鄂尔多斯盆地西北部石千峰组沉积特征及沉积—层序模式

根据沉积学、地球物理和地球化学等标志,确定研究区石千峰组为辫状河、曲流河、三角洲和湖泊的沉积类型。在沉积特征研究的基础上,进行层序界面的识别和划分,进而在研究区石千峰组内划分并识别出短期、中期、长期、超长期4种类型的旋回层序。通过对各级别层序特征的详细研究,表明中期基准面旋回与沉积体系有很好的响应关系,表现为辫状河和曲流河具有A1和A2型中期基准面变化特征,三角洲平原、三角洲前缘和湖泊沉积分别具有C1、C2、C3和B型的响应特征。结合研究区石千峰期由北至南发育河流—三角洲—湖泊的古地理展布特征,最终将这些丰富的地质信息以沉积—层序模式进行了概括,表现为由北至南发育河流—三角洲—湖泊的沉积类型,具有A1-A2-C1-C2-C3-B型的层序响应特征。建立的这样一套等时模式,能更详尽的了解研究区生储盖的时空配置关系,为下一步油气勘探提供地质依据。

THE SEDIMENTARY CHARACTER AND SEDIMENTATION-SEQUENCE MODEL OF THE SHIQIANFENG FORMATION IN NORTHWESTERN ORDOS BASIN

This article applies the basic theory and methods of sedimentology,high-resolution sequence stratigraphy and lithofacies analysis in the study of the Shiqiangfeng Formation in the northwestern Ordos Basin.Braided river,meandering river,delta and lacustrine sedimentary systems can be identified in the Shiqianfeng Formation.On the basis of depositional characters,and sequence boundaries,the Shiqianfeng Formation can be divided into four-grade base-level cycle sequences:short,middle,long and super-long sequence cycles.Based on the study of sequence characters,it is shown that middle sequence cycles were well responded in sedimentary system.braided river and meandering facies river have characters of A1 and A2 middle sequence cycles;delta plain,delta front and lacustrine facies each have characters of C1,C2,C3 and B middle sequence cycles.On the basis of characters of river-delta-lacustrine from the northern to southern part of the basin,we propose a sedimentation-sequence model to explain these observations.This study has implications for the understanding of source-reservoir trap rocks in the Ordos Basin and future oil-gas exploration in this basin.