摘要
宁夏香山群徐家圈组基本组成单元为细砂岩-粉砂岩-页岩构成的沉积序列,将该沉积序列划分为密度流沉积层(Ⅰ)、牵引流沉积层(Ⅱ)和悬浮沉积层(Ⅲ),进而探讨其成因。结果表明:①层Ⅰ主要由细砂岩和粉砂—细砂岩组成,且在不同厚度层之间无明显的粒度分异;②徐家圈组岩性系列中明显缺失细砂质粉砂岩,而这种缺失正好构成了层Ⅰ和层Ⅱ之间的粒度中断;③层Ⅱ发育两组交错层理,第一组是平行层理、准平行层理、复合流层理和小型丘状交错层理,第二组是单向交错层理、双向交错层理和平行层理;④层Ⅲ中的薄层泥晶石灰岩具有不平整的底面并在侧向上呈现出长的透镜状。结合相关的浊流沉积研究成果,综合分析上述结果,可得出以下结论:①层Ⅰ可能为具有高悬浮负载降落速率的高密度衰减流沉积形成;②层Ⅱ可能受内波、内潮汐作用的控制;③层Ⅲ可能以深海、半深海垂直降落沉积为主,并辅以缓慢的平流;④沉积时的浊流可能具有双层结构。
This paper reports the basic unit（i.e.,the sedimentary sequence is composed of fine-grained sandstone,siltstone,and shale） of Xujiajuan Formation of the Xiangshan Group,Ningxia,China.This unit is divided into a lower dense flow deposit division（Ⅰ）,an intermediate traction flow deposit division（Ⅱ）,and an upper suspension deposit division（Ⅲ）.Our results show that： ① divisionⅠis composed of fine-grained sandstone and silty sandstone with no obvious separation of grain-size in different bed thickness;② fine-grained sandy siltstone is very poorly developed,thus,the grain-size break between divisionⅠand divisionⅡwas occurred;③ perfect divisionⅡincludes two series of cross beddings,one is parallel and quasi-planar and combined-flow-ripple lamination and small-scale hummocky cross stratification,the other is unidirectional and bi-directional cross lamination and parallel lamination;and ④ micrites in division Ⅲ exhibit lenticular thin bedding with irregular surface at the bottom.Compared with the previous research on turbidity currents deposition,these results suggest that： ① divisionⅠcould be the product of high density depletive flow with high suspended-fallout rate;② divisionⅡmay be formed by the processes which is dominated by internal-waves and internal tides;③ division Ⅲ may be formed by a complex process involving both vertical setting and slow lateral advection;and ④ the turbidity currents while depositing can be viewed as bipartite flows.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2011年第4期516-525,共10页
Acta Geologica Sinica
基金
国家自然科学基金项目(编号40672071
41072086)
国家科技重大专项(编号2008ZX05043-005)
中国区域地质志修编项目联合资助的成果
关键词
沉积单元
浊流
香山群
宁夏
sedimentary unit
turbidity currents
Xiangshan Group
Ningxia
