Environmental Changes and Cultural Transition at 4 cal. ka BP in Central Gansu
甘肃中部4000年前环境变化与古文化变迁

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.