Swiss Journal of Geosciences

, Volume 105, Issue 2, pp 299–312

Formation of phyllosilicates in a fault zone affecting deeply buried arkosic sandstones: their influence on petrophysic properties (Annot sandstones, French external Alps)

  • Henri Leclère
  • Martine Buatier
  • Delphine Charpentier
  • Jean-Pierre Sizun
  • Pierre Labaume
  • Thibault Cavailhes
Article

DOI: 10.1007/s00015-012-0099-z

Cite this article as:
Leclère, H., Buatier, M., Charpentier, D. et al. Swiss J Geosci (2012) 105: 299. doi:10.1007/s00015-012-0099-z

Abstract

The Restefond fault, located in the Late Eocene-Early Oligocene Alpine foreland basin, affects the well lithified and low porosity Grès d’Annot. The fault core zone is characterized by the occurrence of highly deformed sandstone lenses. Deformation inside the lenses corresponds to mm to sub-mm-spaced cleavage planes rich in phyllosilicates and up to cm-thick and dm-long quartz-calcite pure extensional veins. The cleavages are mostly composed of newly-formed synkinematic white mica and chlorite. By using thermodynamic thermometers based on the chemical composition of chlorite, a temperature of 200 ± 20 °C of fault activity was computed. This temperature shows that the Restefond fault was active at burial conditions comprised between 6.5 and 8 km, assuming a mean geothermal gradient between 25 and 30 °Ckm−1. The petrophysic properties of sandstones from the core zone and in the hanging and foot wall of the fault were determined on drilled plugs following three spacial directions. The permeability of the highly deformed sandstone from the core zone is about one order of magnitude higher than in the host rock. This increase in permeability occurs in the direction parallel to the S–C structures and is explained by the occurrence of well-connected micropores localized between platy phyllosilicates. This study shows that the fault petrophysic properties are mostly controlled by the precipitation of synkinematic phyllosilicates under deep burial conditions.

Keywords

Fault Phyllosilicates Petrophysics Annot sandstones Temperature External Alps 

Supplementary material

15_2012_99_MOESM1_ESM.xls (40 kb)
Online Resource 1: Chemical compositions of chlorite obtained by microprobe analysis. The atom numbers were calculated on the basis of 14 oxygen atoms; calculations are made for 4 atoms of Si and Al per tetrahedral site. Temperatures and Fe oxidation states are defined by the Vidal et al. (2005, 2006) and Inoue et al. (2009) methods. NF : newly formed, DET : detrital, ND : non determined, SOC : sum of octahedral cations.(XLS 56 kb)
15_2012_99_MOESM2_ESM.xls (56 kb)
Online Resource 2: Chemical compositions of white mica obtained by microprobe analysis. The atom numbers were calculated on the basis of 11 oxygen atoms; calculations are made for 4 atoms of Si and Al per tetrahedral site. NF: newly formed, DET: detrital.(XLS 40 kb)

Copyright information

© Swiss Geological Society 2012

Authors and Affiliations

  • Henri Leclère
    • 1
  • Martine Buatier
    • 1
  • Delphine Charpentier
    • 1
  • Jean-Pierre Sizun
    • 1
  • Pierre Labaume
    • 2
  • Thibault Cavailhes
    • 2
  1. 1.UMR 6249Université de Franche-Comté, CNRSBesançon CedexFrance
  2. 2.UMR 5243Université de Monptellier 2, CNRSMontpellier Cedex 5France

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