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Scientific article
English

Clay Mineral Diagenesis and Thermal History of the Thonex Well, Western Swiss Molasse Basin

Published inClays and Clay Minerals, vol. 44, no. 5, p. 693-705
Publication date1996
Abstract

Results are presented of a diagenetic study from the 1300 m thick Oligocene Molasse deposits penetrated by the Thônex geothermal exploration well (Geneva, Switzerland). The x-ray diffraction (XRD) studies of fine-grained rocks indicate the following diagenetic changes: a decrease of illite/smectite (US) expandability from approximately 90% to 30% with depth, a decrease of the amount of US in the clay mineral fraction, and the appearance of corrensite at depths >750 m. The transition from random US to ordered I/S occurs at the base of the Thônex well (1200 to 1300 m) and is associated with a coal rank of about 0.7% Rr (mean random vitrinite reflectance) corresponding to paleotemperatures of 110 to 115 °C Corrensite appears at a vitrinite reflectance value of 0.6% Rr and a corresponding paleotemperature of 100 °C. The amount of post-Molasse erosion is estimated to be approximately 2 km. Thermal history modeling of the Thônex well suggests maximum paleotemperatures of 80 to 115°C and an average paleogeothermal gradient of 27 °C/km during Late Miocene maximum burial conditions.

Keywords
  • Chlorite/Smectite
  • Corrensite
  • Diagenesis
  • Erosion estimate
  • Illite/Smectite
  • Paleotemperatures
  • Thermal modeling
  • Vitrinite reflectance
  • XRD
Funding
  • Swiss National Science Foundation - 2000-037585.93/1
Citation (ISO format)
SCHEGG, Roland Albert, LEU, Werner. Clay Mineral Diagenesis and Thermal History of the Thonex Well, Western Swiss Molasse Basin. In: Clays and Clay Minerals, 1996, vol. 44, n° 5, p. 693–705. doi: 10.1346/CCMN.1996.0440513
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Article (Published version)
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Identifiers
ISSN of the journal0009-8604
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