澳大利亚波拿巴盆地大陆边缘裂陷期海陆过渡相烃源岩地球化学特征与发育模式

Geochemical characteristics and development model of transitional source rocks during the continental margin rifting stage, Bonaparte Basin, Australia

侯宇光 何生 杨香华 段威 朱光辉 许晓明 董田

Hou Yuguang He Sheng Yang Xianghua Duan Wei Zhu Guanghui Xu Xiaoming Dong Tian

中国地质大学(武汉)构造与油气资源教育部重点实验室, 武汉 430074 2. 中海石油(中国)有限公司 北京研究中心, 北京 100027

Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China University of Geosciences, Wuhan, Hubei 430074, China 2. Beijing Research Center of China National Offshore Oil Corporation, Beijing 100027, China

对构造地质背景、沉积充填特征以及有机地球化学特征等综合分析表明,海陆过渡相烃源岩形成于波拿巴(Bonaparte)盆地大陆边缘裂陷的主裂陷期;河流—三角洲的发育为陆源高等植物输入提供了沉积空间,强烈的差异裂陷活动不但为烃源岩的形成提供了高可容纳空间和欠补偿的沉积环境,同时"隆凹相间"的沉积格局有利于相对稳定的半封闭—半开放沉积环境的形成。海陆过渡相烃源岩形成于相对氧化、陆源物质供给充足的沉积环境,岩性上以碳质泥页岩为主,广泛发育含煤层系,富含陆源植物碎片与孢粉化石,及少量海相浮游化石。陆源碎屑对烃源岩有机质富集具有重要影响,沿着陆源输入方向,烃源岩有机质丰度逐渐降低,有机质类型由以腐殖型为主向腐泥腐殖混合型变化;气相色谱由后峰型、后双峰型向前双峰型过渡,(n-C21+n-C22)/(n-C28+n-C29)和αααC27R/αααC29R比值逐渐增加,Pr/Ph比值降低,也说明有机质母源由以陆源高等植物为主向陆源和水生生物混合来源转变,沉积环境由氧化向弱氧化—弱还原过渡。

The comprehensive analyses of tectonic settings, depositional fillings and organic geochemical characteristics indicated that the source rocks in the Bonaparte Basin were deposited during the main stage of continental margin rifting, and the well-developed river delta sedimentary system was beneficial for terrigenous organic matter input. The episodic rifting of the basin and the differential subsidence of contemporaneous faults provided both plentiful accommodation space and an underfilled depositional environment. Moreover, the pattern of "uplift alternating with sag" was favorable for the development of a semi-restricted depositional environment. The transitional source rocks were deposited in an oxic depositional environment with a large amount of terrigenous input. They mainly consist of carboniferous mudstones and coal-bearing series. Abundant terrigenous plant debris and some marine planktonic debris were observed. The terrigenous materials played a very important role in organic matter accumulation. With shifting sediment sources, the organic matter enrichment was decreasing and the kerogen was increasingly dominated by sapropelic organic matter. The n-alkane distribution was characterized by a back-end biased and bimodal pattern. The (n-C21+n-C22)/(n-C28+n-C29) and αααC27R/αααC29R ratios were increasing, while the Pr/Ph ratio was decreasing. All these variations also indicated that the source organic matter was changing from terrigenous to marine, and the depositional environment was changing from oxic to dysoxic conditions.

国家油气重大专项(2008ZX05030-02),国家自然基金项目(41302111),中国地质大学(武汉)中央高校基本科研业务费专项资金资助项目(CUGL110247)和中国地质大学(武汉)构造与油气资源教育部重点实验室基金项目(TPR-2013-19)联合资助.

https://doi.org/10.11781/sysydz201503374