Esker formation during deglaciation of the Scandinavian Ice Sheet, northeast Skåne and Blekinge, Sweden

Sammanfattning

Eskers are a key component when it comes to understanding glacier dynamics, in particular during deglaciation. Eskers contain a lot of information regarding ice sheets and glaciers, and may serve as indicators of ice-front positions, meltwater discharge rates, and glacial drainage systems of the downwasting ice masses. Eskers deposited by the Scandinavian Ice Sheet (SIS) in northeast Skåne and west to central Blekinge in Sweden have been investigated in the past to determine the genesis and accumulation of glacial and associated sediments. However, no recent efforts have been made to follow up on these studies. At the same time, a lot of progress has been made within the field of Quaternary geology since their publication. The aim of the study has therefore been to reinvestigate the understanding of the sequencing, distribution, and spatial arrangement of the esker elements and the accretion of associated sediments in northeast Skåne and west to central Blekinge. Two sites with readily available exposures were selected for further studies. The study site Johannishus is located in central Blekinge, in between the towns of Ronneby and Listerby, while the study site Olofström-Näsum is located in the northeastern region of Skåne, between the towns of Olofström and Näsum. The morphology of the investigated esker systems, in which the study sites are located, were mapped and analysed through DEMs and geological data (supplied by the governmental institutions Lantmäteriet and Svergies geologiska undersökning), while the sedimentology of the exposures were analysed through field logging and sampling for both grainsize and clast shape analyses. Both the Johannishus and the Olofström-Näsum esker systems were interpreted to be simple esker complexes and deposited as type II eskers within a glaciolacustrine environment as a series of subaqueous fans derived from the downwasting or retreating ice margin of the SIS most probably around 16 to 15 ka BP. The sediments which make up the esker beads at the study sites were most likely derived from the subglacial regime and got transported through pressurised drainage channels. Drainage fluctuated heavily, either due to seasonal or diurnal effects, and was probably temporarily enforced by supraglacial meltwater. Deformation structures located within some strata hint towards the possibility of an oscillating ice margin and potentially an active ice sheet, but the evidence is scarce and further investigations are needed to determine whether the SIS was actively retreating or had stagnated and was downwasting.