Pyroclastic deposits within the East Greenland Tertiary flood basalts

Stratigraphic, geochemical and mineralogical characterization of pyroclasti c deposits on the Gronau West Nunatak of East Greenland indicates that both alkaline and basaltic tephras occurred during the eruption of flood basalt s associated with the opening of the North Atlantic ocean in the early Tert iary. Within the exposed section of Gronau West Nunatak, c. 1 km thick repr esenting c. 1.6 Ma. 17 of the horizons are phreatomagmatic basaltic tephras . Near the top of the section, an alkaline tuff was dated at 53.8+/-0.3 Ma by Ar-40/Ar-39 method. This tuff contains a distinctive mineralogy (sanidin e, Mg-katophorite, aegirine) and geochemistry (melt inclusion compositions, and trace and rare earth element abundances) that indicate it was erupted from the Gardiner melanephelinite-carbonatite volcanic complex located 175 km to the SE, which was active from c. 55 to 52 Ma. The alkaline tuff can b e correlated to age-equivalent, compositionally similar alkaline pyroclasti c horizons reported in North Atlantic sediment cores and in outcrops in Nor thern Europe, making it an important regional time-stratigraphic marker. Th is study indicates that North Atlantic explosive volcanic events were preva lent, regionally widespread, and originated in East Greenland during contin ental rifting, suggesting the need for reappraisal of the impact of North A tlantic volcanism on climate change during the early Tertiary.