The project continues of study of Ordovician and Silurian K- bentonites in the Iapetus region that was started in 1990. The discovery that the Millbrig K-bentonite in North America represents the same ash fall as the "Big Bentonite" in Baltoscandia makes its possible to use this bed as a unique time plane for various regional geological studies, such as a recently started Ph.D., project on Middle Ordovician conodont biofacies differentiation in the Iapetus region and its ecologic controls. Being apparently the largest volcanic ash fall known, the Millbrig- "Big-Bentonite" offers an unusual opportunity to study mortality and extinction effects of a giant ash fall on marine biota, and such a study will be undertaken. Also, this horizon, along with new biostratigraphic data, will be used for application of Sweet's American graphic correlation scheme to European successions thereby greatly increasing the precision in trans-Atlantic correlations. Geodynamic and event-stratigraphic studies will include chemical fingerprinting of selected beds and modeling of the Millbrig- "Big Bentonite" eruption based on regional grain-size pattern analyses. These will also be used for obtaining a distance figure of the width of the Iapetus in the Middle Ordovician. We also plan to get high-precision U-Pb dates on biostratigraphically well-controlled K-bentonites that will provide significant contributions to the Ordovician-Silurian time scale.
