摘要:
宁夏香山群为一套遭受轻微区域变质的砂岩、页岩、石灰岩和硅岩,可分为徐家圈组、狼嘴子组和磨盘井组。徐家圈组为深海斜坡沉积,狼嘴子组和磨盘井组为深海平原沉积。在宁夏中卫大柳树沟和下石棚的徐家圈组下部发现波痕,波长分别为13~15 cm和8~12.5 cm,波高分别为约2 cm和1.1~2 cm。波痕所在岩层底部和下伏岩层见槽模,波痕上覆岩层中见交错层理。通过对波痕、槽模、交错层理进行野外资料的采集,对古流向进行了分析。大柳树沟的波痕、槽模、交错层理反映古流向分别为SSE向、SSE向和NE向;而在下石棚地区分别为NW向、SSW向和SWW向。本文用复合流模式分析了波痕的成因,并对槽模、波痕、交错层理组成的沉积构造组合的形成过程进行了阐述。
关键词:
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香山群
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徐家圈组
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波痕
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复合流
Abstract:
The Xiangshan Group in Ningxia consists of the Xujiajuan Formation in the abyssal slope environment,and the Langzuizi and Mopanjing Formations in the abyssal plain environment.The ripple marks from the lower part of the Xujiajuan Formation of the Xiangshan Group in Ningxia have the wave lengths in 13~15 cm and the wave heights about 2 cm in Daliushugou,and the wave lengths in 8~12.5 cm and the wave heights in 1.1~2 cm in Xiashipeng.The flute casts are observed in the basal and underlying beds,while the cross-beddings appear in the overlying beds.The palaeocurrents indicated by the ripple marks,flute casts and cross-beddings are oriented to SSE,SSE and NE,respectively in Daliushugou while to NW,SSW and SWW,respectively in Xiashipeng.The ripple marks in the study area may owe their origin to the combined flows.
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