Geyserite in hot-spring siliceous sinter: Window on Earth's hottest terrestrial (paleo)environment and its extreme life

Abstract

Siliceous hot-spring deposits, or sinters, typically form in active, terrestrial (on land), volcanic terrains where magmatically heated waters circulating through the shallow crust emerge at the Earth's surface as silica-charged geothermal fluids. Geyserites are sinters affiliated with the highest temperature (~75-100 °C), natural geothermal fluid emissions, comprising localized, lithologically distinctive, hydrothermal silica precipitates that develop around geysers, spouters and spring-vents. They demarcate the position of hot-fluid upflow zones useful for geothermal energy and epithermal mineral prospecting. Near-vent areas also are -extreme environment‖ settings for the growth of microbial biofilms at near-boiling temperatures. Microbial biosignatures (e.g., characteristic silicified microbial textures, carbon isotopes, lipid biomarkers) may be extracted from modern geyserite. However, because of strong taphonomic filtering and subsequent diagenesis, fossils in geyserite are very rare in the pre-Quaternary sinter record which, in and of itself, is patchy in time and space back to about 400 Ma. Only a few old examples are known, such as geyserite reported from the Devonian Drummond Basin (Australia), Devonian Rhynie cherts (Scotland), and a new example described herein from the spectacularly well-preserved, Late Jurassic (150 Ma), Yellowstonestyle geothermal landscapes of Patagonia, Argentina. There, geyserite is associated with fossil vent-mounds and silicified hydrothermal breccias of the Claudia sinter, which is geologically related to the world-class Cerro Vanguardia gold/silver deposit of the Deseado Massif, a part of the Chon Aike siliceous large igneous province. Tubular, filament-like micro-inclusions from Claudia were studied using integrated petrographic and laser microRaman analysis, the results of which suggest a biological origin. The putative fossils are enclosed within nodular geyserite, a texture typical of subaerial near-vent conditions. Overall, this worldwide review of geyserite confirms its significance as a mineralizing geological A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT 3 archive reflecting the nature of Earth's highest temperature, habitable terrestrial sedimentary environment. Hot-spring depositional settings also may serve as analogs for early Earth paleoenvironments because of their elevated temperature of formation, rapid mineralization by silica, and morphologically comparable carbonaceous material sourced from prokaryotes adapted to life at high temperatures.

Earliest signs of life on land preserved in ca. 3.5 Ga hot spring deposits

“…2). These sedimentologic relations are typical of high-energy events in very shallow water and are consistent with formation as fluvial deposits in the outflow channels of hot spring pools19.…”

“…Anatase has also been reported in Jurassic geyserites19. Kaolinite+illite is a diagnostic alteration mineral suite in shallow, advanced to intermediate argillic alteration (∼<120 °C) zones of high-sulfidation epithermal systems24, including that of the Dresser Formation, which displays steam-heated acid-sulfate kaolinite+illite alteration of underlying pillow basalts4.…”

The Fascinating and Complex Dynamics of Geyser Eruptions

“…The diagenesis, morphology, biota, and chemical composition of sinter deposits from many active thermal fields were summarized by Renaut & Jones (2011) and Campbell et al (2015). Physical properties of sinter, including porosity, permeability, seismic velocity and electrical conductivity, were reported by Munoz-Saez et al (2016).…”

Origins of geothermal gases at Yellowstone

“…Because these waters become super-saturated with respect to opaline silica, terraces of silica sinter are created as the waters flow away from their vents (Jones and Renaut, 2003). Other forms of silica, such as geyserite are created where abundant splashing and spraying of silica-saturated water forms knobby-towers and benches (Campbell et al, 2015). Virtually all geysers are associated with neutral to alkaline (neutral chloride) water and spout through vents made of silica.…”