FACTORS CONTROLLING MICROBIAL BIOSIGNATURE PRESERVATION IN HOT SPRING DEPOSITS

Hydrothermal springs are environments where high rates of microbial productivity often coexist with high rates of mineral precipitation, a situation generally regarded as highly favorable for microbial fossilization. However, work over the past decade has revealed that despite this favorable situation, taphonomic and diagenetic processes typically impose a strong filter on the nature and quality of biosignature preservation, both in comparatively modern deposits, as well as their equivalent ancient analogs. Important factors include: 1) the intrinsic properties of the dominant organisms present (e.g., cell size and morphology, types of cellular metabolism, the presence of sheaths, or other extracelluar materials and their ability to act as nucleation sites for precipitating minerals, patterns of cellular growth and biofilm accretion to produce distinctiive biofabrics, or higher order mat structures, etc. ), and 2) extrinsic physical, chemical and mineraological factors (e.g. the types and concentrations of dissolved gases and solutes present, temperature and pH, the types of minerals precipitated and their grain size and stability during diagenesis). In this talk, I will explore this conceptual framework by drawing on examples from modern and ancient hydrothermal systems, with the goal to better understand the paleontological potential of ancient hydrothermal deposits.