Paleontology and Microfacies of the Serpukhovian in the Verkhnyaya Kardailovka Section, South Urals, Russia: potential candidate for the GSSP for the Visean-Serpukhovian boundary

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A uniquely complete carbonate sequence spanning a large portion of the Visean and the entire Ser- pukhovian is exposed on the Ural River, opposite the village of Verkhnyaya Kardailovka (South Urals, Bashkortostan, Russia). The Upper Visean and Serpukhovian beds in this section are composed of deep- water carbonates containing ammonoids, conodonts, ostracodes and foraminifers. The section is well-sampled, measured, its lithology is now described, and a sedimentary environment near the seaward end of a carbonate platform and deep shelf is suggested. Abundant fossils allow the recognition of four successive ammonoid and four successive conodont zones, which allow reliable correlations of the regional Serpukhovian stages outside the South Urals, although the type section of the Serpukhovian in the Moscow Basin is in the shallow-water facies. The base of the Serpukhovian in the Moscow Basin and in the South Urals is defined by the first ap- pearance datum (FAD) of the conodont Lochriea ziegleri. This level coincides with the base of the Koso- gorskian in the Urals, correlates with the entry of the foraminifer Millerella tortula near the base of the Taru- sian in the Moscow Basin and is close to the earliest occurrences of Dombarites paratectus and Cravenoceras at the base of the Uralopronorites-Cravenoceras Genozone and of the latter genus at the base of the British E1 Zone. Because of its accessibility, abundant fossils, and its well studied lithology, the Verkhnyaya Kar- dailovka Section is an excellent candidate for the GSSP of the Visean-Serpukhovian boundary.