鄂尔多斯盆地天生桥剖面盒8下段辫状河沉积特征

Depositional characteristics of braided river in the lower member of He-8 in the Fugu Tianshengqiao section, Ordos Basin, China

以鄂尔多斯盆地东北部府谷县天生桥实测剖面资料为基础,通过岩石学特征、碎屑结构、沉积构造等相标志分析,对中二叠统下石盒子组盒8下段沉积相特征进行解剖,进而建立其沉积模式。盒8下段以灰白色粗粒岩屑砂岩及岩屑石英砂岩为主,结构成熟度中等-较低,槽状交错层理、板状交错层理及楔状交错层理等沉积构造发育,垂向上具"二元结构"特征不明显的正粒序特征,为典型的辫状河沉积。其中可识别出河道与堤泛2种亚相及滞留沉积、心滩、废弃河道、河道充填、越岸沉积和泛滥平原等6种微相。结合沉积微相的垂向变化规律,建立了研究区多河道的缓坡型辫状河沉积模式。

The characteristics of sedimentary facies of the middle Permian He-8 lower member in the Ordos Basin are studied through the measured cross section at Tianshengqiao, combined with the analysis of lithology, clastic texture and sedimentary structure in order to establish its depositional model. It shows that the lower member of He-8 in the Tianshengqiao section is mainly composed of gray and white colored, coarse grained lithic sandstone and lithic quartz sandstone with medium-low structural maturity and with binary structure in profile, characteristic of a typical braided river deposition. Two subfacies of channel and embankment can be recognized which can be subdivided into six kinds of microfacies, such as lag deposit, braided river bar, abandoned channel, channel filling, overbank deposit and flood plain. Based on vertical variation rule of sedimentary microfacies, the sedimentary model of multi-channel gentle slope braided river in the study area is established.