OR/17/003 Geology
| Terrington, R, Thorpe, S and Jirner, E. 2017. Enköping Esker pilot study - workflow for data integration and publishing of 3D geological outputs. British Geological Survey Internal Report, OR/17/003. |
The Enköping esker is part of a larger system of eskers starting south of lake Malaren (Dunker, east of Malmkoping) and continuing north towards Heby and Tarnsjo. The model area was originally isostatically-depressed beneath sea-level by the weight of the Fennoscandian Ice Sheet. Immediately following the removal of glacier ice from the model area, the landscape was submerged beneath sea-level (Åse & Bergström, 1984[1]). However, following deglaciation, ongoing isostatic rebound has led to the uplifting of the model area well above modern sea-level. Winnowing of the glaciofluvial deposits by coastal processes (wave action) during uplift has resulted in the removal and re-sedimentation of finer-grained deposits as a thin drape across the area (Åse & Bergström, 1984[1]). The preservation of this fine-grained layer, which occurs widely throughout the study area, implies that isostatic uplift following deglaciation was rapid.
The southern part the esker is about 35 meters above sea-level, and its thickness is about 25 m. Large areas of the esker are covered by silt and clay. In central Enköping, the esker is even thicker, up to 40 m. The esker is usually situated directly on the bedrock that locally consists of granite, syenite, and metagreywacke.
The northern part of the esker, situated to the north of the urban area of Enköping, is wider than the southern part and generally not covered my fine-grained sediments. The thickness here is up to 30 m, and the highest part is situated at 50 meters above sea level. The esker has been locally quarried for sand and gravel pit. The esker/glaciofluvial deposit is used for the municipal drinking water supply. In areas beyond the esker, there is usually a thin (1–5 m) layer of silty-sandy till directly on the bedrock.