Do Archean chemical sediments record ancient seawater rare earth element patterns?
The paper investigates whether Archean chemical sediments, particularly banded iron formations (BIFs) and other chemical precipitates, faithfully preserve the rare earth element (REE) composition of ancient seawater. By comparing shale‑normalized REE patterns from Archean and Proterozoic chemical sediments with modern seawater, Holocene microbial carbonates, corals, and a suite of groundwaters from central México, the authors assess the reliability of REE signatures as paleo‑ocean proxies. Statistical analyses (ANOVA, Wilcoxon tests) and REE fractionation metrics such as (La/Yb)SN and Ce anomalies reveal that many modern groundwaters exhibit seawater‑like REE patterns, driven by carbonate complexation and redox conditions. Consequently, the study argues that terrestrial waters can mimic seawater REE signatures, cautioning against a straightforward interpretation of Archean chemical sediments as direct records of ancient ocean chemistry. The paper outlines methodological considerations (ICP‑MS analysis, normalization), discusses the influence of redox, complexation, and source‑rock contributions on REE distributions, and provides recommendations for more nuanced paleoenvironmental reconstructions.
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Reassessing Archean Chemical Sediments as Direct Recorders of Ancient Seawater REE Patterns
The paper challenges the assumption that BIFs and other Archean chemical precipitates preserve the REE composition of the Archean ocean. By comparing shale‑normalized REE patterns from Archean and Proterozoic sediments with modern seawater and other analogs, the authors show that multiple depositional and post‑depositional processes can modify the original signal, limiting the straightforward use of these rocks as paleo‑seawater proxies.