Stromatolites from the 3.48 Ga Dresser Formation are widely considered as a benchmark for the oldest preserved evidence of life on Earth. However, since their discovery in the 1980s, biogenic interpretations have mostly relied on morphological and textural characteristics. Recent research on pyritized Dresser stromatolites from unweathered drill cores has provided additional evidence for biogenicity through the discovery of: i) putative microbial remains; ii) micromineralogy enriched in organic matter that is consistent with sulfidization of microbial substrates; iii) enrichments of transition metals and metalloids - especially nickel, zinc, and arsenic - within crinkly stromatolite laminae, consistent with an adsorption of these elements onto microbial substrates (Baumgartner et al., 2019; Baumgartner et al., 2020a,b). In 2019, new wide-diameter cores of the Dresser Formation were obtained under clean drilling conditions to intersect an extensive array of mostly pyritized stromatolites. Here, we expand on previous studies to gain from morphologically diverse Dresser stromatolites a better understanding of the interplays between geological and biological processes in their formation. Supported by elemental mapping across the wide core sections, microanalytical characterizations aid documentation of microbial growth structures dominated by earliest formed mineral-organic associations – organic matter-rich microspherulitic barite as well as nanoporous pyrite containing convincing microbial remains – that interfere with demonstrably abiotic textures in the dominantly hydrothermally influenced, barite-rich host strata of the stromatolites. Overall, the Dresser stromatolites are believed to have formed in a volcano-sedimentary context in which restricted shallow-water marine regimes were influenced by voluminous hydrothermal exhalations. When our observations are integrated with paleoenvironmental models, it becomes apparent that all stromatolites, though texturally diverse due to growth under contrasting conditions (e.g., proximal versus distal to hydrothermal venting), are dominated by the same mineral-organic biosignature assemblages. Hence, our research represents a critical step forward in demonstrating a biological origin of Dresser stromatolites. Moreover, our data have implications for deciphering microbe-environment interactions and providing a better understanding of the habitability of hydrothermally influenced environments in Paleoarchean times.

Reference(s)

Baumgartner RJ, Van Kranendonk MJ, Wacey D, Fiorentini ML, Saunders M, Caruso S, Pages A, Homann M and Guagliardo P 2019, Nano−porous pyrite and organic matter in 3.5-billion-year-old stromatolites record primordial life. Geology, v. 47, p. 1039–1043.

Baumgartner RJ, Van Kranendonk MJ, Fiorentini ML, Pages A, Wacey D, Kong C, Saunders M and Ryan C 2020a, Formation of micro-spherulitic barite in association with organic matter within sulfidized stromatolites of the 3.48 billion-year-old Dresser Formation, Pilbara Craton. Geobiology.

Baumgartner RJ, van Kranendonk MJ, Pagès A, Fiorentini ML, Wacey D and Ryan C 2020b, Accumulation of transition metals and metalloids in sulfidized stromatolites of the 3.48 billion–year–old Dresser Formation, Pilbara Craton. Precambrian Research, v. 337, 105534