DINOCYSTS AND NANNOFOSSILS FROM THE MARNES DE DONZACQ, BASAL LUTETIAN (MIDDLE EOCENE) OF SOUTHWESTERN FRANCE

The Marnes de Donzacq are dark gray to blue clays deposited under circalittoral to bathyal conditions. The outcrop studied here, the Saint-Geours claypit, corresponds to the deepest setting.

The occurrence of the nannofossil Blackites inflatus in all samples studied indicates that the section is of Lutetian age: the lowest occurrence of this species is the biostratigraphic criterion selected to define the Global Stratotype Section and Point (GSSP) for the base of the Lutetian stage in the Gorrondatxe section, Northern Spain (Molina et al. 2001).

The palynological assemblages are rich, varied and well preserved. They are characterized by the high frequency of Cleistosphaeridium diversispinosum.

The main dinocyst datums recorded in the section are the following:

The Wetzeliellaceae are represented mostly by Wetzeliella articulata and Charlesdowniea tenuivirgula. Typical Ypresian taxa such as Charlesdowniea columna or Wetzeliella meckelfeldensis were not recorded, in line with their extinction in the Early Eocene (Williams et al. 2004).

• The highest occurrence of representatives of the genus Eatonicysta was recorded at the base of the section. This event is calibrated at 48.5 Ma in the Northern Hemisphere mid-latitudes (Williams et al. 2004).
• Areosphaeridium diktyoplokus group is scarce. The base of this species is calibrated at 48.5 Ma in the Northern Hemisphere mid-latitudes, i. e. in the upper part of the Ypresian (Williams et al. 2004).
• The highest occurrence of Damassadinium impages was recorded in the lower part of the section.
• Representatives of the genus Distatodinium (D. cf. ellipticum) are present throughout the section.
• The earliest members of the genus Wilsonidium have their lowest occurrence in the upper part of the section.

Selected dinocyst and nannofossil taxa are illustrated and a comprehensive dinocyst range chart provided.

References

Molina E., Alagret L. et al. 2011. The Global Stratotype Section and Point (GSSP) for the base of the Lutetian Stage at the Gorrondatxe section, Spain. Episodes Vol. 34 N° 2.

Williams G. L., Brinkhuis H. et al. 2004. Southern Ocean and Global Dinoflagellate cysts events compared: index events for the Late Cretaceous-Neogene. In: Exon N. F. et al.(Eds). Proc. ODP, Sci Results, 189.