Refined conodont stratigraphy at Martenberg (Rhenish Massif, Germany) as base for a formal middle/upper Frasnian substage boundary

AbstractThe famous Martenberg section of the eastern Rhenish Massif, Germany, type-section of classical Frasnian goniatite and conodont zonations, has been restudied in order to document the microfacies development and to refine the conodont stratigraphy around the globalsemichatovaeEvent/Transgression, the proposed level to define a future upper Frasnian substage. More than 8.000 platform elements were identified and include new taxa.Palmatolepis jamieaeis subdivided into the subspeciesPa.jamieae jamieae,Pa.jamieae savagein. ssp.,Pa. jamieae rosan. ssp., andPa. jamieaessp. δ. Another new species,Pa.adorfensisn. sp., was previously partly identified asPa. jamieae, whilePa. descendensn. sp. has previously been described in open nomenclature from Inner Mongolia. Morphotypes are defined inIcriodus symmetricus, Pa. ljaschenkoae, andPa. proversa. A global literature survey shows that the eustaticsemichatovaeEvent can be recognised in more than 20 regions of all continents with (sub)tropical Upper Devonian outcrops. At Martenberg, the transgression is preceded by a thin but distinctive interval with unconformities, microbial mats, sheet cracks, and currents that brought in the regionally youngest volcaniclastics. The new conodont data confirm that no typicalPa. jamieae(sensu the holotype) occur in the two beds originally supposed to represent thejamieaeZone in its reference section. We fully support the conclusion of Ovnatanova and Kononova (2020) that thejamieaeZone should be abandoned. EarlyPa. jamieaesubspecies and the related new taxa enter at Martenberg and in a few other regions in the globally easily recognisable Frasnian Zone 10 (=planaZone). Frasnian Zone 11 (feistiZone) is subdivided into subzones FZ 11a (=feistiSubzone) and FZ 11b (=nasutaSubzone). The base of the latter coincides with thesemichatovaeTransgression, thesemichatovaeSubzone of more shallow shelf settings, and is proposed to define in future the upper Frasnian substage base. On a global scale, the Martenberg section is currently the best bed-by-bed documented section for facies changes, conodont and goniatite biostratigraphy at the middle/upper Frasnian transition. Therefore, it is a prime candidate for a future GSSP selection. A global literature survey identified more than 20 other pelagic conodont successions that have the potential for precise correlation and a better understanding of the environmental changes associated with thesemichatovaeEvent.