• DOI:10.2113/GSSGFBULL.177.5.237
• Corpus ID: 128996373

The “Schistes carton” of Quercy (Tarn, France): a lithological signature of a methane hydrate dissociation event in the Early Toarcian. Implications for correlations between Boreal and Tethyan realms

@article{Emmanuel2006TheC,
  title={The “Schistes carton” of Quercy (Tarn, France): a lithological signature of a methane hydrate dissociation event in the Early Toarcian. Implications for correlations between Boreal and Tethyan realms},
  author={Laurent Emmanuel and Maurice Renard and Ren{\'e} Cubaynes and Marc de Raf{\'e}lis and Micha{\"e}l Hermoso and Laurence Lecallonnec and Antoine le Solleuz and Jacques Rey},
  journal={Bulletin De La Societe Geologique De France},
  year={2006},
  volume={177},
  pages={237-247}
}

• L. Emmanuel, M. Renard, +5 authors J. Rey
• Published 1 September 2006
• Environmental Science, Geography
• Bulletin De La Societe Geologique De France

The geochemical events (negative shifts in [sigma]13C and [sigma]18O, and Mn peak) associated with the "Schistes carton" of Quercy (SW France) do not appear to be due only to lithological variations and a differential diagenesis. They correspond to the Lower Toarcian global event and seem to be connected to a destabilization phase of gas hydrates. During its oxidation by seawater, the release of methane gas with a very low carbon isotopic ratio (- 60%) led to the production of CO2 and carbonates with a negative [sigma]13C. The consumption of oxygen in the seawater resulted in conditions that were first dysoxic and then anoxic. The reduction of burrowing and bioturbation associated with this oxidation resulted in the laminated appearance of the "Schistes carton". The decrease in the oxygen content led to a decrease in MnO2 microparticles present in the water column and sediments. This created a complementary source of Mn2+ that was incorporated into the carbonates produced during this event. Furthermore, an increase in the average seawater temperature ([sigma]18O) appears associated with this event. Finally, the apparent diachronism of geochemical events in the Boreal and the Tethyan realms is discussed.