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根据西安东郊任家坡黄土剖面中第5层古土壤样品的电子显微镜观察和能谱分析,在该层古土壤中发现了极少见的能够指示典型干旱气候环境的AgSO4矿物和钼矿物等.次生银矿物一般呈现椭球形结晶粒状形态,具有孔洞和裂隙化学沉淀结晶的特点,钼矿物具有胶体物质的特点.次生银矿物有两种类型,一是AgSO4矿物,二是氧化银矿物.次生银、钼和钴矿物与新生粘土矿物及Fe2O3和Al2O3的明显迁移指示该层土壤发育时经历了较为强烈的化学风化和矿物分解作用,银、钼和钴能够从原生矿物中释放出来,当时西安地区降水量丰富,达到了酸性化学风化阶段.在西安地区S5下部分层古土壤发育末期,出现了由温暖湿润季风气候向非季风干旱气候的大变化.在比CaSO4还易于溶解的AgSO4形成时期,关中平原为非季风干旱气候,强烈的蒸发造成了土壤水溶液中SO42的富集和AgSO4的形成.当时东亚夏季风活动极弱,一般不能越过秦岭到关中平原地区,那时西安地区年降水量为300mm以下,比现今兰州地区的气候还要冷干.
According to the electron microscope observation and energy spectrum analysis of the fifth-layer paleosol in the loess section of the Renjiapo, eastern Shandong suburb, rare AgSO4 minerals and molybdenum minerals can be found in the paleosol of this layer, which can indicate the typical arid climatic environment The secondary silver minerals generally show the shape of ellipsoidal grains, which have the characteristics of chemical precipitation and crystallization of vugs and fissures.The molybdenum minerals have the characteristics of colloidal materials.The secondary silver minerals have two types, one is AgSO4 minerals and the other is silver oxide minerals . The significant migration of secondary silver, molybdenum and cobalt minerals and newborn clay minerals and Fe2O3 and Al2O3 indicates that the soil underwent more severe chemical weathering and mineral decomposition during the development of the soil, and silver, molybdenum and cobalt could be released from primary minerals , When the rainfall in Xi’an area was rich and reached the stage of acidic chemical weathering.A large change of warm-humid monsoon climate to non-monsoon arid climate appeared at the end of subsoil palaeosol development in the lower part of Xi’an area of S5. During the formation period, the Guanzhong plain was a non-monsoon arid climate, and strong evaporation caused the enrichment of SO42 and the formation of AgSO4 in the soil water solution Very weak summer monsoon activity, generally can not cross the Qinling Mountains to the Guanzhong Plain, when annual rainfall of 300mm or less in Xi’an, but also cold and dry climate than today in Lanzhou region.