Carbonates and cherts as archives of seawater chemistry and habitability on a carbonate platform 3.35 Ga ago:

Autor(en)
Sebastian Viehmann, Joachim Reitner, Nathalie Tepe, Simon V. Hohl, Martin Van Kranendonk, Thilo Hofmann, Christian Köberl, Patrick Meister
Abstrakt

Carbonates and cherts in the 3.35 billion-year-old Strelley Pool Formation (Fm.; Australia) host stromatolites
that are among the oldest remnants of life on Earth. However, it is still not entirely clear whether these mineral
phases are authigenic precipitates, and whether they represent reliable geochemical archives of early Earth
environments. Here we present major/trace-element and Nd-isotope data of stromatolitic carbonates, associated
crystal-fan carbonates, and cherts in the Strelley Pool Fm. (i) to assess the reliability of these chemical sediments
as geochemical archives of the fluids from which they precipitated, (ii) to date the time of formation of carbonate
and silica phases, and (iii) to trace the sources of elements prevailing in microbial habitats 3.35 Ga ago.
Stromatolitic carbonates plot together with the stratigraphically underlying Marble Bar cherts on a Sm-Nd
regression line yielding 3253 ± 320 Ma. In contrast, associated crystal-fan carbonates together with altered
Marble Bar cherts yield 2718 ± 220 Ma, suggesting that their Sm-Nd isotope system was reset after deposition.
Both types of carbonates, as well as white cherts, show shale-normalized rare earth element and yttrium patterns
(REYSN; with the exception of redox-sensitive Ce and Eu and heavy REYSN to middle REYSN depletion) that are
parallel to those of modern seawater, indicating a predominantly seawater-derived origin. Positive EuSN
anomalies (2.1–2.4), combined with heterogeneous ɛNd3.35Ga values between −3.2 and +5.8 within individual
alternating stromatolite laminae, further support that the dissolved fraction of seawater on the ancient carbonate
platform was variably affected by both continental weathering and high-temperature hydrothermal fluids
contributing elements of both young mafic or older felsic rocks. In conclusion, trace element and Nd isotope data
presented here match well with the depositional environment, as characterized based on lithological, geochemical,
and stratigraphic relationships, on an early continent, showing at least episodic emergence above the
sea level, supporting microbial life on a shallow marine platform.

Organisation(en)
Institut für Geologie, Department für Umweltgeowissenschaften, Department für Lithosphärenforschung
Externe Organisation(en)
Georg-August-Universität Göttingen, Tongji University, University of New South Wales
Journal
Precambrian Research
Band
344
Anzahl der Seiten
15
ISSN
0301-9268
DOI
https://doi.org/10.1016/j.precamres.2020.105742
Publikationsdatum
2019
Peer-reviewed
Ja
ÖFOS 2012
105105 Geochemie, 105906 Umweltgeowissenschaften
Schlagwörter
ASJC Scopus Sachgebiete
Geochemistry and Petrology, Geology
Sustainable Development Goals
SDG 14 – Leben unter Wasser
Link zum Portal
https://ucris.univie.ac.at/portal/de/publications/carbonates-and-cherts-as-archives-of-seawater-chemistry-and-habitability-on-a-carbonate-platform-335-ga-ago(f3956351-6cfd-46b5-980b-618ab6935a64).html