甘肃中部4000年前环境变化与古文化变迁

通过对甘肃中部黄土剖面孢粉和其他环境代用指标的分析，表明距今4000年前后气候迅速干凉化。粒度、有机质、孢粉和软体动物指示距今4000年以前夏季风总体强盛，气候湿润, 距今4000年后夏季风强烈退缩， 气候迅速变干。距今4000年的干旱在我国北方有普遍表现。气候的干旱化及其引起的环境变化对齐家文化晚期的面貌造成了明显的影响，原始农业衰落，畜牧经济占据主要地位，并使得齐家文化和辛店、寺洼文化之间出现了断层。

Environmental Changes and Cultural Transition at 4 cal. ka BP in Central Gansu

In Gansu Province, the thick, continuous accumulated loess makes a high-resolution climatic sequence available. Accompanied by abundant ancient cultural relics, all these make it an proper region for the study of the relationship between human adaptation and paleoenvironmental change. The Sujiawan and Dadiwan sections, located in the heartland of Gansu, are ideal places for further investigations on Holocene climatic variations and their impact on human activity. Both field observations and analytical results confirm the abrupt environmental change at 4 cal. ka BP. And all proxies present the same trend. Decreased organic matter content indicates low vegetation coverage. Increased grain size shows the weakening summer monsoon and accumulation of loess. Abundant snails were eliminated because of the deteriorated environment. This event around 4 cal. ka BP is ubiquitous in northern China. Before 4 cal. ka BP, Majiayao Culture (5.5-4.2 cal. ka BP) and Qijia Culture (4.2-3.9 cal. ka BP) were basically distributed in the Gansu-Qinghai region. In late Qijia Culture, agriculture in the Gansu-Qinghai region came down. Villages became small and sparse. Splendidly painted potteries were replaced by crude potteries. Funerary objects were absent, meanwhile, the prevalent porcine mandibles were replaced by sheep bones. This is a significant symbol of the cultural transition. In short, we strongly suggest that rapid environmental deterioration, identified by the abrupt fluctuation of all proxies at 4 cal. ka BP, caused the decline of agriculture and gave birth to the stockbreeding.