渭河流域全新世黄土与环境变迁

根据黄土理化性质与风化成壤类型,孢粉分析与植被,人类聚落位置迁移与河流水文和气候干湿变化关系等,阐明了渭河流域全新世包含三个寒冷干旱—温暖湿润气候变化旋回,每一旋回的周期约为3700年。现在处于第三旋回暖湿阶段后期,隋唐以来的气候状况还将延续500年左右。

THE LOESS AND ENVIRONMENTAL CHANGES OF HOLOCENE IN THE WEIHE RIVER BASIN

Through analysis of strata structure, lithological chracteristics, ¹⁴C dates and depositing environments, stratigraphical subdivision and comparison of Holocene loess are made in the Weihe River Basin within the Loess Plateau. According to the physico-chemical characteristics and weathering-soilization of the loess, sporo-pollen and vegetation, as well as river-water-level changes and the arid-humid changes of climate reflected hy the location migration of ancient cultural sites, the environmental changes of Holocene is exposed in the Weihe River Basin.That is.Q₄¹:10,500-8500 year B.P., the Northwest Monsoon was prevailing, dust-storm and dustrain occurred often, eolian loess deposi ted(L₁).Mean temperature was 6-10℃, rainfall 300-500 mm, semi-arid chimate of the Temperate zone, drygrassland vegetation.Q₄²:8500-6800 year B.P. the southeast Monscon was prevailing, Burozem formed in valley and Black Loesslike Soil in high plain (So-Lower).Mean temperature was 14-16℃, rainfall 700-900mm, semi-humid climate of the Subtro-pic zone, deciduous broad-leaf forest vegetation.The Cishan-Peiligang Culture arose, people lived in high land because of the threat of flood.Q₄³:6800-3000 year B.P., the Northwest Monsoon was prevailing, dust-storm and dust-rain occurred often, Icess deposited(L_v).Mean temperature was 8-12℃, rainfall 400-600mm, semi-arid climate cf the Temperate Zone, forest-grassland vegetation. The famous Yangshao Culture becmed pecole lived in low land near river Since drought and water shertage.Q₄⁴:5000-3120 year B.P., the Southeast Monsoon was prevailing, Burozem and Black Loesslik Soil fermed (So-upper).Mean temperature was 13-15℃, rainfall 700-800mm, semi-humid climate cf warm Temperate Zone, deciduous broad-leaf forest vegetation. Entering the Luongshan Culture and the early Zhou dynasty, people moved to high land because of the threat of flood.Q₄⁵:3120-1400 year B.P., the Norrhwest Monsoon was prevailing, dust-storm and dust-rain occurred, loess deposited (L₀).Mean temperature was 8-12℃, rainfall 300-500mm, semiarid climate of th Temperate Zone, forest-grassland vegetation.The capital cities of the west Zhou, Qing and west Han dynasties in the area were all established in the low land near river because of water shortage.Q₄⁶:last 1400 years, climate has become warm and humid, modern soil is Brown Soil and Black Loess-ilke Soil (MS).Mean temperature is 10-14℃, ra-infall 600-700mm, deciduous broadleaf forest vegetation. The capital cities of the Suei and Tang dynastest were moved to high terrace because of the threat of flood and the rising of underground water-level in low land.According to this regularity of environmental changes, we can find out that there are three climatic cycles whose periodity is about 3700 years in a changing process of coldarid to warm-humid. Now we are living in the warm-humid stage of the third climatic cycle, the modern climate situation since 580 A.D. will continue for about 500 years.