The Mora 001 and Solberga 1 drill cores provide the best available overview on the early Silurian (Llandovery, Rhuddanian to Telychian) graptolite succession available for the Siljan Ring impact structure of central Sweden. The Solberga 1 succession includes a nearly complete graptolite succession from the Pernerograptus revolutus Biozone (late Rhuddanian) to the Oktavites spiralis Biozone (late Telychian). Older graptolite faunas are unknown from the Siljan region. The Mora 001 drill core includes a graptolitic succession from the Monoclimacis crenulata Biozone to the O. spiralis Biozone, found in two lithostratigraphically separated lithological units here identified as the Kallholn Formation. A slice of the Orsa Sandstone Formation of possible later Silurian age is tectonically introduced into the Kallholn Formation in the Mora 001 drill core. The strong tectonic deformation of the Kallholn Formation in both drill cores can easily be understood through the Devonian impact history of the region
