Conodonts across the Devonian/Carboniferous boundary in SE Sardinia (Italy)

摘要

The Bruncu Bullai section, located in SE Sardinia, exposes limestones from the styriacus Zone (upper Famennian) to the Upper duplicata Zone (Tournaisian), but the Upper praesulcata Zone is not documented; at the Devonian/Carboniferous boundary a black shales level, equivalent to the Hangenberg Shales, is present. Fifty-six conodont taxa were recovered, three of which are here described as new species: Polygnathus bicristatus, Po. nuragicus, Pseudopolygnathus granulobatus; two more species, probably new, are described, but left in open nomenclature because of the low number of specimens collected. The relative high abundance of Protognathodus and low abundance of Siphonodella in some levels and the opposite in others is discussed, and a new hypothesis on the occurrences of protognathodids as influenced by ecological factors is suggested. The early phase of the Hangenberg crisis is testified by a faunal turnover in an impoverished fauna within the deposition of limestones of the Lower praesulcata Zone.