Acta Scientiarum Naturalium Universitatis Pekinensis

Previous Articles     Next Articles

Organic Matters from the Fossil-bearing Phosphorites of the Neoproterozoic Doushantuo Formation in Guizhou, South China

YIN Chungu1, ZHANG Yun2, JIANG Naihuang3   

  1. 1Department of Geology, Peking University, Beijing, 100871; 2College of Life Science, Peking University, Beijing, 100871; 3Research Institute of Petroleum Exploration & Development, Beijing, 100083
  • Received:1998-07-09 Online:1999-07-20 Published:1999-07-20


殷纯嘏1, 张昀2, 姜乃煌3   

  1. 1北京大学地质学系,北京,100871; 2北京大学生命科学学院,北京,100871; 3石油勘探开发科学研究院,北京,100083

Abstract: The Neoproterozoic Doushantuo phosphorite has been well known for its well-preserved multicellular thallophytes, animal embryos, acritarchs, bacteria and other organism's remains. An organic geochemical analysis of the fossil-bearing phosphorite samples has been carried out and yielded the following results: (1) the extracted organic matters show relatively high maturity, the maximum pyrolitic temperature (tmax) is 597℃; (2) the extracted organic fractions are composed mainly of non-hydrocarbons and asphaltenes, and the content of hydrocarbons less than 20%; (3) GC-MS analysis of the extracts shows a normal alkane distribution pattern with a wide range of carbon atom numbers, distinct peaks that represent the n-alkanes between n-C19 and n-C31 can be seen in the mass spectrum, an odd-even predominance of the alkanes is also distinct; (4) in addition to the alkanes, the hydrocarbons fractions contain terpane, steranes, aromatics and isoprenoids. The composition of the pounds, specially the biomarkers from the extracts of the phosphorite samples, indicate that the main sources of the organic matters are the non-vascular plants, protists, bacteria and archaeobacteria; these organisms lived in the basin during Neoproterozoic time, and their remains were preserved in the phosphate deposit. Some of the biomarkers indicate the depositional environment of the phosphorites: strong reduced condition, high salinity and low terrigenous input. Some aromatics, such as benzo-fluoranthrenes, methyl-phenathrene, pyrene and benzo-pyrene, were possibly formed and transported from local hydrothermal or volcanic activities of nearby region. These match well with the sedimentological observation.

Key words: Neoproterozoic, phosphorite, biomarkers

摘要: 对保存有多细胞藻类原植体、细菌和疑原类化石的贵州瓮安陡山沱组磷块岩所作的地球化学分析表明,磷块岩有机质演化程度较高,最高热解温度tmax达597℃。岩石抽提物中以非烃化合物和沥青质为主要成分,烃类含量不足20%。色谱-质谱(GC-MS)分析图谱显示正烷烃的碳数范围很宽,有显著的高碳数正烷烃峰群(C19—C31),奇偶优势明显,烃类有机组分中除正烷烃外还包含有萜烷、甾烷、芳香烃和类异戊二烯烃等。其中生物标记化合物及其组成特征指示了有机物的主要来源是当时生存的真核的多细胞藻类、细菌和古细菌,这与所观察到的磷块岩中保存的古生物化石组成相吻合。某些特征有机物和生物标记物还指示了磷块岩沉积环境特征:强还原性、高盐度、低陆源输入以及与水热活动相关的局部高温。这与沉积学和岩石学的观察相符。

关键词: 新元古代, 磷块岩, 生物标记化合物

CLC Number: