Benthic foraminiferal assemblages record major environmental perturbations during the Late Pliensbachian–Early Toarcian interval in the Peniche GSSP, Portugal

Abstract

This is the first ecostratigraphic and palaeoecological analysis of the benthic foraminiferal assemblages, defined as morphogroups, in the Pliensbachian–Toarcian transition and the Toarcian Oceanic Anoxic Event (T-OAE) of the Peniche section, the Toarcian Global Boundary Stratotype Section and Point. Foraminiferal assemblages from the uppermost Pliensbachian (Emaciatum Zone) reveal the presence of a stable benthic environment, with good oxygen and availability of trophic resources, as evidenced by the high diversity of specialists. The Pliensbachian–Toarcian transition reveals high foraminifera abundance, mainly specialists, although it is considered a slightly condensed interval. The base of the Levisoni Zone shows dramatic changes in life-style of foraminifera (increase of epifauna and potentially deep infauna), an increase in opportunistic forms, and a decrease in diversity. These changes suggest unfavourable conditions, related to food availability diminution and depleted oxygenation, corresponding to the beginning of the δ13C negative excursion. Palaeoenvironmental conditions become severe in the lower to middle Levisoni Zone, where there is a barren interval for foraminifera, coincident with the highest values of total organic carbon. After this interval, foraminiferal assemblages experienced a recovery with increasing diversity and occurrence of specialists, consistent with a well oxygenated environment and good food availability. These changes observed in benthic foraminiferal fauna from the Peniche section through the uppermost Pliensbachian–Lower Toarcian are comparable to what was reported previously on ostracods, brachiopods and calcareous nannofossils. Foraminiferal assemblages from Peniche section are comparable to other Tethyan (Spain, Italy, North Africa) and NW European sections (England) from the same stratigraphic interval, with the suborder Lagenina dominating the assemblages.