【摘要】 宁夏中奥陶统香山群为一套遭受轻微区域变质的陆源碎屑岩,并夹有少量碳酸盐岩和硅质岩,主要为深水浊流沉积。其中,徐家圈组主要由灰绿色、黄绿色轻变质细砂岩、钙质砂岩及粉砂岩和页岩组成,顶部发育有薄层石灰岩。在该组的中—薄层钙质粉—细砂岩、细粉屑质石灰岩和粉砂质页岩中发现了双向交错层理及纹层倾向与区域斜坡倾向相反或有较大夹角的单向交错层理,其中双向交错层理形态丰富、纹层清晰,其纹层倾向有沿斜坡向上的,有沿斜坡向下的。在深水环境中,这些交错层理不应是等深流沉积或浊流沉积的产物,而应为内波产生的沿斜坡上下水流交替流动所形成的。从沉积背景、沉积构造和古水流等方面对徐家圈组的内波、内潮汐沉积进行了详细的研究,认为其形成于水道不发育的深水斜坡环境,并对斜坡环境中内波、内潮汐沉积中不发育脉状、波状和透镜状层理的现象进行了解释。更多还原

【Abstract】 The Xiangshan Group of the Middle Ordovician in Ningxia is dominated by deep water turbidity current deposits which are mainly a set of lightly metamorphic terrigenous clastic rocks with lower content of carbonate rocks and chert interbeds. The Xujiajuan Formation of the Lower Xiangshan Group is composed of grayish green,yellowish green,fine-to medium-grained lightly metamorphic sandstone,calcareous sandstone,siltstone and shale(slate) ,and thin bedded limestone at the top. Cross laminations including bi-directional cross bedding with abundant shapes and clear lamina and unidirectional ones with dipping up-slope or large angle between them are found in thin-to medium-bedded and very fine-to fine-grained sandstones,silty micrite and silty shale. Those lamina of bi-directional cross bedding are also inclined bi-directionally up-and down-slope. These cross beddings in deep water environment may not be formed by contour currents or turbidity currents,but be formed by alternating up-and down-slope currents produced by internal waves and internal tides. This paper has made detailed researches on the internal-wave and internal-tide deposits in the Xujiajuan Formation from sedimentary background,sedimentary structures and paleocurrents. A deep-water slope environment was suggested for the internal-wave and internal-tide deposits and an interpretation was made for the deletion of flaser bedding,wavy bedding and lenticular bedding in this case.更多还原