Compositional and structural analysis of Paleo- and Neoarchean stromatolites from the Pilbara Craton (Western Australia)

Abstract

Petrographic, physicochemical, and geochemical analyses of samples from the Dresser, Strelley Pool and Tumbiana Formations revealed insight and partial evidence on some of the earliest microbial organisms that inhabited Earth during the Paleo- (3.49 and 3.42 to 3.37Ga) and Neoarchean (2.71Ga), that were presumably sulfate-reducing bacteria. A better understanding on this topic helps constraining the search for the environments where life might exist, both in and outside our planet. This investigation aimed to answer questions on the extent to which and how biogenicity criteria can be useful while working with ancient rocks conditioned by secondary post-depositional processes. Limited samples on the complex Strelley Pool Formation, however, prevented a full understanding on the role of microbial life and their interaction with different elements' biogeochemical processes and cycles. Using non-destructive methods such as X-Ray Fluorescence and Raman Spectroscopy, it was possible to obtain and identify a few characteristics for rocks associated with sulfate reducing bacteria in shallow marine and lacustrine settings, such as the circulation of elements like Mn and Zn, and the spectral differences between biogenic and abiogenic pyrite.