浊流与等深流的流态转化

Transformation from Turbidity Current to Contour Current

小型交错纹理、大型纵向交错层和粘性交错层不可能在浊流沉积体中存在,从B、C、D、E段的沉积特征上唯一能得出的结论是组成这些单元的颗粒在沉积前或搬运的最后阶段是被牵引流搬运的,并非浊流成因。浊流沉积仅仅是发育在A段的重力流沉积,在B、C、D、E段转化为等深流,等深流在浊流的后期广泛发育并占主体地位。从沉积相、相组合、古流向以及遗迹化石的生态特征等方面,详细阐述了内蒙古桌子山中奥陶统拉什仲组碎屑岩沉积特征和沉积类型,识别出碎屑岩等深岩体,认为拉什仲组不存在鲍玛序列。

The small cross lamination, the large vertical cross-bed and the glutinous cross-bed dould not exist in the sedimentary system. The conclusion from all the sedimentary characters of B, C, D and E segments is that the grains for forming these segments are transported by the tractive current in the last stage or before the sedimentation, not formed by turbidity current. The turbidite deposit is simply gravity current deposit in A segment, which is converted into contour current in B, C, D and E segments, hence being widely developed and dominant in the late stage of the turbidity current. In this paper, the clastic sediments and types of Lashizhong formation of Middle Ordovician in Zhuozishan area in Inner Mogolia are presented in view of sedimentary facies, facies family, paleo-current direction and the ecologic features of fossil ichnocoenosis. And the identified clastic contourite indicates that no Bouma sequence occurs in this formation.