TY - JOUR

T1 - Carbonates and cherts as archives of seawater chemistry and habitability on a carbonate platform 3.35 Ga ago

T2 - Insights from Sm/Nd dating and trace element analysis from the Strelley Pool Formation, Western Australia

AU - Viehmann, Sebastian

AU - Reitner, Joachim

AU - Tepe, Nathalie

AU - Hohl, Simon V.

AU - Van Kranendonk, Martin

AU - Hofmann, Thilo

AU - Koeberl, Christian

AU - Meister, Patrick

N1 - Funding information: We thankfully acknowledge Monika Horschinegg and Wolfgang Obermaier for their assistance in the laboratory and in operating the TIMS and ICP-OES, respectively. We also would like to thank the Deutsche Forschungsgemeinschaft (DFG) for sponsoring the field workshop 2017 in Australia under the majority program SPP1833 “Building a habitable Earth” and to the organizers of the workshop that led to the cooperation of this project. Sebastian Viehmann received funding for project ELEMIN from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No. 746033. We thankfully acknowledge Monika Horschinegg and Wolfgang Obermaier for their assistance in the laboratory and in operating the TIMS and ICP-OES, respectively. We also would like to thank the Deutsche Forschungsgemeinschaft (DFG) for sponsoring the field workshop 2017 in Australia under the majority program SPP1833 ?Building a habitable Earth? and to the organizers of the workshop that led to the cooperation of this project. Sebastian Viehmann received funding for project ELEMIN from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No. 746033. All data related to this article are published as tables in the manuscript or supplemental information. Data tables can also be requested without charge from the corresponding author.

PY - 2020/7/15

Y1 - 2020/7/15

N2 - 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.

AB - 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.

KW - Authigenic dolomite

KW - Chert

KW - Early life

KW - Nd isotopes

KW - Pilbara Supergroup

KW - Strelley Pool Formation

KW - Stromatolites

KW - Trace elements

UR - http://www.scopus.com/inward/record.url?scp=85084035533&partnerID=8YFLogxK

U2 - 10.1016/j.precamres.2020.105742

DO - 10.1016/j.precamres.2020.105742

M3 - Article

AN - SCOPUS:85084035533

VL - 344

JO - Precambrian research

JF - Precambrian research

SN - 0301-9268

M1 - 105742

ER -