中生代-新生代大陆边缘盆地海相烃源岩成因类型

Genetic types of marine source rock in Meso-Cenozoic continental margin basins

中生代-新生代大陆边缘盆地海相烃源岩虽沉积于海洋环境,但有机质生源输入复杂。海相烃源岩显微组分组成中不仅有代表低等水生生物输入的腐泥组分,而且有较多指示陆生高等植物成因的镜质组、惰质组或壳质组。烃源岩生物标志化合物的分布特征也呈现出有机质生源输入二元性的特点,具体表现在饱和烃正构烷烃的分布面貌以双峰态为主,部分呈单峰态。C27-C29规则甾烷的分布型式以不对称的"V"字型为主,部分呈"L"型或反"L"型分布;除指示水生生物输入的C23三环萜烷外,代表陆源有机质输入的奥利烷、四环萜烷和其他低分子量的三环萜烷均有分布。中生代-新生代大陆边缘盆地海相烃源岩生源组成复杂,这一特殊现象是大陆边缘盆地海洋和大陆两种地质营力、低等水生生物和陆生高等植物双重生源输入共同作用的结果。根据生源构成可将中生代-新生代大陆边缘盆地海相烃源岩划分为3种成因类型,即以藻类生源输入为主的内源型、以高等植物输入为主的陆源型及介于两者之间的混合生源型,并进一步揭示海相烃源岩的成因类型与干酪根类型之间可以通过显微组分组成、有机元素组成以及生物标志化合物分布联系起来。

Marine source rocks in Meso-Cenozoic continental margin basins are deposited under marine environment,but with complex biogenesis of organic matters. The maceral composition of marine source rocks not only include the sapropelic components representing the input of lower aquatic organisms,but also contain more vitrinite,inertinite and exinite indicating the genesis of terrestrial higher plants. The distribution of source rock biomarker is characterized by binary biogenic input of organic matters,shown as the distribution of saturated nalkanes dominated by a bimodal state with partial unimodality. The distribution pattern of regular sterane C27- C29 is dominated by asymmetric 'V'shape,partially with 'L'and anti-'L'shape. Except C23 T indicating the input of aquatic organisms,there are distributed oleanane,tricyclic terpane and other tetracyclic terpane with low molecular weight representing the input of terrestrial organic matters. The biogenic compositions of marine source rocks in Meso-Cenozoic continental margin basins are complicated,which is a special phenomenon resulted from the combined effects of marine-continental geological stresses in continental margin basins and dual biogenic input of lower hydrobiont and terrestrial higher plant. Based on biogenic structure,marine source rocks in Meso-Cenozoic continental margin basins can be divided into three genetic types,i. e.,endogenous type dominated by algae biogenic input,terrigenous type dominated by higher plant input,and hybrid biogenic type between the both,further revealing the relation between the genetic types of marine source rocks and kerogen types through maceral composition,organic element components and biomarker distribution.