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浙江省开化县底本乡皮园村组硅质岩和荷塘组黑色泥岩为埃迪卡拉纪-寒武纪过渡时期(Ediacaran-Cambrian transition,E-C transition)下扬子盆地典型深水相沉积,对其研究有助于认识古海洋的氧化还原环境.本文共采集岩石样品53件,分析岩样中铁组分包括黄铁矿的铁(FePy)、碳酸盐矿物中的铁(FeCarb)、氧化铁和氢氧化铁(FeOx)、磁铁矿的铁(FeMag)、总铁(FeT)的含量和δ13Corg值.结果表明:(1)底本剖面皮园村组硅质岩和荷塘组黑色泥岩样品中的黄铁矿含量普遍较低,大部分小于1%;FePy/FeHR的值在<0.01~0.81之间,绝大多数样品低于0.5;FeHR/FeT的值在0.39~0.93之间,绝大多数样品高于0.5.(2)从碳同位素的对比可以看出底本剖面与其他剖面具有很好的对应关系,并且界定出埃迪卡拉纪与寒武纪的分界点在底本剖面皮园村组中下部δ13Corg值的最大负偏处.浙西皮园村组硅质岩和荷塘组黑色泥岩的沉积环境主体上以缺氧含铁为主,较高的高活性铁含量和较低的黄铁矿含量指示当时盆地深水中H2S相对缺乏,Fe2+是富余的;且在荷塘组下部和上部海水含氧量似乎有逐渐增加的趋势,但氧气的增加量还不足以使深海达到完全氧化.因此,E-C过渡时期古海洋环境是缺氧含铁的,这样的环境制约了后生动物在深水区的出现和演化,并且为充分认识“寒武纪生命大爆发”的时空顺序和过程提供了重要的参考.
The siliceous rocks of the Piyuancun Formation and the black mudstones of the Hetang Formation in the Jiben County, Kaihua County, Zhejiang Province are typical deep-water sediments in the Yangtze basin under the Ediacaran-Cambrian transition (EC transition) Which helps to understand the redox environment of ancient oceans.In this paper, a total of 53 rock samples were collected to analyze the distribution of iron components including pyrite (FePy), carbonate minerals (FeCarb), iron oxide and hydroxide (FeOx), magnetite (FeMag), total iron (FeT) content and δ13Corg value.The results show that: (1) the pyrites in the Pianyuan Formation chert and the Hetang Formation black mudstone The ore content is generally low, mostly less than 1%; FePy / FeHR values between <0.01 ~ 0.81, the vast majority of samples less than 0.5; FeHR / FeT values between 0.39 ~ 0.93, the vast majority of sample height At 0.5. (2) It can be seen from the comparison of carbon isotopes that this section has a good correspondence with other sections, and defines the boundary point of Eddicala and Cambrian at the middle lower part of Piyuancun Formation, δ13Corg The largest negative deviations of the value are the sedimentary rings of the siliceous rocks in the Piyuan Village Formation and the black mudstone in the Hetang Formation The main body of the main hypoxia iron content, high activity of high iron content and lower pyrite indicates the relative lack of H2S in deep basin water, Fe2 + is surplus; and in the lower part of the pond group and upper seawater oxygen The amount seems to be increasing gradually, but the amount of oxygen added is not enough to completely oxidize the deep ocean. Therefore, the ancient marine environment during the transitional period of EC was anoxic and iron-deficient. Such an environment restricted the emergence of metazoans in the deepwater zone and Evolution, and provide an important reference for fully understanding the temporal and spatial order and process of the “Cambrian explosion of life”.