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Successive Paleocene and Eocene infillings of polyphase paleokarsts within the Cretaceous limestones of the Empordà thrust sheets (Catalan Pyrenees, Spain) : relationships between tectonics and karstification

¹ UMR-CNRS 5573 (Dynamique de la Lithosphère), Université Paul-Sabatier, 17 rue A. de Gargas, 31500 Toulouse, France. e-mail : peybernesb{at}aol.com
² UMR-CNRS 5563 (LMTG), Université Paul-Sabatier, 14 avenue Edouard-Belin, 31400 Toulouse, France
³ UMR-CNRS 5573 (Dynamique de la Lithosphère), Université de Montpellier II, place E. Bataillon, 34095 Montpellier cedex, France

The Mesozoic series of the southern units of the Pyrenean Empordà thrust sheets (Montgrí and Figueres nappes, Catalonia, Spain) were finally emplaced over the autochthonous basement and its Cenozoic cover during Eocene times. However, they have originally been folded by the "Laramian" compressional event (Late Cretaceous/Early Paleocene), while they were still in their root zone more than 50 km to the N-NE. Postdating the Santonian, the emersion of the Cretaceous tectorogen induced karst formation at the expense of Berriasian to Santonian limestone sequences. Karst cavities of this paleokarst 1 (lapiaz and canyons) were subsequently coated with a fine, red or black, Microcodium-bearing, continental silt, and infilled with marine chaotic breccias. Following a new episode of emersion then erosion, the original paleokarst 1 was cross-cut by newly formed cavities of the paleokarst 2, filled with Lutetian-Bartonian marine breccias. Both types of marine breccias (Paleocene then Eocene in age) are now relatively well dated by means of planktonic foraminifera (Globigerinacea) occurring within the argillaceous-sandy matrix, and for the older ones, within the argillaceous-sandy or carbonate, finely laminated, interbedded hemipelagites, that mark the top of marine sequences tens of centimetres thick. The relationships of the "Laramian" and "Pyrenean" compressional tectonic events, occurring from latest Cretaceous to Bartonian, with the development of paleokarsts 1 and 2 are analysed in the perspective of the progressive southwards emplacement of the Montgrí thrust sheet, during Eocene time.

Key Words: Breccias • Hemipelagites • Paleocene/Eocene planktonic foraminifera • Paleokarsts • Folding • Catalan Pyrenees • Spain