Origin of pedogenic needle-fiber calcite revealed by micromorphology and stable isotope composition—a case study of a Quaternary paleosol from Hungary |
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| Authors: | Bernadett Bajnczi Viktria Kovcs-Kis |
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| Institution: | aInstitute for Geochemical Research, Hungarian Academy of Sciences, Budaörsi út 45, H-1112 Budapest, Hungary;bResearch Institute for Technical Physics and Materials Science, Hungarian Academy of Sciences, Konkoly Thege M. út 29-33, H-1121 Budapest, Hungary |
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| Abstract: | Pedogenic needle-fiber calcite was studied regarding its morphology, texture and stable isotope composition from the paleosol of the Quaternary Várhegy travertine (Budapest, Hungary). The needle-fiber calcite is composed of 40–200 μm long monocrystals. Smooth rods as well as serrated-edged crystals with calcite overgrowths were identified by SEM. Needles have several textural varieties: randomly distributed crystals in vugs and pores with calcite hypocoatings, bundles of subparallel crystals forming coatings around grains and alveolar structure with bridging needles in vugs.The morphological study of needle-fiber calcite suggests that needles are calcified fungal sheaths and produced by fungal biomineralization, a common process in recent and fossil soils and calcretes. The stable isotope composition of needle-fiber calcite (average: δ18O=-7.1‰ and δ13C=-7.3‰ vs. V-PDB) indicates significant incorporation of organically derived CO2 and probably biological influence on needle genesis. Dissolved host rock travertine and/or atmospheric CO2 could also contribute some carbon to the acicular calcite. |
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| Keywords: | Needle-fiber calcite Pedogenic carbonate Paleosol Biomineralization Micromorphology Alveolar texture Stable isotope Fungi Travertine Quaternary |
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