Abstract: Hirnantian (latest Ordovician) rocks and fossils have still not been sufficiently documented in the western Yangtze region of South China (today’s southwestern Sichuan and northeastern Yunnan provinces, Southwest China). Compilation of published and new data results in refined Hirnantian stratigraphy and palaeogeography of the region. The lower Hirnantian is typified by the dark-grey cacareous mudstone or argillaceous limestone of the Kuanyinchiao Formation yielding cool-water Transitional Benthic Fauna 1 (TBF 1). The middle Hirnantian strata, however, can be grouped into a near-shore lithofacies belt with distinctive grainstones of the upper Kuanyinchiao Formation yielding warm-water TBF 2, and a more offshore belt characterized by black shales of the basal Lungmachi Formation. A similar facies differentiation occurs in the upper Hirnantian of the region, but the near-shore sediments are in places represented by TBF 3-bearing calcareous siltstones, for which a new lithostratigraphic unit, the Weiba Formation, is proposed. On this basis, refined Hirnantian paleogeographic reconstructions of the western Yangtze Platform are presented.

Key words: stratigraphy, palaeogeograpy, Ordovician, Hirnantian, western Yangtze region