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Frequent natural hazards cause huge damage to human life and society in the mountainous regions along the eastern rim of the Tibetan Plateau. A massive landslide damming event has been reported in the Jishixia Gorge on the upper Yellow River as it emerges from the NE Tibetan Plateau. It was speculated that a breach of the dammed lake might have resulted in a super flood disaster that ruined the major Neolithic settlement at Lajia (4.20–3.95 ka BP) within the Guanting Basin that is located in the downstream. However, our detailed investigations along the Jishixia Gorge and Guanting Basin indicate that the dammed lake became shallower and desiccated gradually rather than breaching suddenly. The Yellow River has cut into the dammed lake deposits forming well-exposed profiles on the riverbanks. The dammed lake deposits are considered to provide an accurate natural record of the life-span of the dammed lake. Optically Stimulated Luminescence (OSL) dating was carried out on a series of eight samples taken from the profile. The OSL ages of the dammed lake deposits fall within the range of 8.25 ± 0.39 to 5.65 ± 0.21 ka at the Yisiri site about 2.5 km upstream of the landslide dam. These results indicate that the massive landslide damming event and the corresponding dammed lake occurred at 8.25 ka in the early Holocene. The dammed lake existed for about 2600 years and desiccated gradually and disappeared at 5.65 ka because the landslide dam was dissected slowly by the Yellow River. This means that the landslide dammed lake on the Yellow River disappeared about 1700 years before the Neolithic settlement at Lajia became ruins. The landslide damming event in the Jishixia Gorge is not related to the prehistorical catastrophic disasters that overcame the Lajia settlement within the Guanting Basin. [ABSTRACT FROM AUTHOR]

The reconstruction of prehistoric temperature and precipitation variations in the upper reaches of the Yellow River is essential for understanding the cultural evolution of the region, but related information is sparse due to the limitations of the available proxies. Recent studies have shown that microbial glycerol dialkyl glycerol tetraethers (GDGTs) are promising tools for reconstructing mean annual temperature (MAT) and mean annual precipitation (MAP) in terrestrial deposits. In this study, we reconstructed mid-late Holocene climatic changes using GDGT distributions in a loess-paleosol sequence in the Lajia Ruins of the Neolithic Qijia Culture, Guanting Basin, in the southwestern end of the Chinese Loess Plateau. Our GDGT records show that MAP decreased from ca. 600 mm to 430 mm, while MAT decreased from 11.9 °C to 8.0 °C, during the past ca. 7000 yr, and a drastic decline in MAP (70 mm), accompanied by a 0.8 °C decline in MAT, occurred at 3800–3400 yr BP. Our results provide direct evidence supporting a hypothesis that the flourishing (4200–4000 yr BP) and decline (4000–3600 yr BP) of the Qijia culture (mainly based on millets cultivation) and subsequent rise of the Xindian/Kayue culture (3600–2600 yr BP), based on mixed agriculture of sheep husbandry and millets cultivation were triggered by climate change. [ABSTRACT FROM AUTHOR]

The Lajia Ruins in the Guanting Basin, NW China, are a product of the prehistoric Qijia Culture. Like Pompeii, they are a rare example of an archaeological site preserved by a natural disaster and are therefore important in archaeology, anthropology and geology. However, the nature of the disaster(s) responsible for the destruction of the site remains controversial. Most studies have focused on an earthquake and a red clay layer directly overlying the site and a detailed stratigraphic study of the mid-Holocene sedimentary strata combined with other intervals of red clay deposition (hence possible disasters) is lacking. We identified a mid-Holocene paleosol sequence (the Shanglajia section) at the site which contains two layers of red clay, dated to 3950 a BP and 3500 a BP, intercalated within the mid-Holocene paleosol (S 0 ). Subsequent multi-proxy analysis indicated that the characteristics of the two red clay layers resemble those of typical Tertiary red clay deposits and the modern gully deposit at the foot of the Great Red Hills, but are distinctly different from those of the slackwater deposits of the Yellow River and the mid-Holocene paleosol. Our results suggest that, at 3950 a BP and 3500 a BP, two large-scale rainstorm-induced mudflow events, originating from the gullies to the north, flooded the Lajia area on the second terrace of the Yellow River, devastating and burying the human settlements. We infer that the intensified erosion and mass wasting were caused by human activity; in addition, natural factors such as rainstorms and earthquakes, may also have played an important role in triggering catastrophic mudflow events in the Tertiary Red Clay deposits. Overall, our results provide further insights into prehistoric man-land relationships in this environmentally sensitive region which may have implications for modern land use in this region of China and elsewhere. [ABSTRACT FROM AUTHOR]