柴达木盆地滩坝沉积特征、成因及沉积模式:以扎哈泉地区上干柴沟组为例

Sedimentary Characteristics, Oriqin, and Model of Beach-Bar in the Qaidam Basin: A Case of the Upper Ganchaigou Formation in the Zhahaquan Area

文章在对600多米岩芯颜色、沉积构造、粒度分析、薄片等进行研究的基础上,分析了柴达木盆地扎哈泉地区滩坝沉积特征,研究了滩坝在层序地层格架中的分布及成因,建立了滩坝砂体沉积模式。结果表明,上干柴沟组滩坝单砂体厚度较薄,滩坝中发育较多典型的波浪作用形成的沉积构造,粒度概率累积曲线多以跳跃和悬浮两个总体为主。坝砂体主要发育于中长期基准面旋回的可容纳空间较大处,且多分布于短期基准面旋回上升半旋回可容纳空间较大处;滩主要发育于各级别基准面旋回中可容纳空间较小处。滩坝的形成与可容纳空间的大小及沉积水动力条件有关,在高可容纳空间条件下,水体较深,湖泊面积大,易形成大的湖浪和湖流,从而发育坝砂体。最后,根据瓦尔特定律,结合一个中短期基准面旋回过程中沉积类型垂向变化,建立了上干柴沟组滩坝沉积模式。

Based on comprehensive analyses of color,sedimentary structure,particle size and thin sections for 600 meters cores,this paper analyzed the sedimentary characteristics of beach-bar in the Zhahaquan area,Qaidam Basin,studied the distribution and origin of the beach-bar in the sequence stratigraphic framework,and finally established the beach-bar sedimentary model.Results show that the single sand body of beach-bar is thin in the Upper Ganchaigou Formation.There are many typical sedimentary structures formed by wave action in beach-bar.The probability accumulation curve of particle size is mainly composed of two population: jumping and suspended types.The bar is mainly developed in the large accommodation space of medium-and long-term base level cycle,and mostly distributed in the large accommodation space of rising half cycle of short-term base level cycle.The beach is mainly developed in the small accommodation space of base level cycle.The formation of the beach-bar is related to the accommodation space and the sedimentary hydrodynamic conditions.Under the condition of high accommodation space,the water body is deep and the lake area is large,which is favorable for forming large lake waves and lake flows.As such,the bar is developed.According to Walter’s law,the sedimentary model of the Upper Ganchaigou Formation is established in combination with vertical variation of sedimentary types in a medium- to short-term base level cycle.