Terrestrial records of weathering indicate three billion years of dynamic equilibrium
Terrestrial records of weathering indicate three billion years of dynamic equilibrium
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DOI：
10.1016/j.gr.2022.05.009
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发表时间：
2022-05
影响因子：
6.1
通讯作者：
Rebecca M. Dzombak;N. Sheldon
中科院分区：
文献类型：
--
作者：
Rebecca M. Dzombak;N. Sheldon
虽然大陆风化强度在地质历史上被认为是地球化学、构造和碳循环的主要控制因素，但在地球历史上它仍然缺乏量化。作为大陆风化的直接产物，古土壤（化石土壤）提供了对过去风化强度的独特见解，但它们在限制地质时期陆地风化模式的努力中仍然没有得到充分利用。在这里，我们汇编了迄今为止最大的陆地风化记录，包括248个跨越30亿年的古土壤和风化剖面。我们分析了一套风化指数，以测试常见的假设周围的状态变化，由于大气变化和陆地生物圈扩张的陆地风化强度。与通常援引的假设相反，我们发现，这些风化指数反映了一致的平均陆地风化强度随时间的推移。没有单向的状态变化的平均风化强度，如以前所假设的，是可检测的记录。然而，古生代古土壤保持增加的总范围的化学蚀变指数（CIA）的值，增加CIA范围的外观驱动的高CaO古土壤。我们将古土壤风化记录与选定的河流砂岩和杂砂岩记录的风化强度进行比较。我们将大陆风化记录的总体稳定性解释为反映了地球系统在扰动期间偏离的风化基线水平（即，主要的气候转变，快速的构造活动）。在地质时间尺度上，风化强度一致，记录支持地表下出现的大陆面积作为对海洋总潜在侵蚀通量和营养通量的关键控制。古土壤界应努力建立一个更完整的古土壤地球化学数据库，以便对陆地风化进行更细致的分析。
Although continental weathering intensity has been invoked as a primary control on biogeochemistry, tectonics, and the carbon cycle throughout geologic history, it remains poorly quantified over Earth’s history. As a direct product of continental weathering, paleosols (fossil soils) offer unique insight into past weathering intensity, but they remain underused in efforts to constrain terrestrial weathering patterns over geologic time. Here, we compile the largest terrestrial weathering record to date, comprising 248 paleosol and weathering profiles that span three billion years. We analyze a suite of weathering indices to test common hypotheses around state-changes in terrestrial weathering intensity due to atmospheric changes and terrestrial biosphere expansion. Contrary to commonly invoked assumptions, we find that these weathering indices reflect consistent average terrestrial weathering intensity through time. No unidirectional state changes in average weathering intensity, as have previously been hypothesized, are detectable in the record. However, Phanerozoic paleosols preserve an increase in the total range of Chemical Index of Alteration (CIA) values, with the increased CIA range driven by the appearance of high-CaO paleosols. We compare the paleosol weathering record to weathering intensities recorded by select fluvial sandstones and diamictites.We interpret the overall stability of the continental weathering record as reflecting the baseline level of weathering from which the Earth system deviates during periods of perturbation (i.e., major climate transitions, rapid tectonic activity). With consistent weathering intensity over geologic timescales, the record supports subaerially-emerged continental area as a critical control on total potential erosional flux and nutrient flux to the oceans. The paleosol community should work to build an even more complete database of paleosol geochemistry to allow more nuanced analyses of terrestrial weathering through time.