GEOCHEMISTRY OF TELYCHIAN METABENTONITES FROM VIK, RINGERIKE DISTRICT, OSLO REGION

Thirteen metabentonites from the Garntangen Member, a succession of mu dstones and nodular limestones within the Silurian Vik Formation, were analysed for major and trace elements. Bulk-rock chemical composition s indicate two parent volcanic ash sources, one rich in incompatible e lements (Zr, Nb, Th) called the 'evolved' set, the other higher in com patible elements (Ni, Ti, V) and named the 'primitive' set. Microcryst als of apatite, which represent former phenocrysts, were analysed for their rare earth element content and these data confirmed the existenc e of two populations. These two volcanic sources were contemporaneous and are thought to have lain to the south or southwest of Oslo. Simila r 'evolved' and 'primitive' compositions are found in bentonites from the Lower Visby Formation of Gotland, Sweden, and a tentative correlat ion is made between the Garntangen Member of the Oslo Region and the L ower Visby Formation of Gotland, with the consequent convergence of th ese two horizons into the M. spiralis Biozone.