摘要:西秦岭北缘构造带是现今青藏高原东北缘重要构造边界带。该构造带内新生代沉积地层出露完整，包括渐新统—中新统巨厚的河流相—洪泛相—三角洲相—浅湖相—深湖相多旋回沉积地层和角度不整合其上的上新统冲积扇砾岩层，其中漳县含盐盆地沉积序列底部渐新统砾岩层（孙家峡砾岩）和上新统砾岩层（韩家沟砾岩）是两套代表性砾岩沉积。虽然两套砾岩都为粗砾岩，但沉积特征却存在显著差异。本文通过对两套砾岩的地貌特征、沉积岩石组合、砾岩的砾石结构和成分及古流向等特征的比较，提出了孙家峡砾岩是一套典型的河流加积砾岩层，而韩家沟砾岩则是一套典型的冲洪积扇粗砾岩的认识。结合对两套砾岩空间分布、地层产状和其上覆、下伏地层的接触关系以及其与区域断层之间的构造配置关系等分析，认为渐新统孙家峡砾岩是伸展正断层控制的断陷河谷沉积，而上新统韩家沟砾岩则是逆冲断层控制的冲洪积扇沉积。这为西秦岭北缘新生代不同阶段的构造属性、构造转换和青藏高原东北缘隆升过程等提供了新的地质约束。
关键词: 西秦岭北缘/
新生代/
上新统砾岩/
渐新统砾岩/
砾石特征
Abstract:The northern margin tectonic belt of the West Qinling is an important tectonic boundary zone in the northeastern margin of Qinghai-Tibet Plateau. There are exposed the complete Cenozoic sedimentary stratigraphic sequences in this tectonic belt which include Oligocene-Miocene thickened fluvial-lacustrine-delta facies and salt bearing sedimentary sequence and Pliocene alluvial fan conglomerate unconformable covering on the Oligocene-Miocene sequence. The Oligocene Sunjiaxia conglomerate developed at the bottom of the Oligocene-Miocene sequence and Pliocene Hanjiagou conglomerate are two typical conglomerates. Although the two sets of conglomerates are all coarse conglomerates, there are significant differences in sedimentary characteristics. By comparing the geomorphic features, sedimentary rock association, gravel size, roundness, sorting and composition of the two sets of conglomerates, it is proposed that the Sunjiaxia conglomerate is a typical fluvial aggradational conglomerate, while the Hanjiagou conglomerate is a typical alluvial fan coarse conglomerate. Furthermore, based on the analysis for the spatial distribution, occurrence, contact relationship with their overlying and underlying strata and as well as the tectonic configuration relationship with the regional faults, it is suggested that the Oligocene Sunjiaxia conglomerate is the fault valley deposits controlled by the extensional normal fault, while the Pliocene Hanjiagou conglomerate is the alluvial fan deposit controlled by thrust fault. The above understandings provide new geological constraints for the tectonic attribute, tectonic transformation and uplift process of the northeastern margin of the Qinghai Tibet Plateau in different stages of Cenozoic.
Key words:The northern margin of West Qinling/
Cenozoic era/
The Oligocene Sunjiaxia conglomerate/
Pliocene Hanjiagou conglomerate/
Gravel characteristics
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