A sedimentological study on the formation of a hummocky moraine at Törnåkra in Småland, southern Sweden

Abstract: A detailed sedimentological study was made on a section along the side of a moraine hummock at Törnåkra in Småland, south Sweden. Two sedimentary units, A and B, were identified, based on their sediment characteristics. Unit A, the lower one, was formed due to vertical stacking of sediment gravity flow deposits (diamict beds) in combination with melt water disaggregation of such beds, leaving residual lags and redeposited sorted sediment beds. This stacked sequence was laid down into a depression or a low in stagnant/dead ice. Syn- and post-depositional deformation as indicated from folds, faults and injection structures were also identified in unit A. Unit B overlies unit A and was formed due to continued deposition of debris flows. However, this unit is distinct from unit A by its lack of sorted sediments, suggesting that the melt water activity had ceased in the late stage of depression infilling. The overall bed configuration in the investigated section suggests that this was in an ice-proximal location; the sediment beds were both syn- and post-depositionally tilted towards the direction of the lost ice support. The section thus shows the sediment composition at the edge of a moraine hummock, and the sediment composition and architecture here might thus differ from that of the interior part.