266 The Neoproterozoic Earth and Life Co-evolution (Posters)

This session aims to enhance discussions and foster interdisciplinary collaborations to advance understanding of the Neoproterozoic Earth and life co-evolution. Contributions from paleontologists, geochemists, sedimentologists, Earth system modelers, and related fields are highly encouraged.

Wednesday, 22 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Pyritized filaments from the Ediacaran Tamengo Formation indicate diverse microbial and algal communities

Paper number: 266-3
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The Ediacaran Period marks the debut of animals and other complex macroscopic forms in the fossil record. Although many late Ediacaran body fossils are recognized as metazoans, their exact position within the animal family tree remain uncertain. Abundant yet minute trace fossils from the terminal Ediacaran and earliest Cambrian of Brazil have been proposed as evidence for early small-sized (meiofaunal) bilaterians, but their interpretation is challenging due to their resemblance to non-metazoan structures. In this study, we reexamine the oldest proposed meiofaunal trace fossils from the Tamengo Formation (ca. 541 million years ago) in the Corumbá Group, Brazil. We analyze newly discovered specimens using multiple analytical methods to understand their morphologies, distribution, and how they were preserved. We also report a new fossil site, confirmed to be of similar age as the classic Corumbá outcrops through U-Pb dating of zircon crystals in volcanic ash layers, with approximate Concordia ages of 544 ± 2.6 Ma and 539,03 ± 2,27 Ma, as revealed by LA-MC-ICP-MS and LA-ICP-MS, respectively. Fossils from the different two locations show features consistent with body fossils, including visible cells, divisions between cell walls, and organic content preserved in the walls as evidenced by the typical D and G bands of kerogen in their Raman spectra. Alignment of the filaments, significant variation in width, and no evidence of cross-cutting further corroborates this interpretation. Moreover, the high concentration of early diagenetic pyrite within the filaments but not in encompassing sediments is best interpreted in terms of microbial sulfate reduction of organic filaments. We thus interpret these fossils as filamentous microorganisms preserved by pyritization. The fossils show different specific ranges of sizes, suggesting the presence of at least three distinct microbial and/or algal populations, as revealed by mixtures analysis. Together with their alignment and occasional vertical orientation, these results point to an original benthic microbial-algal consortium. Though their exact identities are still unclear, the largest forms resemble bottom-dwelling algae and possibly some large sulfur-oxidizing bacteria (SOB), while the smallest populations can represent algae, cyanobacteria, or SOB. Our findings weaken the proposed fossil evidence for meiofaunal bioturbation during the Ediacaran to Cambrian transition.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412996

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