Silica Biomineralization of Calothrix-Dominated Biofacies from Queen's Laundry Hot-Spring, Yellowstone National Park, USA

Kyle R. Hager,Craig L. Moyer,Sean M. McAllister,Wendy F. Smythe,Bradley M. Tebo,Kevin W. Hager

doi:10.3389/fenvs.2016.00040

Abstract

Experiments on microorganisms capable of surviving silicification are often conducted to gain a better understanding of the process of silica biomineralization and to gain insights into microbially influenced rock formations and biofabrics like those found in ancient deposits such as the Early Archean Apex Chert formation (House et al., 2000; Schopf, 1993). An ideal microorganism for studying silicification is the large sheathed cyanobacterium Calothrix, which form distinctive organo-sedimentary structures in the low to moderate temperature regions of hydrothermal springs or columnar stromatolitic structures in aquatic systems. Our ability to identify and characterize microfossils from ancient deposits allows us to gain a better understanding of environmental conditions on early Earth. Here we characterized Calothrix-dominated biofacies along the outflow apron of Queen’s Laundry Hot-Spring in Yellowstone National Park using microscopy and molecular techniques to examine biofacies morphology and phylogenetic diversity. We found that flow regime and temperature had a profound effect on community composition as identified by the observation of five distinct Calothrix-dominated communities and on biofacies architecture along the outflow apron.

Highlights

Precambrian cherts have been found to yield silicified microfossils suggesting that ancient microbial communities present in marine waters and hydrothermal ecosystems became embedded in colloidal amorphous silica and were subsequently entombed and preserved in the fossil record as distinct textures (Westall et al, 1995; House et al, 2000)
The dark coloration is due to the presence of the pigment scytonemin in the sheath and is typically found to be synthesized in environments where cyanobacteria are exposed to intense light and UV irradiation (Ehling-Schulz et al, 1997; Dillon and Castenholz, 2003)
Previous studies have shown that the extensive fibular sheath around Calothrix filaments plays a significant role in mineral templating as dissolved silica ions nucleate on the sheath and associated EPS and LPS, thereby promoting microfossil formation (Gilbert et al, 2005; Hugo et al, 2011)

Summary

Introduction

Precambrian cherts have been found to yield silicified microfossils suggesting that ancient microbial communities present in marine waters and hydrothermal ecosystems became embedded in colloidal amorphous silica and were subsequently entombed and preserved in the fossil record as distinct textures (Westall et al, 1995; House et al, 2000). Characterization of extant hot-spring environments provides us the opportunity to better understand and interpret the paleoenvironment in which ancient biofacies formed, allowing us to take a glimpse into Earth’s early environments. Silica deposits, referred to as sinter, form in and around the hot-spring once hydrothermal fluids. As hydrothermal fluids cool the solubility of amorphous silica is exceeded, e.g., due to changes in pH or temperature and supersaturation through evaporation, resulting in the polymerization of dissolved silica and subsequent precipitation (White et al, 1956; Rimstidt and Barnes, 1980; Benning et al, 2005; Hugo et al, 2011). Siliceous deposits in YNP can be studied as extant analogs of early Earth allowing for the study of biogenic silica deposition and microfossil formation (Channing and Butler, 2007)

Methods

Results

Conclusion