CRETACEOUS-PALAEOGENE UPLIFT AND SUBSIDENCE EVENTS IN THE FÆROE-SHETLAND BASIN: CONSTRAINTS FROM ISOTOPE GEOCHRONOLOGY AND THE MAGMATIC AND SEDIMENTARY ROCK RECORD

The sedimentary and magmatic rocks of the Faroe-Shetland area occur in onshore exposures and an extensive offshore well database, allowing simultaneous analysis of the thick, Early Tertiary lavas on the stretched continental crust of the Faroe Islands, Northern Ireland and Scotland and the offshore, pre-, syn- and post-breakup (c. 54 Ma) sedimentary sequences of the Faroe-Shetland Basin (FSB). In this setting, magmatic rocks are key palaeobathymetric indicators and, when precise radiometric ages are available, can be used as chronologic ties for the Cretaceous-Palaeocene geomagnetic polarity time scale and the biostratigraphic record. In the Faroe-Shetland area, numerous studies of the sedimentary and crystalline rock record have demonstrated that the magnetostratigraphic, biostratigraphic, and isotope geochronologic time scales cannot yet be consistently correlated throughout the late Cretaceous-Palaeocene. New ⁴⁰Ar/³⁹Ar ages from the Faroe Islands Lower Basalts in this study are most consistent with Danian-Selandian subaerial eruption, similar to ⁴⁰Ar/³⁹Ar and U-Pb ages documented for the lowermost basalts exposed elsewhere around the NAIP and corresponding primarily to C26r time (60.92 – 57.91 Ma). The isotopic ages are from rocks that are correlated to lavas that lie above the distinct biostratigraphic marker Apectodinium, itself globally correlated to the Late Paleocene-Eocene Thermal Maximum (LPETM, ca. 55 Ma). These age discrepancies compromise the ability to make confident correlations through the magmatic and sedimentary stratigraphy on- and offshore, and add uncertainty to seismic and well ties. Resolution of the age discrepancies will be addressed, as they impact not only regional time-stratigraphic calibrations but also the proposed start of this magmatic activity relative to an observed shift from predominantly western to eastern provenance sources for Palaeocene sediments of the FSB.