Karsts polyphasés, faciès marins et continentaux dans le Paléocène de la partie orientale des Pyrénées françaises

Abstract

In the Eastern part of French Pyrenees, the Cucugnan area (Southern Corbieres) corresponded during the early/Mid-Paleocene (Danian/Selandian) to a narrow transitional zone between the sea to the South (“Pyrenean Paleocene Trough”) and the continent (fluvio-palustrine and lacustrine “Vitrollian” deposits) to the North. To the South, in the North-Pyrenean Zone, the polygenic marine breccias and the associated Dano-Selandian Globigerinid-bearing hemipelagites have been preserved within successive paleokarsts superimposed onto the carbonate substratum (ante-Albian). Four paleosurfaces are recognized, principally filled by marine internal sediments with proximal and distal facies. To the North, in the “Sub-Pyrenean Zone”, a continental foreland basin is characterized by four formations of variegated Microcodium-bearing marls and channelized conglomerates, separated by erosional paleosurfaces underlining well-marked unconformities. An event correlation (chronodiagrams) between the marine realm to the South and the continental realm to the North is proposed, using the successive paleosurfaces and the lithological sequences (same number within the two realms). Our paleogeographic reconstruction shows, to the North, the “Lake of Cucugnan” and, to the South, a calcareous mountainous zone broken by the juxtaposition of deep paleocanyons (eroded in a continental context) later converted into rias submitted to marine oscillations. Several palinspastic transects are reconstructed: they show the polyphase control of the Frontal North-Pyrenean Overthrust on the Paleocene sedimentation and the importance of the successive intra-Vitrollian compressions/ transpressions (“phase fini-cretacee” auct.) inducing, within the two juxtaposed realms, emersions, erosions and karstic features which give a very contrasted paleogeography during a period characterized by plate convergence and creation of steep topographies.