THE LOESS STRATIGRAPHY IN SANMENXIA AREA
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摘要: 位于黄土高原东南缘的三门峡黄土地层,以陕县张汴乡曹村剖面为其典型代表。厚度153m的曹村剖面由上部厚145m的黄土地层和下伏红粘土沉积组成,黄土地层为L1-L33的连续风尘沉积。磁性地层研究显示:B/M界线位于L7下部,J事件位于S11-S12,O事件位于L23-L26,M/G界线位于黄土与红粘土界线之上20cm处。古季风代用指标的磁化率、碳酸盐及>30μm的粒度组分均显示了约2.6Ma以来季风变迁的阶段性特点。曹村黄土剖面具有持续时间在4万年以上的黄土沉积所指示的13次气候寒冷事件,所反映的古气候变化具有周期性。应用粒度年龄模式建立曹村剖面高分辨率的年代地层序列,通过曹村剖面近30万年来的磁化率及粒度变化与深海氧同位素对比,曹村黄土剖面与深海沉积有良好的可比性。Abstract: 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.
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