“巫山黄土”氧化物地球化学特征与古气候记录  

Oxide geochemical characteristics and paleoclimate records of “Wushan loess”

作　　者：张玉芬[1] 李长安[2,3] 熊德强[1] 周耀[1] 孙习林[3] 

机构地区：[1]中国地质大学地球物理与空间信息学院.湖北武汉430074 [2]中国地质大学生物地质与环境地质教育部重点实验室,湖北武汉430074 [3]中国地质大学地球科学学院,湖北武汉430074

出　　处：《中国地质》2013年第1期352-360,共9页Geology in China

基　　金：国家自然科学基金(40971008和40771213);中国地质调查局项目(1212010814057和1212011121142)联合资助

摘　　要：根据73个"巫山黄土"样品的氧化物测试结果,对"巫山黄土"氧化物地球化学特征和记录的古气候特征进行了分析和讨论,结果表明:(1)"巫山黄土"主要的化学成分为SiO2、Al2O3、Fe2O3,(SiO2+A12O3+Fe2O3)的平均含量大于洛川黄土和甘孜黄土,与洛川古土壤接近,小于安徽宣城风积红土和镇江下蜀土;(2)"巫山黄土"SiO2、Al2O3、Fe2O3、TiO2含量具有随深度逐渐减少,而FeO、CaO、Na2O、P2O5含量则呈现逐渐增多的特点;(3)巫山剖面Fe3+/Fe2+比值变化曲线与全铁含量曲线显示明显的正相关,而与SiO2/(Al2O3+Fe2O3)曲线呈反相关;(4)"巫山黄土"的残积系数和风化指数由老到新其量值逐渐变小,而退碱系数的量值却是逐渐变大的;(5)"巫山黄土"堆积时该区古气候总体上较北方黄土堆积时要偏暖湿,沉积物遭受的淋溶及氧化作用强度与洛川古土壤相当,明显强于北方洛川黄土和川西的甘孜黄土,但较安徽的宣称风尘红土和镇江下蜀土要弱。剖面中沉积介质的酸度由下向上逐渐减弱,碱度加强,表生带所遭受的风化作用强度愈来愈弱,风尘堆积的沉积环境则由开始的较为偏湿润逐渐向偏干凉方向发展。(6)"巫山黄土"堆积时期古气候演变还具有阶段性特点,以剖面6～6.5 m为界可分为上下两段,下段古气候总体较上段偏温湿,气候冷(干)暖(湿)波动频繁、波动幅度较大,而上段古气候相对较为干冷,气候比较稳定,波动幅度也较小。In this paper, based on analytical results of 73 oxide samples of ＂Wushan loess＂, the authors analyzed and discussed oxide geochemical characteristics of ＂Wushan loess＂ and their recorded paleoclimate characteristics. In the average content of the main chemical compositions in ＂Wushan loess＂, SiO2, A1203, Fe203, are higher than those in Luochuan loess and Ganzi loess. The values are close to the values of Luochuan paleosols but lower than those in Xuancheng aeolian red clay in Anhui and Xiashu loess profile in Zhenjiang. The values of SiO2, A1203, Fe2O3 and TiO2 in ＂Wushan loess＂ gradually decrease with depth, whereas those of FeO, CaO, Na20 and P2Os gradually increase. In Wushan section, the Fe^3＋/Fe^2＋ ratio curve shows a significant positive correlation with the total iron content curve but a negative correlation with the curve of SiO2/（A1203＋Fe203）. From old to young, values of residual coefficients and weathering indexes become smaller and smaller, but de-alkali coeflficients become larger. In the period of＂ accumulation of ＂Wushan loess＂, the ancient climate in this area was partially warm and partially humid in general. The intensity of leaching and oxidation that sediments experienced ＂was equivalent to Luochuan paleosols, it was significantly stronger than the north Lu0chuan loess and Ganzi loess of western Sichuan but weaker than the eolian red clay in Xuancheng of Anhui and Xiasu loess in Zhenjiang. In this profile, from bottom upward, the acidity in the deposition was moderately weakened, the alkalinity was enhanced, the weathering intensity that the supergene band suffered became weaker and weaker. Eolian depositional environment changed from the beginning of＂ partially hot and partially humid gradually to dry and cold. In the period of accumulation of ＂Wushan loess＂, paleoclimate evolution showed stage characteristics. The section was divided into upper and lower parts with 6-6.5 m as the boundary; the paleoclimate in the lower part was partially hot and humid

关 键 词：“巫山黄土” 氧化物地球化学 古气候特征 长江上游 

分 类 号：P534.63[天文地球—第四纪地质学] P532[天文地球—古生物学与地层学]