Widespread chemical remagnetization: Orogenic fluids or burial diagenesis of clays?

Paleomagnetic, rock magnetic, and geochemical results from Mesozoic carbonates in the Vocontian trough in southeast France support a hypothesized acquisition of a chemical remanent magnetization (CRM) during burial diagenesis of smectite and are inconsistent with an orogenic fluid remagnetization mechanism. The geographic and vertical distribution of a widespread CRM, which resides in magnetite, is parallel to the degree of burial diagenesis of clays. The CRM is absent only where there is no evidence for clay diagenesis. The CRM is poorly developed where significant smectite is still present and is well developed with higher natural and anhysteretic remanent intensities where smectite has completely altered to illite. Strontium isotope results do not support alteration by orogenic-type fluids, a commonly invoked mechanism for similar CRMs. The results suggest that the burial diagenesis of clays is a viable remagnetization mechanism for limestones in the Vocontian trough.