Integrated isotope and biostratigraphy of a Lower Cretaceous section from the Bakony Mountains (Transdanubian Range, Hungary): A new Tethyan record of the Weissert event

Abstract

An integrated stratigraphic subdivision, on the basis of ammonites, belemnites, calpionellids and stable isotope ratios is proposed for the Lower Cretaceous carbonate succession of the Hárskút, Közöskút Ravine profile (HK-12), (Bakony Mts, Hungary). Abundant and diverse cephalopod assemblages occur in middle and late Berriasian Rosso Ammonitico facies, in a nearly complete sequence spanning the Tirnovella occitanica and Fauriella boissieri Zones. A new belemnite species, Duvalia hungarica, is described from this level. The overlying Lower Valanginian strata are condensed, but also yield rich assemblages of the Thurmanniceras pertransiens and Busnardoites campylotoxus Zones. The cephalopod fauna of the Late Valanginian Saynoceras verrucosum Zone is much less diverse. The overlying 19 m interval of Biancone-type marl yielded no megafossils. The uppermost part of the profile late Hauterivian cephalopods were found. Stable isotope analysis shows a well-defined positive δ 13C excursion in the Valanginian strata, identified for the first time in Hungary. Although correlated with a possible anoxic event (known as ‘the Weissert event’), as in many other sections, no black shale or organic-rich level is recorded at Hárskút.