冲积扇沉积向滨岸沉积的转变——以华北克拉通南缘中元古界兵马沟组为例

An Alluvial Fan to Coastal Transition: A case study of Mesoproterozoic Bingmagou Formation,southern margin of the North China Craton

中国华北克拉通南缘的前寒武纪沉积地层发育齐全、出露较好,具有较高的研究价值。但前寒武纪的沉积地层年代久远,缺少佐证的生物依据,对沉积环境的判断更多依赖于构造背景、地理环境、岩石类型和沉积构造等,导致前人研究有较多的争议。以华北克拉通南缘汝阳群兵马沟组为例,通过精细分析岩石特征、古水流和沉积相,结合相关地层的区域对比及古地貌的重建,解释了兵马沟组的沉积成因和环境转换。汝阳群沉积地层不整合覆盖在华北克拉通南缘太古宙变质结晶基底或古元古代熊耳群火山—沉积岩系之上,兵马沟组作为汝阳群底部的地层单元,受地形和断裂的明显控制,接受丰富的物源供给,发育了一套极具特色的"双层叠加"沉积地层,代表了从冲积扇沉积到砂砾质滨岸沉积的环境转变,作为华北克拉通南缘以海相为主控的沉积开端,具有重要的科学价值。

The Precambrian sedimentary strata in the southern margin of the North China Craton are well developed,and widely exposed,it has a high value to study further. But no unambiguous biogenic criteria exist to discriminate Precambrian ancient sedimentary strata,the judgement of sedimentary environment is often based on the tectonic background,geographical environment,rock types and sedimentary structure,resulting in previous research have some controversies. This paper takes Bingmagou Formation in the Ruyang Group in the southern margin of the north China craton as an example,through the analysis of rock features,paleocurrent and sedimentary facies,combined with the regional comparison of relevant strata and the reconstruction of ancient landform,to explain the depositional genesis and the environmental transition of Bingmagou Formation. The sedimentary strata of the Ruyang Group unconformably onlaps Archean crystalline basement or Proterozoic Xionger Group,the Bingmagou Formation as the bottom unit of the Ruyang Group,obviously controlled by topography and fracture,accepted the rich fragment deposition,was a very particular ＂bilayer superimposition＂sedimentary strata,represented an alluvial fan to coastal transition,and it also was the beginning of marine deposition in the southern margin of the North China Craton.