鄂尔多斯盆地延长组7段有机质富集主控因素

鄂尔多斯盆地延长组7段(长7段)富有机质页岩中的有机碳含量呈异常高值,其有机质的富集从根本上来说是受古构造、古气候、古沉积环境和事件作用综合控制的。对这些控制因素进行分析,并探讨了他们在富有机质页岩形成过程中的作用。结果表明:长7段沉积期强烈的构造活动对有机质的富集起到了非常重要的作用,一方面导致盆地整体沉降,湖盆面积扩大,从而使得可容空间增大;另一方面诱发了多期的火山和湖底热液活动,并借此向湖泊中输送了大量的营养物质。充足的生长空间、丰富的营养物质和适宜的气候条件使得水生生物异常繁盛(湖泊初始生产力极高),这为富有机质页岩的形成提供了丰富的物质基础。尽管长7段沉积期氧化-亚氧化的底水环境不利于有机质的保存,但是在供给量充足的前提下,仍然使得大量的有机质保存了下来,从而造成了有机质在沉积物中的大量富集。

Main controlling factors for organic matter enrichment in Chang 7 member of the Yanchang Formation,Ordos Basin

The TOC content of organic-rich shales in Chang 7 member of the Yanchang Formation in Ordos Basin is abnormally high.The organic matter enrichment is essentially controlled by a combination of paleostructures,paleoclimate,paleosedimentary environments and events.We have analyzed these controlling factors and discussed their roles in the formation of organic-rich shales of the study area.The results show that the strong tectonic activity in the depositional period of Chang 7 member played a very important role in its enrichment of organic matter.Firstly,it led to a wide-scale subsi-dence of the whole basin and to an expansion of the lake water surface,producing more accommodation space.Furthermore,it induced multi-stage volcanic and submerged hydrothermal activities,and thereby delivered a large amount of nutrients to the lake.Sufficient growth space,rich nutrients supply and suitable climatic conditions have made aquatic orga-nisms flourish(the lacustrine primary productivity was extremely high),which has provided a rich material basis for the formation of organic-rich shales.Although the oxydic-suboxydic bottom-water environment in Chang 7 sedimentary period is not ideal to the preservation of organic matter,a large number of organic matters are still preserved due to adequate influx,resulting in the enrichment of organic matter in the sediments.