Ra. Batchelor et al., GEOCHEMISTRY OF TELYCHIAN METABENTONITES FROM VIK, RINGERIKE DISTRICT, OSLO REGION, Norsk geologisk tidsskrift, 75(4), 1995, pp. 219-228
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.