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根据古地磁、磁化率、粒度和重矿物分析及电镜扫描石英砂表面特征等测试手段的综合研究,西宁地区的黄土可分出从S_0至L_(17)的连续黄土——古土壤序列。它包括全新世黄土、马兰黄土、离石黄土和午城黄土,形成的时间为1.2MaB·P.。黄土粒度粗,且含有两个风成细砂分层。重矿物以不透明矿物、角闪石为主,次为绿泥石、锆石和金红石等。石英砂颗粒以次棱角状为主,其次为棱角状。石英砂表面机械结构中有众多的冰川作用痕迹和风力作用痕迹。本区黄土主要来源于青藏高原第四纪局部冰盖、冰川及其外围广大冰缘地区所产生的粉砂物质。西宁大墩岭黄土剖面详细地记录了1.2MaB·P.的环境变化信息。其中1.1MaB·P.形成的L_(15)顶部的细砂分层代表1.2Ma以来最为干冷的严酷时期。L_1和L_2是末次冰期和倒数第二次冰期的产物。倒数第二次冰期比末次冰期更为干冷,极盛时期为0.155MaB·P.。S_1S_3和S_4可能代表1.2Ma以来本区最为温暖湿润的时期。
Based on the comprehensive study of paleomagnetic, magnetic susceptibility, granularity, heavy mineral analysis and surface microscopic examination of quartz sand by electron microscopy, the loess in Xining can be divided into successive loess-paleosol sequences from S_0 to L_ (17). It includes Holocene loess, Malan loess, Lishi loess and Wucheng loess, forming a time of 1.2MaB · P. Loess coarse particle size, and contains two wind into fine sand layered. Heavy mineral opaque minerals, amphibole-based, followed by chlorite, zircon and rutile. Quartz sand particles to the second corner-shaped, followed by angular. Quartz sand surface mechanical structure has many traces of glacial action and wind traces. The loess in this area mainly comes from the Quaternary local ice sheets on the Qinghai-Tibet Plateau, glaciers and the silt material produced in the vast ice margin areas outside the glaciers. The Dadunling loess section in Xining recorded the environmental change information of 1.2MaB · P · in detail. Among them, the thin layer of fine sand on the top of L_ (15) formed by 1.1MaB · P represents the most dry and harsh period since 1.2Ma. L_1 and L_2 are the products of the last glacial period and the penultimate glacial period. The penultimate glaciation was drier than the last glacial age, with an exuberant period of 0.155Mpa · P. S_1S_3 and S_4 may represent the warmest and wetter periods in this region since 1.2Ma.