松辽盆地齐家—古龙凹陷青山口组黑色页岩岩相类型与沉积环境

Study on lithofacies types and sedimentary environment of black shale of Qingshankou Formation in Qijia-Gulong Depression,Songliao Basin

为研究松辽盆地齐家-古龙凹陷白垩系青山口组黑色页岩的沉积环境,利用岩心描述、薄片资料及地球化学数据开展岩相分析与沉积模式建立。结合有机碳含量和矿物组成划分出6种岩相,即富有机质黏土质页岩、富有机质长英质页岩、富有机质含生屑长英质页岩、贫有机质长英质泥岩、贫有机质含生屑长英质泥岩及贫有机质介壳灰岩。青山口组富有机质页岩并不全是静滞水体中悬浮沉积的产物,大量微米级的微波状纹层、透镜状层理、交错层理、粒序层理、冲刷充填构造以及定向排列的介屑佐证了浊流和底流作用的存在。微量元素分析表明,青一段湖盆面积大,水体深,虽有底流和浊流作用,但保持较强的还原环境,形成富有机质的黏土质页岩、粉砂质页岩和含生屑粉砂质页岩的互层,发育各种纹层。青二段、青三段随着湖平面下降,三角洲注入能力增强,贫氧环境受到破坏,有机质保存条件变差,岩相向贫有机质块状泥岩转变。

In order to study the sedimentary environment of the black shale of Qingshankou Formation in Qijia-Gulong Depression,lithofacies analysis and sedimentary model were established by using core description,thin section data and geochemical data.According to the content of organic carbon and mineral composition,six lithofacies can be divided:organic rich clay shale,organic rich silty shale,organic rich shell-bearing silty shale,organic lean silty shale,organic lean shell-bearing silty shale,organic lean shell-bearing limestone.The organic-rich shale of Qingshankou Formation is not always able to deposit in a suspending form under the low-energy hydrodynamic conditions.A large number of silt ripple laminations,lenticular bedding,ripple cross bedding,graded bedding,scouring filling structure and directional arrangement of shell indicate the existence of bottom current deposition.Trace element analysis shows that in the first member of Qingshankou Formation,lake has a large area and a deep water body.Although bottom flow and turbidity flow existed,it maintains a strong anoxic environment,forming interbeds of organic rich clay shale,organic rich silty shale,organic rich shell-bearing silty shale,and developing various lamination.Then,lake level gradually declined,the injection capacity of the delta sandstone,the anoxic environment is destroyed,resulting in worsening preservation conditions of organic matter,the lithofacies changes to the organic-poor massive mudstone.