中文摘要：

山西平陆黄底沟入三门峡水库北侧发育了一级湖滨阶地（T3）和两级河流阶地（T2和T1）。阶地上覆黄土地层野外划分和室内磁化率测试结果与蓝田段家坡黄土地层的对比结果表明，T3上覆黄土地层最底部为古土壤层S2；T2最底部为黄土层L2中弱发育古土壤层L2-2;T1最底部为马兰黄土L1中弱发育古土壤层L1-4.根据黄土-古土壤年代序列及光释光（OSL）年龄测试结果，T3，T2和T1阶地分别于245kaB．P．，149kaB．P．和50kaB．P．前形成。其中，T3和T2阶地的形成时间。分别代表了山西平陆古三门湖开始消亡和最老黄河阶地形成的年代。古三门湖消亡与黄河贯通三门峡的时代是否一致，有待进一步研究。

英文摘要：

Two fluvial terraces （ T2 and T1） and one lacustrine terrace （ T3 ） can be observed near the mouth of the Huangdigou Ditch （34°50′N, 111°17′E ） which is located at the north bank of the Sanmen Gorge Reservior in Pinglu County, Shanxi Province. As the studied area is in the east of the Chinese Loess Plateau once the terrace is exposed in air it starts its loess deposition. Through field observation, measurements of magnetic susceptibility, and OSL dating of the loess sequences on the terraces at the Huangdigou section, together with the correlation of the curve of the magnetic susceptibility of loess sequences at this section with that at the well-studied Duanjiapo section in the south of the plateau, we suggest that the bottom of the loess sequences on T3, T2 and T1 are palaeosol S2, weakly developed palaeosol L2-2, and weakly developed palaeosol L1-4, respectively. Based on the chronological series of the loess-palaeosol sequences and the results of the OSL dating, T3, T2, and T1 are believed to be formed at 245kaB. P., 149kaB. P., and 50kaB. P., respectively. The ages that T3 and T2 were formed also represent the disappearance of the Sanmen palaeolake and the formation of the Huanghe River terrace respectively. It has been a subject of great interest and vigorous debate as to when the current eastward drainage of the Huanghe River started to form. Available information seemingly suggests that different sections of the river had their separate evolutionary history, depending on regional settings. The Sanmen Gorge is located at the transition of the middle segment and the lower segment of the Huanghe Rive and is considered as the last bar to the river to be unified as its current form to run through to the sea. The disappearance of the Sanmen Palaeolake that once existed at the west of the Sanmen Gorge area is believed to be caused by the running of the Huanghe River through the Sanmen Gorge. However, whether the time of the disappearance of the palaeolake is the time when the Huanghe Rive