青海官亭盆地二方村遗址全新世土壤沉积物地层序列与OSL测年研究

Holocene pedo-stratigraphic sequence and OSL chronology of the Erfangcun ruins in the Guanting basin of Qinghai Province

通过野外考察观测,结合土壤学与沉积学多种指标测试分析,在官亭盆地喇家遗址东侧的二方村遗址建立了完整的全新世土壤沉积物地层序列。选择关键层位系统采集年代学样品,应用单片再生剂量法(SAR),进行光释光(OSL)年代测定,结合文化层考古断代,建立了可靠的土壤与沉积物地层年代框架。发现在全新世大暖期温暖湿润气候条件之下,以风成堆积为主的基础上,发育形成了肥沃疏松的黑垆土类古土壤,成为史前人类种植农业开发利用的宝贵资源。但是全新世大暖期后期全球性气候恶化背景条件下,在二方村遗址OSL年龄3940~3780a BP之间,对应喇家遗址14C年龄3850~3600a BP期间,官亭盆地发生多场大地震,加上全球气候恶化致使青藏高原边缘频繁发生强对流天气,造成大规模暴雨山洪泥流事件频繁发生,导致黑垆土发育的突然中断。黄河北岸第二级阶地的肥沃黑垆土类土壤被厚达1.0~4.0 m坚硬贫瘠的红色黏土覆盖。这不仅毁灭了以稷粟类谷物种植为主的喇家村齐家文化大型聚落(4150~3850a BP),也导致土壤与土地资源严重退化。由此可知,从4200a BP开始的全球性气候恶化,对青藏高原东北边缘环境敏感带造成了严重影响,灾害性地表过程造成了黄河第二级阶地土壤土地资源严重退化。这些都成为驱动官亭盆地在3600a BP时期辛店/卡约文化原始农牧混合型土地利用方式形成的重要因素。该研究结果对于深入理解青藏高原东北边缘资源环境演变、自然灾害以及人地关系演变规律等,都具有十分重要的科学价值。

Holocene pedo-stratigraphic sequence was established for the Erfangcun Ruins to the east side of the Lajia Ruins in the Guanting Basin of Qinghai Province through field investigation and pedological and sedimentological analysis. A reliable chronology framework for soil and sediments was made using SAR and OSL for the samples systematically collecting from key strata. The results indicate that the fertile Heilu soil, which formed on the eolian loess deposit over the Yellow River terrace land during the Holocene climatic optimum, became valuable land resource and facilitated the development of the primitive arable farming in the Guanting Basin. However, global climatic decline from about 4200 a BP caused serious disasters for the region. The multiple earthquakes, in combination with storm rain in related to strong convections along the margin of the Tibetan Plateau, induced enormous flashfloods and mudflows during OSL age 3940~3780 a BP, equivalent to 14C age 3850~3600 a BP. These disastrous surface processes resulted in an interruption of the Heilu soil formation. The farmland with fertile cultivable Heilu soil was blanketed by rigid clay or sand of about 1.0~4.0 m thick. These had not only ruined the large settlement(4150~3850 a BP) of the Qijia Culture which sustained on millet cultivation, but also caused a decline of the soil and land resources over the Yellow River terrace land. These mean that the global climatic deterioration from about 4200 a BP affected the environmentally sensitive region over the northeast margin of the Tibetan Plateau. Disastrous surface processes caused the serious degeneration of soil and land resources along the Yellow River banks. These factors all drove the primitive arable farming of millet cultivation to shift into mixed nomadic and arable farming of the Xindian/Kayue Cultures at 3600 a BP. These results are very important in understanding environment change, natural disasters and evolution of the human-land relations in the northeastern margin of the Tibetan Plateau.