The late Palaeocene to early Eocene Balder and Sele Formations of the North Sea Basin contain over 200 air-fall, water-lain tephras. These occur over the entire North Sea area, extending onshore into Denmark, NW Germany, The Netherlands and SE England; they have also been recorded in the Bay of Biscay and Goban Spur areas of the NE Atlantic and offshore mid-Norway. Results from cores drilled in two widely separated areas of the North Sea have been integrated with earlier work on the northern North Sea and Danish sequences, to demonstrate that the stratigraphic and geochemical development of the tephra sequence is regionally consistent. This indicates that a single source or group of sources was responsible, rather than a number of geographically-separated intrabasinal volcanoes for which little geophysical evidence can be found. The sequence comprises a lower group of sporadic thin tephras of variable composition, including tholeiitic, alkalic, trachytic, trachyandesitic and peralkaline varieties, and an upper group of thicker, more abundant tephras, almost exclusively of Fe-Ti tholeiitic composition. General thickness trends and geochemical evidence indicates that the source volcanoes lay on the proto-Greenland-Scotland Ridge, with the tephras showing several features that ally them to the early Palaeogene Faeroe-Greenland igneous province. The reasons behind the highly explosive nature of the basaltic magmatism remain enigmatic.

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