European Platform (northern part of the Baltic Basin). A stratigraphic succession of micro- and macrofossil associations has been recognised in the Taitsy-2 drill-core section comprising three Upper Vendian associations: (I) Aataenia reticularis, (II) Vendotaenia antiqua – Incertae sedis Forma 1, and (III) Bicuspidata fusiformis – Vanavarataenia insolita of the Kotlin Regional Stage; and two Lower Cambrian associations: (IV) Ceratophyton sp. – Teophipolia lacerate of the combined Rivne–Lontova Regional Stage, and (V) Archaeodiscina umbonulata – Globosphaeridium cerinum – Skiagia orbiculare of the Dominopol Regional Stage. The early Cambrian taxa Ceratophyton sp., Granomarginata squamacea, Teophipolia lacerata, and Platysolenites antiquissimus first appearing at the base of the Lomonosov Formation and extending their stratigraphic range into the overlying Siverskaya Formation define the position of Precambrian–Cambrian boundary. The Rivne and Lontova regional stages are indistinguishable based on palaeontological data. The cooccurrence of fragmented metazoan fossils and acanthomorph acritarchs in the Lükati Formation expands the palaeontological characteristics of the Dominopol Regional Stage of the European part of Russia. We also conducted isotope-geochronological studies of sand-stone-hosted glauconite from the Lower Cambrian Siverskaya Formation that yielded a Rb–Sr date of 457 ± 3 Ma. The glauconite appears to be altered and rejuvenated as suggested by mineralogy and crystallochemistry data, is not suitable for stratigraphic purposes, but provides information on timing and contribution of later geological processes.