Integrated stratigraphy and paleoenvironmental reconstruction of the Miocene series of the Châteauredon Dome, S.E. France

Abstract

This study presents the results of a palynological analysis (dinocysts, spores and pollen) that are discussed with those obtained from stable isotopes geochemistry (δ13C and δ18O) on Miocene coastal and continental deposits in the southern area of the Digne Valensole Basin. Palynology study has been conducted on dark levels while isotopic analysis was performed on paleosol carbonate nodules. Stratigraphic attributions based on palynology are restricted to dinoflagellate cysts associations as spore and pollen assemblages are scarcely identified. They confirm the stratigraphy based on the micromammal fossil sites and propose an Aquitanian to early Serravallian age. From a selection of ODP-DSDP sites, the marine δ13C chemostratigraphy shows several characteristic isotopic intervals. These were also identified on the continental signal from the paleosols. Stratigraphic interpretation from the isotopic continental signal is in good agreement with both palynological data and micromammal sites attributions. It can offer a high resolution correlation, a few 100 kyr when paleosols are frequent and δ13C fluctuations significant. The method puts also in evidence hiatuses (during middle Aquitanian and late Burdigalian) and precise the age of formations interbedded between micromammal sites. Regarding paleoenvironmental reconstruction, the palynological study is more efficient than isotopic data and shows a flora evolution from mesothermic riparian and coastal vegetation during Aquitanian/Burdigalian to herbaceous and more open vegetation during the Langhian period in association to a drier and warmer climate. This study brings also new insights on paleogeographic reconstructions. The studied area was located close to the sea coast during the lower Miocene. Marine incursions occurred during the middle Aquitanian and from late Burdigalian to early Serravallian. These are characterized by tidal facies as well as dinoflagellate cysts and benthic foraminifera occurrences. These marine incursions, better recorded in the eastern part of the Châteauredon Dome, argued for a northern or a southern connection with the Miocene sea in relation to the foreland basin geodynamic evolution.