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Formation of micro‐spherulitic barite in association with organic matter within sulfidized stromatolites of the 3.48 billion‐year‐old Dresser Formation, Pilbara Craton
Author(s) -
Baumgartner Raphael J.,
Van Kranendonk Martin J.,
Fiorentini Marco L.,
Pagès Anais,
Wacey David,
Kong Charlie,
Saunders Martin,
Ryan Chris
Publication year - 2020
Publication title -
geobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.859
H-Index - 72
eISSN - 1472-4669
pISSN - 1472-4677
DOI - 10.1111/gbi.12392
Subject(s) - geology , chemosynthesis , organic matter , mineralization (soil science) , geochemistry , stromatolite , sedimentary structures , archean , dolomite , hydrothermal circulation , pyrite , sedimentary rock , sedimentary organic matter , hydrothermal vent , subaerial , mineralogy , microbial mat , precambrian , sponge spicule , sedimentary depositional environment , paleontology , carbonate , chemistry , cyanobacteria , organic chemistry , structural basin , bacteria , soil science , soil water
The shallow marine and subaerial sedimentary and hydrothermal rocks of the ~3.48 billion‐year‐old Dresser Formation are host to some of Earth's oldest stromatolites and microbial remains. This study reports on texturally distinctive, spherulitic barite micro‐mineralization that occur in association with primary, autochthonous organic matter within exceptionally preserved, strongly sulfidized stromatolite samples obtained from drill cores. Spherulitic barite micro‐mineralization within the sulfidized stromatolites generally forms submicron‐scale aggregates that show gradations from hollow to densely crystallized, irregular to partially radiating crystalline interiors. Several barite micro‐spherulites show thin outer shells. Within stromatolites, barite micro‐spherulites are intimately associated with petrographically earliest dolomite and nano‐porous pyrite enriched in organic matter, the latter of which is a possible biosignature assemblage that hosts microbial remains. Barite spherulites are also observed within layered barite in proximity to stromatolite layers, where they are overgrown by compositionally distinct (Sr‐rich), coarsely crystalline barite that may have been sourced from hydrothermal veins at depth. Micro‐spherulitic barite, such as reported here, is not known from hydrothermal systems that exceed the upper temperature limit for life. Rather, barite with near‐identical morphology and micro‐texture is known from zones of high bio‐productivity under low‐temperature conditions in the modern oceans, where microbial activity and/or organic matter of degrading biomass controls the formation of spherulitic aggregates. Hence, the presence of micro‐spherulitic barite in the organic matter‐bearing Dresser Formation sulfidized stromatolites lend further support for a biogenic origin of these unusual, exceptionally well‐preserved, and very ancient microbialites.