Palaeogene volcanism: the sedimentary record in Denmark

Summary Approximately 200 volcanic ash layers are known from Palaeocene and Eocene marine clays in Denmark. The oldest layers are present in the upper part of the Upper Palaeocene and are sporadic, thin and acidic in composition. The main volcanic phase took place at the Palaeocene-Eocene transition. During the main phase, a supply from the N to NE is indicated, while a few layers probably had a source to the NW or W. A later volcanic phase is represented by thin and more sporadic ashes in the Lower to Middle Eocene. These are almost totally transformed to smectite. In the Upper Palaeocene, and partly in the Lower Eocene, smectite is a highly dominant clay mineral in the interbedded clays. Zeolites of the heulandite-clinoptilolite type are also present, while cristobalite is sporadically present in the lower part. A major supply of smectite from the N Atlantic may be indicated. Below the ash-bearing sequence the only evidence for volcanic activity is the presence of very smectite-rich, zeolitic clays with scattered opal-CT and slightly silicified horizons. Calculated chemical compositions of smectites from both ash layers and clay layers between ash layers and below the ash-bearing sequence are almost identical, indicating a volcanic source for the smectite.