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Fossilized microorganisms preserved as fluid inclusions in epithermal veins, Vani Mn-Ba deposit, Milos Island, Greece

By M. Ivarsson, S.P. Kilias, C. Broman, J. Naden and K. Detsi


Fossilized microorganisms preserved as fluid inclusions are found in barite silica-Mn oxide veins in the marine rift basin-related Quaternary Mn-Ba deposit of Vani, Milos . Basin fill consists of 35-50 m thick sequence of glauconitic sediments sandwiched between volcaniclastic sandy tuffs, and, bedding-parallel barite Mn oxide( silica) horizons, pebble horizons, and massive gravel. Exhalative barite-rich deposits characteristic of sea-floor venting, such as white smoker(sulphate) structures in glauconitic sediments, feeder veins, bedding-conformable horizons, and extensive microbial mat- related structures in sandy tuffs, were recognized. The feeder veins host the microfossils and consist chiefly of banded barite and minor colloform quartz, Fe-oxyhydroxides, and hollandite-group minerals and MnO2 phases, and display epithermal textures characteristic of open-space precipitation. Curvilinear, branched filamentous microfossils with distinct segmentation of septa and a turgid appearance of knob-like outgrowths occur associated with spheroidal spore-like microfossils and small twisted microstructures. Both filamentous and spheroidal microstructures are filled with aqueous (liquid + vapour) and/or hydrocarbon phases. Oil and solid hydrocarbons in the fluid inclusions may represent decomposed biological material. Chitin was detected by the pigment Wheat Germ Agglutinin conjugated with Fluorescein Isothiocyanate (WGA-FITC) in some of the microfossils, indicating that they are fossilized fungi; a fungal interpretation is further supported by microfossil morphology. Smaller, often twisted filamentous microfossils with a simpler morphology in which chitin was not detected probably represent fossilized prokaryotes and, if so, prokaryotes and eukaryotes co-existed in the geothermal system of Vani. Fluid inclusion microthermometry shows that microfossils were trapped at temperatures of ~100°C in boiling water, probably evolved seawater. Preservation of microfossils occurred at shallow sub-marine conditions of <10 m depth. Our results show that fluid inclusions may contain valuable palaeobiological information and can be used both for establishing biogenicity but also for the reconstruction of the palaeoenvironment of fossilized microorganisms

Topics: Earth Sciences
Publisher: Aristotle University of Thessaloniki
Year: 2010
OAI identifier:

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