Fossilization of Precambrian microfossils in the Volyn pegmatite, Ukraine

Abstract. We report on Precambrian microfossils from igneous rocks of the Volyn pegmatite district, associated with Paleoproterozoic Korosten pluton, northwestern Ukraine. The fossils were recovered meter-sized miarolitic cavities and show a well-preserved 3D morphology, mostly filamentous but large variety types also in irregular, flaky shapes reminiscent former biofilms, as well rare spherical objects. Based literature data, pyrolysis experiments, reflected light microscopy results, organic matter (OM) is characterized (oxy-)kerite. Further investigations microscopic techniques, including scanning transmission electron microscopy, microprobe analysis that fossilization likely occurred during hydrothermal, post-pegmatitic event by silicification dominantly outermost 1–2 µm microfossils. hydrothermal fluid, derived pegmatitic environment, was enriched SiF4, Al, Ca, Na, K, Cl, S. OM shows O enrichment which N S content low, indicating simultaneous loss anaerobic oxidation. Mineralization Al silicates starts at rim microfossils, continuing its outer parts into identifiable encrustations intergrowths clay minerals, feldspar, Ca sulfate, phosphate, Fe sulfide, fluorite. Breccias, formed collapse some cavities, contain decaying OM, released high concentrations dissolved NH4+, responsible for late-stage formation tobelite-rich muscovite buddingtonite. age can be restricted to time between formation, ∼1.760 Ga, breccia ∼1.49 Ga. As geological environment growth microorganisms fossilization, we assume geyser system essential biological components C, N, S, P organisms surface. Fossilization induced magmatic SiF4-rich fluids. occurrence distinct uncommon example fossils, results underline importance granitic possible habitat preserved deep biosphere.