鄂尔多斯盆地南缘下寒武统地层划分及沉积演化特征

Stratigraphic division and sedimentary evolution characteristics of Lower Cambrian in the southern margin of Ordos Basin

为研究鄂尔多斯盆地南缘下寒武统的地层发育特征与沉积演化规律,开展了大地构造背景分析、地层对比和岩相古地理研究。结果表明:①鄂尔多斯盆地南缘辛集组之下发育东坡组和罗圈组地层,为主要烃源岩系,可归属到下寒武统,TOC 质量分数为 0.19%~11.18%,平均为 3.14%,为寒武系最优质的烃源岩。②整个华北地区在早寒武世早期发生海侵,沉积了一套海进地层,鄂尔多斯盆地南缘经历了深水海湾沉积、海岸沉积和碳酸盐岩缓坡沉积过程。③鄂尔多斯盆地南缘寒武系沉积厚度为 500~1 300 m,局部可达 1 500 m 以上,其中张夏组鲕粒滩分布广泛,发育溶孔和晶间孔,为相对优质的储集体,与东坡组和罗圈组构成了良好的源储组合。该研究成果对鄂尔多斯盆地寒武系油气勘探具有重要意义。

In order to study the stratigraphic development and sedimentary evolution of Lower Cambrian in the southern margin of Ordos Basin,geotectonic background,stratigraphic correlation and lithofacies palaeogeo- graphy were studied. The results show that:(1)Dongpo Formation and Luoquan Formation are the main source rocks developed under Xinji Formation in the southern margin of Ordos Basin,which can be classified into Lower Cambrian. The TOC mass fraction is 0.19%-11.18%,with an average of 3.14%,so they are the best source rocks of Cambrian.(2)The entire North China region transgressed in the early Early Cambrian and deposited a set of transgression strata. The southern margin of Ordos Basin underwent deep-water bay deposition,coastal deposition and carbonate gentle slope deposition.(3)The sedimentary thickness of Cambrian in the southern margin of Ordos Basin is 500-1 300 m,and it can reach more than 1 500 m locally. The oolitic shoals of Zhangxia Formation are widely distributed,with dissolved pores and intergranular pores developed. They are relatively high-quality reservoirs and form a good source-reservoir assemblage with Dongpo Formation and Luoquan Formation. The research results are of great significance to the Cambrian oil and gas exploration in Ordos Basin.