关键词: 新元古代, 磷块岩, 生物标记化合物

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 (t_max) 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