没有幻灯片标题_9495.ppt

* Changes of the Deserts in Northern Central China during the last Glacial Cycle: Implications for Causes of Recent Desert-Forming Process Z.L. Ding, J.M. Sun, S.L. Yang and T.S. Liu (Institute of Geology and Geophysics, CAS, Beijing) Desrtified Land : 3436 km2/year Causing tremendous environmental and social problems Heavy Agriculture Overgrazing Causes for the desert-forming are not fully understood: Natural processes or human activities? Or both? What measures should be taken to stop the desert-forming process? If geological records can provide any implication for it? Western deserts: 150mm Eastern deserts: 200-450mm Helan Mts. Annual precipitation Temporal and spatial changes of the deserts in the last glacial-interglacial period Paleo-records: Wind-blown loess deposits in the Loess Plateau Loess-sand deposits in the loess-deserts border Sand-soil deposits from within the deserts Holocene Soil (11ka) LGM Loess (21-11ka) Loess Section Relationship between Loess grain-size and the distance of the Loess Plateau to the deserts Desert expansion Desert retreat Coarse loess grain-size Fine loess grain-size Shorter distance Longer distance Loess grain-size links to monsoon Northward move of monsoon rainfall belt Northward retreat of desert margin Increase in the distance of deserts to the LP Fine-sized eolian loess deposited in the Plateau Sampling sites in the Loess Plateau Map of the LP and deserts in northern China 10?1 27?2 48?4 55?4 101?11 130?10 88?7 75?9 Age(ka) Eolian sand Loess Soil Holocene Soil LGM Eolian Sand Loess Horizon Last Interglacial Soil Loess-Sand-Soil Section Along the Border Direct evidence for desert advance during the LGM (S0) (L1-1,) (L1-2) (L1-3) (L1-4) (L-5) (S1) Grain-size records of the loess sections along the transitional area of the Loess Plateau to the deserts LGM LGM LGM LGM LGM LGM LGM LGM Eolian section within deserts LGM Sand Holocene Soil Rocky desert in the northern part Dry grasslands in the northern part sand-dunes