BACTERIALLY INDUCED PRECIPITATES IN HOT SPRING SETTINGS
The shrubs most commonly occur in layers that range from incipient microscopic forms to 4 cm in height. Generally, the shrubs do not form in the extreme proximal hot spring environments immediately adjacent to the spring vents, these settings are dominated by abiotic precipitates due to the harsh environment inhibiting organic growth and the highly supersaturated conditions of the waters. Nor do the shrubs occur at the distal ends of the deposits, these are sites at which the conditions have ameliorated and the structures are commonly dominated by higher taxa of organisms. Shrubs most commonly form between these two environmental settings.
Mn- and Fe-rich bacterially induced precipitates are presently forming associated with Artesia Geyser, Lower Geyser Basin, Yellowstone. The Mn- and Fe-rich precipitates are immature, XRD patterns do not display well developed crystallinity and, in contrast to the more common bacterially induced precipitates, they do not display a shrub-like morphology. The Mn- and Fe-rich precipitates form millimeter thick continuous laminae intercalated with centimeter thick layers of fan-shaped calcite crystals near the spring orifice (T=90oC, pH=7.7) to thick diffuse black masses downflow (T=45oC, pH=8.0).