Bulletin of the Geological Society of Finland (Dec 1998)
Extent of the northern Baltic Sea during the Early Palaeozoic Era - new evidence from Ostrobothnia, western Finland
Abstract
This study reports new evidence of the extent of the northern Baltic Sea during the Cambrian and Ordovician periods. A drillcore (DC304) from the Lappajärvi impact crater, western Finland, and erratics from the surrounding area were studied for acritarchs. The acritarchs from the drillcore were reworked by the explosion but indicate, however, that the Baltic Sea extended beyond the western coast of central Finland during the Lower Cambrian Vergale and the Middle Cambrian Kibartai regional stages as well as during Middle Ordovician transitions from Aseri to Lasnamägi and from Idavere to Jöhvi regional stages. The provenance of the erratics was the Bothnian Bay, further north than the Lower Palaeozoic deposits previously known in the Bothnian Sea. The age could be determinated by their acritarch composition which shows that the sea also covered Central Ostrobothnia during the Lower Ordovician Billingen and early Middle Ordovician Lasnamägi regional stages. The drillcore samples contained also unknown spores. They suggest that there have been sediments and/or a terrestrial flora later than Ordovician in the Lappajärvi area.
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