The lower–middle Viséan boundary interval in the Palaeotethys: refinements for the foraminiferal zonal schemes

Abstract

A new foraminiferal subzone (Cf5α or MFZ12α) in between the classical foraminiferal zonal biozones is characterized by the first occurrence of Archaediscus at concavus stage, primitive species of Pojarkovella, as well as the first Endothyranopsis s.s. This interval is represented in England, France and Morocco (in the western Palaeotethys) and in South China, and more widely in Iran (in the eastern Palaeotethys), where it is partly similar to the MFZ11B subzone defined by previous authors. The position of this new biozone within the Livian or Holkerian substages suggests that it has to be considered as part of the middle Viséan substage. We therefore propose the abandonment of the notation MFZ11B, which includes lower Viséan rocks, and the subdivision of the middle Viséan zones MFZ12 and Cf5 into two subzones MFZ12α or Cf5α, and MFZ12β or Cf5β, with the latter subzone containing the classical Livian–Holkerian foraminiferal guides Pojarkovella nibelis and Koskinotextularia. Furthermore, the lower Viséan MFZ11 zone can be subdivided in most Palaeotethyan basins into three subzones: a lower MFZ11α subzone (characterized by the first occurrence of Uralodiscus rotundus, as well as most species of Glomodiscus); a middle MFZ11β subzone (characterized by the first occurrence of Archaediscus at involutus stage and Conilidiscus); and an upper MFZ11γ subzone (characterized by the first occurrence of Nodosarchaediscus, Consobrinellopsis and Lituotubella).

A late Asbian (Mississippian) stratotype for England: Trowbarrow Quarry, Cumbria, UK

“…Unfortunately, the specimen from bed d of Strank (1981) is a misidentified Plectogyranopsis settlensis (Conil & Longerstaey in Conil et al ., 1980), which is first recorded from the upper part of the Arundian or early Visean (Cózar et al . 2020 a ).…”

A reassessment of Arundian–Holkerian (Viséan) carbonates in South Cumbria, UK

“…However, the foraminiferal-defined base of the Holkerian in the Barker Scar section has now been revised (Cózar et al, 2022), demonstrating that the microfauna previously proposed by George et al (1976), Conil et al (1980, Ramsbottom (1981), Strank (1981) and Fewtrell et al (1981), as well as other worldwide middle Viséan taxa (Cózar et al, 2020a), first occur in much lower levels in the Barker Scar section, at bed C. Cózar et al (2022), proposed to reposition the base of the Holkerian to coincide with the foraminiferal markers at bed C in the upper Dalton Formation, thereby, giving the base Holkerian a robust international correlation with the middle Viséan. The alternative position of maintaining the base of the Holkerian at bed K is problematic, since there are no fossil markers to recognise it beyond Barker Scar.…”

“…Thus, Forschiella prisca is considered also a valid guide for the Cf4γ subzone. This subzone is equivalent to the MFZ11β of Cózar et al (2020a).…”

Foraminifers in upper Viséan–lower Serpukhovian limestones (Mississippian) from South Wales: regional correlation and implications for British foraminiferal zonal schemes

“…Thus, in summary, the foraminiferal data suggests that the Stormy Limestone Formation in South Wales reached the highest level of the Holkerian substage, the Cf5β subzone of Cózar et al (2020).…”

“…Another group of transitional forms with important biostratigraphic implications are those within the evolutionary stages in Archaediscus. Thus, the transitional forms between the involutus and concavus stages (with some whorls at concavus stage), first occur from the top of the early Viséan (Cf4δ or MFZ11γ subzones; Cózar et al 2020).…”