贵州瓮安陡山沱组含磷岩系沉积序列及磷块岩的形成
Depositional sequences of the phosphatic rock series and formation of the phosphorites in the Doushantuo Formation in Weng’an,Guizhou
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摘要: 贵州瓮安陡山沱组磷块岩为碳酸盐岩型含磷岩系,属于浅海碳酸盐岩台地沉积区。对瓮安磷矿大塘剖面进行沉积环境研究,将Marinoan冰期后沉积的陡山沱组地层分为6个向上变浅的沉积序列。瓮安含磷岩系大部分为多旋回的叠置体,其常见的交错层理、波状层理、透镜状层理等表明了磷块岩形成于水体较浅的高能环境。南沱冰期后,陡山沱期剧烈的海侵作用引发上升洋流,携带富磷海水涌入浅水区,在海平面间歇性波动的条件下,为磷块岩的形成提供了物源与动力条件。Abstract: The phosphorites in Weng’an,Guizhou are hosted in the lower and upper parts of the Doushantuo Formation,and made up of carbonate rock-type phosphatic rock series on a shallow marine carbonate platform.The strata of the Doushantuo Formation deposited after the Marinoan glacial period may be grouped into six shallowing-upward depositional sequences.The bulk of phosphatic rock series is built up of polycyclic stacking deposits in which cross-bedding,wavy bedding and lenticular bedding are common,implying that the phosphorites rested in the shallow marine high-energy environments.From the Nantuoan glacial period onwards,the large-scale transgressions gave rise to the upwelling oceanic currents and carried plentiful phosphatic sea water into the shallow marine areas as sites of phosphorites development.The repeated sea-level fluctuations contributed to the phosphatic source and development of polycyclic depositional sequences of the phosphorites.
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Keywords:
- Guizhou /
- Weng'an /
- Doushantuo Formation /
- phosphorite /
- depositional sequence
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