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五台山北麓断裂为山西断堑系北部繁代盆地南缘的控制断裂,其南峪口段断层陡坎类型大致有洪积台地陡坎、基岩陡坎和黄土陡坎。本文对选取的6个较为典型位置开挖的探槽进行分析,通过分别分析对比其坎前堆积的特点及各位置的特点,认为五台山北麓断裂南峪口段坎前沉积特征可分别从冲沟沟口、沟口与扇间洼地过渡带、洪积扇扇间洼地和洪积扇扇缘四类地貌单元进行探讨。冲沟沟口坎前沉积最主要的特征为:可见多级冲积锥,未见崩积楔;沟口与扇间洼地过渡地带坎前沉积特征为少量黄土参与陡坎演化过程并发育条带状古土壤,洪积相砂砾石层大量分布并与坡积物呈侵蚀接触关系;扇间洼地坎前沉积特征为同深度发育较多级崩积楔,大量发育风成黄土,洪积相砂砾石层以透镜体形状发育于黄土中;洪积扇扇缘的黄土陡坎坎前沉积特征为黄土沉积参与的陡坎演化过程,崩积楔之上顺层发育黄土状坡积物或黄土夹砂砾石层坡积物,该坎前沉积受洪积作用影响极小。崩积楔发育特征为:开挖同样深度下由沟口向扇间洼地可揭露崩积楔数量逐渐增多;洪积相砂砾石层由扇顶到扇缘所占比重逐渐减小,对坎前沉积的影响逐渐减小,成层性逐渐变好;坎前黄土沉积由扇顶到扇缘比重逐渐增大,由薄层的黄土状坡积物逐渐变为厚层的黄土沉积。该结论为山西地堑系正倾滑断层坎前沉积特点提供了对比依据,并对该地区古地震研究探槽开挖有一定指导意义。
The northern foot of Wutai Mountain is the controlled fault in the southern margin of the Fan-Fan Basin in the northern part of Shanxi Graben System. The faulty scarp of the Nanyukou fault section is roughly the Hongjian platform scarp, bedrock ridge and loess scarp. In this paper, the analysis of six typical trenches excavated is made. By comparing and analyzing the characteristics of the pre-emplacement and the characteristics of each location, it is concluded that the sedimentary features of the Nan- Ditch Mouth, Mizoguchi and fan depression transitional zone, alluvial fan depression and alluvial fan margin four types of geomorphological units are discussed. The most important features of pre-depositional deposition in the gully ditch mouth are: visible multi-stage alluvial cones, no wedging wedge; sedimentary characteristics of the transitional zone between Mizoguchi and fan-depression depressions are that a small amount of loess participates in the evolution of scarp and develops banded Paleosols and alluvial facies sand and gravel layers are distributed in a large amount and are in eroded contact with the slope sediments. The pre-emphysemic sedimentary features of the inter-depressions are those with more levels of sedimentation wedges, and abundant aeolian loess, alluvial facies gravel And the layer developed in loess with lenticular shape. The pre-sediment characteristics of the loess horizons in the margin of the alluvial fan are the evolution of steep valleys involved in the loess sedimentation. Loess-shaped slope sediments or loess sand gravel Stratum sediment, the pre-emplaced sedimentation effect is minimally affected. The characteristics of the accumulation wedge are: the number of the accumulation wedge can be exposed gradually from the Mizoguchi to the inter-sub-depression at the same excavation depth; the proportion of the gravel layer of the alluvial phase gradually decreases from the fan- The influence of sedimentation is gradually reduced and the stratification becomes better gradually. The proportion of loess sediments from fan-head to fan-edge increases gradually from the thin loess-like slope sediments to the thick loess sediments. This conclusion provides a comparative basis for the preanodal sedimentary characteristics of the positive-tilting fault in Shanxi Graben and provides some guidance for the research on the exploration of troughs in paleoearthquakes in this area.