Carbonates and cherts as archives of seawater chemistry and habitability on a carbonate platform 3.35 Ga ago:
- Author(s)
- Sebastian Viehmann, Joachim Reitner, Nathalie Tepe, Simon V. Hohl, Martin Van Kranendonk, Thilo Hofmann, Christian Köberl, Patrick Meister
- Abstract
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(s)
- Department of Geology, Department of Environmental Geosciences, Department of Lithospheric Research
- External organisation(s)
- Georg-August-Universität Göttingen, Tongji University, University of New South Wales
- Journal
- Precambrian Research
- Volume
- 344
- No. of pages
- 15
- ISSN
- 0301-9268
- DOI
- https://doi.org/10.1016/j.precamres.2020.105742
- Publication date
- 2019
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105105 Geochemistry, 105906 Environmental geosciences
- Keywords
- ASJC Scopus subject areas
- Geochemistry and Petrology, Geology
- Sustainable Development Goals
- SDG 14 - Life Below Water
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/f3956351-6cfd-46b5-980b-618ab6935a64