PIs will investigate the tectonic setting, magmatic originand stratigraphic significance of altered volcanic ash beds (K.bentonites) in the Middle and Upper Ordovician strata ofBaltoscandia and to compare these data with similar data fromNorth America. Preliminary studies strongly suggest these K.bentonite beds on both sides of lapetus had a common source and acommon tectonic setting. If this indication proves correct, themost widespread of these beds will have profound event.stratigraphic implications for the Ordovician, and ourunderstanding of Laurentia and Baltica plate positions during theTaconian orogeny will be substantially improved. Similarly, theabundance of Silurian K.bentonites throughout Baltoscandia andthe UK indicates ongoing plate.margin volcanism from Llandoverythrough Ludlow time. PIs will collect samples of the mostextensive beds from cores and outcrops in Estonia, Sweden andNorway. They will add to existing information on thebiostratigraphic position of these beds and use chemicalfingerprinting of both bulk samples and selected phenocrysts tomake accurate correlations with North American beds. These willbe compared with trans.Atlantic stratigraphic relations of K.bentonites suggested by traditional biostratigraphy and bygraphic correlation using conodonts. We will also obtain high.resolution Ar age spectra and U.Pb dates from biotite and zirconseparates from biostratigraphically well.constrained K.bentonitesthat will add key ages to the Ordovician time scale. Traceelement data will be plotted on discrimination diagrams tointerpret the tectonic and magmatic settings of these beds.
