鄂尔多斯盆地陇东地区延长组长8段沉积特征及水动力条件分析

Sedimentary characteristics and hydrodynamic conditions of Chang 8 member of Yanchang Formation in Longdong Area,Ordos Basin

以陇东地区延长组长8段为研究对象,运用岩心观察所得到的岩石类型、沉积构造及古生物标志特征,对长8期沉积特征进行分析。在此基础上,根据不同沉积构造与水动力条件的形成关系,对长8期水动力条件进行分析,并确定平面上不同水动力条件的影响范围。研究认为,陇东地区长8段主要发育浅水辫状河三角洲前缘亚相,在吴起一带发育浅湖沉积,长8中期存在湖平面下降,短期暴露水面的过程;研究区长8期主要受河流作用以及湖浪作用的影响,根据其主要发育的沉积构造类型,将长8期水动力条件划分为河控作用及浪控作用2类;平面上,浪控作用影响区主要发育在研究区的东北部,长81期河流作用较强,长82期受浪控影响区范围更大,符合长8期沉积演化的特征。

The paper takes Chang 8 member of Yanchang Formation in Longdong Area as the study object. The sedimentary characteristics of the Chang 8 period are analyzed by using the rock types, sedimentary structures and paleo-biotic features obtained from the core observation. On this basis, according to the formation relationship between different sedimentary structures and hydrodynamic conditions, the hydrodynamic conditions of Chang 8 period are analyzed, and the influence scope of different hydrodynamic conditions on the plane is determined. According to the analysis, the Chang 8 member of the Longdong Area mainly develops the braided river delta frontal subfacies, and shallow lake sediments develop in the Wuqi Area. During the mid-Chang 8 period, there is a decline of the lake surface and short-term exposure of the water surface. The study period is mainly affected by river flow and lake wave action. According to the main types of sedimentary structures, the hydrodynamic conditions in the Chang 8 period are divided into two types： River control and wave control. In the plane, the wave control area is mainly developed in the northeast of the study area.The river control of late Chang 8 period is relatively stronger, and the wave control area of early Chang 8 period has a wider range.This is consistent with the characteristics of sedimentary evolution of Chang 8 period.