High precision geochronology of Silurian bentonites in the Oslo area
The Silurian was a climatically and biologically dynamic period. Two major biotic and associated perturbations of the global carbon cycle occurred in the middle Silurian. This period also marks the final consumption of the Iapetus Ocean and the initiation of the continental collision between Baltica and Laurentia.
In the Oslo rift, most notably in the Ringerike area, there are several exposures of bentonites (ash beds) in middle Silurian sections. Some of these bentonites are geochemically well characterised and their value for regional stratigraphic correlation is highly significant. There is also relatively well-established biostratigraphy in parts of the section.
However, none of the Silurian bentonites in the Oslo rift have been dated by absolute methods. We propose a Master's thesis that will include the detailed logging of sections containing bentonites, high precision U-Pb dating of these bentonites and magnetic susceptibility measurements on selected sections to investigate potential cyclicity. There will also be the possibility of doing carbon isotope stratigraphy.
Through this work, a new-age model will be created for the studied sections that will tie the biostratigraphy to absolute ages and have the potential of improving Silurian chronostratigraphy, and resolve questions related to the occurrence of major climate perturbations and biotic events. This work may also constrain the final stages of Iapetus subduction if these bentonites are, as previous workers have suggested, related to Iapetus arc magmatism.
Thesis work will comprise fieldwork in the Ringerike and greater Oslo area, and laboratory work at the TIMS laboratory, UiO.