Hangenberg Black Shale with cymaclymeniid ammonoids in the terminal Devonian of South China

Abstract

The Hangenberg Crisis at the end of the Devonian is marked by a sudden global mass extinction (main Hangenberg Event), which was especially severe for ammonoids. Among the order Clymeniida, only the cymaclymeniids survived for a short time. We report the first discovery of Postclymenia cf. evoluta in South China in equivalents of the Hangenberg Black Shale (the regional Changshun Shale) at the Jiarantang section in Guizhou. The South China plate was far away and completely different from the Euramerica continent, where the Hangenberg Event/Crisis was first recognised. The presence of similar ammonoids as in contemporaneous beds of the Rhenish Massif, Germany, suggests close faunal relationship through the Palaeotethys Ocean. It agrees with a sudden spread of opportunistic extinction survivors with the initial Hangenberg Transgression. The regional facies and faunal succession at Jiarantang confirms previous concepts of a eustatically driven, significant transgressive-regressive couplet in the lower/middle crisis interval. The near-global distribution of cymaclymeniid survivors shows that their extinction at the end of the extended crisis interval must have been caused by a so far neglected, small-scale global extinction event in the open marine realm.