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Journal of the Geological Society

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Microbial silicification in Iodine Pool, Waimangu geothermal area, North Island, New Zealand: implications for recognition and identification of ancient silicified microbes

^{1 1}Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada (e-mail: Brian.Jones@ualberta.ca)
^{2 2}Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5E2, Canada

Silicified microbes provide evidence for some of the earliest life forms on Earth. They are extremely important to understanding the early development of life and the conditions that allowed its development. Such discussions commonly rely on comparisons with extant taxa and therefore depend upon the preservation style of the microbes and, in particular, the preservation of the taxonomically important features. Silicified microbes are deceptive: they commonly appear to be well preserved even though their taxonomically critical features have been destroyed by silicification. An understanding of the early taphonomic processes that influence microbial silicification can be obtained by studying extant microbes that are being silicified in modern hot spring pools. Iodine Pool, located in the Waimangu geothermal area on the North Island of New Zealand, is ideal for this purpose. The spring water has a temperature of 69–100 °C, a pH of 8.3–9.0, and 440–457 ppm SiO₂. Glass slides left in the shallow marginal waters of this pool for 90 h became covered with thin layers of opaline silica, discrete opal-A spheres, unsilicified microbes, pseudofilaments, partly silicified microbes and silicified microbes. The rapidly silicified microbes appear well preserved with their general morphology, diameter, length, and presence or absence of septa being readily apparent. Most of the silicified microbes, however, lack the key features that would allow accurate comparisons with extant taxa. Only two of the silicified microbes can be tentatively allied with the unsilicified forms, despite being found side by side on the same glass slide. These problems in identifying modern, rapidly silicified microbes suggest that identifications of ancient silicified microbes can be problematic and must be treated with caution.

KEYWORDS: New Zealand, Waimangu geothermal area, silicification, microbes, hot springs

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