An expanded lower Eocene shelf sequence from the eastern Aquitaine Basin, SW France: biostratigraphy, biofacies, and stable carbon and oxygen isotopes

Abstract

Abstract. The early Eocene is characterized by a succession of orbitally-controlled global stable carbon isotope excursions, with some being linked to climatic and related biotic perturbations. The impact of these isotopic excursions has been primarily studied in deep-sea sections under comparably stable conditions. In order to investigate the impact of global post-PETM isotopic signals on shallow marine settings, the Ypresian neritic ʻBlue Marls' of the Corbières (SW France) were investigated. High-resolution records of microfossil biota and stable carbon and oxygen isotopes pinpoint biostratigraphic, paleoecologic and geochemic constraints. Calcareous nannofossil biostratigraphy positions the sequence in the upper part of zone NP11, possibly ranging into basal NP12, which is conformable with larger benthic foraminifera data indicating shallow benthic zone SBZ8. This implies a time span of about 0.4 Myr and high overall sedimentation rates of about 32 cm/kyr for the section. A shallowing upward trend from outer neritic to coastal settings is observed in the development of the lithostratigraphy and the microfossil assemblage. The assemblages can be subdivided in seven larger biofacies and four ostracod assemblage zones. The lower third of the section is characterized by strongly fluctuating and partly high plankton/benthos-ratios for neritic settings. A final pronounced peak in plankton occurrence is associated with strong decrease of benthic biota, suggesting anoxic conditions in the outer neritic environment. Several local negative δ 13 C-and δ 18 O-excursions can be identified in the section. The upper, most pronounced and consistent negative δ 13 C excursion is tentatively linked to global carbon isotope excursion K (ETM3) based on the biostratigraphic constraints.

Early Eocene environmental development in the northern Peri-Tethys (Aktulagay, Kazakhstan) based on benthic foraminiferal assemblages and stable isotopes (O, C)

“…3). Ages in this paper are based on the Geologic Time Scale of the Paleogene (Vandenberghe et al, 2012), with corrections on the ages of the nannoplankton zones by Pirkenseer et al (2013). Ages are inferred from bio-and chemostratigraphic correlation (Fig.…”

A diverse crinoid fauna (Echinodermata, Crinoidea) from the Lower Eocene of the Gulf of Languedoc (Corbières, Aude, southern France)

“…It lies 90 meters below the first emersion indices reported by Plaziat (1964), which corresponds to a thickness of decompacted sediment of >150 meters. In the section studied by Pirkenseer et al (2013), it corresponded approximately to the uppermost strata in which planktonic foraminifera substantially predominated over benthic ones, and at the upper limit of the "outer neritic" biofacies with the ostracod Krite angusta. With reference to biotopes inhabited by the extant Democrinus japonicus, we can predict a depth of at least 140 meters for the environment corresponding to the sites with P. lavadensis n. sp.…”

“…The onset of the Ilerdian transgression is placed in biozone NP9 (Yans et al 2014). Pirkenseer et al (2013) noted that, to the south of Pradelles-en-Val, 130 meters of middle blue marls belonged to biozone SBZ8 and the upper part of biozone NP11, with the transition to the SBZ9 and NP12 biozones situated in the upper blue marls. From this, we deduce that the crinoid sites within the lower blue marls, still deposited later than the formation of the Solenomeris bioconstructions, correspond to biozone NP10 and the lower part of NP11, and that the younger sites (i.e., Lavade-Fontcouverte and La Côte-Moux) belong to the upper part of NP11.…”

“…From this, we deduce that the crinoid sites within the lower blue marls, still deposited later than the formation of the Solenomeris bioconstructions, correspond to biozone NP10 and the lower part of NP11, and that the younger sites (i.e., Lavade-Fontcouverte and La Côte-Moux) belong to the upper part of NP11. The entire series may reach a thickness of 500 to 550 meters, deposited over a period of ~3 to 5 million years, which implies rapid subsidence at least during transgression and a high sedimentation rate estimated, on average, at ~32 cm/kyr by Pirkenseer et al (2013) during the final stage of infill of the bay. The available space required to accumulate this series finds its origin not only from a rise in global sea level, in part related to the thermal optimum (PETM), but also from large wave tectonic deformations (Plaziat 1984b;Plaziat and Perrin 1992).…”