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- Weimann, L., et al.
(författare)
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Carbonaceous matter in ∼ 3.5 Ga black bedded barite from the Dresser Formation (Pilbara Craton, Western Australia) – Insights into organic cycling on the juvenile Earth
- 2024
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Ingår i: Precambrian Research. - : Elsevier. - 0301-9268 .- 1872-7433. ; 403
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Tidskriftsartikel (refereegranskat)abstract
- Carbonaceous matter (CM) in Archean rocks represents a valuable archive for the reconstruction of early life. Here we investigate the nature of CM preserved in ∼ 3.5 Ga old black bedded barites from the Dresser Formation (Pilbara Carton, Western Australia). Using light microscopy and high-resolution Raman mapping, three populations of CM were recognized: (i) CM at the edges of single growth bands of barite crystals (most frequent), (ii) CM within the barite matrix, and (iii) CM in 50–300 µm wide secondary quartz veins that cross-cut the black bedded barite. Raman spectra of CM inside black bedded barite indicated peak metamorphic temperatures of ∼ 350 °C, consistent with those reached during the main metamorphic event in the area ∼ 3.3 Ga ago. By contrast, CM in quartz veins yielded much lower temperatures of ∼ 220 °C, suggesting that quartz-vein associated CM entered the barite after 3.3 Ga. Near edge X-ray absorption fine structure (NEXAFS) and solid-state nuclear magnetic resonance (NMR) revealed a highly aromatic nature of the CM with a lower aliphatic content, which is in line with the relatively elevated thermal maturity. Catalytic hydropyrolysis (HyPy) did not yield any hydrocarbons detectable with gas chromatography–mass spectrometry (GC–MS). Secondary ion mass spectrometry (SIMS) based δ13C values of individual CM particles ranged from − 33.4 ± 1.2 ‰ to − 16.5 ± 0.6 ‰ and are thus in accordance with a biogenic origin, which is also consistent with stromatolitic microbialites associated with the black bedded barite. Based on these results we conclude that CM at growth bands and inside the barite matrix is syngenetic and only the CM inside quartz veins, which represents a minor portion of the total CM, is a later addition to the system. Furthermore, we discuss different pathways for the input of CM into the barite-forming environment, including the cycling of biological organic material within the hydrothermal system.
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| 2. |
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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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| 4. |
- 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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