Karst landscape evolution in the littoral area of the Bay of Biscay (north Iberian Peninsula)

Abstract The western Pyrenean area contains extensive karst areas, however, their genesis and development are still mostly unknown. In this work, we make a general description of the karst landscape in different karst areas: 1) Rasa type; 2) Cone-type karst; and 3) Alpine-type karst. The first two types are present in the littoral area, where geomorphological evolution mostly depends on sea level and climatic changes. We focused our study in two karst areas of the littoral cone-type karst. We correlate different caves created from different stable water table levels. Three representative caves are studied in detail, studying their stratigraphic record based on allostratigraphy. Finally we dated the different phases of speleothem formation in the three caves. Using all this information, we defined four stable paleowater table levels, at 50, 150, 220 and 350 m asl, controlled by sea level changes and isostatic uplift events. The lowest level is the youngest, with an age of c. 1 Ma. We discovered that the interior of the three caves display very similar endokarst allostratigraphic sequences, characterized firstly by an erosion phase, a fluvio-karst input, flowstone speleothem formation and finally dripping speleothem formation. The chronological data shows a correlation between these phases and Pleistocene climatic phases; the erosion phase is related to the falling sea level, fluviokarst detrital input is related to cold (glacial) stages and the formation of speleothems is related to the warmest (interglacial) moments and high sea level periods.