Albertiana Working Group Report : The case for the Global Stratotype Section and Point (GSSP) for the base of the Norian stage

Hounslow, Mark W (2021) Albertiana Working Group Report : The case for the Global Stratotype Section and Point (GSSP) for the base of the Norian stage. Albertiana, 46. pp. 25-57. ISSN 0169-4324

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Abstract

The Norian Stage is the longest stage in the Phanerozoic, and consequently it is important to define its base precisely for chronostratigraphy with a global stratotype section and point (GSSP). Previous work over many decades has indicated two possible candidate sections at Black Bear Ridge (British Columbia, Canada) and Pizzo Mondello (Sicily, Italy). Based on prior datasets the working group evaluated the global correlation potential of the two proposed primary markers, the conodont Metapolygnathus parvus and ‘flat-clam’ Halobia austriaca. We also evaluated secondary markers for these boundary datums for correlation, and the veracity of the proposed sections for GSSP status. The factual data and arguments for the proposed sections and datums are presented here. Through a two-stage process of option elimination in a voting process conforming with ICS guidelines, the working group decided by 60% majority to propose that the first occurrence datum (FAD) of Halobia austriaca in the Pizzo Mondello section at the base of bed FNP135A should become the ‘golden spike’ for the Norian. A secondary biotic marker for this boundary is the FAD of Primatella gulloae, in sample NA43, ca. 0 m below FNP135A and the FAD of Dimorphites noricus (sample NA42.1) ca. 3.5 m above bed FNP135 (indicating first subzone of the Jandianus Zone). The best physical secondary marker is magnetozone PM5n with the proposed boundary ca.40% from the base of PM5n. The strengths of this choice are that it also mains historical priority for ammonoid zonations, which placed the base Norian near to this level in Europe, North America and probably NE Asia, and Halobia austriaca is widely distributed in all paleolatitudes and is well established taxon.