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  • 1.
    Bengtson, Stefan
    et al.
    Swedish Museum of Natural History, Department of Paleobiology.
    Ivarsson, Magnus
    Swedish Museum of Natural History, Department of Paleobiology.
    Astolfo, Alberto
    Paul Scherrer Institute.
    Belivanova, Veneta
    Swedish Museum of Natural History, Department of Paleobiology.
    Broman, Curt
    Stockholm University.
    Marone, Federica
    Paul Scherrer Institute.
    Stampanoni, Marco
    ETH Zürich.
    Deep-biosphere consortium of fungi and prokaryotes in Eocene sub-seafloor basalts.2014In: Geobiology, ISSN 1472-4677, E-ISSN 1472-4669, Vol. 12, no 6, p. 489-496Article in journal (Refereed)
    Abstract [en]

    The deep biosphere of the subseafloor crust is believed to contain a significant part of Earth’s biomass, but because of the difficulties of directly observing the living organisms, its composition and ecology are poorly known. We report here a consortium of fossilized prokaryotic and eukaryotic microorganisms, occupying cavities in deep-drilled vesicular basalt from the Emperor Seamounts, Pacific Ocean, 67.5 meters below seafloor (mbsf). Fungal hyphae provide the framework on which prokaryote-like organisms are suspended like cobwebs and iron-oxidizing bacteria form microstromatolites (Frutexites). The spatial interrelationships show that the organisms were living at the same time in an integrated fashion, suggesting symbiotic interdependence. The community is contemporaneous with secondary mineralizations of calcite partly filling the cavities. The fungal hyphae frequently extend into the calcite, indicating that they were able to bore into the substrate through mineral dissolution. A symbiotic relationship with chemoautotrophs, as inferred for the observed consortium, may be a prerequisite for the eukaryotic colonization of crustal rocks. Fossils thus open a window to the extant as well as the ancient deep biosphere.

  • 2. Chi Fru, E.
    et al.
    Ivarsson, M.
    Swedish Museum of Natural History, Department of Geology.
    Kilias, S. P.
    Frings, Patrick J
    Swedish Museum of Natural History, Department of Geology.
    Hemmingsson, C.
    Broman, C.
    Bengtson, S.
    Swedish Museum of Natural History, Department of Paleobiology.
    Chatzitheodoridis, E.
    Biogenicity of an Early Quaternary iron formation, Milos Island, Greece2015In: Geobiology, ISSN 1472-4677, E-ISSN 1472-4669, Vol. 13, no 3, p. 225-244Article in journal (Refereed)
    Abstract [en]

    A ~2.0-million-year-old shallow-submarine sedimentary deposit on Milos Island, Greece, harbours an unmetamorphosed fossiliferous iron formation (IF) comparable to Precambrian banded iron formations (BIFs). This Milos IF holds the potential to provide clues to the origin of Precambrian BIFs, relative to biotic and abiotic processes. Here, we combine field stratigraphic observations, stable isotopes of C, S and Si, rock petrography and microfossil evidence from a ~5-m-thick outcrop to track potential biogeochemical processes that may have contributed to the formation of the BIF-type rocks and the abrupt transition to an overlying conglomerate-hosted IF (CIF). Bulk δ13C isotopic compositions lower than -25‰ provide evidence for biological contribution by the Calvin and reductive acetyl–CoA carbon fixation cycles to the origin of both the BIF-type and CIF strata. Low S levels of ~0.04 wt.% combined with δ34S estimates of up to ~18‰ point to a non-sulphidic depository. Positive δ30Si records of up to +0.53‰ in the finely laminated BIF-type rocks indicate chemical deposition on the seafloor during weak periods of arc magmatism. Negative δ30Si data are consistent with geological observations suggesting a sudden change to intense arc volcanism potentially terminated the deposition of the BIF-type layer. The typical Precambrian rhythmic rocks of alternating Fe- and Si-rich bands are associated with abundant and spatially distinct microbial fossil assemblages. Together with previously proposed anoxygenic photoferrotrophic iron cycling and low sedimentary N and C potentially connected to diagenetic denitrification, the Milos IF is a biogenic submarine volcano-sedimentary IF showing depositional conditions analogous to Archaean Algoma-type BIFs.

