澳大利亚Bonaparte盆地大陆边缘裂陷期局限海相页岩发育特征与模式

发育于大陆边缘裂陷阶段以局限海相为主要沉积环境的富含浮游藻类泥页岩可能是Bonaparte盆地潜在的重要“油”源岩。从构造地质背景、沉积充填特征以及有机地球化学特征等多方面进行综合分析表明，局限海相页岩形成于大陆边缘裂陷阶段的衰减期，盆地基底的差异裂陷活动为页岩的形成提供了高可容纳空间和欠补偿的沉积环境，同时，“小隆大凹”的沉积格局更加有利于大规模相对稳定的半封闭的局限海沉积环境的形成和海相浮游藻类的繁盛。以扇三角洲和海底扇为主的物源体系带来大量“陆源”营养物质，同时，保持营养物质的供给与欠补偿条件的平衡。局限海相页岩主要形成于弱氧化、陆源物质供给较弱、局限海范围较大的沉积环境；岩性上以海相泥岩为主，陆源孢粉化石与沟鞭藻化石均较发育，或后者含量略高；沉积厚度适中、分布范围局限；有机质丰度相对较高，以混合型有机质为主，成熟度较低，气相色谱以前峰型为主，(nC₂₁+nC₂₂)/(nC₂₈+nC₂₉)和Pr/Ph比值相对较高，甾萜等生物标志化合物参数以低C₁₉三环二萜和C₂₄四环萜烷、高孕甾烷、高αααC₂₇R/αααC₂₉R为特征。

Characteristics and Development Model of Restricted Sea Shale atContinental Margin Rifting Stage in Bonaparte Basin,Australia

The argillutite with significant marine planktonic debris which mainly deposited in restricted sea during the continental margin rifting stage is likely the potential important oil source rock of the Bonaparte basin, north-western Australia. Comprehensive analyses on the tectonic geology settings, depositional filling characteristics and organic geochemistry characteristics showed that: The restricted sea shale developed during the decline rifting stage of the continental margin rifting stage in Bonaparte basin. Not only did the episodic rifting of the basin and differential subsidence of contemporaneous faults provide the high accommodation space and the undercompensation depositional environment, but also formed the depositional pattern of “big sag surrounding by little uplifts” which is more benefit for the development of relative-permanent semi-enclosed restricted sea and the propagation of marine planktonic algae. The provenance systems were consisted of the fan delta and the submarine fan, accompanying the significant terrigenous organic matter input to keep the balance of the organic matter supplying with the undercompensation depositional situation. The restricted sea shale deposited in slight oxidation marine depositional environment with large scale restricted sea and minor terrestrial organic matter input, and were mainly the margin mudstone with rich terrigenous organic matter and marine planktonic debris or the latter is higher. The sediment has a moderate thickness and restricted distribution. Geochemical characteristics show relatively high organic matter abundance, dominantly mixed kerogen type and low maturity. The gas chromatograms display front end biased distributions, and are characterized by relatively high (nC₂₁+nC₂₂)/(nC₂₈+nC₂₉) and Pr/Ph ratios. Biomarker fingerprints are characterized by low C₁₉ tricyclic terpane and C₂₄ tetracyclic terpane, high pregnane and C₂₇/C₂₉ regular steranes.