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Geochemical Variability |
1 Ecole des Mines—Centre SPIN, 158 cours Fauriel, F 42023 St-Etienne, France
2 Institut Français du Pétrole, Géologie-Géochimie, 1 avenue de Bois-Préau, F 92506 Rueil Malmaison, France
3 UMR CNRS, 6524
The deep marine Grès d’Annot Formation is one of the best exposed analogues to sand-rich turbidite sub-surface systems. Provenance and reservoir heterogeneities have been investigated through a geochemical study of different areas and facies in this formation. Most compositions may be described as mixtures between carbonate and three clastic end-members, i.e. clay, framework grains and a subset of the heavy minerals (zircon, Tioxide, apatite, monazite). These end-members have a nearly uniform chemistry over the studied area and a granite-dominated provenance consistent with a Corsica-Sardinia source hypothesis. This rather uniform provenance makes the Annot Formation a favourable case for exploring the relationships between facies and geochemistry. Not only do different facies differ in average composition, but chemical variations at the bed scale fingerprint the depositional mechanism: archetypal (graded) turbidites and traction-dominated (over-bank) deposits display contrasting variation trends in geochemical plots. The local-scale variation patterns and the general relationship between grain size and chemistry are tentatively integrated in a single differentiation model, providing a rationale for the use of geochemistry in provenance studies, and a possible way to characterize sedimentary facies.
