Microbial Construction of Siliceous Stalactites at Geysers and Hot Springs: Examples from the Whakarewarewa Geothermal Area, North Island, New Zealand

Abstract

Abstract Siliceous stalactites, formed of opal-A laminae that are concentrically arranged around a hollow soda-straw, are common features structures in some of the geyser and hot spring deposits at Whakarewarewa and other geothermal areas of New Zealand. These siliceous stalactites contain diverse biota of bacteria (including cyanobacteria), fungi, and diatoms that lived on the stalactite surfaces, with locally abundant pollen grains, and springtails. The microbes are the templates for much of the opaline silica precipitation and thereby controlled most of the fabrics that form the stalactite laminae. Siliceous stalactites form at sites of dripping water below the overhanging edges of geyserite rims that surround geyser vents, and along the steep margins of sinter terraces on discharge aprons. Stalactites may hang as isolated individuals or may coalesce to form dripstone draperies along terrace or rim margins. Stalactite growth is controlled by the volume, temperature, and the silica concentration of the ...