  • 3. Chi Fru, Ernest
    et al.
    Ivarsson, Magnus
    Swedish Museum of Natural History, Department of Paleobiology.
    Kilias, Stephanos
    Christoffer, Hemmingson
    Broman, Curt
    Bengtson, Stefan
    C, Chatzitheodoridis
    Biogenicity of an early Quaternary iron formation, Milos Island, Greece2015In: Geobiology, ISSN 1472-4677, E-ISSN 1472-4669, Vol. 13, p. 225-244Article in journal (Refereed)
  • 4. Gallagher, M.
    et al.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Kamber, B.S.
    The Neoarchaean surficial sulphur cycle: an alternative hypothesis based on analogies with 20th century atmospheric lead.2017In: Geobiology, ISSN 1472-4677, E-ISSN 1472-4669, Vol. 15, p. 385-400Article in journal (Refereed)
    Abstract [en]

    We revisit the S-isotope systematics of sedimentary pyrite in a shaly limestone from the ca. 2.52 Ga Gamohaan Formation, Upper Campbellrand Subgroup, Transvaal, South Africa. The analysed rock is interpreted to have been deposited in a water depth of ca. 50–100 m, in a restricted sub-basin on a drowning platform. A previous study discovered that the pyrites define a nonzero intercept δ34SV-CDT–Δ33S data array. The present study carried out further quadruple S-isotope analyses of pyrite, confirming and expanding the linear δ34SV-CDT–Δ33S array with an δ34S zero intercept at ∆33S ca. +5. This was previously interpreted to indicate mixing of unrelated S-sources in the sediment environment, involving a combination of recycled sulphur from sulphides that had originally formed by sulphate-reducing bacteria, along with elemental sulphur. Here, we advance an alternative explanation based on the recognition that the Archaean seawater sulphate concentration was likely very low, implying that the Archaean ocean could have been poorly mixed with respect to sulphur. Thus, modern oceanic sulphur systematics provide limited insight into the Archaean sulphur cycle. Instead, we propose that the 20th-century atmospheric lead event may be a useful analogue. Similar to industrial lead, the main oceanic input of Archaean sulphur was through atmospheric raindown, with individual giant point sources capable of temporally dominating atmospheric input. Local atmospheric S-isotope signals, of no global significance, could thus have been transmitted into the localised sediment record. Thus, the nonzero intercept δ34SV-CDT–Δ33S data array may alternatively represent a very localised S-isotope signature in the Neoarchaean surface environment. Fallout from local volcanic eruptions could imprint recycled MIF-S signals into pyrite of restricted depositional environments, thereby avoiding attenuation of the signal in the subdued, averaged global open ocean sulphur pool. Thus, the superposition of extreme local S-isotope signals offers an alternative explanation for the large Neoarchaean MIF-S excursions and asymmetry of the Δ33S rock record.

  • 5.
    Sallstedt, Therese
    et al.
    Swedish Museum of Natural History, Department of Paleobiology.
    Bengtson, Stefan
    Swedish Museum of Natural History, Department of Paleobiology.
    Broman, Curt
    Stockholm University.
    Crill, Patrick M.
    Stockholm University.
    Canfield, Donald E.
    University of Southern Denmark.
    Evidence of oxygenic phototrophy in ancient phosphatic stromatolites from the Paleoproterozoic Vindhyan and Aravalli Supergroups, India.2018In: Geobiology, ISSN 1472-4677, E-ISSN 1472-4669, Vol. 16, p. 139-159Article in journal (Refereed)
    Abstract [en]

    Fossil microbiotas are rare in the early rock record, limiting the type of ecological information extractable from ancient microbialites. In the absence of body fossils, emphasis may instead be given to microbially derived features, such as microbialite growth patterns, microbial mat morphologies, and the presence of fossilized gas bubbles in lithified mats. The metabolic affinity of micro-organisms associated with phosphatization may reveal important clues to the nature and accretion of apatite-rich microbialites. Stromatolites from the 1.6 Ga Chitrakoot Formation (Semri Group, Vindhyan Supergroup) in central India contain abundant fossilized bubbles interspersed within fine-grained in situ-precipitated apatite mats with average δ13Corg indicative of carbon fixation by the Calvin cycle. In addition, the mats hold a synsedimentary fossil biota characteristic of cyanobacterial and rhodophyte morphotypes. Phosphatic oncoid cone-like stromatolites from the Paleoproterozoic Aravalli Supergroup (Jhamarkotra Formation) comprise abundant mineralized bubbles enmeshed within tufted filamentous mat fabrics. Construction of these tufts is considered to be the result of filamentous bacteria gliding within microbial mats, and as fossilized bubbles within pristine mat laminae can be used as a proxy for oxygenic phototrophy, this provides a strong indication for cyanobacterial activity in the Aravalli mounds. We suggest that the activity of oxygenic phototrophs may have been significant for the formation of apatite in both Vindhyan and Aravalli stromatolites, mainly by concentrating phosphate and creating steep diurnal redox gradients within mat pore spaces, promoting apatite precipitation. The presence in the Indian stromatolites of alternating apatite-carbonate lamina may result from local variations in pH and oxygen levels caused by photosynthesis–respiration in the mats. Altogether, this study presents new insights into the ecology of ancient phosphatic stromatolites and warrants further exploration into the role of oxygen-producing biotas in the formation of Paleoproterozoic shallow-basin phosphorites.

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