A Reconstructed Subaerial Hot Spring Field in the ∼3.5 Billion-Year-Old Dresser Formation, North Pole Dome, Pilbara Craton, Western Australia

Abstract

Recent discoveries of geyserite and siliceous sinter with textural biosignatures in the ∼3.5 Ga Dresser Formation of the Pilbara Craton, Western Australia, extended the record of inhabited subaerial hot springs on Earth by ∼3 billion years, back to the time when siliceous sinter deposits are known to have formed on Mars (e.g., at Columbia Hills, Gusev Crater). Here, we present more detailed lithostratigraphic, petrographic and geochemical data collected from 100 measured sections across a ∼14 km strike length in the Dresser Formation. The data indicate deposition of a wide range of hot spring and associated deposits in a restricted interval that directly overlies a hydrothermally influenced volcanic caldera lake facies, with shoreline stromatolites. Hot spring deposits show abrupt lateral facies changes and include associated channelized clastic deposits that support fluvial, subaerial hot spring deposition. All Dresser hot spring and associated lithofacies have direct analogs with proximal, middle, and distal apron hot spring facies that are characteristic of those from New Zealand, Yellowstone National Park, USA, and Argentina. Rare earth element and yttrium geochemistry shows that the Dresser geyserite shares identical patterns with Phanerozoic hot spring sinters. This geochemical data further supports textural and contextual evidence that indicate the Dresser geyserite formed as a subaerial hot spring sinter. Further, the Dresser hot spring deposits are temporally associated with a diverse suite of textural biosignatures that indicate a thriving microbial community existed within in a Paleoarchean hot spring field. The results presented here underscore the importance of continued study of the early geological record for astrobiological research. In particular these findings reinforce the long-standing hypothesis that hydrothermal systems are optimal places to search for past life on Mars.