From the central Jura Mountains to the Molasse Basin (France and Switzerland) Autor(en): Sommaruga, Anna Objekttyp: Article Zeitschrift: Swiss bulletin für angewandte Geologie = Swiss bulletin pour la géologie appliquée = Swiss bulletin per la geologia applicata = Swiss bulletin for applied geology Band (Jahr): 16 (2011) Heft 2 PDF erstellt am: 08.10.2021 Persistenter Link: http://doi.org/10.5169/seals-327746 Nutzungsbedingungen Die ETH-Bibliothek ist Anbieterin der digitalisierten Zeitschriften. Sie besitzt keine Urheberrechte an den Inhalten der Zeitschriften. Die Rechte liegen in der Regel bei den Herausgebern. Die auf der Plattform e-periodica veröffentlichten Dokumente stehen für nicht-kommerzielle Zwecke in Lehre und Forschung sowie für die private Nutzung frei zur Verfügung. Einzelne Dateien oder Ausdrucke aus diesem Angebot können zusammen mit diesen Nutzungsbedingungen und den korrekten Herkunftsbezeichnungen weitergegeben werden. 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Keywords: Jura Mountains, Swiss Molasse Basin, foreland fold-and-thrust belt, décollement zone. 1. Geological setting The Jura Mountains represent a small, arcuate ment s. 1. includes all the units below the fold-and-thrust belt in a frontal position Late-Middle Triassic evaporite décollement of the northwestern Alpine arc. The Jura arc zone, i.e. Pre-Mesozoic crystalline or is surrounded by Tertiary basins of different sedimentary rocks (Permo-Carboniferous types: to the north the Rhine Graben, to the sediments) and Early Triassic beds where present west the Bresse Graben and to the south- (e.g. Buntsandstein unit). According to southeast, the Molasse Basin (Fig. 1). The Laubscher (1961), Burkhard (1990) and Rhine and Bresse Grabens are associated Burkhard & Sommaruga (1998) tectonics of with the Eocene and younger West European the Jura belt and the Molasse Basin are rift system, whereas the Molasse Basin intimately linked. corresponds to an Oligo-Miocene foredeep, which developed in front of the Alpine The Jura Mountains orogeny. The Jura and the Molasse Basin represent the most external foreland fold- The Jura is divided into an external and an and-thrust belt and the youngest (from Middle internal part based on different tectonic Miocene onward) external deformation styles. The external Jura consists of flat zone of the northwestern Alps. At its southern areas, Plateaux, limited to the north and termination, the Jura belt merges with separated from each other by so called the Subalpine Chains which were folded during «Faisceaux», narrow corridors consisting of the same period. Along its western border, numerous small imbricates and tear faults the Jura overthrusts the Bresse Graben, (Fig. 1). The internal Jura, also referred to as whereas to the north it overrides the Tabular the Haute Chaîne or Folded Jura, consists of Jura. At its external eastern end the most a well-developed fold train. At a large scale remote Jura fold (Lägeren) dies out within deformation is characterized by major folds, the Molasse Basin. The Jura Mountains and the trend of which turns from east to south. the Molasse Basin consist of a folded cover Major tear faults oriented at a high angle to of Mesozoic and Cenozoic beds, which is fold axes cut the Haute Chaîne Jura at regular detached over a basement sensu lato. Base¬ intervals. The Swiss Molasse Basin The of Institut de Géophysique, Université de Lausanne, Bât. clastic wedge the Cenozoic Molasse Amphipôle, CH-1015 Lausanne, Suisse. Basin develops in a foreland basin (Sinclair 63 et al. 1991, Homewood et al. 1986, Schluneg- Molasse corresponds to an erosional limit ger et al. 2007), and is subdivided into four along the most internal high amplitude folds geological units (Fig. 1): the Jura Molasse, of the Jura belt. The Folded Molasse is a narrow the Plateau Molasse, the Folded Molasse zone that follows the thrust of the Sub- and the Subalpine Molasse (Homewood et alpine Molasse. It is dominated by folds with al. 1989, swisstopo 2005). Classically the steep limbs dipping toward the north. The Jura Molasse represents the northern Subalpine Molasse is a narrow zone along peripheral edge of the Molasse Basin that the southern border of the Molasse Basin. has been «passively» involved in the Jura This zone is characterized by a stack of folding and thrusting. Isolated patches of thrust sheets of Tertiary sediments Tertiary Molasse sediments are preserved detached along a décollement zone located within major synclines of the internal Jura. within these Cenozoic layers (Trümpy 1980). The Plateau Molasse represents the major In the central and eastern area, the structures part of the Molasse Basin. The structures within the Folded Molasse and the consist of broad anticlines oriented NE-SW Subalpine Molasse form a triangle zone. The and tear faults trending N-S, NW-SE and southern limit of this zone is buried below WNW-ESE. The northern limit of the Plateau the Alpine nappes and corresponds to the 5°00' 6"00 8°00' 9"00 Vosges Black Forest URG Ì r Basel Dijon Besançon <..'