海洋埋藏成因过程中浅水碳酸盐硼同位素值的重置

IF 1.9 3区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY
Mingyu Zhao, B. Beaty, L. Tarhan, Noah Planavsky
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引用次数: 0

摘要

块状碳酸盐的硼同位素组成(δ11B)可以为重建海洋 pH 值的变化提供档案。根据古碳酸盐进行重建时,通常假定在海洋埋藏成岩过程中,δ11B 没有发生明显的重置。然而,我们对与这一过程相关的 B 同位素行为的了解仍然有限。在此,我们提供了大巴哈马海岸附近一个经历过海洋埋藏成岩作用的现代近地台碳酸盐序列的 B/Ca 和 B 同位素组成(δ11B)的测量结果。我们的研究结果表明,随着深度的增加,块状碳酸盐的 δ11B(约 13 ‰)和 B/Ca(约 80 %)都明显下降。我们将这种模式归因于文石溶解过程中向孔隙水释放了同位素轻的硼(δ11B ~20 ‰),而新形成的低镁方解石从孔隙水中吸收了同位素实质上较轻的硼酸根离子(δ11B ~-1 ‰)。定量模型为这一解释提供了进一步的支持,并提供了平均新形速率(k0)的估计值,其范围在1×10-6至5×10-6 yr-1之间,与之前对陨石成因过程中新形和/或再结晶速率的估计值相当。我们的研究结果表明,在重结晶过程中,重置块状碳酸盐岩中的δ11B特征具有很大的潜力,在今后试图根据这些记录重建pH和pCO2时必须考虑到这一点,并且可能需要对现有记录进行重新解释。我们的研究结果还表明,B同位素有可能成为碳酸盐再结晶/形貌和原始碳酸盐矿物学的替代物。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Resetting of Shallow-Water Carbonate Boron Isotope Values During Marine Burial Diagenesis
The boron isotopic composition (δ11B) of bulk carbonates may provide an archive to reconstruct changes in ocean pH. Reconstructions from ancient carbonates typically assume that no significant resetting of δ11B occurred during marine burial diagenesis. However, our understanding of B isotopic behavior associated with this process remains limited. Here we provide measurements of B/Ca and B isotopic composition (δ11B) from a modern peri-platform carbonate sequence near the Great Bahama Bank that has undergone marine burial diagenesis. Our results reveal significant decreases in both δ11B (~13 ‰) and B/Ca (~80 %) of bulk carbonates with depth. We attribute this pattern to the release of isotopically light B (δ11B ~20 ‰) to porewater during aragonite dissolution, with uptake of substantially isotopically lighter borate ions (δ11B ~-1 ‰) from porewater by newly forming low-Mg calcite. A quantitative model adds further support for this interpretation and provides an estimate of average neomorphism rate ( k0) in the range of 1×10-6 to 5×10-6 yr-1, which is comparable to previous rate estimates for neomorphism and/or recrystallization during meteoric diagenesis. Our results demonstrate the strong potential for resetting δ11B signatures in bulk carbonates during recrystallization, which must be considered in future attempts to reconstruct pH and pCO2 from these records and may require reinterpretation of existing records. Our results also suggest the potential of B isotopes as a proxy for carbonate recrystallization/neomorphism and original carbonate mineralogy.
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来源期刊
American Journal of Science
American Journal of Science 地学-地球科学综合
CiteScore
5.80
自引率
3.40%
发文量
17
审稿时长
>12 weeks
期刊介绍: The American Journal of Science (AJS), founded in 1818 by Benjamin Silliman, is the oldest scientific journal in the United States that has been published continuously. The Journal is devoted to geology and related sciences and publishes articles from around the world presenting results of major research from all earth sciences. Readers are primarily earth scientists in academia and government institutions.
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