In lacustrine sediments,aragonite is a widespread mineral,whereas monohydrocalcite is a rare carbonate mineral. In the cold and high-attitude Xizang (Tibetan) Plateau,where aragonite has been commonly found in lacustrine sediments,there is no aragonite,but low-Mg calcite,monohydrocalcite and trace dolomite. The lake receives solutes primarily from surface runoffs and remains fairly constant water chemistry for a long time. The total CaCO3 percentage in sediments could be controlled by evaporation and inflow of detrital materials. The absence of aragonite is unusual when compared to other lacustrine sediments from the Tibetan Plateau. This could be due to low Ca/Mg ratio,low salinity,low Mg and Ca concentration. Monohydrocalcite might precipitate from the lake water mediated by biological activities. Low-Mg calcite originated from minor ostracoda shell and the precipitation of lake water with biological activities.
LI MinghuiKANG ShichangZHU LipingWANG FeiyueWANG JunboYI ChaoluFANG XiaominXIE Manping
This article investigates the soil properties in two soil profiles from the terraces of the Nam Co Lake in Tibet,China. Profile 1,with a slope aspect to east,is 37 m,and profile 2,to southwest,is 32 m above the lake level. Twelve and nine layers were identified in profile 1 and profile 2,respectively,based on the color,texture,structure,moisture content,presence of carbonate,and root density. Grain sizes and measurements of water content,total organic carbon,total inorganic carbon,total carbon,pH value and electrical conductivity were all analyzed for each sample. The results show that soil is poorly developed because of sparse vegetation coverage and weak chemical weathering in the cold and arid area. The results also indicate that the soil properties are different between the two profiles and suggest that soil is better developed in profile 1 than in profile 2. These differences are ascribed to the dissimilarity of landform,vegetation and timing. Profile 1 faces to east as compared with profile 2 facing to southwest and gets less insolation and therefore less evaporation. Thus,vegetation grows better in profile 1 than in profile 2. Radiocarbon dating and OSL dating show that profile 1 underwent a longer soil forming process than profile 2,which is helpful for the soil development in profile 1.
WANG LiqiangYI ChaoluBrigitta SehiittLIU KexinZHOU Liping
云南点苍山是大理冰期的命名地,通过文献查询明确了大理冰期这一概念提出的过程.基于多次的实地考察,对云南点苍山冰川地貌进行了系统研究,建立了该地区第四纪以来冰川活动可靠的年代序列,明确了冰川发育的规模.研究结果表明,点苍山最早的冰川活动发生于30～40 ka BP,之后经历了末次冰期晚阶段、晚冰期、新冰期等各次冰川前进,直至1.2～1.5 cal ka BP前后冰川最后消失.空间上,该地区的冰川活动仅局限于海拔3600m以上的主体部分,低海拔及其周边山体上没有冰川发育.
The term of ''Tali Glaciation'' is nominated from Massif Diancang in Yunnan Province. The confusing process of the term''s being put forward is confirmed through literature checking. Based on several times of field trip, the glacial landforms in this region are studied in detail, and the magnitude of the glaciation was determined. According to the numerical ages from TL, AIMS ^(14)C and OSL dating, the earliest glacial advance on Massif Diancang occurred at 30—40 ka BP, followed by the advances at the last stage of the last glaciation, the late glacial and neoglations in turn, until glaciers vanished at 1.2—1.5 ca. a BP in this region. It can be concluded that glaciers were limited above 3600 m a.s.l., and no glaciers existed on the lower part and adjacent mountains since the last glaciation.
YANG JianQiang1, CUI ZhiJiu2, YI ChaoLu1, SUN JiMin3 & YANG LiRong3 1 Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085, China
