Foraminiferal assemblages and geochemical proxies for interpreting the impact of the early Toarcian Oceanic Anoxic Event in the Lusitanian Basin (Rabaçal section, Portugal)

Abstract

This work pretends to evaluate the influence of the Toarcian Oceanic Anoxic Event (T-OAE) on the foraminiferal assemblages from the Rabaçal section (Lusitanian Basin, Portugal) through a geochemical proxies analysis. Polymorphum – Levisoni zones boundary (early Toarcian) records a high productivity event, indicated by increased values of Ba/Al and P/Ti ratios and total organic carbon. The lower part of the Levisoni Zone (around 7 m) is marked by a negative carbon isotopic excursion, coincident with a biotic crisis phase for benthic foraminifera (low abundance and diversity). Redox proxies, such as U/Th, Mo/Al and Ni/Al, increase just in this interval indicating depleted oxygen conditions. After this interval, geochemical proxies, stable isotopes and foraminiferal data return to values equivalent to those of the Polymorphum Zone, suggesting a recovery from the stress conditions related with the T-OAE. This trend is similar and comparable to the trend observed in the Peniche reference section (Lusitanian Basin) but also with other Tethyan and NW European sections.