ANISOTROPY OF MAGNETIC SUSCEPTIBILITY TILL FABRICS AND THE LATE GLACIAL BEHAVIOR OF THE BALTIC ICE STREAM IN SOUTHERN SWEDEN

The Weichselian glacial history of Southern Sweden and the dynamic ice flow history of the Scandinavian Ice Sheet (SIS) and the Baltic Ice Stream (BIS) are poorly constrained. Normal northeasterly ice flow from the SIS is thought to be punctuated by two advances of the BIS at approximately 21 ka and 13 ka BP, but significant questions remain regarding the behavior of the BIS and the ages of BIS tills. Anisotropy of Magnetic Susceptibility (AMS) till fabrics provide an unbiased, precise approach to measure the preferred orientations of non-equant silt-sized and smaller particles and to decipher ice flow history from the resulting ellipsoid. Lineated fabrics show characteristic flow-parallel, up-ice plunging orientations of the k₁ (max) axis; when fabrics are foliated, flow direction is inferred from the orientation of the k₃ (min) axis. In the first application of AMS fabrics to Swedish tills, multiple fabrics measured within an 8 meter thick exposure of BIS silt-clay till in a quarry ESE of the village of Dalby, Skȧne County, Sweden, reveal the dynamic behavior of the BIS. The lower three meters of the unit possess triaxial to oblate AMS fabrics consistent with a predominant ice flow direction from the ENE. These are followed up-section by rotational fabrics progressing towards flow from the SW. This rotation occurs within less than one meter and terminates coincident with a boulder line and discontinuous sand lenses up to 1 decimeter thick. Above the boulder line, fabrics maintain orientations indicating ice flow from the SW. The flow directions from the SW found in the upper portion of the unit are consistent with flow directions inferred from bedrock striations and landforms associated with the Young Baltic Advance. The lower section of the till was likely deposited during an early phase of the Young Baltic Advance and reworked under progressively changing flow directions. Alternatively, the portion of this till below the boulder line could be a remnant of the Old Baltic Advance. In either case, the change in flow coincident with the boulder line likely involved reworking of existing BIS sediments and little long distance transport from the Baltic basin. Additionally, if the lower section of this exposure is Old Baltic in age, this work may have implications for deforming bed conditions during the Young Baltic Advance.