New mineralogical and organic carbon-isotope data from the Tithonian of Boulonnais (France) – relationship with the VOICE

Authors

  • Jean-Francois Deconinck Université Bourgogne Europe, UMR 6282, Biogéosciences, 6 Boulevard Gabriel, 21000 Dijon
  • Francis Amédro 26 rue de Nottingham, 62100 Calais
  • Jacek Grabowski Polish Geological Institute – National Research Institute, Rakowiecka 4, 00-975 Warsaw

Keywords:

Tithonian, Jurassic/Cretaceous boundary, VOICE (VOlgian Isotope Carbon Excursion), global correlation, northern France

Abstract

As part of the research initiated by the Berriasian Working Group, we have conducted a detailed study of the Tithonian sedimentary successions of Boulonnais (northern France), given their interest as being deposits which are contemporaneous with the Kimmeridge Clay Formation (KCF) of Dorset (southern England), but situated in more proximal environments on the edge of the London-Brabant massif. The determination of d13Corg highlights a negative excursion of approximately –2‰ which probably corresponds to the VOICE (VOlgian Isotope Carbon Excursion). The chemostratigraphic data were correlated with the Geologic Time Scale using a compilation of orbital and magnetic stratigraphy. As in the KCF, the onset of this negative excursion occurs in the Pallasioides Zone (M21r to lower M21n). Further, a detailed study of the clay mineralogy shows an increase in the proportion of smectite at the expense of illite and kaolinite in the Albani Zone (M20r to lower M20n), which correlates with the lower part of the middle Volgian. This widespread mineralogical change marks the onset of the period of significant aridification which characterizes the Jurassic/Cretaceous boundary interval regionally. The onset of the aridification phase was nearly synchronous with, or slightly preceded the paleoceanographic changes in some Tethyan basins including the Nannofossil Calcification Event, stratification of water masses, and trace metal enrichments. All these environmental changes in the Alpine Tethys took place around the early/late Tithonian boundary, in the early M20n magnetochron.

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Published

2025-10-22

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