Phytoplankton (acritarch) community changes during the Permian-Triassic transition in South China

Abstract

The Permian-Triassic boundary (PTB) at ~252 Ma coincided with the largest mass extinction of the Phanerozoic. Previous research on diversity and abundance changes during this event has focused mainly on the terrestrial vertebrate and marine invertebrate records, with little attention to date given to the phytoplankton that form the base of the marine trophic web. Although the fossil record of Permian-Triassic phytoplankton is relatively poor owing to preservational factors, sufficient material is now available to evaluate secular changes in acritarch communities through the mass extinction interval. In this contribution, we evaluate diversity and abundance changes among 8 genera and 25 species of acritarchs, including large-spherical, small-spherical, long-spined, and short-spined forms ranging from the Upper Permian Clarkina yini to the Lower Triassic Isarcicella isarcica zones in eight sections representing different sedimentary facies of the South China Craton. Acritarchs declined sharply from the latest Permian (C. meishanensis Zone) to the earliest Triassic (I. staeschei Zone), with extinctions and abundance changes concentrated at two horizons, the first in the latest Permian C. meishanensis Zone (Bed 25 at Meishan D) and the second in the earliest Triassic I. staeschei Zone (Bed 28 at Meishan D), mirroring the pattern of mortality among marine invertebrates. Differences in the nature and intensity of these two extinction episodes (the second having a relatively larger effect on acritarch community composition) suggest that these events may have resulted from different types of environmental perturbations.