GEOCHRONOLOGY, GEOCHEMISTRY AND STRATIGRAPHY OF THE NEOPROTEROZOIC HECLA HOEK SUCCESSION, SVALBARD, NORWAY

The Tonian Period (1000-717 Ma) was a time of global upheaval with large-scale perturbations to multiple geochemical cycles, the diversification of early eukaryotes, and a number biological firsts, such as eukaryotic predation and biomineralization. All of these changes were set against the backdrop of tectonic reorganization and magmatism associated with the formation and breakup of the supercontinent Rodinia. However, the lack of temporal constraints for the Tonian hinders our ability to answer first-order questions surrounding the timing and causes of these biospheric and biogeochemical events. The ca. 950-600 Ma Hecla Hoek succession of Svalbard, Norway, consisting of the Tonian Veteranen and Akademikerbreen groups and the Cryogenian-Ediacaran Polarisbreen Group, represents one of the most complete and well-preserved Neoproterozoic sedimentary successions worldwide. These strata provide a unique opportunity to construct a temporally-calibrated geochemical, biological, and geological framework in which to assess Tonian biogeochemical change and the timing and triggers of early eukaryotic evolution; however, despite containing assemblages of well-preserved microfossils that were initially reported over three decades ago, mixed carbonate and siliciclastic strata of the Veteranen Group remain poorly studied with no detailed sedimentological, geochemical, or geochronological data. Here, we present new major and trace element geochemical data from mudrocks spanning an ~4 km thick, near-complete section of the Veteranen Group from northeastern Spitsbergen. In addition, we implement new sedimentological and stratigraphic analyses, in conjunction with carbon isotope chemostratigraphy, to make preliminary correlations between Tonian strata on Spitsbergen and Nordaustlandet. Preliminary Re concentration data suggest that organic-rich shale horizons from the Veteranen Group are suitable for Re-Os geochronology and may provide the first radiometric depositional age constraints on these strata. Combined with future radiometric age constraints on fossiliferous strata, this framework will permit us to evaluate the tempo and drivers of eukaryotic diversification during the Tonian.