New weathering index improves paleorainfall estimates from Vertisols
New weathering index improves paleorainfall estimates from Vertisols
复制标题
DOI：
10.1130/g30689.1
复制
发表时间：
2010-05
期刊：
影响因子：
5.8
通讯作者：
L. Nordt;S. Driese
中科院分区：
文献类型：
--
作者：
L. Nordt;S. Driese
垂直土壤是在岩石记录中被广泛认可的粘土、收缩膨胀土壤，因此需要更好地了解元素浓度对气候解释风化指数发展的动态影响。通过对四种主要成碱氧化物（CaO、MgO、Na 2o、k2o）的风化性能进行研究，发现土壤中CaO和MgO浓度与年平均降水量（MAP）的相关性最强。在此基础上，我们引入了CALMAG风化指数，定义为al2o3 / (al2o3 + CaO + MgO) × 100，相对于已建立的CIA-K（蚀变化学指数-钾）风化指数，该指数改善了对Vertisols的降雨估计。在versols中，CALMAG主要追踪来自碳酸钙、碎屑粘土和可交换的ca2 +和mg2 +的钙和镁的通量，而不是记录许多其他土壤目中常见的耐气候矿物的水解。对两个中生代古土壤的应用表明，在干旱气候条件下，CIA-K的MAP值高于CALMAG，而在湿润气候条件下则相反。这项工作改进了来自versols的古降雨量估计，并表明需要一组风化指数来适应不同的古土壤类型。
Vertisols are clayey, shrink-swell soils that are widely recognized in the rock record, thus generating the need to better understand the dynamics of elemental concentrations on the development of weathering indexes for climate interpretations. We assessed the weathering performance of the four major base-forming oxides (CaO, MgO, Na 2 O, K 2 O) along a modern Vertisol climosequence spanning a strong precipitation gradient, and discovered that the concentration of bulk soil CaO and MgO yields the strongest correlation to mean annual precipitation (MAP). Based on this fi nding, we introduce the CALMAG weathering index, defi ned as Al 2 O 3 / (Al 2 O 3 + CaO + MgO) × 100, which improves rainfall estimates for Vertisols relative to the wellestablished CIA-K (chemical index of alteration minus potassium) weathering index. Rather than documenting the hydrolysis of weatherable minerals common in many other soil orders, in Vertisols CALMAG principally tracks the fl ux of calcium and magnesium sourced from calcium carbonate, detrital clay, and exchangeable Ca 2+ and Mg 2+ . Application to two Mesozoic paleosols reveals that in drier climates CIA-K yields higher MAP estimates than CALMAG, but that the reverse is true in wetter climates. This work improves paleorainfall estimates from Vertisols and suggests that a family of weathering indexes is needed for different paleosol types.