Palaeoclimatology and provenance of black shales from Wufeng-Longmaxi Formations in southwestern Sichuan Province:From geochemical records of Well Xindi-2
Mou Chuan-Long1,3, Ge Xiang-Ying1,2, Yu Qian1, Men Xin1,3, Liu Wei1, He Jiang-Lin1, Liang Wei1,3
1 Chengdu Institute of Geology and Mineral Resources,Chengdu 610081,China; 2 China University of Geosciences(Beijing),Beijing 100083,China; 3 Shandong University of Science and Technology,Qingdao 266590,China
Abstract The Late Ordovician-Early Silurian transition was a critical interval in Earth’s history,marked by mass extinction,the Gondwana Glaciation and volcanic events. The end of Ordovician glaciations had a short-lived duration and there is no direct evidence for the glaciation in China. In order to confirm whether the palaeoclimatic changes ever existed during the end of the Ordovician-Early Silurian, we carried out major and trace elemental analyses on the core mudstone samples from the Wufeng-Longmaxi Formations of Well Xindi-2 in southwestern Sichuan Province,and reconstructed palaeoweathering conditions and palaeoclimatology through various chemical weathering indices. The ICVs(index of chemical varition)of all samples are greater than 1,indicating that they are compositionally inmature and first cycle deposits in tectonically active areas. The REE patterns are similar to the granite’s,which are characterized by slight LREE enrichments and accompanied by flat HREE trends with weakly negative Eu anomalies,suggesting that the source rocks are mainly pro-granite and felsic. The A-CN-K triangular diagram,Al2O3/TiO2, Cr/Zr, and Th/Sc ratios indicate that the provenance of the rocks is also primarily felsic. Indicated by the CIA(Chemical Index of Alteration),CIW(Chemical Index of Weathering)and PIA(Plagioclase Index of Alteration),the sediments experienced from moderate to weak then to moderate chemical weathering in the source area,and palaeoclimate shifted from warm to cold and then to warm again during the Late Ordovician-Early Silurian. The low CIA values of the Upper Wufeng Formation(CIAaver=64.14),Guanyinqiao Formation(CIAaver=61.7)and the bottom of Longmaxi Formation(CIAaver=64.61)reflect that there was a short cold climate time in Hirnantian Age,and represent indirect geochemical records in the South China of Gondwana Glaciation.
Fund:Financially supported by the second-level project“Fundamental Geology Survey of the Lower Paleozoic Marine Shale Gas in Sichuan Basin”(No. DD20160176),which is set under the China Geological Survey Project“The Fundamental Geology Survey Project of the Shale Gas of South China”
About author: Mou Chuan-Long,male,born in 1965,professor,doctoral supervisor,is engaged in sedimentary geology and petroleum geology. E-mail: cdmchuanlong@163.com.
Cite this article:
Mou Chuan-Long,Ge Xiang-Ying,Yu Qian et al. Palaeoclimatology and provenance of black shales from Wufeng-Longmaxi Formations in southwestern Sichuan Province:From geochemical records of Well Xindi-2[J]. JOPC, 2019, 21(5): 835-854.
Mou Chuan-Long,Ge Xiang-Ying,Yu Qian et al. Palaeoclimatology and provenance of black shales from Wufeng-Longmaxi Formations in southwestern Sichuan Province:From geochemical records of Well Xindi-2[J]. JOPC, 2019, 21(5): 835-854.
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