下扬子中二叠统上升流相与烃源岩的关系研究

Relationship between middle Permian upwelling facies and hydrocarbon in lower Yangtze area

下扬子区面积177020km2,包括江苏、浙江、安徽、江西和上海绝大部分地区,这一区域的构造属性为被动大陆边缘,通过对该区古生界中二叠统的几十条剖面的实测、分析和对比,得出该区古生界中二叠统地层中的黑色碳质页岩、硅质页岩、硅质岩、硅质条带和结核以及磷矿层和磷结核等沉积是古特提斯海中上升流作用形成的。上升流水体中富营养盐和SiO2,在古生代低纬度的下扬子地块生物大量繁殖,引发缺氧事件,形成上述硅质和磷质沉积以及有机质丰富的烃源岩、石煤和磷矿层等,由于上升流水体富营养盐和SiO2,生物化石属种丰富,个体大,多营底栖或固着浅海底生活,硅质生物放射虫等丰富。区内烃源岩有机质与上升流的强度呈正相关关系,可见它们之间存在着成因联系。

Acreage of the Lower Yangtze area is 177 020 km^2 including Jiangsu, Zhejiang, Anhui, Jiangxi provinces and most part of Shanghai, and it＇s a passive continental margin. Through analysis and correlation of some Paleozoic profiles across this area, it is considered that the upwelling in the Paleotethys caused deposition of danks, siliceous shale, silica rock, siliceous bands and nodules, phosphorite layers and nodules of middle Permian. Since upwelling water is rich in nutrient salt and SiO2, high bioproductivity and anoxic events appeared in the southeastern margin of the low-latitude Paleozoic lower Yangtze block. The upwelling resulted in the deposition of organic-rich carbonaceous and phosphorite sediments such as source rocks, bone coal and phosphorite, etc. There are rich big fossil organisms in the sedimentary strata of the upwelling current. The biocoenosis belongs to benthonic and anchoring faunas in the shallow sea and siliceous radiolarite boomed. The positive relationship between the TOC content and strength of the upwelling current is evident.