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The recovery of conodonts associated with ash beds and magnetostratigraphy in the key Zhongzhai Section, near Langdai, Liuzhi, Guizhou Province, provides precise and definitive control on the position of the Permian–Triassic boundary in the transition from marine to non-marine facies of western Guizhou and eastern Yunnan Provinces of southwestern China. In the Zhongzhai Section the boundary interval consists of a lower limestone, 20 cm thick, that contains fragments of 'Hindeodus' sp. and 'Clarkina' sp. This is overlain by a 50 cm thick black shale bed containing an abundant brachiopod fauna, but only a single conodont fragment. This bed is in turn overlain by a 23 cm thick limestone that contains 'Clarkina meishanensis', 'Merrillina ultima', 'Hindeodus changxingensis', 'H. praeparvus' and 'H. eurypyge'. Directly over this limestone is a 5 cm thick ash bed followed by a 10 cm thick black shale, which is overlain by a second, upper, ash bed that is 3 cm thick. On top of the upper ash bed is a 20 cm thick silty limestone containing an abundant dwarf conodont fauna, dominated by 'Hindeodus', and containing 'H. parvus' but also including 'Clarkina tulongensis'. The Permian–Triassic boundary is placed at the level of the black shale located between the two ash beds. |
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