| 1. |
- Weimann, Lena, et al.
(författare)
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Insights Into Carbonaceous Matter in ∼3.5 Ga Hydrothermal Barites from the Dresser Formation (Pilbara Craton, Australia)
- 2023
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Ingår i: IMOG 2023.
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Konferensbidrag (refereegranskat)abstract
- The emergence of life on the juvenile Earth is still poorly understood and remains one of the major questions in geobiological research. Some of our planet´s most ancient rocks contain carbonaceous matter (CM) that may represent a valuable archive to trace earliest life.However, it is often difficult to prove the origin and syngeneity of such CM. Here we report on CM preserved in ∼3.5 Ga old barites from the Dresser Formation (Pilbara Carton, Western Australia). On outcrop scale, spatial associations between bedded and vein-hosted barites suggest that the bedded barite may have formed from hydrothermal fluids discharging into subaquatic caldera environments [1]. Bedded barites associated with stromatolites contain abundant CM (total organic carbon = 0.3 wt% [2]) whose nature has been investigated further. Three populations of CM were recognized by means of light microscopy and high-resolution Raman mapping: (i) CM flakes at the edges of single growth bands of barite crystals, (ii) CM dispersed within barite crystals, and (iii) CM in 50–300 µm wide secondary quartz veins that cross-cut barite crystals. Raman spectra of the CM indicate peak metamorphic temperatures of approximately 300 ± 50 °C, corresponding to lower greenschist-facies conditions which are consistent with the metamorphic overprint by granitic intrusions in the area ∼3.3 Ga ago [3]. Near edge X-ray absorption fine structure (NEXAFS) and solid-state nuclear magnetic resonance (NMR) measurements revealed a highly aromatic nature of the CM which is in line with relatively high thermal maturity. As all three CM populations experienced the major metamorphic overprint ∼3.3 Ga ago, a syngenetic formation of the CM with the host barite can be assumed or, in case of the vein-hosted secondary CM, an emplacement soon after barite growth.
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| 2. |
- Duda, Jan-Peter, et al.
(författare)
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Molecular fossils within bitumens and kerogens from the ~ 1 Ga Lakhanda Lagerstätte (Siberia, Russia) and their significance for understanding early eukaryote evolution
- 2021
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Ingår i: Palaeontologische Zeitschrift. - : Springer Nature. - 0031-0220 .- 1867-6812. ; 95, s. 577-592
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Tidskriftsartikel (refereegranskat)abstract
- The emergence and diversification of eukaryotes during the Proterozoic is one of the most fundamental evolutionary developments in Earth’s history. The ca. 1-billion-year-old Lakhanda Lagerstätte (Siberia, Russia) contains a wealth of eukaryotic body fossils and offers an important glimpse into their ecosystem. Seeking to complement the paleontological record of this remarkable lagerstätte, we here explored information encoded within sedimentary organic matter (total organic carbon = 0.01–1.27 wt.%). Major emphasis was placed on sedimentary hydrocarbons preserved within bitumens and kerogens, including molecular fossils (or organic biomarkers) that are specific to bacteria and eukaryotes (i.e. hopanes and regular steranes, respectively). Programmed pyrolysis and molecular organic geochemistry suggest that the organic matter in the analyzed samples is about peak oil window maturity and thus sufficiently well preserved for detailed molecular fossil studies that include hopanes and steranes. Together with petrographic evidence as well as compositional similarities of the bitumens and corresponding kerogens, the consistency of different independent maturity parameters establishes that sedimentary hydrocarbons are indigenous and syngenetic to the host rock. The possible presence of trace amounts of hopanes and absence of steranes in samples that are sufficiently well preserved to retain both types of compounds evidences an environment dominated by anaerobic bacteria with no or very little inputs by eukaryotes. In concert with the paleontological record of the Lakhanda Lagerstätte, our study adds to the view that eukaryotes were present but not significant in Mesoproterozoic ecosystems.
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| 3. |
- Reinhardt, Manuel, et al.
(författare)
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Aspects of the biological carbon cycle in a ca. 3.42-billion-year-old marine ecosystem
- 2024
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Ingår i: Precambrian Research. - : Elsevier. - 0301-9268 .- 1872-7433. ; 402, s. 107289-107289
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Tidskriftsartikel (refereegranskat)abstract
- Microbial life on Earth was well established in the Paleoarchean, but insight into early ecosystem diversity and thus, the complexity of the early biological carbon cycle is limited. Here we investigated four carbonaceous chert samples from the lower platform facies of the ca. 3.42-billion-year-old Buck Reef Chert, Barberton greenstone belt. The analysis on multiple scales revealed exceptionally well-preserved carbonaceous matter, even on molecular level (aliphatic and aromatic hydrocarbons), resulting from rapid silicification. Geochemical evidence from stable carbon and multiple sulfur isotopes supports the presence of different microbial metabolisms in the Paleoarchean ecosystem. The local biological carbon cycle was dominated by photoautotrophs, but autotrophic sulfate reducers and methane- or acetate-producing microbes were also present. In areas of microbial methane or acetate release, methanotrophs or acetotrophs contributed to the overall biomass. These results highlight the metabolic diversity in the lower platform environment of the Buck Reef Chert, and underline that an advanced biological carbon cycle already existed in the early Archean.
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