“Glacial curvilineations”: New glacial landforms produced by longitudinal vortices in subglacial meltwater flows

The glacial landscape of the Dobrzyń Plateau in central Poland contains a complex suite of enigmatic bedforms consisting of elongate and sinuous sediment ridges occurring within an anabranched network of tunnel channels terminating at a former ice margin marked by extensive glaciofluvial fans. The term “glacial curvilineations” is proposed to describe these enigmatic bedforms that occur as fields of parallel, sinuous ridges separated by troughs. The regional pattern of glacial curvilineations replicates the morphology and pattern of tunnel channel margins and suggests a common genesis. Tunnel channels and glacial curvilineations are eroded in the interbedded diamictons and glaciofluvial sediments of the plateau. We propose that tunnel channels and glacial curvilineations are the products of subglacial meltwater erosion. Curvilineations are erosional remnants produced by longitudinal vortices within the tunnel channel-forming flows. Parallelism of curvilineations reflects spacing of turbulent structures within the subglacial flow. Tunnel channel margins also control the sinuosity of curvilineations by dictating both the path and curvature of longitudinal vortices. Arguments for meltwater erosion are strengthened by the presence of extensive glaciofluvial fans at tunnel channel termini: they are the depositional counterparts to the extensive subglacial fluvial dissection of the plateau. Understanding curvilineation genesis may shed light on glacier hydrologic processes. Tunnel channels develop abruptly in the plateau surface suggesting localized point sources of meltwater, such as drainage of subglacial and/or supraglacial lakes. The extent of tunnel channels and lateral continuity of glacial curvilineations suggests broad sheet-like flows as wide as a few kilometres.