贵州涟江惠水段河流阶地特征与地貌演化研究

River terrace characteristics and their geomorphic significance in Huishui Basin along Lianjiang River in Guizhou Plateau

贵州涟江惠水段级次清晰的四级阶地是流域地貌阶段性演化的直观记录。笔者等利用差分GPS测量法精确厘定了涟江阶地的级序和高程,结合剖面观测发现从上游到下游,涟江惠水段阶地标高和级差逐渐降低,地貌面整体呈“收拢”趋势;阶地沉积物呈现砾石层厚度变小,砾石含量降低、砾径减小,砂质沉积占比增大趋势;阶地类型从基座阶地为主向堆积阶地为主演变。光释光(OSL)测年显示,T1阶地埋藏年龄31.2±2.0 ka BP到14.7±1.3 ka BP,T2阶地122.4±8.5 ka BP到66.9±3.8 ka BP,阶地年龄与贵州高原其他流域十分相近,具有同步演化特征。结合阶地时代和发育特征,认为贵州高原河流阶地是构造运动的产物。涟江四级阶地记录了在更新世以来四次构造抬升背景下,流域经过多期自北向南“削高补低”的地貌改造,逐步由构造洼地演变为山间盆地的地貌过程。

Objectives:River terrace contains a lot of paleo-environmental information such as hydrology,climate and neotectonics.Therefore,terrace research is always an important means to reconstruct the geomorphic process of the basin.In Huishui Basin of Lianjiang River,well-preserved river terraces are perfect indicators for studying the geomorphic evolution process of the basin in Guizhou Plateau.Methods:Through field investigation,the sequence and sedimentary characteristics of terraces were analyzed in different sections along the Lianjiang River.Differential GPS was used to accurately determine the elevation of these terraces.Optically stimulated luminescence(OSL)dating was used to discuss the ages of the terraces.Results:In Huishui Basin,the terraces in the upper reaches along the Lianjiang River are more developed and better preserved than those in the lower reaches.From north to south,the altitude,the elevation above river level and the height difference of the terraces both decrease along the Lianjiang River,which shows the terrain of Huishui Basin tends to converge from upstream to downstream.Along the Lianjiang River,the thickness of terrace gravel layer gradually decreases,the gravel content and size also gradually decrease,and the sandy sediment in terrace gradually increase from the upstream to the downstream.There are more base terraces in the upstream and more accumulation terraces in the downstream.The OSL ages of terrace T1 are from 31.2±2.0 ka BP to 14.7±1.3 ka BP and those of T2 are from 122.4±8.5 ka BP to 66.9±3.8 ka BP,which are comparable with the ages of other basins in Guizhou Plateau.Conclusions:Combined with the dating of terraces in other basins of Guizhou Plateau,it is believed that terrace T1 in Huishui Basin was formed from the end of the Late Pleistocene to the early Holocene,and terrace T2 was formed in the middle of the Late Pleistocene.This work hold that the tectonic uplift is the main driving force for the development of river terraces,and the four terraces along the Lianjiang River are the geomorphic records of four tectonic uplifts in Guizhou Plateau since the Pleistocene.The formation of the Huishui Basin records the staged geomorphic transformation process of the basin by eroding upstream and supplying downstream from north to south.