浙江江山寒武系碳酸盐岩碳氧同位素特征及其古环境意义探讨

A PROBE INTO THE CARBON AND OXYGEN ISOTOPIC CHARACTERISTICS OF THE CAMBRIAN CARBONATE ROCKS IN JIANGSHAN,ZHEJIANG AND ITS PALEO-ENVIRONMENT SIGNIFICANCE

对浙江江山碓边下寒武统上部—下奥陶统下部碳酸盐岩进行了碳氧同位素测定。δ1 3C、δ1 8O值变化范围和均值分别为 - 1.9‰～ 3.7‰、- 13.0‰～ - 1.3‰和 0 .86‰、- 9.76‰。碳氧同位素地层曲线与 Veizer et al.(1986 )的同位素年代演化曲线形状相似 ,在寒武纪—奥陶纪界线附近没有明显的δ1 3C、δ1 8O漂移现象。δ1 3C地层曲线具旋回性变化特征 ,大陈岭组、杨柳岗组各形成一个完整的演化旋回 ,与根据露头层序地层研究推测的海平面变化曲线吻合性较好 ,表现出δ1 3C值的高值区是海盆水体变深的反映。一个明显的碳同位素正漂移发生于晚寒武世早期 (华严寺组下部 ) ,与 Matthew etal.(2 0 0 0 )报道的在美国内华达州中东部、哈萨克斯坦 Malyi Karatau地区、澳大利亚昆士兰州西北部和湘西桃源瓦儿岗等地发现的 δ1 3C正漂移记录 (SPICE— The Steptoean Positive CarbonIsotope Excursion)和 Veizer et al.(1986 )碳同位素年代演化曲线中的正漂移波峰一致 ,为晚寒武世全球性碳同位素正漂移提供了一个佐证。

The studied carbonate rocks dealt with in this paper were collected from the classic section of the Cambrian to Lower Ordovician age at Duibian of Jiangshan, Zhejiang. Variation range and average of δ 13 C and δ 18 O are respectively -1.9‰～3.7‰, -13.0‰～-1.3‰ and 0.86‰,-9.76‰. The shape of the stratum curve of the Carbon and Oxygen isotopes resembles that of isotope curve in the geological time given by Veizer et al . (1986). No obvious shift of δ 13 C and δ 18 O was found near the Cambrian-Ordovician boundary. The stratum curve of δ 13 C is characterized by obvious cyclicity variety. Dachenling Formation's and Yangliugang Formation's cyclic evolutions coincide with the variation curve of sea level inferred from the outcrop sequence stratigraphy. The deepening of sea-water conforms to the peak of δ 13 C value. An obvious positive excursion happened in the early stage of Late Cambrian(lower part of Huayansi Formation). It conforms to the SPICE (The Steptoean Positive Carbon Isotope Excursion) from the report of Matthew R.S. et al .(2000), which was found in Middle-East of Nevada of USA, Malyi Karatau of Kazakhstan, North-west of Queensland of Australia, Wa`ergang of Taoyuan in the west of Hunan Province, and coincides with the peak of carbon isotope evolution curve from Veizer et al . (1986). It is a case in point of global positive excursion of the carbon isotopes in the Late Cambrian.