BENTONITE LAYERS IN SVALBARD: CONSTRAINING SOURCES OF VOLCANISM, GEOCHRONOLOGY, AND RELATIVE PLATE MOTIONS DURING THE PALEOCENE AND EOCENE

The Central Basin in southern Svalbard formed as a strike-slip foreland basin during the Paleogene, adjacent to the West Spitsbergen Orogeny between Greenland and Eurasia. The creation of this basin is inherently linked to the changes in the relative plate motions of North America, Greenland, and Eurasia, driven in part by the propagation of seafloor spreading in the Labrador and Norwegian-Greenland Seas. These events are intrinsically linked to the climatic and environmental changes that occurred throughout the Paleocene and Eocene. However, the exact timings of these key events are poorly refined. An improved chronostratigraphy of the formation and evolution of the Central Basin can therefore be used to improve the regional geochronology.

Throughout the sedimentary sequence are prominent bentonite clay horizons of volcanic origin. There are a number of potential sources of these layers, including continental rifting events in the high Arctic and the formation of the North Atlantic Igneous Province (NAIP). Here we focus on the chemical fingerprinting and high precision U-Pb dating of Paleocene bentonites. Geochemical analyses indicates that ash layers just above the basal unconformity bear a close chemical affinity with the Kap Washington Group in north Greenland, while later Paleocene ashes appear to have come from rift volcanism in the Nares Straight. Bentonites of unknown provenance have been used to date the PETM in this stratigraphic sequence. The basal bentonites are successfully dated here, providing a precise time of foreland basin formation and therefore also the change in plate motions that instigated the West Spitsbergen Orogeny. Dating of later layers provides accurate deposition rates in the basin, which appear to increase as the Central Basin matured. These findings corroborate previous findings of the timing of rift volcanism in the Arctic, they provide a precise time of first active spreading in the Labrador Sea, and improve the regional geochronology for the mid- to late-Paleocene.