Weathering, alteration and reconstructing Earth's oxygenation.

Area of Science:

• Earth and Life Sciences
• Geochemistry
• Paleontology

Background:

• Reconstructing Earth's redox history is key to understanding the evolution of complex life.
• Geochemical redox proxies are widely used but often yield conflicting interpretations of oxygenation events.
• Secondary alteration, particularly oxidation, is a frequently overlooked factor affecting geochemical data fidelity.

Purpose of the Study:

• To investigate the impact of secondary alteration on geochemical redox proxies.
• To address the causes of conflicting interpretations in Earth's oxygenation history.
• To propose quality control measures for improving the reliability of paleoredox data.

Main Methods:

• Analysis of a large shale geochemistry database.
• Comparison of cerium (Ce) anomalies between outcrop and drill core samples.
• Review of existing literature on geochemical proxy systems and sample alteration.

Main Results:

• Significant differences in cerium anomalies were observed between outcrop and drill core samples, indicating widespread alteration.
• Geochemical data from altered samples are frequently published, contributing to conflicting paleoredox reconstructions.
• The study supports the hypothesis that secondary oxidation significantly impacts geochemical proxy data.

Conclusions:

• Secondary alteration is a pervasive issue in paleoredox proxy studies, necessitating improved quality control.
• Public archiving of samples is essential for verifying geochemical data and ensuring reproducibility.
• The geochemical community must adopt stricter measures to enhance the reliability of paleoredox proxy research.