Fossil Geyserite and Testate Amoebae in Geothermal Spring Vent Pools: Paleoecology and Variable Preservation Quality in Jurassic Sinter of Patagonia (Deseado Massif, Argentina).

Autor: Sagasti AJ; School of Biological Sciences, Institute of Molecular Plant Sciences, The University of Edinburgh, Edinburgh, UK.; CONICET and Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Instituto de Recursos Minerales (UNLP-CICBA), La Plata, Argentina., Campbell KA; School of Environment and Te Ao Mārama-Centre for Fundamental Inquiry, Faculty of Science, The University of Auckland, Auckland, New Zealand., García Massini JL; Centro Regional de Investigaciones Científicas y Transferencia Tecnológica (CRILAR), Provincia de La Rioja, UNLaR, SEGEMAR, UNCa, CONICET, Anillaco, La Rioja, Entre Ríos, Argentina., Galar A; CONICET and Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Instituto de Recursos Minerales (UNLP-CICBA), La Plata, Argentina., Guido DM; CONICET and Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Instituto de Recursos Minerales (UNLP-CICBA), La Plata, Argentina., Gautret P; Université d'Orléans, CNRS/INSU, BRGM, Institut des Sciences de la Terre d'Orléans (ISTO), UMR 7327, Orléans, France.
Jazyk: angličtina
Zdroj: Geobiology [Geobiology] 2024 Sep-Oct; Vol. 22 (5), pp. e12621.
DOI: 10.1111/gbi.12621
Abstrakt: Geyserite is a type of terrestrial siliceous hot spring deposit (sinter) formed subaerially in proximal vent areas, with near-neutral pH, alkali chloride discharge fluids characterized by initial high temperatures (~73°C to up to 100°C) that fluctuate rapidly in relation to dynamic hydrology, seasonality, wind, and other environmental parameters. We analyzed sinters at the Claudia paleogeothermal field from the Late Jurassic (~150 Ma) Deseado Massif geological province, Argentinean Patagonia. The geyserite samples-with spicular to columnar to nodular morphologies-contain abundant microfossils in monotypic assemblages that occur in three diagenetic states of preservation. The best-preserved microfossils consist of vesicle-like structures with radial heteropolar symmetry (~35 μm average diameter), circular apertures, smooth walls lacking ornamentation, and disk- or beret-like shapes. Comparisons with extant, morphologically similar organisms suggest an affinity with the testate amoebae of the Arcella hemisphaerica-Arcella rotundata complex and Centropyxis aculeata strain discoides. These species occur in active geothermal pools between 22°C and 45°C, inconsistent with the temperature of formation of modern geyserites. We propose that the testate amoebae may have colonized the geyserite during cooler phases in between spring-vent eruptive cycles to prey on biofilms. Silica precipitation through intermittent bathing and splashing of fluctuating thermal fluid discharge could have led to their entrapment and fossilization. Petrographic analysis supports cyclicity in paleovent water eruptions and later diagenesis that transformed the opal into quartz. Spatially patchy degradation and modification of the silicified microorganisms resulted in variable preservation quality of the microfossils. This contribution illustrates the importance of microscale analysis to locate early silicification and identify high-quality preservation of fossil remains in siliceous hot spring deposits, which are important in early life studies on Earth and potentially Mars.
(© 2024 The Author(s). Geobiology published by John Wiley & Sons Ltd.)
Databáze: MEDLINE
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