Can NanoSIMS probe quantitatively the geochemical composition of ancient organic-walled microfossils? A case study from the early Neoproterozoic Liulaobei Formation

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dc.contributor.authorDelarue, Fredericen
dc.contributor.authorRobert, Francoisen
dc.contributor.authorTartese, Romainen
dc.contributor.authorSugitani, Kenichiroen
dc.contributor.authorTang, Qingen
dc.contributor.authorDuhamel, Remien
dc.contributor.authorPont, Sylvainen
dc.contributor.authorXiao, Shuhaien
dc.contributor.departmentGeosciencesen
dc.date.accessioned2019-09-10T19:24:30Zen
dc.date.available2019-09-10T19:24:30Zen
dc.date.issued2018-07en
dc.description.abstractAssessing the biogenicity of Precambrian putative remnants of life requires solid criteria. Among possible criteria, searching for evidence of pristine biological signatures and identifying various biological organic matter (OM) precursors in close association with microfossil morphology are of interest. Nano-scale Secondary Ion Mass Spectrometry (NanoSIMS) can provide a quantitative geochemical proxy at the scale of the individual microfossil but its use has remained limited because of potential analytical biases related to matrix effects and microtopography that may result in inaccurate NanoSIMS-derived measurement. No study so far has assessed whether these potential analytical biases were strong enough to preclude any identification of pristine OM degradation products and of organic precursors in ancient sediments. In this study, we characterized the geochemical composition of organic-walled microfossils from the early Neoproterozoic Liulaobei Formation in North China using NanoSIMS. The (CH-)-C-12/C-12(2)- ionic ratio allows us to distinguish filament from spheroid acritarchs, revealing the co-occurrence of two distinct pristine OM signatures that differ by their H and/or aliphatic contents. In addition, NanoSIMS data show that morphological degradation was tightly linked to a loss of H and/or hydrogenated organic compounds in spheroid acritarchs. In contrast, in situ N/C atomic ratios are homogeneous across all organic-walled microfossils studied. Although highly coherent with Proterozoic N/C atomic ratios from the literature, such homogeneity may alternatively reflect (i) a similar N content for different organic precursors or (ii) an extensive homogenization related to early degradation. Overall, these data obtained on microfossils from the Proterozoic Liulaobei Formation are the first to demonstrate that the quantitative capability of NanoSIMS can be used to track ancient OM precursors and to probe the effects of degradation on pristine OM. These findings open up tremendous perspectives and put forward new criteria for assessing the biogenicity of the putative early traces of life found in Archean metasediments.en
dc.description.notesThe authors are thankful to J.J. Pantel for his help in sample crushing. This research is supported by ERC Grant No. 290861 - PaleoNanoLife (PI F. Robert), the Japanese Society for the Promotion of Science (a grant-in-aid No. 24654162), and NASA Exobiology and Evolutionary Biology Program (NNX15AL27G). The authors warmly thank Roger Hewins for English editing and Xiaotong Peng and Guochun Zhao for their constructive comments.en
dc.description.sponsorshipERC Grant [290861 - PaleoNanoLife]; Japanese Society for the Promotion of Science [24654162]; NASA Exobiology and Evolutionary Biology Program [NNX15AL27G]en
dc.format.mimetypeapplication/pdfen
dc.identifier.doihttps://doi.org/10.1016/j.precamres.2018.03.003en
dc.identifier.eissn1872-7433en
dc.identifier.issn0301-9268en
dc.identifier.urihttp://hdl.handle.net/10919/93525en
dc.identifier.volume311en
dc.language.isoenen
dc.rightsCreative Commons Attribution-NonCommercial-NoDerivatives 4.0 Internationalen
dc.rights.urihttp://creativecommons.org/licenses/by-nc-nd/4.0/en
dc.subjectAcritarchsen
dc.subjectEarly lifeen
dc.subjectHydrogenen
dc.subjectMicrofossilsen
dc.subjectNanoSIMSen
dc.subjectNitrogenen
dc.titleCan NanoSIMS probe quantitatively the geochemical composition of ancient organic-walled microfossils? A case study from the early Neoproterozoic Liulaobei Formationen
dc.title.serialPrecambrian Researchen
dc.typeArticle - Refereeden
dc.type.dcmitypeTexten
dc.type.dcmitypeStillImageen

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