Volume n° 2 - from B16 to B33 32nd INTERNATIONAL GEOLOGICAL CONGRESS WESTERN PYRENEES FOLD-AND- THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION Field Trip Guide Book - B16 Field Trip Leaders: R. Bourrouilh, L. Moen-Maurel, J. Muñoz, A. Teixell Florence - Italy August 20-28, 2004 Pre-Congress B16 The scientific content of this guide is under the total responsibility of the Authors Published by: APAT – Italian Agency for the Environmental Protection and Technical Services - Via Vitaliano Brancati, 48 - 00144 Roma - Italy Series Editors: Luca Guerrieri, Irene Rischia and Leonello Serva (APAT, Roma) English Desk-copy Editors: Paul Mazza (Università di Firenze), Jessica Ann Thonn (Università di Firenze), Nathalie Marléne Adams (Università di Firenze), Miriam Friedman (Università di Firenze), Kate Eadie (Freelance indipendent professional) Field Trip Committee: Leonello Serva (APAT, Roma), Alessandro Michetti (Università dell’Insubria, Como), Giulio Pavia (Università di Torino), Raffaele Pignone (Servizio Geologico Regione Emilia-Romagna, Bologna) and Riccardo Polino (CNR, Torino) Acknowledgments: The 32nd IGC Organizing Committee is grateful to Roberto Pompili and Elisa Brustia (APAT, Roma) for their collaboration in editing. Graphic project: Full snc - Firenze Layout and press: Lito Terrazzi srl - Firenze Volume n° 2 - from B16 to B33 32nd INTERNATIONAL GEOLOGICAL CONGRESS WESTERN PYRENEES FOLD-AND- THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION AUTHORS: R. Bourrouilh1, L. Moen-Maurel2, J. Muñoz3, A. Teixell4 1 Laboratoire CIBAMAR, Université Bordeaux 1, Talence Cedex - France 2 TOTAL, Pau Cedex - France 3 Departament de Geodinamica i Geofisica, Facultat de Geologia, Universitat de Barcelona - Spain 4 Departament de Geologia, Universitat Autònoma de Barcelona, Bellaterra - Spain Florence - Italy August 20-28, 2004 Pre-Congress B16 Front Cover: 1. Thrusts and Folds structures of Les Eaux Chaudes in the Ossau Valley, France. DAY 2, Stop 2.5b. 2. Thrusts and Folds structures of the External Sierras, Spain. DAY 5, Stop 5.3. 3. Thrusts and Folds of Gavarnie at La Estiba, Spain. DAY 6, Stop 6.2. WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16 Leaders: R. Bourrouilh, L. Moen-Maurel, J. Muñoz, A. Teixell Introduction General geological This fi eld trip along a geotraverse through the north- setting (Plate 1, fi g.1 and 2). western and south-western Pyrenees area has three main purposes: Introduction 1. To analyse the present-day structures in the fold Situated between the European plate and the Iberian and thrust belt and to reconstruct their structural plate, the Pyrenean orogenic belt extends from the evolution in order to better understand the subsurface NW part of Spain or Galicia, to the Southern part of foreland structures (some of them being oil/gas traps the Alps and the Gulf of Genoa, in the Mediterranean. or prospects). It is thus a belt almost 2,000 km long, of which only 2. To describe the stratigraphic evolution of the the central part, or the Pyrenees, is a visible collisional Mesozoic and Tertiary formations (with respect to orogen, whereas both the Western part or the Bay of plate tectonics and to the Iberian plate drift) on several Biscay and the Eastern part or the Gulf of Lion and transects: along the Ossau Valley, the Aspe Valley, the Gulf of Genoa remain at subsea. Mendibelza and Orhy Massifs for the northern side, The Pyrenees resulted from an orogeny which and from the Orhy Massif to Jaca and Aïnsa for the developed over a previously thinned continental crust, southern side. but without an intervening oceanic crust between the 3. To give petroleum geoscientists the recent concepts two diverging plates. Underplating of the Iberian plate and keys for the Pyrenean foreland and foothills underneath the European plate led to the sinking of a hydrocarbon exploration. deep crustal root along a north-dipping plane while coeval delamination of the upper crust led to the The scenic landscapes of the Pyrenees mountain range propagation of a major fold-and-thrust belt to the provide an exceptional laboratory for examining the south as well as of a conjugate north-verging back- orogenic processes, from rifting to collision, both thrust system. Thus the range is characterized by a in the crustal lithosphere as well as in the foreland doubly-verging asymmetric thrust stack wedge: basins. - the southern fold-and-thrust belt (FTB) represents A comparison to more classical fold-and-thrust belts a south-verging imbricate fan affecting cover will be proposed along the way and in the wrap-up formations (Mesozoic and Cenozoic in age) conclusion of the fi eld trip. rooting into an antiformal stack of basement rocks (Precambrian to Paleozoic variscan folded series) in Field References: the axial zone. The piggy-back thrust sheets indicate