川西龙门山前陆盆地南段前缘砾石层成因及青衣江演化过程:基于宇宙成因核素26Al/10Be埋藏年龄
Origin of the Gravel Layer and Evolution of the Qingyi River in Front of the Southern Longmen Shan Foreland Basin:Insights from the Burial Age of Cosmogenic Nuclides 26Al/10Be
周游 1李斌 1吴中海 2左嘉梦 3邹任洲 4郑丽萍5
作者信息
- 1. 韩山师范学院地理科学与旅游学院·潮菜学院,广东潮州 521041
- 2. 中国地质科学院地质力学研究所,北京 100081
- 3. 山东省水利勘测设计院有限公司,山东济南 250013
- 4. 中国建筑材料工业地质勘查中心广东总队,广东广州 510450
- 5. 韩山师范学院现代教育技术中心,广东潮州 521041
- 折叠
摘要
四川西部(川西)龙门山前陆盆地自中新世以来发生强烈隆升,形成了陡峻的地形梯度带.在紧邻龙门山断裂带的四川盆地堆积一系列砾石层,其中包括名邛(名山—邛崃)砾石层、丹思(丹棱—思蒙)砾石层.名邛砾石层、丹思砾石层为古青衣江堆积砾石层,是古青衣江改道的产物,也是探究青衣江演化及该地区古环境变化的良好对象.基于龙门山前缘地区野外调查和名邛砾石层、丹思砾石层的宇宙成因核素26Al/10Be定年测试,发现名邛砾石层埋藏年龄为(0.6089±0.0187)Ma,丹思砾石层埋藏年龄为(0.2180±0.0941)Ma,由此推断名邛砾石层形成时间为早更新世晚期—中更新世早期(Q31—Q12),丹思砾石层形成时间为中更新世中期(Q22).结合前人研究结果分析,两套砾石层分别对应于深海冰心δ18O曲线和中国黄土序列曲线,都形成于温暖的间冰期.结合前人对该地区的砾石成分、砾径、砾向统计分析和古流向分布等研究,认为青衣江水系经历三次主要的改道事件,早期的青衣江由雅安往北北东方向流向建山,随着熊坡背斜的隆起和名邛台地的持续抬升,由南西-北东流向的青衣江被迫在草坝东南方向切断熊坡背斜从而改道南东方向.
Abstract
Since the Miocene,strong thrust uplift has occurred in the Longmen Shan nappe tectonic belt,resul-ting in the formation of a steep topographic gradient zone.In the foreland region,ancient alluvial fans composed of gravels have been widely developed,primarily including the Mingshan-Qionglai(MQ)and Danling-Simeng(DS)gravel layers.These layers,deposited by the ancient Qingyi River,are ideal for exploring the river's evo-lution and the paleoenvironmental changes in this region.We conducted field investigation in the Longmen Shan Foreland region and performed cosmogenic nuclide 26Al/10Be dating analysis on the MQ and DS gravel layers.The analysis indicates that the burial age of the MQ gravel layer is 0.608,9±0.018,7 Ma,and the burial age of the DS gravel layer is 0.218,0±0.094,1 Ma.Therefore,we conclude that the MQ gravel layer formed in the late Early Pleistocene to early Middle Pleistocene(Q31-Q12),and the DS gravel layer formed in the Middle Pleistocene(Q22).Combing previous research results,the two gravel layers correspond to the δ180 curve of deep-sea ice core and the sequence curve of Chinese loess,indicating they formed during a warm interglacial period.Based on statistical analysis of gravel composition,size,orientation,and paleoflow directions in the re-gion,three major diversion events have been identified in the Qingyi River system.In the early stage,the Qingyi River flowed from Ya'an in a north-northeast direction towards Jianshan.With the uplift of the Xiongpo anticline and the continued uplift of the Mingshan Qionglai terraces,the Qingyi River,which initially flowed from the southwest-north to the northeast,was forced to cut through the Xiongpo anticline and divert southeast at Caoba.
关键词
宇宙成因核素定年/名邛砾石层/丹思砾石层/青衣江Key words
cosmogenic nuclide/Mingshan Qionglai gravel bed/Danling-Simeng gravel bed/the Qingyi river引用本文复制引用
基金项目
韩山师范学院2021年教授博士启动项目(QD202106)
出版年
2024
国家科技期刊平台
NSTL
万方数据