内蒙古桌子山中奥陶统的“特殊”浊积岩系

The “Special” Turbidite Measure of the Middle Ordovician Series in Zhuozishan Area, Inner Mongolia

内蒙古桌子山中奥陶统拉什仲组是由鲍马层序清晰的多层浊积岩组成的浊积岩系,然而其沉积序列总厚度以及浊积岩内部特征等诸多方面,又与那些形成于不稳定或次稳定型外陆架边缘直至深海盆内的巨厚浊积岩系有着明显的差异,因此将拉什仲组以“特殊”浊积岩系称之。文中在对这两种浊积岩系进行多方面的对比研究后,进而从沉积相、相组合、浊流的古流向以及遗迹化石群落的生态特征等方面,阐述了形成拉什仲组浊流盆地的特征,并认为:充填这套“特殊”浊积岩系的海盆是位于稳定地块之间、盆地地形简单、坡度不大、海水深度在浪基面以下 200m左右、含氧量较充足的深水浊流盆地。

The Lashizhong Formation of the middle Ordovician in Zhuozishang area, Inner Mongolia is a set of turbidite measures, which is composed of lots of turbidite beds with clear Bouma sequence. However, the eminent differences exist between Lashizhong formation and those formed in the unstable and sub-stable continental shelf margin to the deep-sea basin, such as in their total sequence thickness and internal features. This is the reason that we call the turbidite of the Lashizhong Formation as the special' turbidite measure. In this paper, the comparison study is performed according to the two turbidite measures, and, furthermore, elucidate the basin characteristics based on the depositional facies, combination, paleocurrent direction and trace fossil, etc., and reached the conclusion that the Lashizhong turbidite is formed in the stable deep-sea basin, which is located between the stable massifs with simple landscape and gentle slope, and the water depth is 200m under the wave base with ample oxygen.