a Topographic and Road maps : for example: crustal shortening which reaches over 100 km along, Michelin n°234 Aquitaine 1/ 200,000 i.e. 90% of the total orogen collision; Michelin n°573, Regional 1/400,000: - the northern fold-and-thrust belt is confi ned over Pais Vasco/Euskadi, Navarra, La Rioja. a narrower zone north of the axial zone or the High Michelin n°574, Regional:1/400,000: Chain, in a conjugate position to the underplating Aragon, Cataluña/Catalunya process (Moen-Maurel et al., 1999). Geological maps : The relatively minor inversion in the Northern FTB S.N.P.A. (Société Nationale des Pétroles d’ Aquitaine) protected the rifting series and structures from uplift (1972). Carte géologique des Pyrénées, scale and erosion, thus permitting the examination of the 1:250,000, P. Soler ed. 4 plates. initial processes of the orogenesis. B.R.G.M. (1980). Carte Tectonique de la France, The genesis of the Pyrenean belt is the result of: B16 to B33 n° 2 - from Volume scale 1:1,000,000, B.R.G.M. Ed. - 1. the break-up of the 250 Ma old Wegener’s Pangea B.R.G.M.: 1/50,000 geological Maps: n° XIII-46, St and reactivation of its structural inherited fabrics, Jean Pied de Port; XIV-46, Tardets-Sorholus; XIV-47, - 2. the correlative propagation of the Atlantic Mid- Larrau ; XV-45, Pau; XV-46, Oloron Sainte Marie; Oceanic Ridge from Central Atlantic to the North, XV-47, Laruns (under press). with an Atlantic RRR triple junction along its Instituto Geologico y Minero de Espana, Geological Eastward opening branch entering Bay of Biscay, Maps at 1/ 250,000 and at 1/50,000: n°118 Zuriza, - 3. the Late Jurassic - Late Cretaceous diachronous n° 144 Anso, n°145 Sallent. Eastward opening of the Bay of Biscay which 3 - B16 Leaders: R. Bourrouilh, L. Moen-Maurel, J. Muñoz, A. Teixell B16 Plate 1 - 1. Structural Map of the Pyrenees with location of cross section AB. 2. Transversal cross section AB of the Pyrenees, from the Ebro Basin (South) to the Aquitaine Basin (North). resulted in the drift and progressive rotation of the “aulacogen”, Iberian plate and in the birth of rifted interplate - 4. the northward push by the large African plate basins, such as the N- Pyrenean basin at the tip of the Stopping the free drift of the Iberian plate toward the Bay of Biscay. In Turonian the Eastward Atlantic R south-east. This drift is due to the Cretaceous oceanic junction point aborted (R-->r), the North-Pyrenean opening of both the South Atlantic and Indian Oceans, rift never produced oceanic crust: it can thus be called as well as by the closure of the Tethys, which provoked Volume n° 2 - from B16 to B33 n° 2 - from Volume Figure 1 - Crustal scale balanced cross section, ECORS seismic profi le, from Choukroune et al. , 1989. B16 - WESTERN PYRENEES FOLD-AND-THRUST-BELT: GEODYNAMICS, SEDIMENTATION AND PLATE BOUNDARY RECONSTRUCTION FROM RIFTING TO INVERSION B16 Figure 2 - Cross-section passing through the Lacq and Meillon gas fi elds (Moen-Maurel et al.1999). the migration of the African plate towards the NE and compensation responded to the collision and the then towards the N. This plate motion crushed the associated crustal thickening, creating a large open space between Europe and Africa and formed intraplate foreland over the Iberian plate, (the South- the Pyrenean-Alpine orogenic belt in a diachronous Pyrenean basin), and a retro-foreland basin on the compression which proceeded westwards along the Northern edge of the Iberian plate and over the northern margin of the Iberian plate. As a result of the collision between the Iberian and European plates, which began during the Turonian and continued: - 1. the rifted N-Pyrenean basin became a foredeep basin Volume n° 2 - from B16 to B33 n° 2 - from Volume - 2. a lithospheric Plate 2 - 1. Transect Of The West-central Southern Pyrenees, from A. Teixell. 2. Cross-section of the Western Jaca basin and Ainsa basin across the Boltaña anticline, from J. Muñoz. 5 - B16 Leaders: R. Bourrouilh, L. Moen-Maurel, J. Muñoz, A. Teixell B16 European plate (the Aquitaine basin). verging subduction. To the east, the Pyrenean orogenic - 3. the Pyrenean orogenic belt displays a fan-shaped belt extends in the Alps of Provence, exhibiting minor cross-section, resulting from the crustal ductile inversion thrusts and folds (Debelmas, 1974). More underthrusting or underplating of the Pre-Pangean to the south, the Neogene Mediterranean extension, basement (Precambrian-Paleozoic) of the Iberian consecutive to the Betico-Rifean compressional plate underneath the European plate. Since the initial events (Bourrouilh and Gorsline, 1979) overprints the stages of the Pyrenean collision at Late Santonian- Pyrenean belt. Campanian times two foreland basins developed, one Between these belt-tip areas, where the European and on each side of the double-wedge (Figs. 1 and 2).