Genesis of a till/sand breccia (Pleistocene, Noteć Valley near Atanazyn, central Poland)

The study area in Atanazyn in Noteć Valley, NW Poland, is located on the surface of terrace III in Toruń–Eberswalde ice-marginal valley. Terrace III is correlated with the Pomeranian Phase and the Oldest Dryas, during which most of the fluvio-periglacial sedimentation in the Noteć Valley took place.Four units are distinguished in the terrace: (1) horizontally stratified, ripple-drift cross-laminated and massive sand (unit Sh, Src, Sm) deposited in a shallow, sand-bed channel with a low-energy current; (2) a unique till/sand breccia formed by disintegration of a lodgement till due to drying out and frost activity under periglacial conditions, which was fluvially transported over a short distance; (3) a massive gravelly diamicton (DGm) representing a subaerial, cohesive debris flow; and (4) sand with low-angle cross-stratification (Sl) forming a coversand layer over the terrace.The presence of the till/sand breccia, which is unique for Quaternary sediments, sheds new light on the depositional conditions in ice-marginal valleys. The till/sand breccia lithofacies can be considered to be a diagnostic criterion for fluvio-periglacial conditions in ice-marginal valleys.