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通过对黄河上游官亭盆地喇家遗址周围黄河第二级阶地广泛的野外考察,在官亭镇下喇家村段发现了典型的风成黄土土壤层。在地层剖面可见其齐家文化层古地面被数组地震裂隙分割。有一层团块状的、鲜艳的红色粘土质泥流层覆盖了遗址的古地面,并且填充了地震裂隙。经过详细观测和采集光释光样品,应用单片再生剂量法(SAR)获得该剖面样品的光释光(OSL)年龄值。在此基础上,结合大量14C年龄数据和地层对比方法,确定官亭盆地黄河第二级阶地形成在35.00kaBP,其后风成黄土土壤剖面开始发育。同时断定全新世古土壤S0中间所夹红色粘土泥流沉积层及其下的地震裂隙的形成年代为3.95kaBP。结合磁化率和粒度成分等气候替代指标分析,表明在35.00～11.50kaBP晚更新世晚期,亦即末次冰期的晚期(MIS-2),气候寒冷干燥,沙尘暴活动旺盛,在官亭盆地第二级阶地上堆积了典型的马兰黄土层(L1-1)。在11.50～8.50kaBP全新世早期,沙尘暴活动堆积了具有过渡性质的黄土层(Lt),反映气候逐渐变暖。在8.50～3.10kaBP全新世中期大暖期,气候变得温暖湿润,降水量增多,沙尘暴活动减弱,风化成壤作用强烈,堆积形成了黑垆土类古土壤层(S0下、S0上)。
Through extensive field investigation of the second terrace of the Yellow River around the Lajia site in the Guanting basin in the upper reaches of the Yellow River, a typical aeolian loess layer was found in the Lajia village of Guanting town. Seen in the stratigraphic section of the Qijia cultural layer of the ancient ground is divided by an array of seismic fractures. A lumpy, bright red clay muddy layer covers the ancient ground of the site and fills the seismic fissure. After detailed observation and collection of optical luminescence samples, the optical luminescence (OSL) values of the samples were obtained by using single-cell regeneration dose method (SAR). On this basis, combining with a large number of 14C age data and stratigraphic correlation, it was determined that the second terrace of the Yellow River in Guanting Basin was formed at 35.00ka BP, and the aeolian loess soil profile began to develop. At the same time, it was concluded that the formation age of the red clay mud-stream sediment and the seismic fissure beneath the middle Holocene S0 was 3.95kaBP. Based on the analysis of the indices of susceptibility and susceptibility to magnetic susceptibility and grain size, it is shown that in the late Late Pleistocene (MIS-2) from 35.00 to 11.50kaBP, the climate is cold and dry with strong sand and dust storm activity. In the second stage of Guanting Basin A typical Malan loess layer (L1-1) is accumulated on the terraces. In the early Holocene from 11.50 to 8.50 kaBP, sandstorms accumulated loess layers of transitional nature (Lt), reflecting gradual warming. In the warm period of 8.50 ~ 3.10kaBP during mid-Holocene, the climate became warm and humid, the precipitation increased, the sandstorm activity weakened and the weathering and pedogenesis were strong. The ancient soil layer of black soil was formed by accumulation (S0, S0).