The role of end-Cretaceous and Eocene tectonics in the external part of the Pyrenees. The "Garumnian" of Cucugnan and its relations with the North-Pyrenees frontal thrust (southern Corbieres, France)

In the Eastern part of the Pyrenees, the Cucugnan area (Southern Corbieres), at the boundary between the North and the Sub-Pyrenean Zones, shows different outcrops of "Garumnian" fluvio-lacustrine sediments, Latest Cretaceous to Paleocene in age. These deposits are generally interpreted as specific units involved in one of the main Eocene crustal faults named the North Pyrenean Frontal Thrust (NPFT). Nevertheless, in 1967, Mattauer and Proust considered that the "Garumnian" Cucugnan formation overlapped unconformably the North and Sub-Pyrenean structures and gave evidence for a Late Cretaceous main tectonic phase. This new geodynamic interpretation, which gives to the Eocene phase little influence, has been recently supported by two independent articles (Charriere & Durand-Delga, 2004; Combes, Peybernes & Fondecave-Wallez,, 2004). Both papers indicate an angular unconformity between the Cucugnan "Garumnian" Fm and the underlying North Pyrenean Triassic Fm and the Sub-Pyrenean Albian Fm. In addition to this conclusion, Combes, et al. (2004) consider that marine, transgressive Dano-Selandian deposits, including breccias and hermpelagites, are associated to continental Cucugnan sediments. both to the South, in the North-Pyrenean Galamus mountain, and to the North East, in the Sub-Pyrenean Tauch block. In the present work, we present a new description and interpretation of the same "Garumnian" outcrops, that lead to quite different conclusions: a) the Cucugnan "Garumnian" I'm is involved in successive tectonic slices stretching along the NPFT, between the North-Pyrenean Triassic complex and the folded Albian of the Cucugnan Sub-Pyrenean slices; all the contacts between these different units are tectonic: b) the marine Dano-Selandian deposits including breccias and hemipelagites do not exist; c) the present structures are closely linked to the Eocene tectonic phase that corresponds really to the main orogenic event of the Pyrenean range.