鄂尔多斯盆地陇东地区延长组沉积相特征与层序地层分析

晚三叠世鄂尔多斯盆地是一个东缓西陡的不对称坳陷盆地。通过岩心、录井、测井等资料综合研究,识别出陇东地区延长组发育河流、三角洲、浊积扇和湖泊等4种沉积相类型,其中河流沉积和浊积扇发育在湖盆的西缘陡坡带,三角洲则在西缘和东部缘坡均有发育。根据层序地层学原理,将延长组划分出5个三级层序;延长组地层经历过5次大的湖泛,在层序演化上具有早期形成、中期鼎盛、晚期衰退的特点。利用恢复后的原始地层厚度,绘制的陇东地区延长组地层的F ischer图解,与本区5次显著的湖平面上升-下降旋回之间有很好的对应关系,这不仅证实了上述层序地层分析的正确性,同时揭示了F ischer图解在划分地层层序方面的潜在意义。

Sedimentary Facies Characteristic and Sequence Stratigraphy Analysis of Yanchang Formation in Longdong Area, Ordos Basin

At Late Triassic,Ordos Basin is an asymmetry depressed-type lacustrine basin with gentle slope in the east and steep slope in the west.By the research of core,logging profiles and seismic data,four types of sedimentary facies have been recognized.Among these sedimentary facies,river facies and turbidity fans are found on the steep slope in the west of the depression,while braid river deltas are found on both the steep slope in the west and the gentle in the east of the depression.Based on the classic pattern of sequence stratigraphic framework,five three-order sequences have been identified in Yanchang formation,Longdong area.Five times of lake transgression can be distinguished.The sequence evolution is that they formed in early time,reached the maximum in middle time and declined in late time.Fischer's plots of Yanchang formation stratigraphy are scaled with retrieved stratigraphic thickness in Longdong area.There are well corresponding relations between the plots and five times of lake transgression.The classification of the sequence stratigraphy has been verified by using Fischer's plots,which may be a potential tool for sequence analysis.