SCHINTEIE, CAMPBELL, & BROWNE |
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CONCLUSIONSEnvironmental variables, acting on a micro-scale over a few centimetres (or less) at the Parariki study site, have a differential effect on sinter textures and microbiology. Hence, four different microfacies of stromatolitic sinter occur, featuring distinctive deposit morphologies, textures, formation mechanisms, and microbial communities. Constraints on their distribution include: 1) the size and shape of the subaerial substrate surfaces; 2) the relative exposure to thermal waters; 3) water flow rate; 4) the presence, nature, and taphonomy of mat-forming microorganisms; 5) water and ambient temperature; and 6) potential exposure to acid steam condensate. The dynamic interplay between silica deposition and microbial activity is a major factor in the formation of a variety of sinter textures, particularly spicules. Laminae develop in these sinters due to abiotic and/or alternating abiotic and biotic processes. Different microbial communities also exhibit variable preservation potential as sinter accumulates, regardless of microbial abundances. Results of this study are consistent with previous studies of acid hot spring deposits. In terms of the associated biota, eukaryotes, namely diatoms and the rhodophyte taxon Cyanidiophyceae, are a ubiquitous sinter component at temperatures <52.5°C. Lobed coccoidal and bacilliform morphotypes of prokaryotic dimensions also were confined to different microfacies settings, with the former largely restricted to the hotter setting of Microfacies 1, and the latter observed elsewhere at the site. Clay minerals, as well as fungi, were not observed in this study. Mineralogically, sinters of Microfacies 1 are similar to silica residue and siliceous deposits around fumaroles; namely a gnarled, possibly corrosive, surface texture and/or faint silica sphere shapes. |
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