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Occurrence of fossil organic matter in modern environments: Optical, geochemical and isotopic evidence
Authors:Y Graz  C Di-GiovanniY Copard  M ElieP Faure  F Laggoun DefargeJ Lévèque  R MichelsJE Olivier
Institution:a ISTO, Université d’Orléans/Université François Rabelais de Tours, CNRS/INSU UMR 6113, 1A rue de la Férollerie, 45072 Orléans, France
b M2C, UMR 6143 CNRS/Université de Rouen, place E. Blondel, Bat. Irese A, Université de Rouen, 76821 Mont Saint Aignan Cedex, France
c G2R UMR 7566 CNRS/Université Henri Poincaré, BP 239, 54506 Vandœuvre-lès-Nancy Cedex, France
d UMR A111 INRA/Université de Bourgogne - GéoSol, 6 bd Gabriel, 21000 Dijon, France
e CEMAGREF, Grenoble, Unité de recherche ETNA, BP 76, 38402 Saint Martin d’Hères, France
Abstract:This study relates to the input and fate of fossil organic matter (FOM) in the modern environment, and focuses on two experimental watersheds overlying Jurassic marls: Le Laval and Le Brusquet (1 km2 in area), located near Digne, Alpes-de-Haute-Provence, France. Considering that FOM delivery is mainly a result of different processes affecting sedimentary rocks (bio)chemical and mechanical weathering], samples from different pools were collected: bedrocks, weathering profiles, soils and riverine particles. The samples were examined using complementary techniques: optical (palynofacies methods), geochemical (Rock-Eval 6 pyrolysis, C/N ratio), molecular (gas chromatography/mass spectrometry) and isotopic (stable C isotopic composition). As a result, FOM markers were identified and tracked through the different pools. The results highlight the contribution of FOM, which can be found in all the studied pools. Transfer of FOM between bedrocks/weathering profiles (governed mainly by chemical weathering) and bedrocks/riverine particles (governed mainly by mechanical weathering) reveals any qualitative change. Weathering profiles/soils transition governed by (bio)chemical weathering] is characterized by alteration of the FOM, which is difficult to describe because fossil material is mixed with recent organic matter (ROM). Despite this latter point, the study provides evidence for a relative resistance of FOM to weathering processes and points to its contribution to the modern geosystem and the C cycle.
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