The laminated lake sediments of the Eckfeld maar (Middle Eocene, Germany): Types of stratification and role of organic matter

The Middle Eocene lake sediments of the Eckfeld maar are situated on the southwestern margin of the Tertiary High-Eifel volcanic field (Germany) and are well known for excellently preserved fossil remains. During a drilling campaign in 1996 six well sections Were cored at three different locations. Three cores (E1/96, E2/96 and E3/96) penetrated deposits of the central lake facies, which is dominated by laminated organic-rich pelites within the uppermost 40 m. It is the aim of this paper to present a brief survey over the main types of stratification observed within the organic-rich portions of the Eckfeld lake sediments. Based on the varying distribution of mineral and organic matter three sediment sequences are distinguished representing different phases of lake development. The "minerogenic laminites" represent the purely elastic mineral sedimentation in a lake, which was surrounded during this early phase by a tephra rim barren of vegetation. The gradual overgrowth of the tephra rim by vegetation is reflected by the predominance of land plant detritus in the sediments of the "transition beds", though the siliciclastic input is still significant. In contrast, the succeeding sequence of the "biogenic laminites" is characterised by the frequent occurrence of centric diatoms (mainly of the planktonic species Aulacoseira cf. granulata) and Chlorophyceae (mainly Botryococcus and Tetraedron) documenting the increase in autochthonous organic sedimentation in a meromictic lake.