Marnes de Berrias

Marnes de Berrias is a lithostratigraphic unit of marl and marly limestones located in southeastern France, marking strata near the Jurassic–Cretaceous transition. The formation has been described in regional studies by geologists associated with institutions such as the Muséum national d'Histoire naturelle, the Société Géologique de France, and researchers from the Université Pierre et Marie Curie, and has been compared with contemporaneous units in the Basque Country, Portugal, and the United Kingdom. It is notable in debates on chronostratigraphy involving the International Commission on Stratigraphy, the definition of the Berriasian stage, and correlations with the Tithonian and Valanginian stages.

Geology

The formation consists predominantly of marls interbedded with marly limestones and includes horizon markers used in regional tectono-sedimentary reconstructions by teams from the Centre National de la Recherche Scientifique, the CNRS UMR, and field parties linked to the BRGM. Studies reference structural controls from Hercynian and Alpine reactivation documented in the Alps, Massif Central, and along the Rhone Valley. Petrographic analyses have invoked techniques developed at the University of Montpellier, while geochemical work has been undertaken using facilities at the Collège de France and laboratories collaborating with the European Geosciences Union. The succession records changes in depositional environments contemporary with global events discussed in syntheses by the International Ocean Discovery Program, the Paleobiology Database, and authors publishing in journals like Geobios and Palaeogeography, Palaeoclimatology, Palaeoecology.

Stratigraphy

Stratigraphic frameworks for the unit reference biostratigraphic data anchored to ammonite zonation established by researchers from the Natural History Museum, London, the Universität Tübingen, and the Universidad Complutense de Madrid. Correlations have been proposed between horizons within this unit and the standard ammonite zones used across the Tethys Ocean realm, with crosschecks against magnetostratigraphic work by teams at the University of Oxford and isotope stratigraphy datasets curated by the Scripps Institution of Oceanography. The unit is integrated into regional chronostratigraphic charts assembled by the International Commission on Stratigraphy and compared with sections from the Portuguese Lusitanian Basin, the Basque-Cantabrian Basin, and the English Channel coastlines near Dorset.

Paleontology

The fossil record includes marine invertebrates and microfossils documented by paleontologists affiliated with the Muséum national d'Histoire naturelle, the Natural History Museum, London, and the Institut de Paléontologie. Notable taxa reported from the succession have been discussed in systematic treatments alongside collections from the National Museum of Natural History, Washington, the Smithsonian Institution, and comparative faunas from the Solnhofen and Holzmaden Lagerstätten. Ammonite assemblages used for zonation link to faunal lists compiled by researchers at the University of Paris, the Université de Pau et des Pays de l'Adour, and the University of Lyon. Microfossil studies, including foraminifera and ostracods, have involved collaborators from the University of Barcelona and the Vrije Universiteit Amsterdam, while palynological analyses have been carried out with contributions from the University of Copenhagen and the University of Bergen.

Geographic distribution

Exposures occur primarily in the Ardèche region and the historic province of Vivarais, with additional occurrences mapped near the Haute-Loire and along margins of the Massif Central. Field surveys and mapping projects by the BRGM and regional geological services document surface and subsurface continuity with units in the Languedoc and contacts toward the Rhone Valley basins. Outcrops accessible to researchers and visitors have been recorded in regional guides produced by the Conseil Général and academic field courses run by the Université Joseph Fourier and the University of Montpellier II.

Economic and scientific significance

Although not a major resource unit like neighboring carbonate reservoirs exploited by energy companies such as TotalEnergies or quarrying enterprises operating in the Provence-Alpes-Côte d'Azur region, the formation holds local importance for construction materials and soil studies consulted by regional planners and agencies including the Ministry of Ecological Transition. Scientifically, it provides critical data for resolving the Jurassic–Cretaceous boundary debated within panels of the International Commission on Stratigraphy and in high-profile syntheses published by the Geological Society of London and the American Geophysical Union. Ongoing multidisciplinary research continues through collaborations with the European Union research programs, university consortia, and museum collections such as those at the Muséum d'histoire naturelle de Lyon.

Category:Geologic formations of France Category:Jurassic stratigraphy Category:Cretaceous stratigraphy