Proterozoic and early Palaeozoic microfossils in the Karikkoselkä impact crater, central Finland

• Published in: Bulletin of the Geological Society of Finland
• Main Author: A. Uutela
• Format: Article in Journal/Newspaper
• Language: English
• Published: Geological Society of Finland 2001
• Subjects: impact craters; sedimentary rocks; microfossils; acritarchs; cyanobacteria; Chlorophyta; Paleozoic; Proterozoic; Karikkoselkä; Finland; Geology; QE1-996.5; Fennoscandian
• Online Access: https://doi.org/10.17741/bgsf/73.1-2.006; https://doaj.org/article/3c4a0bfb09d1479d95b73a99937c4a34

The Karikkoselkä impact crater is located at Petäjävesi (Lat. 62°13.3' N, Long. 25°14.7' E), in central Finland. The crater is filled with impact-generated breccias and redeposited sedimentary rock yielding microfossils. The assemblage consists of Proterozoic, Cambrian and Ordovician acritarchs, cyanobacteria and green algae thoroughly mixed in the deposit. The late Ordovician acritarch Diexallophasis striatum indicates the maximum age of the impact event in the Keila Regional Stage, middle Caradocian in British Series, 458–449 Ma or later. A till sample overlying the sediments that infill the crater yields only Quaternary pollen and spores, indicating that the impact event occurred prior to the Fennoscandian Ice Age. The most likely palaeomagnetic age of 260–230 Ma (late Permian to early Triassic) is neither excluded nor supported by the microfossil results. However, other palaeomagnetic ages are excluded leaving this the most likely age. This article presents new evidence of Proterozoic and early Palaeozoic deposits that covered central Finland.