Ordovician-Silurian palynostratigraphy (Chitinozoa and acritarchs) of the G14-1/86 borehole, southern Baltic Sea

Borehole G 14-1/86, located in the Baltic Sea between the Tornquist Zone and the Caledonian Deformation Front/Thor Suture, penetrates a Lower Palaeozoic sedimentary succession deposited on the south-western margin of the East European Platform. Detailed palynological analysis of the Ordovician and Silurian successions enables precise dating and facilitates provenance interpretation of the sedimentary sequence. The following chitinozoan biozones are identified: Cyatho-chitina primitiva Biozone (early - early late Arenig); Laufeldochitina striata Biozone (late Abereiddian - late Llandeilan) and Ancyrochitina merga Biozone (Cautleyan - Rawtheyan, middle Ashgill). A further chitinozoan assemblage is possible to be correlated with the global Spinachitina maennili Biozone (uppermost Rhuddanian - lower Telychian). A relatively diversified acritarch assemblage of Ashgill age (independently dated by Chitinozoa) also occurs. This assemblage contains numerous reworked forms of Llanvirn, Tremadoc and late Cambrian ages. The reworked Llanvirn acritarchs are typical of the high-latitude Perigondwanan micro-phytoplankton palaeobioprovince and testify to detrital input of Gondwanan-related source during the Ashgill, suggesting that by this time the Tornquist Ocean was closed.