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Temperature and salinity effects on ~(18)O fractionation for rapidly precipitated carbonates: Laboratory experiments with alkaline lake water

机译:温度和盐度对快速沉淀的碳酸盐〜(18)O分馏的影响:碱性湖水的实验室实验

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The precipitation of lacustrine carbonates can occur relatively rapidly over large ranges of salinity, alkalinity and temperature. Few studies have directly addressed oxygen fractionation of stable isotopes during the formation of these carbonates. We present results from experiments that elucidate the factors which regulate the isotopic composition of carbonates precipitated from lake water. Water from Mono Lake was diluted by different amounts with Creek water from the Mono Basin. Carbonates were precipitated in these solutions by adding CaCl_2 solution or powder. The experimental results show that rapidly precipitated inorganic calcite, typical of some lacustrine environments, may record equilibrium ~(18)O fractionation as has been demonstrated previously for slowly inorganically growing, or biologically precipitated carbonates. However, apparent disequilibrium fractionation is observed in carbonates precipitated rapidly from waters of extremely high salinities and low temperatures. This appears to result from the formation of carbonate poly-morphs, such as gaylussite. Rapidly precipitated pure calcite exhibits ~(18)O enrichments with respect to predicted equilibrium values. The temperature correlation of ~(18)O fractionation appears to hold at relatively high temperatures ( > 10℃) but the slope of the tempera-ture/fractionation equation is salinity dependent, although the cause is presently unclear.
机译:在较大的盐度,碱度和温度范围内,湖相碳酸盐的沉淀可能相对较快地发生。很少有研究直接解决这些碳酸盐形成过程中稳定同位素的氧分馏问题。我们目前的实验结果阐明了调节从湖水中沉淀出的碳酸盐同位素组成的因素。来自莫诺湖的水用来自莫诺盆地的溪流水不同程度地稀释。通过添加CaCl_2溶液或粉末使碳酸盐在这些溶液中沉淀。实验结果表明,快速沉淀的无机方解石(某些湖相环境中的典型特征)可能会记录平衡的〜(18)O分馏,如先前已证明的缓慢无机增长或生物沉淀的碳酸盐。但是,在盐度极高且温度极低的水中迅速沉淀出的碳酸盐中,观察到明显的不平衡分馏。这似乎是由于形成了碳酸盐多晶型物,例如gaylussite。快速沉淀的纯方解石相对于预测的平衡值表现出〜(18)O富集。 〜(18)O分馏的温度相关性似乎在相对较高的温度(> 10℃)下保持,但温度/分馏方程的斜率与盐度有关,尽管目前的原因尚不清楚。

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