Biotic and stable-isotope characterization of the Toarcian Ocean Anoxic Event through a carbonate–clastic sequence from Somerset, UK

Abstract This study focuses on a condensed sequence of alternating carbonate–clastic sediments the Barrington Member, Beacon Limestone Formation (latest Pliensbachian to early Toarcian) from Somerset (SW England). Abundant ammonites confirm (apart absence Clevelandicum and Tenuicostatum ammonite subchronozones) presence Hawskerense Subchronozone Fallaciosum–Bingmanni subchronozones. Well-preserved, sometimes diverse assemblages ostracods, foraminifera, nannofossils low-diversity dinoflagellate support chronostratigraphic framework. Stable-isotope analyses demonstrate carbon isotope excursion, relating Toarcian Oceanic Anoxic Event, within Toarcian. Faunal, geochemical sedimentological evidence suggest that deposition largely took place in relatively deep-water (subwave base), mid-outer shelf environment under well-mixed water column. However, reduced benthic diversity, weakly laminated changes microplankton assemblage composition Event indicates dysoxic, but probably never anoxic, bottom-water conditions during this event. The onset excursion coincides with extinction benthos, including disappearance ostracod suborder Metacopina. Faunal connectivity Mediterranean region, not previously recorded for UK