鄂尔多斯盆地中东部奥陶系马五_4亚段沉积演化及岩相古地理

综合野外露头及钻井岩心、薄片观察,总结了鄂尔多斯盆地中东部奥陶系马五4亚段沉积微相类型及纵向微相序结构类型。并选取膏盐岩累计厚度及膏盐岩累计厚度/地层厚度等单因素,以单因素分析多因素综合作图法理论为指导,对马五43、马五42、马五41b、马五41a等4个小层进行深入研究。分析结果表明,马五4亚段沉积时期处于一个干旱炎热、海平面相对较低的沉积环境,其内部存在隆洼相间的古沉积格局,从马五43沉积时期至马五41沉积时期,相对海平面逐渐上升,海水含盐度逐渐降低,这些是控制各小层沉积微相发育和空间分布的重要因素。

Sedimentary evolution and lithofacies palaeogeography of the 4thsub-member of Member 5 of Majiagou Formation in Ordovician of central and eastern Ordos Basin

Based on the analysis of outcrops,drilling core samples and thin sections,this paper summarized the sedimentary microfacies and its vertical sequence types of the 4th sub-member of Member 5 of Majiagou Formation in Ordovician of central and eastern Ordos Basin. The palaeogeography of four periods which are M5₄³,M5₄²,M5₄^1b and M5₄^1a of Majiagou Formation is studied,mainly based on the parameters including the cumulative thickness of gypsum-salt rock and its ratio to the whole formation. The result shows that the study area is an arid environment with a low sea level during the 4th sub-member of Member 5 of Majiagou depositional period. The sedimentary pattern was uplifts alternate with depressions. From the early to later,the relative sea-level gradually rose and the salinity reduced,which controlled the development and spatial distribution of sedimentary microfacies of these sub-members.