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Morphological and geochemical variation in framboidal pyrite aggregates and implications for use as a methane seepage proxy.

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Title: Morphological and geochemical variation in framboidal pyrite aggregates and implications for use as a methane seepage proxy.
Authors: Song, Qiang1,2 (AUTHOR), Wang, Jiasheng1,2 (AUTHOR) js-wang@cug.edu.cn, Algeo, Thomas J.2,3,4 (AUTHOR), Wang, Zhou1,2 (AUTHOR), Chen, Can5 (AUTHOR), Geng, Kunlong1,2 (AUTHOR), Li, Qing6 (AUTHOR)
Source: Geochimica et Cosmochimica Acta. Jul2026, Vol. 424, p91-101. 11p.
Subjects: Pyrites, Analytical geochemistry, Paleoenvironmental studies, Morphology, Trace elements, Iron sulfides, Cold seeps
Abstract: Framboidal pyrite in modern sediments occurs predominantly as isolated framboids and aggregates of a few distinct morphotypes (e.g., irregular-shaped, rod-like, and foram-fill). However, there has been little study to date of potential disparities in geochemical proxy signals among these aggregate morphotypes. Here, we present a morphotype-specific morphological and geochemical dataset comprising framboid size, δ34S, and trace-element compositional data for framboidal pyrite aggregates recovered from IODP Expedition 311 Site U1329C on the Cascadia Margin, an area of both modern and ancient methane seepage. Our results demonstrate that there is significant geochemical variation among different co-occurring aggregate morphotypes. The observed heterogeneity reflects differences in formation microenvironments (e.g., porewater connectivity, spatial confinement, local material supply) and, more fundamentally, the polygenetic nature of pyrite populations. We demonstrate that the traditional approach of analyzing bulk pyrite consisting of a mixture of isolated framboids and aggregate morphotypes likely obscures or distorts paleo-environmental signals. Therefore, we conclude that morphotype-specific analysis is essential for accurate interpretation of pyrite-based geochemical proxies. This study provides a valuable framework for research that relies on pyrite-based geochemical indicators to reconstruct paleoenvironmental and methane seepage history. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:Framboidal pyrite in modern sediments occurs predominantly as isolated framboids and aggregates of a few distinct morphotypes (e.g., irregular-shaped, rod-like, and foram-fill). However, there has been little study to date of potential disparities in geochemical proxy signals among these aggregate morphotypes. Here, we present a morphotype-specific morphological and geochemical dataset comprising framboid size, δ34S, and trace-element compositional data for framboidal pyrite aggregates recovered from IODP Expedition 311 Site U1329C on the Cascadia Margin, an area of both modern and ancient methane seepage. Our results demonstrate that there is significant geochemical variation among different co-occurring aggregate morphotypes. The observed heterogeneity reflects differences in formation microenvironments (e.g., porewater connectivity, spatial confinement, local material supply) and, more fundamentally, the polygenetic nature of pyrite populations. We demonstrate that the traditional approach of analyzing bulk pyrite consisting of a mixture of isolated framboids and aggregate morphotypes likely obscures or distorts paleo-environmental signals. Therefore, we conclude that morphotype-specific analysis is essential for accurate interpretation of pyrite-based geochemical proxies. This study provides a valuable framework for research that relies on pyrite-based geochemical indicators to reconstruct paleoenvironmental and methane seepage history. [ABSTRACT FROM AUTHOR]
ISSN:00167037
DOI:10.1016/j.gca.2026.05.023