Inorganic and organic carbon isotopes from Early Cambrian Yangchang phosphate deposit in Zhenxiong County, Yunnan Province
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P597;P619.21+3

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    Abstract:

    The recently discovered Yangchang deposit in Zhenxiong County, Zhaotong City, Yunnan Province is an ultra-large-scaled buried phosphate deposit. Previous research on this deposit mainly focused on the metallogeny, while the study of sedimentary geochemistry and the paleoenvironment is lacked. More importantly, the inorganic (δ13Ccarb) and organic (δ13Corg) carbon isotopes as well as their relationships in the early Cambrian were rarely reported. In this study, three drill cores (ZK001, ZK0701, ZK1512) in Yangchang phosphate deposit were selected for high-resolution investigations of δ13Ccarb and δ13Corg. Both δ13Ccarb and δ13Corg show negative shifts in the top Precambrian Dengying Formation and the bottom of its overlying Zhujiaqing Formation, which is consistent with the global Basal Cambrian Carbon Isotopic Excursion (BACE), likely due to the oxidation of organic carbon reservoir. However, we did not find significant positive shifts in the overlying strata (i.e., Zhujiaqing Carbon Isotopic Excursion, ZHUCE), which may be caused by sedimentary hiatus given that the Yangchang phosphate deposit is mostly intra-clastic phosphorus-rich deposits. Nevertheless, we propose that this phosphate deposit was mainly formed during the Fortunian according to the comparison between the δ13Ccarb in the three drill cores and the composite profile of δ13Ccarb in South China. The comparisons for the δ13Ccarb and δ13Corg values in the drill cores ZK001 and ZK0701, show that the average value of the ΔCcarb-org (difference between δ13Ccarb and δ13Corg) is 28.8‰ and 22.2‰ in the Dengying Formation, and these values change to 31.7‰ and 31.7‰ at the bottom of the Zhujiaqing Formation, and 29.6‰ and 29.8‰, in the middle and upper of the Zhujiaqing Formation, respectively. We propose that the decoupled δ13Ccarb and δ13Corg occurring in the middle of the Zhujiaqing Formation may be caused by the increased primary productivity or buried organic carbon. In summary, the high-resolution paired inorganic and organic carbon isotopes in this work indicate the formation time of Yangchang phosphate deposit and shed light on associated paleoenvironmental changes, which also support the regional stratigraphic correlation.

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刘文杰,周艳玲,米云川,牛奕宁,吴佳怡,周余国,陈剑波,2024,云南镇雄羊场磷矿早寒武世无机碳、有机碳同位素研究[J].岩石矿物学杂志,43(5):1086~1098. LIU Wen-jie, ZHOU Yan-ling, MI Yun-chuan, NIU Yi-ning, WU Jia-yi, ZHOU Yu-guo, CHEN Jian-bo,2024,Inorganic and organic carbon isotopes from Early Cambrian Yangchang phosphate deposit in Zhenxiong County, Yunnan Province[J]. Acta Petrologica et Mineralogica,43(5):1086~1098.

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History
  • Received:May 14,2024
  • Revised:July 19,2024
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  • Online: September 25,2024
  • Published: September 25,2024
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