Early Weichselian biostratigraphy and vegetational development at Horonkylä, Pohjanmaa, Western Finland

Abstract

A diatomite layer covered by two till units was found at Horonkylä, Teuva, Pohjanmaa, western Finland. The diatomite layer represents infill sediment in a freshwater lake formed within a dead ice hollow in a glaciofluvial formation interpreted as an esker. The deposition of diatomite was terminated by advancing ice, which deformed underlying sediments and deposited the first till unit (Horonkylä till) in the sequence. During the ice retreat a silty clay layer was formed in the basin close to the ice front. A renewed glacal advance deposited the upper till unit (Horonpää till). According to the diatom flora the diatomite was deposited in a shallow, freshwater basin in which at least slight water level changes occurred during the sedimentation. On the basis of biostratigraphy the diatomite was deposited during Brörup interstadial. The pollen flora indicates a forest succession from an initial birch forest to a denser pine forest. Dating of the diatomite layer is based exclusively on the biostratigraphy. The silty clay layer was deposited in a basin close to the ice front and the initial stages of sedimentation were interrupted by a short pulse of secondary Eemian material.

Keywords

• pollen analysis
• diatom flora
• lithostratigraphy
• Brörup interstadial
• Horonkylä
• Teuva
• Pohjanmaa
• Finland