中文摘要：

根据野外考察、粒度分析及历史文献资料，研究了西安北郊草店村剖面在距今900~660 a形成的渭河漫滩沉积和洪水变化。结果表明，在距今900~660 a形成的草店村剖面洪水沉积分层明显，能够指示洪水事件和洪水深度。草店村剖面洪水沉积厚度为525 m，可划分为26个沉积层，指示了26次规模不同的洪水事件。洪水沉积厚度和粒度成分显示，草店村剖面的26个洪水事件发生时河漫滩上的洪水深度均大于2.2m；剖面下部第17~第26层沉积时漫滩上的洪水深度为4.0~7.0 m，河床水深为6.2~8.5 m；中部第8~第16层沉积时漫滩上的洪水深度为3.0~5.0 m，河床水深为6.6~9.0 m左右；上部第1~第7层沉积时漫滩上的洪水深度为2.2~3.0 m，河床水深为7.2~8.6 m。草店村剖面中部和下部的洪水沉积以中砂和细砂为主，剖面上部以粉砂和极细砂为主，指示的洪水规模比距今120 a来西安渭河洪水显著大。草店村剖面中的第12、16~26层代表的是特大洪水事件。西安北郊渭河在距今900~660 a发生的大洪水主要是由当年降水量的明显增加引起的。

英文摘要：

Objectives： The purpose of the study is to reveal the scale and the depth of floods in historical periods, so that to provide a scientific basis for the prediction of flood scale and toreduce the losses caused by flood disasters. Methods ： Methods used in the study are field investigation, grain - sizedistribution analyses and compilation of historical data. Results： The flood deposition of the study section,lying in Caodian Village at northern suburb of Xi＇ an, was formed during 900 to 600 years ago. It is 5.25 meters thick and can be divided into 26 layers. It has a significant reflection and resolution on the occurrence of floods and short - term change of precipitation, andan indication of the frequency and depth of floods. There are some special characteristics of the floodplain sediments in this section, including coarse grain composition, high content of medium sand and fine sand, and less content of clay and silt. The content of colloidal particles（ 〈0. 002ram） ranges from 1.15% to 8.03% with an average of 3.33%. The average content of clay particles（0. 002 -0. 005mm） is 4.29% , ranging from 2.12% to 8.61%. The fine silt （0. 005 ~0.01mm） content ranges from2.52% to 11.14%, with an average content of 4.85%. Coarse silt（0.01 -0. 05mm） has a high content but great rangefrom9.89% to 62.33% , with an average of 22.14%. There is a certain amount of very fine sand（0.05 -0.10 mm） in each layer, ranging from2.19% to 30.88% with an average content of 9.32%. The content of fine sand （0. 10 -0.25mm） ranges greatlyfrom0.52% ~ 37.08%, with an average content of 19.46%. The content of medium sand （0.25 ~ 0.50 mm） is high but, again, ranges greatly from 0 to 46.64% with the average 27.07%. The content of coarse sand（0.50 -2.00 mm） changes rapidly from 0 to 26.11% , with an average content of 8.67%. The content of gravel（ 〉 2.00 mm） is very small in the whole profile, and only appears in the 18th, 19th, 22nd, 23rd, 2dth and 26th layers. And they display a maximum content