西宁的黄土研究

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。

THE STUDIES OF XINING LOESS

Based on the analyzed results of paleomagetic measurement, susceptibility, grainsize, heavy mineral and the surface texture of quartz sand in loess, the authors conclude thatthe Xining loess stratigraphy possesses continuous loess-paleosol sequence from S_0 to L_(17),which consisted of Holocene loess, Malan loess, Lishi loess and Wucheng loess. The forma-tion age of the Xining loess is about 1. 2 Ma B. P. The Xining loess originated mainly from ice sheet, glacier and periglacial district ofQuaternary in Qinghai-Tibet Plateau. Dadunling loess profile in Xining recorded rich information of environment changes inQuaternary, among which the aeolian sand layers in L_2 and L_(15) loess reflected the coldest anddriest periods and paleosolS_1, S_3 and S_4 might reflect the warmest and moistest periods inXining area since 1. 2 Ma B. P.