北大巴地区早古生代的缺氧环境和油源岩与水下火山活动之间关系的探讨

APPROACH ON THE RELATION AMONG ANOXIC ENVIRONMENT, SOURCE ROCKS AND SUBAQUEOUS VOLCANIC ACTIVITY OF LOWER PALEOZOIC IN NORTH DABA AREA

早古生代拉张断陷的形成和演化,伴有海底水下火山活动,及含有机质较高的泥质岩、硅质岩等沉积。油源岩主要在该阶段发育,其有机质的含量高。氟和黄铁矿中δ^(34)S值表明该区的油源岩与水下火山活动相关.火山作用过程中。能喷出大量的H_2S、SO_2、SO_3、CO_2及CH_4等气体,除CH_4气外,均能溶于水,且和水中的氧和水起化学反应,致使海水缺氧和发生重力分异而使海水分层。缺氧海水分布于下部,为有机质的保存提供了一个良好的还原环境。CH_4气大部份进入大气圈,发生氧化燃烧反应,生成大量的H_2O和CO_2且放出大量的热,这种作用能促进生物的大量繁荣,为油气的形成提供更多的物质基础.

Lower Paleozoic of North Daba area consists of volcanic rocks, orga-nic-rich argillaceous rocks and siliceous rocks. Its kerogen type is sapr-opelic with high content of organics. The source rocks are rich in fluor-ine and sulfur, and bear a direct relation to subaqeous volcanic activity as indicated by fluorine and s34S of pyrite. Large quantity of H2S,SO2, SO3,and CO2 were extruded in the process of subaqeous volcanism, which caused chemical action with oxygen and water, and gravity differentiation of sea water, and provided good conditions for organic pres-ervation. As CH4 entered atomsphere, combution took place with heat release, growth was promoted, which would provide material basis for oil and gas generation.