PALAEO-ICE STREAM DYNAMICS DERIVED FROM GEOMORPHOLOGICAL AND GEOLOGICAL CHARACTERISTICS OF DRUMLINS IN THE STARGARD DRUMLIN FIELD, NW POLAND

Geomorphological and geological analysis of elongated subglacial bedforms facilitate identification of palaeo-ice streams and yield data to constrain their dynamics in time and space. This study concerns the Stargard Drumlin Field marking the terminal zone of a major palaeo-ice stream in NW Poland where we investigated the spatial characteristics of over 1300 drumlins and examined the geological composition of several of them in trenches and pits.

The distributions of the major morphometric parameters of Stargard drumlins are positively skewed and indicate a modality of drumlin size. Drumlins have a well-defined orientation pattern that reflects an arcuate ice flow path, but local deviations grouped in several discrete zones also occur. Two compositional types of drumlins are found (i) drumlins primarily consisting of massive till and (ii) drumlins mainly made up of sorted sediments with ductile deformations.

The relationships between the orientation of drumlins and the relief of the ice/bed interface suggest that the ice flow pattern was controlled by the bed topography, while variations in the spatial characteristics of the drumlins reflect different subglacial conditions. The geological observations suggest high subglacial pore-water pressure in the vicinity of the ice floatation pressure that generated areas of sediment deformation intervening with areas of ice/bed separation and enhanced basal sliding. Overall, data from the Stargard Drumlin Field reflect a spatial and temporal mosaic of ice movement and sediment transport-deposition-deformation mechanisms modulated by the subglacial topography and geology.