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An accurately delineated Permian-Triassic Boundary in continental successions

Science china Earth Sciences 2007年第9期50卷 1281-1292页

作者： yin hongfu1, yang fengqing2, yu jianxin2, peng yuanqiao1, wang shangyan3.& zhang suxin1 1 laboratory of biological and environmental geology, china university of geosciences, wuhan 43.074, china 2 State Key laboratory of Geological Process and Mineral Resources, china university of geosciences, wuhan 43.074, china 3 Geological Survey of Guizhou Province, Guiyang 550011, china laboratory of biological and environmental geology China University of Geosciences Wuhan 430074 China State Key laboratory of Geological Process and Mineral Resources China University of Geosciences Wuhan 430074 China Geological Survey of Guizhou Province Guiyang 550011 China

The Permian-Triassic Boundary Stratigraphic Set (PTBST), characteristic of the GSSP section of Meishan and widespread in marine Permian-Triassic Boundary (PTB) sequences of South china, is used to trace and recognize the PTB in a continental sequence at Chahe (Beds 66f―68c). Diversified Permian plant fossils extended to the PTBST, and a few relicts survived above that level. Sporomorphs are dominated by fern spores of Permian nature below the PTBST, above which they are replaced by gymnosperm pollen of Triassic aspect. In the nearby Zhejue Section, the continental PTBST is charac- terized by the fungal 'spike' recorded in many places throughout the world. The boundary claybeds (66f and 68a,c) of the PTBST are composed of mixed illite-montmorillonite layers analogous with those at Meishan. They contain volcanogenic minerals such as β quartz and zircon. U/Pb dating of the upper claybed gives ages of 247.5 and 252.6 Ma for Beds 68a and 68c respectively, averaging 250 Ma. In con- trast to the situation in Xinjiang and South Africa, the sediment sequence of the Permian-Triassic tran- sition in the Chahe section (Beds 56―80) become finer upward. Shallowing and coarsening upward is not, therefore, characteristic of the Permian-Triassic transition everywhere. The occurrence of relicts of the Gigantopteris Flora in the Kayitou Fm. indicates that, unlike most marine biota, relicts of this pa- leophytic flora survived into the earliest Triassic. It is concluded that Bed 67 at Chahe corresponds to Bed 27 at Meishan, and that the PTB should be put within the 60-cm-thick Bed 67b④, now put at its base tentatively. This is the most accurate correlation of the PTB in continental facies with that in the marine GSSP.

关键词： Permian-Triassic Boundary, terrestrial sequence, U-Pb age, Chahe section, accuracy

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