Upper pleistocene interstratal piping-cave speleogenesis: The seso cave system (central pyrenees, northern spain)

The Seso Cave System (SCS, South Central Pyrenees, Northeastern Spain) develops in poorly soluble marly interstratum between limestone beds of Eocene age. We propose an innovative and singular pseudokarstic speleogenetic model under vadose conditions based on cave morphological evidence, physicochemical and mineralogical characteristics of the Eocene marly host rock, U-Th dating of cave deposits, and local geological and geomorphological information. Eocene marls are shown to be sensitive to dispersion processes supported by their high clay content and the high concentration of sodium and low electrical conductivity in the seepage water. Runoff inside the cave results from water that infiltrates through joints and seepage water in cave walls. Thereby piping processes become very active, triggering mechanical scouring and outwashing mechanisms. The hydraulic gradient required to develop piping activity is determined by regional fluvial incision. The base level controlling water discharge during opening of the SCS coincides with a terrace of the Ara River dated at 65. ka. BP. Considering this age, as well as the U-Th age of the oldest speleothems dated in the cave at 38. ka. BP, the timing of the SCS interstratal piping-cave speleogenesis is constrained to the Upper Pleistocene; very likely at the end of Marine Isotope Stage 4 during a period characterized by high water availability following glacial retreat in northern Iberian mountains. © 2014 Elsevier B.V.
This research was funded by CGL2009-10455/BTE and CGL2010-16376 (HIDROPAST) projects of the Spanish Government (Ministerio de Ciencia e Inovación) and the European Regional Development Fund (FEDER) and a Sobrarbe Geopark research grant. It is a contribution of the PaleoQ Group (Aragón Regional Government). We thank Julie Retrum and Yanbin Lu (University of Minnesota) and Enrique Oliver (Universidad de Zaragoza) for the help in the laboratory work and Jaume Mas and Xavier Fuertes (Grupd'Espeleologia de Badalona) for field cave mapping support and Josu Aranbarri for Fig. 1 design.We appreciate very much the comments by Prof. Jo De Waele, an anonymous reviewer and Prof. Andrew J. Plater (Editor), which have improved the final version of the manuscript.