Clay mineralogy of the Upper Paleocene and Eocene clay sediments in Denmark

Abstract

The clay mineralogy of the Upper Paleocene and Eocene "plastic clay" sediments has been investigated from a new borehole in the Great Belt of Denmark. Predominant smectite, with small amounts of illite, kaolinite and, in the Holmehus Fm., chlorite, have been identified in the Upper Paleocene sediments. Abundant smectite and increased amounts of kaolinite and illite, with little chlorite, are present in the Eocene sediments. The Tertiary section of the borehole has been divided into two zones; one dominated by smectite with trace amount of kaolinite, including the Upper Paleocene and the Rl-R3 Beds of R!llsnres Clay Fm.; another characterized by the distinct increase of kaolinite and the relative decrease of smectite, including the R4-R6 and the Ll-lA Beds of Eocene sediments. Regionally, smectite content decreases, while kaolinite and illite increase from the north to the south and southeast in the Eocene sediments. No clear trend has been recognized in the Upper Paleocene sediments. The effect of material source, palaeoclimate and depositional environment on clay mineral distribution is discussed. The high content of smectite is considered to be mainly attributed to the alteration and/or weathering of volcanic material, contributions of smectitic clay from carbonate terrains and far trans­ported suspended matter from north-northwest. The change in climatic conditions may also be of importance. The distinct increase in kaolinite content of the Eocene sediments is thought to be related to a elastic source to the south and southeast and to the warmer climatic conditions.