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ACRITARCHS FROM THE CAMBRIAN–ORDOVICIAN BOUNDARY INTERVAL ON KOLGUEV ISLAND, ARCTIC RUSSIA

MAGORZATA MOCZYDOWSKA and MARTIN STOCKFORS

Uppsala University, Department of Earth Sciences, Palaeobiology, Norbyvägen 22, SE-752 36 Uppsala, Sweden e-mail: malgo.vidal{at}pal.uu.se

New evidence from taxonomically rich and age-diagnostic acritarch assemblages is used to recognize Upper Cambrian and Tremadoc strata in the Bugrino 1 and North-Western 202 boreholes on Kolguev Island, Arctic Russia. The position of the boundary between the Cambrian and Ordovician systems in the sedimentologically continuous successions is inferred, as are stratigraphic intervals equivalent to the Late Cambrian Peltura and Acerocare trilobite zones of Baltica. This is the first paleontological documentation of Cambrian strata on the island and, on a regional scale, within the Pechora Basin and northeastern Europe. The newly established biostratigraphy provides the maximum relative age for the basal portion of the sedimentary cover overlying the Timanian angular unconformity, which separates the sediments from deformed and metamorphosed basement. In turn, it constrains the time-span of the hiatus as preLate Cambrian and thus is significant for reconstructing the timing of the major tectonic events in this region of the Baltica palaeocontinent. Twenty-seven acritarch species are described in detail and 10 taxa are left under open nomenclature. The taxonomic attribution of several species is revised. The diagnosis of the genus Acanthodiacrodium is restricted, and those of Dasydiacrodium and Polygonium are emended. New combinations are proposed for the species Actinotodissus crinitus, A. formosus and Solisphaeridium akrochordum, and new emendations and combinations for Actinotodissus polimorphus, A. secundarius, and A. spinutisus. A new species, Solisphaeridium chinese, is recognized. The stratigraphic ranges of taxa are compiled from global records and extension of some species ranges is suggested.