Texture, composition and stratigraphy of volcanic ash beds in lower Palaeocene chalk from the North Sea Central Graben area

A large number of volcanic ash beds have been identified in Danian chalk from the Danish North Sea sector Central Graben area. The volcanic input was prominent during deposition of the lower part of the Danian chalk, whereas it was much less during deposition of the upper part of the Danian chalk. The non-carbonate fraction of the ash beds predominantly consists of smectite with some quartz, illite and minor amounts of kaolinite/chlorite and pyrite and trace amounts of zircon. Fragments of volcanic glass are common in the ash beds. The mineralogical composition of the ash beds varies from bed to bed, which makes ash bed correlation a promising high-precision correlation tool. Volcanic provinces that were active in connection with the opening of the North Atlantic Ocean are possible sources of the volcanic ash. The different composition of the ash layers could indicate that they originate from more than one source area.