摘要
【研究目的】在世界地质公园丹霞地貌区发育较多的河流阶地,但迄今对其研究相对较少,尤其缺乏对相关河流阶地形成年代的研究。旨在获得阶地的可靠年代,重建河流下切过程,并探讨气候变化响应机制。【研究方法】调研了丹霞山地区的锦江和灵溪河(山间溪流)具河流“二元结构”沉积特征的河流阶地剖面,并采用粗颗粒石英和钾长石光释光测年方法获得阶地年代,再结合深海氧同位素及阶地高度进行对比分析。【研究结果】测年结果显示,锦江T_(0)河漫滩、T_(1)、T_(2)阶地及灵溪河T_(1)阶地的堆积年代分别为0.4±0.1 ka、70.1±6.1 ka、300.6±14.7 ka及18.3±3.2 ka。锦江T_(1)和T_(2)阶地沉积时间分别对应深海氧同位素MIS5–MIS4阶段转型期和MIS9–MIS8阶段转型期。这表明,在暖期向冷期转型阶段,锦江的沉积通量超过河流搬运能力,阶地持续沉积。后期气候改变使得河谷下切,前期的河漫滩沉积物与下伏宽谷面形成了阶地。而灵溪河T_(1)阶地形成于MIS2期间,山间溪流携带大量沉积物堆积。根据阶地砾石层和.阶地面高度与年龄的关系,估算出锦江在300~70 ka和约70 ka至今2个时间段的最小下切速率分别为0.05±0.002 mm/a和0.22±0.02 mm/a。【结论】该下切速率显著加快,可能主要由以下3个因素造成:(1)河流侵蚀与加积作用交替,长时间的平均下切速率通常偏低;(2)河流切割冲洪积物速率快于切割基岩;(3)末次冰期以来气候变幅增大,导致河流侵蚀速率增加。这些下切速率数据为丹霞地貌演化过程的恢复和重建提供了重要依据。
[Objective]In the Danxia landform area,numerous river terraces have developed,yet research on them has been relatively limited,particularly concerning their dating.River terraces serve as valuable records of the incision processes of rivers and associated environmental changes.Investigating the chronostratigraphy of these terraces enhances our understanding of Danxia landform evolution,reconstructs river history,and explores responses to climate change.[Methods]In the Danxiashan area of northern Guangdong,the river terrace profiles of the Jinjing River and Lingxi River(intermountain streams)exhibit sedimentary characteristics of a river"dual structure".[Results]Optically stimulated luminescence(OSL)dating reveals deposition ages for the T0 floodplain,T_(1) and T_(2) terraces of Jinjing River,as well as the T_(1) terrace of Lingxi River,at 0.4±0.1 ka,70.1±6.1 ka,300.6±14.7 ka,and 18.3±3.2 ka,respectively.The sedimentation periods for the T_(1) and T_(2) terraces of Jinjing River align with transition phases of deep-sea oxygen isotope stages 5 to 4(MIS5-MIS4)and 9 to 8(MIS9-MIS8),respectively.This suggests that during the shift from warmer to cooler periods,the sediment flux of the Jinjing River exceeded its transport capacity,resulting in ongoing terrace deposition.Subsequent climatic shifts led to valley incision,forming terraces from earlier floodplain deposits and the underlying broad valley surface.The T_(1) terrace of Lingxi River emerged during MIS2,during which the intermountain stream carried a significant amount of sediment.By analyzing the relationship between the gravel layers of the terraces,their heights,and their ages,we estimated the minimum incision rates for the Jinjing River during two periods:300 ka to 70 ka and 70 ka to the present,at 0.05±0.002 mm/a and 0.22±0.02 mm/a,respectively.[Conclusions]The notable increase in incision rate may be attributed to three primary factors:first,the alternation between river erosion and sediment accumulation,leading to a generally low long-term average incision rate;second,the rate of river cutting through alluvial deposits surpassing that through bedrock;and third,the increased climate variability since the last glacial period,which has amplified river erosion rates.These incision rate data provide crucial insights for reconstructing the evolution of Danxia landforms.
作者
罗明
郭福生
龚志军
陈留勤
周万蓬
彭花明
蒋晓鸿
LUO Ming;GUO Fusheng;GONG Zhijun;CHEN Liuqin;ZHOU Wanpeng;PENG Huaming;JIANG Xiaohong(School of Earth Sciences,East China University of Technology,Nanchang 330013,Jiangxi,China)
出处
《地质通报》
北大核心
2025年第9期1722-1735,共14页
Geological Bulletin of China
基金
广东国家公园建设专项资金项目《丹霞盆地地质条件对丹霞地貌形成的制约》(编号:2021GJGY026)
东华理工大学科研发展基金项目《丹霞山地貌与断裂遥感解译》(编号:FZJJ20231220)
中央专项彩票公益金支持未成年人校外教育教育项目《地震灾害科学研究与科学普及项目》(编号:G20200002)。
关键词
丹霞山
河流阶地
光释光
锦江
下切速率
Danxiashan
river terraces
OSL dating
Jinjiang River
incision rates
