New insights on the Late Paleocene - Early Eocene dinoflagellate cyst zonation for the Paris and Dieppe basins

Abstract

The Anglo-Belgo-Paris Basin, historical cradle of the Paleogene stratigraphy since the 19th century, is known by the presence of very specific so-called "Sparnacian"deposits (very diverse and laterally highly variable, predominantly lagoonal to terrestrial facies), which encompass the short stratigraphic interval of the Paleocene-Eocene Thermal Maximum (PETM). Due to the insufficient nature of the paleontological record, the "Sparnacian"succession of the Paris and Dieppe-Hampshire basins still needs to be robustly chronostratigraphically correlated with other Paleogene records worldwide. In order to refine the stratigraphy of the Thanetian-Lower Ypresian succession in northern France a number of cores and outcrop sections have been investigated palynologically. As a result, an updated version of the dinoflagellate cyst zonation for the Paris and Dieppe basins is proposed and contains six new or revised biozones for this stratigraphical interval: Alisocysta margarita, Apectodinium hyperacanthum, Apectodinium-acme, Biconidinium longissimum-acme, Dracodinium astra, and Axiodinium lunare/Stenodinium meckelfeldense. Based on combined bio-, litho- and chemostratigraphic data, it appears that the dinocyst assemblages, corresponding to the PETM event interval ("Sparnacian"deposits, Soissonnais and upper Mortemer formations), are characterized by an acme of Apectodinium spp. (70-98%) in both basins, sometimes alternating with an acme of a few gonyaulacoid groups in the Dieppe Basin. Dinocyst assemblages from the PETM interval contain a significant number of atypical, longer specimens of Apectodinium parvum, which could represent an ecological onshore substitute for Axiodinium augustum in the Paris and Dieppe-Hampshire basins. The establishment of a new Biconidinium longissimum-acme Zone suggests that the stratigraphic hiatus previously inferred within this sequence in the Paris Basin does not exist.