INVERTED TECTONICS AND THRUST SHEET RAMPS - NEW TECTONIC AND STRATIGRAPHIC DATA FROM THE GIANT UNDERGROUND KARSTIC NETWORK OF THE PIERRE-SAINT-MARTIN, PYRENNES-ATLANTIQUES, FRANCE

The giant deep karstic network of the Pierre-Saint-Martin shows shallo w-water marine Devonian carbonates and a flysch-like Lower Carbonifero us culm facies, unconformably overlain by Cenomanian, Coniacian and Sa ntonian limestones, these latter being discordant up to the Palaeozoic . Correlation of superficial and underground data leads to the hypothe sis that the Soum de Leche thrust sheets have been created by inversio n tectonics and that the underground galleries of the Pierre-Saint-Mar tin have a tectonic origin and more probably developed on a ''dead ram p'' of these thrust sheets.