Spherulitic microbialites from modern hypersaline lakes, Rottnest Island, Western Australia
| Autor: | Eva Sirantoine, Moyra E.J. Wilson, Juliana Mendes Monteiro, Karl Bischoff, Annette D. George, Martin Saunders |
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| Rok vydání: | 2020 |
| Předmět: |
Calcite
Geologic Sediments Morphology (linguistics) 010504 meteorology & atmospheric sciences Carbonates Geochemistry Heterotrophic bacteria Western Australia Cyanobacteria 010502 geochemistry & geophysics Geologic record 01 natural sciences Lakes chemistry.chemical_compound chemistry Spherulite General Earth and Planetary Sciences Carbonate Ecology Evolution Behavior and Systematics Geology 0105 earth and related environmental sciences General Environmental Science Geochemical modeling |
| Zdroj: | Geobiology. 18:725-741 |
| ISSN: | 1472-4669 1472-4677 |
| DOI: | 10.1111/gbi.12400 |
| Popis: | Fibrous-radiating carbonate spherulites spatially associated with poorly crystalline Mg-Si substances have formed within conical microbialites in modern hypersaline lakes on Rottnest Island, Western Australia. Two spherulitic fabrics can be distinguished based on compositional and textural differences. The oldest (lowermost) fabric comprises variably intergrown aragonitic spherulites 100-500 mu m wide, containing micritic nuclei with coccoid cell molds in various stages of cell division. Spherulite matrices contain aggregates of individual nanospheres 150-200 nm wide, composed of a poorly crystalline Mg-Si phase, locally containing cell molds with similar dimensions to those within spherulite nuclei. The younger (upper) fabric comprises sub-polyhedral networks of mineralized EPS composed of an Mg-Si substance. The polyhedrons contain aragonite-replaced coccoid cells, voids, and polyhedral spherulites 8-12 mu m wide with a morphology determined by fossil EPS, interpreted to have been produced by coccoid cyanobacteria. These spherulites are composed of high-Mg calcite, inferred to have formed in association with heterotrophic bacteria. Stable isotope data, textural relationships, and geochemical modeling are consistent with cyanobacterial oxygenic photosynthesis influencing the precipitation of Mg-Si substances and aragonitic spherulites by locally increasing the pH. The morphology of the polyhedral spherulites suggests the former presence of EPS and that faceted spherulites with similar dimensions in the geological record may represent biosignatures. The Rottnest Island conical microbialites demonstrate an intimate association between microbial features and processes and spherulitic fabrics, potentially providing insights into texturally and compositionally similar features in the geological record. |
| Databáze: | OpenAIRE |
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