MODELS OF LOESS STRATIGRAPHICAL STRUCTURE ON THE TERRACES IN THE LOESS PLATEAU OF CHINA

There are generally 5~6 terraces along the main rivers and their affluents in the Loess Plateau.The loess is overlying these terraces like mantles.Divided by the Liupanshan Mts.,the loess stratigraphical structure on the terraces may be subdivided into two stratigraphical regions:the west and the east.In the west region,the highest terrace is terrace VI,on which loess section is about 310~505 m thick with 21~23 layers of paleosol,being the thickest loess deposits in the world at present.The loess on terrace VI began to form during 1.43 MaBP.Loess on the terrace consists of layers of soil from L1 to S14 or S16,200~400 m in thickness,and dated at about 1.23 MaBP.Terrace IV loess is made up of layers of soil from L1 to S5 or S6,100~200 m in thickness and dated at about 0.62 MaBP.Terrace Ⅲ loess consists of L1 and S1,about 40~65 m in thickness and dated at about 0.12 MaBP.Terrace Ⅱ loess is about 20~35 m thick and dated at about 0.03 MaBP.Terrace I loess consists of black loam(S0),and upper loess(L0),2~3.5 m in thickness,and dated at about 0.01 MaBP.In the east region,there are generally I-V terraces,which are overlaid by loess,but loess thickness is thinner.Terrace V loess:about 70~90 m thick,with 11~16 layers of paleosol,and dated at about 1.23 MaBP.Terrace IV loess:layers of soil from L1 to S8 or S9,about 40~70 m thick and dated at about 0.80 MaBP.Terrace Ⅲ loess:layers of soil from L1 to S6,about 25~45 m thick and dated at about 0.62 MaBP.Terrace Ⅱ loess:L1 and S1,10~17 m thick,and dated at 0.12 MaBP.Terrace I loess consists of S0,L0 and MS,about 2.0 m in thickness and dated at about 0.01 MaBP.