Mineralogy and geochemistry of the Holocene lacustrine sediments in Nam Co, Tibet |
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| Authors: | Minghui Li Shichang Kang Liping Zhu Qinglong You Qianggong Zhang Junbo Wang |
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| Institution: | aInstitute of Tibetan Plateau Research, Chinese Academy of Sciences (CAS), Beijing 100085, China;bState Key Laboratory of Cryospheric Science, Cold and Arid Regions Environmental and Engineering Research Institute, CAS, Lanzhou 730000, China |
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| Abstract: | The carbonates, clays and major chemical compositions of lacustrine sediments in Nam Co (Lake) were examined by X-ray diffraction, scanning electron microscopy and chemical analysis. Carbonates include monohydrocalcite (MHC, first report from China and in a high-altitude lake), low-Mg calcite and traces of dolomite. MHC in Nam Co is developed in water (1.8 g/L) with high Mg/Ca molar ratios (10.03–15.03), high pH (8.04–9.72) and the presence of bacteria, algae, diatom and ostracoda. Illite and Mg-chlorite provide a strong evidence for physical weathering in the Holocene. Most Ca and Sr in sediments originate from carbonates as the molar ratios of Ca and CO32− are all less than 1 and the curve of Sr is very similar to that of Ca. However, most of the Mg, Fe and Rb are from clays. The lake water shifted from a fresh water environment to an evaporative, alkaline environment by 2.06 cal. ka BP. There was a depositional event that the depositional rate changed from 0.134 to 1.639 mm/a at about 2 cal. ka BP. |
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