气候变化领域集成服务门户(CCPortal): Deconstructing Earth’s oldest ichnofossil record from the Pilbara Craton, West Australia: Implications for seeking life in the Archean subseafloor

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DOI	10.1111/gbi.12399
	Deconstructing Earth’s oldest ichnofossil record from the Pilbara Craton, West Australia: Implications for seeking life in the Archean subseafloor
	McLoughlin N.; Wacey D.; Phunguphungu S.; Saunders M.; Grosch E.G.
发表日期	2020
ISSN	14724677
英文摘要	Microtextures of titanite (CaTiSiO5) in exceptionally preserved Archean pillow lavas have been proposed as the earliest examples of microbial ichnofossils. An origin from microbial tunneling of seafloor volcanic glass that is subsequently chloritized and the tunnels infilled by titanite has been argued to record the activities of subseafloor microbes. We investigate the evidence in pillow lavas of the 3.35 Ga Euro Basalt from the Pilbara Craton, Western Australia, to evaluate the biogenicity of the microtextures. We employ a combination of light microscopy and chlorite mineral chemical analysis by EPMA (electron probe micro-analysis) to document the environment of formation and analyze their ultrastructure using FIB-TEM (focussed ion beam combined with transmission electron microscopy) to investigate their mode of growth. Petrographic study of the original and re-collected material identified an expanded range of titanite morphotypes along with early anatase growth forming chains and aggregates of coalesced crystallites in a sub-greenschist facies assemblage. High-sensitivity mapping of FIB lamellae cut across the microtextures confirm that they are discontinuous chains of coalesced crystallites that are highly variable in cross section and contain abundant chlorite inclusions, excluding an origin from the mineralization of previously hollow microtunnels. Comparison of chlorite mineral compositions to DSDP/IODP data reveals that the Euro Basalt chlorites are similar to recent seafloor chlorites. We advance an abiotic origin for the Euro Basalt microtextures formed by spontaneous nucleation and growth of titanite and/anatase during seafloor-hydrothermal metamorphism. Our findings reveal that the Euro Basalt microtextures are not comparable to microbial ichnofossils from the recent oceanic crust, and we question the evidence for life in these Archean lavas. The metamorphic reactions that give rise to the growth of the Euro Basalt microtextures could be commonplace in Archean pillow lavas and need to be excluded when seeking traces of life in the subseafloor on the early Earth. © 2020 John Wiley & Sons Ltd
语种	英语
来源机构	Geobiology
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/133200
推荐引用方式 GB/T 7714	McLoughlin N.,Wacey D.,Phunguphungu S.,等. Deconstructing Earth’s oldest ichnofossil record from the Pilbara Craton, West Australia: Implications for seeking life in the Archean subseafloor[J]. Geobiology,2020.
APA	McLoughlin N.,Wacey D.,Phunguphungu S.,Saunders M.,&Grosch E.G..(2020).Deconstructing Earth’s oldest ichnofossil record from the Pilbara Craton, West Australia: Implications for seeking life in the Archean subseafloor..
MLA	McLoughlin N.,et al."Deconstructing Earth’s oldest ichnofossil record from the Pilbara Craton, West Australia: Implications for seeking life in the Archean subseafloor".(2020).