A dissolution pipe palaeokarst of mid-Pleistocene age preserved in Miocene limestones near Staszَw, Poland

Many hundreds of solution pipes are exposed in quarries near Staszَw, SE Poland. The pipes are contained in late Badenian (middle Miocene) carbonates of the Chmielnik Formation and are filled with sediment derived from a weathered Sanian (Elsterian) till cover. The pipes average 1 m3 in volume, though the largest is of the order of 15 m3. The average depth is 1.9 m; the average diameter, 0.6 m. The host limestone is fractured by several sets of open master joints, but, in respect of the way inclined pipes cross the joints without deflection in vertical exposures, and the absence of x-axis elongation along master joints in plan, the evidence is unequivocal that the structural fabric of the host-rock had little, if any, influence in determining pipe locus and form. Neither is there any evidence that irregularities of the interface between host and cover determined the points of entry for the focused groundwater flows which created the individual pipes. Therefore, unless the entry points into the upper surface of the limestone host were determined by an irregular network of first-to-decay channels in a relict permafrost zone at the end of the Elsterian cold period, for which there is no independent evidence, the focused flows must relate to selectively permeable pathways through the till cover and/or to concentrations of acid radicals there. Small quantities of organic carbon in the pipe cortices hint at the former presence of an appreciable content of peat in the till cover at the time of piping; this could have been the source of the acidic groundwater flows. The Staszَw piping represents a covered, intraformational palaeokarst system. It is postulated that it developed as a product of fast-acting deglaciation and, possibly also, of irregular permafrost decay below the Elsterian till, early in the Holsteinian warm period.