4.1 Introduction
Effective exploration and development of geothermal energy rely also on the integration of surface and subsurface data in well structured and accessible database which would respond to both archiving and operational objectives (Brentini, in prep.). In the case of the GEother-mie 2020 program, this database should respond to local Geneva Canton land and resources managment requirements, while at the same time should be adopting as much as possible the existing federal nomenclature. This would ultimately result in a homogenized and consistent national dataset which could assist correlations at larger regional scale.
At the early stage of the present work, discrepancies have been highlighted in the stratig-raphy, mainly in the nomenclature, age boundaries and hierarchical organisation of strati-graphic units (formation, members, etc.). These intricate issues have been logically ad-dressed, in order to integrate data in the most coherent and durable way for the State and for ongoing and future studies.
4.1.1 Aims
The aims of this Chapter are to provide constraints on the distribution and geometry of potential reservoir bodies and to integrate the latter in a homogeneous and coherent strati-graphic framework at the basin scale. For this purpose, facies and lateral variations have been identified on new outcrops, and subsurface well data have been integrated to previous regional studies, leading to coherent models of depositional environment developed during se-lected Mesozoic time. Structural aspects and key surfaces derived from 2D seismic data have also provided essential constraints for facies distribution and unit thickness variations across the basin (Clerc, in prep.). These integrated sedimentological observations have allowed the definition of a synthetic stratigraphic cross-section for the GGB, updated according to cur-rently used regional nomenclature and age boundaries. In suitable units, correlations with
1The writting of this Chapter has been co-authoted with Maud Brentini, PhD sponsored by the State of Geneva at the University of Geneva in the framework of the GEothermie 2020 program. Her PhD thesis has started in December 2014 and focuses on the integration of surface and subsurface data in the dynamic database linked to Geographical Information Systems (GIS), which is especially designed to fit with both archiving and operational objectives of the State of Geneva.
4.1. Introduction 85 Wells from the LEP project (CERN)
Deep wells
City
Location of field studies Geological units
Granite and gneiss, external crystalline massifs Fault
Wrench fault in the GGB, interpreted from seismic data Thrust
Figure 4.1: Situation map: the Greater Geneva Basin, wells studied and M.Sc. studies in-cluded. Structural interpretation in the GGB afterClerc, (in prep.), and digitized geological map from Chantraine et al. (1996).
86 Chapter 4. Stratigraphy and sedimentology terminology recently harmonized at national scale by the Swiss geological survey (swisstopo) (HARMOS, (Morard, 2014)) have also been attempted.
4.1.2 Geographical setting
Data have been acquired over the entire GGB. However, in this study, we concentrate on the basin surrounding the Geneva region, i.e., the Geneva Basin s.s., which is bounded to the southeast by the Mount Salève and to the southwest by the Mount Vuache (Figure 4.1).
4.2 Material and methods
This study includes two main study areas, i.e., the outcrops for surface data and the wells for the subsurface domain. The methods applied have encompassed (1) an outcrop review, based first on the extensive literature review of the regional geology, involving the valorisation of numerous unpublished MSc theses carried out in the past at the University of Geneva (Figure 4.1). The outcrop dataset has also been completed by an overall recognition of different units in the field, and sampling for microfacies analysis and cross-validation. (2) With respect to subsurface data, 45 wells reaching at least the Mesozoic strata have been selected. Reports and logs have been collected from the French and Swiss geological surveys (BRGM and Swisstopo). The available core material has been described, and core samples have been retrieved for microfacies analysis on thin sections.
20-30 Grès et Marnes gris à gypse
Molasse grise Complexe des marnes et
calcaires roux Marnes noires à nodules
et à Tisoa
Quater-nary*2TertiaryCretaceousLate Jurassic(Malm) Middle Jurassic(Dogger) Jurassic
Early Jurassic(Liassic)Late Triassic Triassic
MiddleTriassic
*Controlled on one outcrop only Etiollets Fm Main reservoirs Regional seal Primary source rock
? ? ? ? ?
CENOZOICMESOZOICPALAEOZOIC CretaceousJurassicTriassicPermianPalaeogene Age
250 volcanic activity linked
to the break-up
HARMOS after swisstopo / Morard 2014, Strasser et al. 2016, Pictet et al. 2016, Brentini, 2018 Seismic horizons after Clerc 2016
Reservoirs information after BRGM 2015 et Rusillon, 2018.
Time scale after Ogg et al. 2016
Sea level curve after Haq 1987 Environment and Sequence Stratigraphy after Rusillon, 2018.
Geological units after Donzeau et al. 1997, GADZ 1997, Meyer et al. 2000, Piuz 2004,
M. Brentini - E. Rusillon A. Moscariello Version 1.0 (2018)
Geneva Basin Lexicon Surface and subsurface stratigraphy
Charollais et al. 2007 / 2013, Pictet 2016, Rusillon, 2018 and Brentini, 2018 Marnes à amalthées Calc. argileux à cassure conchoïdale
Marnes calc. à bélemnites Marnes noires à nodules et Tisoa
“Schistes carton”
Couches du Chailley
Calc. plaquetésCalc. de Landaize Calc. récifaux Tidalites de Vouglans
Calc. de Tabalcon
Dalle échinodermique Couches de Birmensdorf Couches d’Effingen-GeissbergCalc. pseudolithographiquesCouches à céphalopodesCalc. lités
Calc. gréso-micacés à Cancellophycus Alt. inférieures des calc. fins Calc. à entroques Alt. supérieures de calc. et marnes Calc. terreux
Calc. d’Arnans
Alt. micacées à bancs durs Faciès de transition
Goldberg Fm Pierre-ChâtelVions
Chambotte inférieure Membre du Guiers
Complexe des marnes et calc. roux Complexe des Marnes d’Hauterive et Pierre-Jaune de Neuchâtel
Urgonien jaune Grès et Marnes gris à gypse
Molasse d’eau douce inférieure (USM)
Fulie
Calc. marneux de la Rivière Molasse “aquitanienne”
*2 Geneva soils classification Couverture et remblais Bioturbation / Tisoa Roots
*1 Depositional environ.
1: Continental
Figure 4.2: (a) Schematic chronostratigraphical section of the Geneva Basin sedimentary succession (version 1.0). The horizontal axis is 25km, from the Jura Haute-Chane to Mount Saleve, passing through Humilly-2 well. (b) Correlation between common names used (inserted on the cross-section) and HARMOS nomenclature. (c) Seismic horizons defined in the frame of GeoMol-CH (Clerc, 2016). (d and e) Stratigraphical sequences defined at the 2nd order, and comparison with sea-level curve (Haq et al., 1987). (f) legend for the chronostratigraphical section, including ranges of layer thickness measured in the GGB.