渭河下游咸阳-草滩段河谷沉积对构造活动的响应

渭河下游咸阳-草滩段河道位于西安凹陷向临潼隆起的过渡区，发育河漫滩和T₁～T₃阶地，渭河断裂隐伏于河道北岸。文章对渭河北岸河谷地貌和地层剖面进行了观测和年代学样品的测试，并对跨渭河断裂的系列钻探中的2个深150m的钻孔岩芯进行了年代学样品测试和地层对比。河谷区地层年代测定表明，渭河北岸在距今约10万年前为风成黄土堆积环境，大致在2.5万年以来开始了最新一期的河道沉积。钻孔岩芯揭露的多个黄土-河流冲积的沉积旋回显示第四纪时期渭河河道经历了多次的南北向摆动。受临潼隆起的影响，咸阳-草滩段晚第四纪河谷沉积自西向东厚度明显减薄。通过对渭河断裂两侧钻孔柱状图的对比，认为渭河断裂0.04～0.05m/ka垂向差异运动速率低于河流0.15～0.24m/ka沉积速率，是渭河断裂隐伏于河谷中的原因。

TECTONIC ACTIVITIES ALONG XIANYANG-CAOTAN VALLEY IN THE LOWER REACHES OF WEIHE RIVER RECORDED IN QUATERNARY SEDIMENT

The Xianyang Caotan section of the lower reaches of the Weihe River locates in the transition region from the Xi′an  Depression to the Lintong Uplift，where floodplain and the first，second，and third terraces of the river were deposited. The Weihe Fault is buried on its north bank. We observed the geomorphology of the Weihe river valley and the stratum on the north shore，and carried out stratigraphic correlation between the two cross fault 150m deep drilling cores. The dating result of the River valley stratum revealed that about 100kaB.P. aeolian loess were deposited at the north bank of the Weihe River，and its latest river sedimentation started since approximately 25kaB.P. Several loess alluvial sedimentary cycles recorded in the drilling cores show that the Weihe riverway had experienced south north swings for many times during the Quaternary period. Affected by the Lintong Uplift，the thickness of the Late Quaternary sediment of the Xianyang Caotan section is thinned remarkably from west to east. The comparison between profiles of the two drillings suggest that the speed of vertical differential movements of the Weihe Fault（0.04～0.05m/ka）was lower than that of fluvial sedimentation（0.15～0.24m/ka），causing the fault buried in the rivervalley.