¦¦:¦. ;:.:•¦ Bresse Graben Aar !¦:¦::> .veils nterpreted seismic lines SGPK project 2011 4& Geneva interpreted seismic lines. 1997 50 km MB CD Tabular Jura (Tabular Jura s 1 AR | Avants Monis (Tabular Jura s I j Faisceaux Jura (External Jura) Plateau Jura (External Jura) Prealpes klippen (Penninic) [ Maule Chaîne (Internal Jura) Chambery Vanscan basement massifs Tertiary rift basins External Crystalline Massifs | Jura & Plateau Molasse Subalpine Chains & Helvetic -najor tnrusts nappes Folded S Subalpine Molasse 5°00 6°00 7°00* 00' 9°00' 1 Fig. : Tectonic map of the Jura arc and the Swiss Molasse Basin with seismic interpreted lines. MB Mont- Blanc Massif; AR: Aiguilles Rouges Massif. A, B, C, D correspond to the location of profiles shown in Figs. 5 and 6. Tectonic map modified from Sommaruga (1997) and Bonnet (2007). 64 Oligocene Alpine front represented by the ern Swiss Molasse Basin area and has been frontal Penninic thrust of the Préalpes Klip- published mainly in 1997 (Sommaruga 1997, pen, the Helvetic nappes, etc. which over- 1999). More than 1,500 km of industry seismic thrust the Molasse sediments. reflection lines in the Neuchâtel and Vaud Jura of Switzerland, the French Jura Rock units and the Swiss western Molasse Basin have been interpreted. Seismic lines are from The main rocks units within the Jura and the surveys between 1970 and 1988 (BP survey in Swiss Molasse Basin are from bottom to top: the Neuchâtel Jura). a) Crystalline rocks of Precambrian to Pale¬ The second project has been realized at ozoic age. Grabens of Permo-Carboniferous Lausanne University with Urs Eichenberger and age are present within the basement, François Marillier for the Swiss Geophysical but their precise location is difficult to Commission (SGPK). It consists in a major establish (exception Weiach graben, study of the whole Swiss Molasse Basin from Sprecher & Müller 1986, Nagra 1989). Lake Geneva to Lake Constance (published Crystalline rocks and detrital Permo-Carboniferous by swisstopo, Sommaruga et al. in press). sediments are penetrated by More than 4,350 km of industry seismic lines few drill holes. The top basement is acquired from 1960 to 1990 in the Swiss formed by an erosional surface that gently Molasse Basin have been interpreted. In dips by few degrees toward the SW. addition about 30 deep wells were used for b) Rocks of Mesozoic age composed of Tri¬ calibrating the seismic lines. In both assic, Jurassic and Cretaceous projects, few seismic lines and well data were in sediments. Triassic units consist of continental the public domain, most of them were elastics, carbonates and evaporitic confidential. However, in the frame of the second rocks deposited in an epicontinental project many seismic data along selected shallow water sea. On top, alternations of profiles will be published. limestone, marls and clays represent In this paper, the profile A located in the Jura shelf and slope deposits from Jurassic to fold and thrust belt (Fig. 5) represents a Upper Cretaceous age. geological cross-section based on surface data c) Tertiary clastic rocks form a prism which and completed at depth with information increases from NE to SW (Oligocene to from neighbouring seismic sections. The Miocene age) covering the Mesozoic other profiles (B, C and D in Figs. 5 and 6) series. The discordance surface at the represent interpreted seismic sections base of the Tertiary unit represents the which are converted to depth using seismic foreland unconformity linked to piling of velocities calculated from well data, and the nappes in the South. follow the trace of seismic lines. Additional geological information (conceptual faults) based on geological maps, well reports, 2. Data scientific papers and confidential reports have been added on the seismic interpretation. The data presented here summarize some of These three profiles are a selection among the results from two research projects on 15 transects which were combined to all other the interpretation of paper seismic data seismic lines interpreted in the frame of from industry exploration in Switzerland, the Molasse Basin project in Lausanne and calibrated by well data and depth-conversion the derived horizon depth maps, to obtain of interpreted seismic horizons.