Katian (Ordovician) to Aeronian (Silurian, Llandovery) graptolite biostratigraphy of theYD‐1 drill core, Yuanan County, Hubei Province, China

Abstract

AbstractThe graptolite succession of theYD‐1 drill core provides a new view into the lower Silurian (Llandovery) biostratigraphy of the Yichang region on the Yangtze platform of China. A thick succession of black to greenish, fine to silty shales and siltstones with a variable amount of poorly to well‐preserved graptolite faunas ranges from the upper OrdovicianDicellograptus ornatusBiozone (upper Katian) to the lower SilurianLituigraptus convolutusBiozone (mid Aeronian). TheMetabolograptus extraordinarius/Metabolograptus persculptusandAkidograptus ascensus/Parakidograptus acuminatusBiozone intervals are strongly condensed and bear poorly preserved graptolite faunas. A considerable gap can be detected above theCystograptus vesiculosusBiozone, as the succeeding graptolite fauna indicates the upperPribylograptus leptothecaBiozone. The interval of the upper RhuddanianCoronograptus cyphusBiozone to the Lower AeronianCoronograptus gregariusBiozone is missing.Lituigraptus convolutuswas found from 1322.85 to 950.20 m, indicating a thickness of theLituigraptus convolutusBiozone of at least 378.47 m. The age of the highest available graptolite faunas from the 729.40–750.70 m is inconclusive, but the level may still belong to theLituigraptus convolutusBiozone. The correlation of the succession with other successions on the Yangtze platform of China indicates the need for a considerable modification of the graptolite biostratigraphy of the Yangtze platform in the Yichang region and revision of the described faunas. The Llandovery appears to be highly incomplete in the eastern flank of the Huangling anticline and the age of the biostratigraphically younger part of the succession cannot be dated precisely with graptolite faunas.