Late Ordovician microphytoplankton in Southwest China: recording paleogeographic variations across the Hirnantian glaciation

Abstract

Paleogeographically, South China was located near the equator during Late Ordovician–early Silurian. Well developed graptolite zones and shelly fauna of upper Ordovician successions in South China correlate well with those from Katian and Hirnantian successions elsewhere in the world. We report here acritarch assemblages from the Katian black shales of the Wufeng Formation in the Lingfeng coal section, southeastern Sichuan, and from the Hirnantian carbonate rocks of the Kuanyinchiao Formation in the Yanzikou section of northwestern Guizhou and the Huanggexi section of northeastern Yunnan. This study provides the first description and biostratigraphic data of the acritarch assemblage of the Hirnantian Kuanyinchiao Formation in South China, and enables the interpretation of paleogeographic and paleoenvironmental changes during the major glaciation of the latest Ordovician in South China. These acritarch assemblages represent the microphytoplanktonic communities of preglacial, Hirnantian glacial and postglacial in South China. Two new species, Multiplicisphaeridium pugnusum n. sp., and Perissolagonella irregular n. sp., are described.