Exceptionally fast growth rate of <100-yr-old tufa, Big Soda Lake, Nevada: Implications for using tufa as a paleoclimate proxy
Exceptionally fast growth rate of <100-yr-old tufa, Big Soda Lake, Nevada: Implications for using tufa as a paleoclimate proxy
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内华达州大苏打湖<100年的凝灰岩生长速度异常快：使用凝灰岩作为古气候替代指标的意义
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
M. S. Lico
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作者：
M. Rosen;G. Arehart;M. S. Lico
美国内华达州大苏打湖边缘发现了大型凝灰岩土丘（>3 m 高，底周长 5 m）。这些凝灰岩土丘扎根于当前湖面以下最大 4 m 处，并由地下水渗漏积极形成，从凝灰岩土丘顶部可以看到地下水渗漏。大苏打湖是一个火山口湖，其水位完全由地下水维持。凝灰岩土堆的年龄受到很大限制，因为在 1907 年纽兰兹灌溉项目开发之前，水位比当前湖水位低约 18 m。凝灰岩丘的垂直柱状性质表明它们是在湖下形成的，而不是在地下形成的。因此，石灰华土堆的年龄<100 年，并且生长速度≥30 毫米/年。钙华碳酸盐的稳定氧和碳同位素分析与地下水和湖水的同位素分析以及水化学数据相比表明，造成降水的流体是现代地下水和湖水的简单混合物，并不反映最近的气候特征。凝灰岩丘的异常快速生长表明，大型凝灰岩沉积物可能在地质时期几乎瞬时形成。鉴于这种快速增长的潜力，以及数千年来古气候变化和补给水成分变化来解释凝华沉积物同位素组成变化的事实，在试图确定可能因与地下水混合而引起的凝灰岩同位素或化学成分变化的重要性时应小心谨慎。
Large tufa mounds (>3 m tall, with a basal circumference of 5 m) have been discovered on the margin of Big Soda Lake, Nevada, USA. These tufa mounds are rooted at a maximum of 4 m below the current lake surface and are actively forming from groundwater seepage, which can be seen emanating from the top of the tufa mounds. Big Soda Lake is a volcanic crater lake whose water level is maintained exclusively by groundwater. The age of the tufa mounds is well constrained because prior to the development of the Newlands Irrigation Project in 1907, the water level was ∼18 m lower than the current lake level. The vertical columnar nature of the tufa mounds indicates that they formed under the lake and not subaerially. Thus, the tufa mounds are <100 yr old and have grown at a rate ≥30 mm/yr. Stable oxygen and carbon isotope analyses of tufa carbonate compared to isotopic analyses of groundwater and lake water and hydrochemical data indicate that the fluids responsible for their precipitation are a simple mixture of modern groundwater and lake water and do not reflect a recent climate signature. The exceptionally fast growth of the tufa mounds indicates that large tufa deposits may form almost instantaneously in geologic time. Given this potential for rapid growth and the fact that variations in isotopic compositions of tufa deposits have been interpreted in terms of changes in paleoclimate and changes in the composition of recharge water over thousands of years, care should be taken when trying to determine the significance of variations in isotopic or chemical compositions of tufas that may have been caused by mixing with groundwater.