A dissolution pipe palaeokarst of mid-Pleistocene age preserved in Miocenelimestones near Staszow, Poland

Many hundreds of solution pipes are exposed in quarries near Staszow, SE Po land. The pipes are contained in late Badenian (middle Miocene) carbonates of the Chmielnik Formation and are filled with sediment derived from a weat hered Sanian (Elsterian) till cover. The pipes average 1 m(3) in volume, th ough the largest is of the order of 15 m(3). The average depth is 1.9 m; th e 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 th e structural fabric of the host-rock had little, if any, influence in deter mining pipe locus and form. Neither is there any evidence that irregulariti es of the interface between host and cover determined the points of entry f or the focused groundwater flows which created the individual pipes. Theref ore, unless the entry points into the upper surface of the limestone host w ere determined by an irregular network of first-to-decay channels in a reli ct permafrost zone at the end of the Elsterian cold period, for which there is no independent evidence, the focused flows must relate to selectively p ermeable pathways through the till cover and/or to concentrations of acid r adicals 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 groun dwater flows. The Staszow piping represents a covered, intraformational pal aeokarst system. It is postulated that it developed as a product of fast-ac ting deglaciation and, possibly also, of irregular permafrost decay below t he Elsterian till, early in the Holsteinian warm period. (C) 2001 Elsevier Science B.V. All rights reserved.