内蒙古桌子山中奥陶统拉什仲组岩石特征及沉积环境

Petrological Characteristics and Sedimentary Environment of the Middle Ordovician Lashizhong Formation at Zhuozishan Area, Inner Mongolia Autonomous Region

内蒙古桌子山中奥陶统拉什仲组主要为一套灰黑色页岩、灰绿色砂岩、粉砂岩及褐灰色砾岩,可分为3个岩性段。通过对岩性、沉积构造、古生物及地球化学等资料的分析,认为拉什仲组沉积环境主要为大陆斜坡至盆地边缘。拉什仲组的沉积相主要为斜坡相及盆地边缘相,并进一步可划分为斜坡上部和斜坡下部2个亚相,近端水道沉积、远端水道沉积及天然堤沉积3个微相。整体上,拉什仲组岩性剖面构成了一完整的海进—海退沉积旋回。

The middle Ordocivian Lashizhong Formation in Zhuozishan area contains mainly dark-gray shale, grayish-green sandstone, sihstone and taupe-gray conglomerate, which could be divided into three members. Based on an analysis of the lithologic character, sedimentary structure, palaeobiologic fossils and geochemical indicators, it is believed that the sedimentary environment of Lashizhong Formation is a deep-water slope to basin margin environment. The results of sedimentary facies analysis show that the slope facies and basin margin facies are main depositional facies in the study area, which can be further divided into two subfacies： the upper slope and lower of slope sediments, and three microfacies： proximal channel, distal channel and levee sediments. The litho-seetion on the whole covers a complete sedimentation eycle of marine transgression and marine ingression.