黄河上游乌海宽谷河流阶地特征与地貌演化研究  

River terrace characteristics in the Wuhai broad valley at the upper reachesof the Yellow River and their implications for landform evolution

作　　者：刘晓波 李荣西[1] 全成 吴小力[1] 张皓颖 曹鹏举 LIU Xiaobo;LI Rongxi;QUAN Cheng;WU Xiaoli;ZHANG Haoying;CAO Pengju(Chang'an University,School of Earth Science and Resources,Xi'an,Shaanxi 710054,China)

机构地区：[1]长安大学地球科学与资源学院,陕西西安710054

出　　处：《地质学报》2025年第3期960-975,共16页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号42202022);陕西省基金项目(编号2021JQ-240);中央高校基金项目(编号300102271403,300102262903)联合资助的成果。

摘　　要：位于银川盆地和河套盆地交接处的乌海宽谷的形成,直观记录了黄河上游末段的历史演化过程。然而,该段黄河阶地的地层-年代序列还未建立、黄河的形成和切割历史仍不明确。本文在野外地貌、地层和沉积学调查的基础上,确定了乌海宽谷东侧的4级河流阶地,结合光释光(OSL)测年方法对阶地沉积物进行了定年。结果表明,T1阶地为堆积阶地,阶地废弃年龄大于0.52±0.04 ka;T2~T4阶地为基座阶地,沉积序列相似,上部为河流相沉积,下部为湖相沉积。T2、T3和T4阶地废弃年龄约为41.98±2.70 ka、67.48±4.07 ka和102.32±6.00 ka;阶地T4~T3、T3~T2和T2~T0间的平均下切速率分别为:0.11 mm/a(102~67 ka)、0.24 mm/a(67~42 ka)、0.26 mm/a(42 ka至今),显示黄河下切速率逐渐增加的特征。乌海宽谷T2~T3阶地中湖相地层时代与晚更新世“吉兰泰-河套古大湖”发育时间一致,说明当时该古大湖的范围已到达乌海宽谷。乌海宽谷河流阶地的形成是在古大湖范围缩小、消亡的过程中发育的,代表着晚更新世黄河上游末端湖-河地貌之间的演变。通过与鄂尔多斯盆地周缘各黄河阶地低级序列的详细对比,结合区域构造及气候信息,认为晚更新世乌海宽谷河流阶地的形成及湖-河地貌的演变主要受控于区域构造活动。The formation of the Wuhai broad valley(WBV),located at the junction of the Yinchuan basin and the Hetao basin,provides a visual record of the historical evolution at the end of the upper reaches of the Yellow River.However,the stratigraphic-chronological sequence of the Yellow River terraces in this section has not yet been established,and the formation and cutting history of the Yellow River in this area are still unclear.This paper presents a detailed investigation of the WBV,based on field geomorphological,stratigraphic,and sedimentological analyses.Four levels of fluvial terraces were identified on the east side of the WBV,and their ages were determined using optically stimulated luminescence(OSL)dating.Results show that terrace T1 is a depositional terrace with an abandonment age older than 0.52±0.04 ka.Terraces T2~T4 are basal terraces,characterized by a similar sedimentary sequence consisting of fluvial deposits in the upper part and lacustrine deposits in the lower part.The maximum estimated abandonment ages for terraces T2,T3 and T4 are about 41.98±2.70 ka,67.48±4.07 ka and 102.32±6.00 ka,respectively.The average incision rates from T4 to T3,T3 to T2,and T2 to T0 are calculated to be 0.11 mm/a(102~67 ka),0.24 mm/a(67~42 ka)and 0.26 mm/a(42 ka to modern),respectively.This shows a gradual increase in incision rate since 102 ka.The age of the lacustrine deposits in the terraces T2~T3 coincides with the development of the Late Pleistocene“Megalake Jilantai-Hetao”indicating that the extent of this megalake reached the study area during this period.The formation of the fluvial terraces in the study area was driven by the shrinking and disappearance of the“Megalake Jilantai-Hetao”representing a transition between lake-river landforms at the upper reaches of the Yellow River in the Late Pleistocene.Through detailed comparisons with low-level sequences of various fluvial terraces around the Ordos block,combined with regional tectonic and climatic information,it is concluded that the formation of the

关 键 词：河流阶地 地貌演化 晚更新世 乌海宽谷 黄河上游 

分 类 号：P61[天文地球—矿床学]