宁夏香山群徐家圈组发现深水复合流沉积构造  

Deep-Water Combined-Flow Sedimentary Structure in the Xujiajuan Formation of Xiangshan Group,Ningxia

作　　者：李向东[1] 何幼斌[1] 郑昭昌 刘娜[1] 王丹[1] 罗进雄[1] 李华[1] 

机构地区：[1]长江大学地球科学学院,湖北荆州434023 [2]宁夏地质矿产局,银川750021

出　　处：《地质学报》2010年第2期221-232,共12页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号40672071)资助的成果

摘　　要：宁夏香山群徐家圈组是由灰绿、黄绿色轻微变质中—细粒砂岩、钙质砂岩及粉砂岩和页岩(板岩)组成的深水沉积。在上部灰绿色页岩所夹的中层钙质粉砂岩中发现了复合流层理、准平行层理、不对称小型丘状交错层理;在下部灰绿色厚层—块状中—细粒长石石英砂岩的顶面发现了小型波痕,波痕的形态、波长与波高的分布规律均表现出复合流(combined-flow)的沉积特征。本文根据水槽实验和现代海洋沉积观测所总结出的复合流底床相图和前人在研究地层中较浅海浊流(超重流)与波浪所形成的复合流沉积时给出的复合流沉积示意图,分别对徐家圈组所发现的①小型2D波痕至小型3D波痕的演化和②复合流层理、平行层理、准平行层理和小型丘状交错层理的叠置关系及其纹层所反映的流动方向与沉积时浊流方向的关系,进行了解释。结果表明,所发现的复合流层理、准平行层理、不对称小型丘状交错层理及小型波痕应为复合流沉积,并依据徐家圈组存在内波、内潮汐沉积的事实,推测为深水短周期内波与浊流形成的复合流沉积。这可能是地层中深水复合流沉积构造的首次发现,同时也是内波与浊流形成的复合流沉积的首次发现。Deep-water deposits in the Xujiajuan Formation of Xiangshan Group are composed of grayish green, yellowish green, fine- to medium grained light metamorphic sandstone, calcareous sandstone, siltstone and shale （slate）. Combined-flow-ripple lamination, quasi-planar lamination and asymmetric small-scale hummocky cross stratification are found in the medium-bedded calcareous siltstone interlayer of the upper grayish green shale, and small ripples are also found at top of the lower grayish green thick-bedded, massive and medium-grained feldspar-quartz sandstone. The configuration and wavelength of wave and distribution of wave height all suggest sedimentary characteristics of combined-flow. Based on the flume experiment and observation of modern ocean sedimentation, this study in combination with previous researches set up a facies diagram of combined flow bottom, and a schematic diagram of combined flow sedimentation caused by flows and waves in relatively shallow water, both of which can interpret （1） the evolution of small-scale 2-D ripple marks to 3-D ripple marks and （2） superimposed relation of combined- flow ripple lamination, quasi-planar lamination to small-scale hummocky interleaving stratification as well as the lamina reflecting the relationship between flow direction and turbidity current direction. The result shows that the combined-flows are responsible for the formation of the combined-flow ripple lamination, quasi-planar lamination and asymmetric small scale hummocky cross stratification in the Xujiajuan Formation. Based on the fact of existence of internal wave deposition in the Xujiaquan Formation, it can be assumed that combined-flow deposition was the result of interaction of short-period internal wave and turbidity currents. This perhaps is the first discovery of deep-water sedimentary structures of combined-flow origin as well as the combined flow deposition produced by the internal wave and turbidity currents.

关 键 词：复合流 内波、内潮汐 沉积构造 香山群 宁夏 

分 类 号：P512.2[天文地球—地质学]