The study of main factors controlling the development of Wufeng Formation and Longmaxi Formation organic-rich shales in the Yichang area,Middle Yangtze Region [中扬子宜昌地区五峰组和龙马溪组页岩发育主控因素]

作者：Wang T.-L.; Hao A.-S.; Chen Q.; Li C.; Wang Q.-T.^*; Lu H.; Liu D.-Y.

来源：天然气地球科学, 2018, 29(5): 616-631.

DOI：10.11764/j.issn.1672-1926.2018.03.009

• Major and trace elements
• Middle Yangtze Region
• Organic matter enrichment
• Paleoproductivity
• Sedimentary environment
• Wufeng Formation and Longmaxi Formations

Although the huge potential of shale gas in the Middle Yangtze Region,mechanism of the development of organic-rich shales are not clear.In this study,total organic carbon,major and trace elements analysis were conducted on 25 samples,in order to investigate the relationships between paleoproductivity,sedimentary environment,terrigenous flux and the development of shale.The data show that the shales from Wufeng Formation and Lower Longmaxi Formation have high TOC values and high excess-Si content,which indicates that excess-Si is in biogenic origin.There is no positive relationship between conventional paleoproductivity proxies (P/Ti,Ba/Al,Baxs) and TOC,which is probably attributed to the depletion of those elements in the late diagenesis phase.However,paleoproductivity coefficient composed by excess-Cu,excess-Ni and excess-Zn correlates with TOC well,which illustrates that the development of organic-rich shale has a close relationship with high paleoproductivity.Moreover,redox sensitive elements (U,V,Mo) are more enriched in Wufeng Formation and Lower Longmaxi Formation than Upper Longmaxi Formation,while positive correlations between V,Mo and TOC occurs.These phenomena state that reductive environment is necessary to preserve organic matter.Terrigenous flux proxies (Al2O3) represented that the strongest terrigenous flux in Upper Longmaxi Formation,and TOC shows negative relationship with Al,Ti and Th,which illustrates that the strengthened terrigenous flux diluted organic matter.In conclusion,high paleoproductivity and reductive sedimentary environment and low terrigenous flux are beneficial to the development of marine organic-rich shale.

• 单位
  有机地球化学国家重点实验室; 中国科学院大学; 现代古生物学和地层学国家重点实验室