Associations between redox‐sensitive trace metals and microbial communities in a Proterozoic ocean analogue

Rico, Kathryn; Sheldon, Nathan D.; Kinsman-Costello, Lauren

doi:10.1111/gbi.12388

Cited by 4 publications

(3 citation statements)

References 57 publications

(242 reference statements)

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“…These observations differ from Sforna et al (2017) who suggested biologically controlled accumulation of TE in organic-rich globules in modern microbialites was a consequence of specific metabolic pathways (Sforna et al, 2017). By contrast, our results are similar to Rico et al (2020) who observed that living microbial mats from the Middle Island Sinkhole (located 23 m below the water level of Lake Huron) do not significantly influence bulk TE geochemistry at the sediment-water interface, although highly heterogeneous redox conditions were observed. Considering that the water column redox conditions (e.g., oxygen, sulfate, and iron concentrations) in the Middle Island Sinkhole could be analogous to those that were in Proterozoic shallow-marine environments (cf.…”

Section: Te Geochemistry: a Biosignature Of Benthic Microbial Activity?contrasting

confidence: 85%

Trace element perspective into the ca. 2.1-billion-year-old shallow-marine microbial mats from the Francevillian Group, Gabon

Aubineau

Albani²,

Bekker³

et al. 2020

Chemical Geology

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The sedimentary fabrics of Precambrian mat-related structures (MRS) represent some of the oldest convincing evidence for early life on Earth. The ca. 2.1 billion-year (Ga) old MRS in the FB2 Member of the Francevillian basin in Gabon has received considerable attention not only because they contain remnants of microbial mats that colonized large areas in oxygenated, shallow-marine settings, but they also contain evidence for ancient multicellular organisms that thrived on these microbial mats using them as a food source. Despite these insights, what remains lacking is a full characterization of the geochemical composition of the MRS to test whether the bulk composition of fossilized MRS is distinct from the host sediments (sandstones and shales). Here, we show that the trace element (TE) content of microbial textures belonging to pyritized MRS, poorly pyritized MRS, and "elephant-skin" textures (EST) is highly variable and differs from that of the host sediments. The poorly pyritized MRS contain a unique matrix with embedded Ti-and Zr-rich minerals and syngenetically enriched in TE. The EST, some of which are developed along the same stratigraphic horizon as the poorly pyritized MRS, display a distinct distribution of TE-bearing heavy minerals, suggesting a local difference in physical conditions during sedimentation. Similarly, high chalcophile-element (CE) content in pyritized MRS relative to the host sediments of the FB2 Member further points to local bacterially influenced enrichments with high rates of microbial sulfate reduction during early diagenesis.The geochemical relationship between the MRS and the Francevillian sediments (e.g., FB, FC, and FD formations) indicates that specific biological pathways for CE enrichments (i.e., microbially controlled accumulation) are not apparent. Our findings highlight bulk-rock TE distinction between the 2.1-billion-year-old MRS and their host sediments, but also indicate that environmental conditions, such as hydrodynamic regime and water-column redox chemistry, may simply overwhelm any potential biological signal. Our data suggest that the microbial impact may have only passively influenced TE enrichment in the studied sediments, implying that TE concentrations in MRS are a poor biosignature. Importantly, this work indicates that bulk TE geochemistry does not unveil specific microbiological processes in the rock record, which is consistent with the observed patterns in modern analogues.

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Section: Te Geochemistry: a Biosignature Of Benthic Microbial Activity?contrasting

confidence: 85%

Trace element perspective into the ca. 2.1-billion-year-old shallow-marine microbial mats from the Francevillian Group, Gabon

Aubineau

Albani²,

Bekker³

et al. 2020

Chemical Geology

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Section: Methodsmentioning

confidence: 99%

“…Sediment underlying the ~2 mm‐thick microbial mats is different than the surrounding Lake Huron sediment (Nold et al, 2013; Rico & Sheldon, 2019; Rico et al, 2020). Carbon isotope signatures in the sedimentary organic matter underlying the mats indicate that it is sourced from settling phytoplankton (Nold et al, 2013; Rico & Sheldon, 2019; Rico et al, 2020), and some trace metals such as molybdenum show modest enrichments due to particulate shuttling (Rico et al, 2019). Overall, the MIS sediments have higher total organic carbon, iron, and trace metal concentrations than Lake Huron sediments due to differences in redox chemistry and geomicrobiological conditions between the sinkhole and surrounding environment (Nold et al, 2013; Rico & Sheldon, 2019; Rico et al, 2019, 2020).…”

Section: Methodsmentioning

confidence: 99%

Sedimentary pyrite sulfur isotope compositions preserve signatures of the surface microbial mat environment in sediments underlying low‐oxygen cyanobacterial mats

et al. 2021

Self Cite

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The sedimentary pyrite sulfur isotope (δ34S) record is an archive of ancient microbial sulfur cycling and environmental conditions. Interpretations of pyrite δ34S signatures in sediments deposited in microbial mat ecosystems are based on studies of modern microbial mat porewater sulfide δ34S geochemistry. Pyrite δ34S values often capture δ34S signatures of porewater sulfide at the location of pyrite formation. However, microbial mats are dynamic environments in which biogeochemical cycling shifts vertically on diurnal cycles. Therefore, there is a need to study how the location of pyrite formation impacts pyrite δ34S patterns in these dynamic systems. Here, we present diurnal porewater sulfide δ34S trends and δ34S values of pyrite and iron monosulfides from Middle Island Sinkhole, Lake Huron. The sediment–water interface of this sinkhole hosts a low‐oxygen cyanobacterial mat ecosystem, which serves as a useful location to explore preservation of sedimentary pyrite δ34S signatures in early Earth environments. Porewater sulfide δ34S values vary by up to ~25‰ throughout the day due to light‐driven changes in surface microbial community activity that propagate downwards, affecting porewater geochemistry as deep as 7.5 cm in the sediment. Progressive consumption of the sulfate reservoir drives δ34S variability, instead of variations in average cell‐specific sulfate reduction rates and/or sulfide oxidation at different depths in the sediment. The δ34S values of pyrite are similar to porewater sulfide δ34S values near the mat surface. We suggest that oxidative sulfur cycling and other microbial activity promote pyrite formation in and immediately adjacent to the microbial mat and that iron geochemistry limits further pyrite formation with depth in the sediment. These results imply that primary δ34S signatures of pyrite deposited in organic‐rich, iron‐poor microbial mat environments capture information about microbial sulfur cycling and environmental conditions at the mat surface and are only minimally affected by deeper sedimentary processes during early diagenesis.

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Mysteries of metallome evolution: Integrating insights from the Earth and life sciences

Rico,

Garcia,

Saito

et al. 2025

Treatise on Geochemistry

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Associations between redox‐sensitive trace metals and microbial communities in a Proterozoic ocean analogue

Abstract: This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

Cited by 4 publications

References 57 publications

Trace element perspective into the ca. 2.1-billion-year-old shallow-marine microbial mats from the Francevillian Group, Gabon

Trace element perspective into the ca. 2.1-billion-year-old shallow-marine microbial mats from the Francevillian Group, Gabon

Sedimentary pyrite sulfur isotope compositions preserve signatures of the surface microbial mat environment in sediments underlying low‐oxygen cyanobacterial mats

Mysteries of metallome evolution: Integrating insights from the Earth and life sciences

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