THE LOESS STRATIGRAPHY IN SANMENXIA AREA

The Caocun loess profile in Zhangbian township located at the southeast margin of the Loess Plateau is typical of the Sanmenxia area. In the profile there occurs a loess-paleosol sequence from L₁ to L₃₃ 145m thick,underlain by a red clay bed. The B/M boundary was recorded at the bottom of L₇,the J magnetic event at S₁₁ to S₁₂,the O magnetic event at L₂₃ to L₂₆,and the M/G boundary at the bottom of L₃₃ near the red clay. The magnetic susceptibility of the loess deposits,as well as the carbonates and macrograined components contained all indicate that there have been many periodic monsoon changes totalling 13 cold events,with each lasting more than 40000 years. A high-resolution chronostratigraphy of the profile has been established by an age model according to grains. There exists a clear correlation between the records of paleomonsoon in the Caocun loess succession and SPECMAP from 3×10⁵-year BP to the present.