The clay-sized Cr/Zn ratios as a lithology-constraint weathering fingerprint

IF 4 1区地球科学 Q1 GEOGRAPHY, PHYSICAL

Global and Planetary Change Pub Date : 2025-03-27 DOI:10.1016/j.gloplacha.2025.104804

Xianming Zhang , Fei Ye , Wanfu Zhao , Xianqiang Meng , Yongjun Jiang , Wancang Zhao

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Abstract

Chemical weathering of differential lithologies is the primary factor causing redistribution of the elements chromium (Cr) and zinc (Zn) in Earth's surface. Clay-sized fractions (< 2 μm, CSFs) as the ubiquitous weathering products play a critical role in hosting Cr and Zn. However, currently inadequate knowledge of CSFs from sedimentary rocks to soils might hamper a clear understanding regarding Cr and Zn enrichment process in the derived soils across these regions, accordingly limiting the further deciphering of Cr/Zn ratios' geochemical signals. Here we analyzed the Cr and Zn among CSFs of carbonate rocks, clastic rocks and derived saprolites. The results illustrated the Cr and Zn abundance (48.6–181.8 mg kg⁻¹ and 98.2–219 mg kg⁻¹) in CSFs of sedimentary rocks, revealing that over 70 % Cr was constrained by phyllosilicates, while Zn dispersed among the mineral phases. These results confirmed the CSFs as the Zn and Cr-rich reservoirs in parent materials. In comparison, major Cr in CSFs remained stable during weathering, while up to 4.1-fold enrichment of Zn was observed among all clay-sized mineral phases in the saprolites derived from carbonate rocks, suggesting the Zn enrichment is linked to both the minerals-inheritance from parent rocks and secondary accumulation in CSFs. Furthermore, the comparison of Cr/Zn ratios of CSF indicated a substantial decline during the weathering of carbonate rocks (from 1.02 to 0.44), implying the Cr/Zn ratios of CSFs have potential to be a fingerprint sensitive to weathering of carbonate rocks.

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黏土大小的Cr/Zn比值作为岩性约束的风化指纹

不同岩性的化学风化作用是导致地球表面铬、锌元素重新分布的主要因素。粘土大小的分数(<；2 μm, CSFs)作为普遍存在的风化产物，对Cr和Zn的吸附起着至关重要的作用。然而，由于目前对沉积岩到土壤的CSFs认识不足，可能会影响对这些地区衍生土壤中Cr和Zn富集过程的清晰认识，从而限制了对Cr/Zn地球化学信号的进一步解读。本文分析了碳酸盐岩、碎屑岩和衍生腐殖岩的碳水化合物中Cr、Zn的含量。结果表明，沉积岩CSFs中Cr和Zn的丰度分别为48.6 ~ 181.8 mg kg - 1和98.2 ~ 219 mg kg - 1，表明70%以上的Cr受到层状硅酸盐的约束，而Zn则分散在矿物相中。这些结果证实了CSFs是母物质中富锌、富铬的储层。碳酸盐岩腐殖岩中各泥粒级矿物相中锌的富集程度高达4.1倍，表明锌的富集与母岩中矿物的继承和次生富集有关。此外，CSF的Cr/Zn比值在碳酸盐岩风化过程中呈明显下降趋势（从1.02降至0.44），表明CSF的Cr/Zn比值具有作为碳酸盐岩风化特征指纹的潜力。

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来源期刊

Global and Planetary Change 地学天文-地球科学综合

CiteScore

7.40

自引率

10.30%

发文量

226

审稿时长

63 days

期刊介绍： The objective of the journal Global and Planetary Change is to provide a multi-disciplinary overview of the processes taking place in the Earth System and involved in planetary change over time. The journal focuses on records of the past and current state of the earth system, and future scenarios , and their link to global environmental change. Regional or process-oriented studies are welcome if they discuss global implications. Topics include, but are not limited to, changes in the dynamics and composition of the atmosphere, oceans and cryosphere, as well as climate change, sea level variation, observations/modelling of Earth processes from deep to (near-)surface and their coupling, global ecology, biogeography and the resilience/thresholds in ecosystems. Key criteria for the consideration of manuscripts are (a) the relevance for the global scientific community and/or (b) the wider implications for global scale problems, preferably combined with (c) having a significance beyond a single discipline. A clear focus on key processes associated with planetary scale change is strongly encouraged. Manuscripts can be submitted as either research contributions or as a review article. Every effort should be made towards the presentation of research outcomes in an understandable way for a broad readership.