Microbialite Biofacies of Hydrothermal Springs

Terrestrial hot springs support highly productive microbial ecosystems that often coexist with high rates of mineral precipitation. Rapid and pervasive mineralization in these systems can create optimal conditions for the capture and preservation of biological information within their associated sedimentary deposits (or “sinters”). To a first order in these systems, mineral precipitation rates are controlled by abiotic factors (e.g. rates of cooling, degassing and evaporation of hydrothermal fluids). However, microorganisms have also been shown to contribute in fundamental ways to sinter deposition through the genesis of biosedimentary structures (microbialites) and associated fabric types commonly seen in hydrothermal spring deposits. The present study seeks to create process-based facies models for hydrothermal springs that can be usefully applied in the exploration for ancient hydrothermal deposits on the early Earth and potentially on other planets, like Mars.

The genesis of hot spring microbialites can be viewed as a scale-integrated process, whereby cells and exopolymers provide low activation energy surfaces for the initial nucleation and growth of minerals. Variations in patterns of microbial growth and taxis provide morphological templates that control subsequent mineral growth. This is expressed at higher levels of integration in the production of distinctive microbialite morphotypes. In terrestrial hot springs, systematic variations in microbial community composition along environmental gradients are mirrored by systematic variations in microbialite form and microstructure in associated sinters, thereby creating a record of the geobiology and environmental context of the original system. Sedimentary “biofacies” may be defined as characteristic associations of biological features that reflect certain types of organism-environment interactions and processes. In this talk, I will review microbialite-based biofacies models developed for travertine and siliceous hot springs in Yellowstone National Park and New Zealand and their applications in paleoenvironmental studies of some closely related ancient analogs.