Molecular fossils of Aptian–Albian blue marls of the Vocontian Basin (France), depositional conditions and connections to the Tethys Ocean

Abstract

The Mesozoic witnessed some episodes of marked accumulation and burial of organic matter (OM) in the Tethys Ocean and satellite basins, such as the Vocontian Basin (SE-France). These famous episodes, termed Oceanic Anoxic Events (OAEs), resulted from various factors, acting in complex synergies; the consensus about the key factors has not been reached yet. The Aptian–Albian Blue Marls Formation (Fm.) of the Vocontian Basin recorded the various substages of OAE1, plus additional organic-rich levels of regional extension. The semi-pelagic marlstones of the Blue Marls Fm. allow to carry out a detailed examination of the molecular fossils, to assess the respective weights of the factors involved in the OM storage process. In this work, we examined the lipid biomarkers of six organic-rich levels ranging from the Goguel Level to the Paquier Level in stratigraphic order. Biomarkers reputed to be characteristic of some OAEs are observed here: 2-methylhopanoids in the Goguel Level (OAE1a) and archaeal lipids in the Jacob, Kilian and Paquier Levels (OAE1b). This study shows that, in the Vocontian Basin, OM deposition resulted mostly from local factors and that each level has its own peculiarities; however, overarching connections with the Tethys Ocean were critical for the recording of global anoxic events.

Keywords

• Vocontian basin
• Organic matter
• Lower Cretaceous
• OAE1a
• OAE1b
• Biomarkers