The case for the Global Stratotype Section and Point (GSSP) for the base of the Norian stage

The Norian Stage is the longest stage in the Phanerozoic, and some members of the boundary working group have been evaluating suitable Carnian-Norian boundary sections for roughly two decades. This has identified two possible candidate boundary sections, at Black Bear Ridge (British Columbia, Canada) and Pizzo Mondello (Sicily, Italy). After a formal voting procedure within the working group, ending on the 26th July, 2021, the Pizzo Mondello section was selected as the global stratotype section and point for the base of the Norian. We evaluated the global correlation potential of the two proposed primary markers, the conodont Metapolygnathus parvus and the ‘flat-clam’ Halobia austriaca. Secondary markers were also evaluated around these boundary datums for correlation potential, and the veracity of the proposed sections for GSSP status. Data and arguments for the proposed sections and datums are presented here. Through a two-stage process of option elimination in voting, conforming with ICS guidelines, the working group decided by 60% majority to propose that the first occurrence datum of Halobia austriaca in the Pizzo Mondello section at the base of bed FNP135A should become the ‘golden spike’ for the base of the Norian. A secondary biotic marker for this boundary is the first occurrence of Primatella (Carnepigondolella) gulloae, in sample NA43, ca. 0 m below FNP135A, and the FA of Dimorphites noricus (sample NA42.1) ca. 3.5 m above bed FNP135 (indicating the first subzone of the Jandianus Zone). The best physical secondary marker is the magnetozone PM5n with the proposed boundary ca.40% through the thickness of PM5n. Strengths of the chosen datum are: 1) it also maintains historical priority for ammonoid zonations, which had placed the base Norian near to this level in Europe, North America and probably NE Asia; 2) Halobia austriaca is widely distributed in all paleolatitudes and is a long-established taxon.