Authigenic clays as precursors to carbonate precipitation in saline lakes of Salar de Llamara, Northern Chile

Abstract

The Salar de Llamara, Atacama Desert is host to saline lakes known as Puquios, which are possible analogs for lakes on early Earth or Mars. Here we examine associations between microbial communities, Mg-clay minerals, and carbonates in microbial mat samples from the Puquios using scanning electron microscopy, energy dispersive X-ray spectroscopy, focused ion beam nanotomography, and transmission electron microscopy. We observe micrometer-scale aggregates of nanocrystalline Mg-clay around cyanobacterial cell sheaths and throughout alveolar networks of microbial extracellular polymeric substances. High-Mn calcite occupies pore spaces and surfaces within the clay matrix. We propose a sequence whereby extracellular polymeric substance networks serve as surfaces for precipitation of Mg-clay, which permineralizes the original microorganisms. Formation of the clay reduces kinetic barriers and provides a suitable substrate for the formation of carbonate minerals. We therefore suggest that authigenic clays are important in the preservation of microbial communities and the precipitation of carbonates in non-marine settings such as the saline lakes of the Atacama Desert.

Microbialite Accretion and Growth: Lessons from Shark Bay and the Bahamas

“…Finally, understanding microbialite growth in terms of accretion, early taphonomy, and diagenesis is a holistic approach that can be applied to any microbe-mineral interaction. Microbes and the environment, interacting within the framework of the MBA, alter mineral-to-organicmatter ratios and produce variable mineral phases, including carbonates, clays, and evaporites (e.g., Allwood et al 2013, Babel 2005, Burne 2016, Burne et al 2014, Moore et al 2020, Pace et al 2016, Suosaari et al 2022a, Zeyen et al 2015. The challenge to geoscientists now is to reconstruct MBA configurations and disentangle initial products from those impacted by early taphonomy and diagenesis.…”

Combined Genomic and Imaging Techniques Show Intense Arsenic Enrichment Caused by Detoxification in a Microbial Mat of the Dead Sea Shore

“…Examples from the Tumbiana stromatolites show potential cell remnants and micro‐pyrites tightly linked to ancient organic matter laminae bearing specific As enrichment (Marin‐Carbonne et al., 2018; Sforna et al., 2014), and well‐preserved trace metal‐organic associations were indeed found in stromatolites and fossilized biofilms, such as the Dresser Formation stromatolites (Baumgartner et al., 2020). However, this phenomenon of exceptional organic matter preservation appears rare; modern examples of comparable sheet‐like microbial mats actively accreting in locations such as Big Pond (Bahamas) or Hamelin Pool (Western Australia) exhibit poor preservation of organic material even at shallow depths (Glunk et al., 2011; Sforna et al., 2016; Suosaari, Lascu, et al., 2022; Suosaari, Reid, et al., 2022). In the microbial mat from the Dead Sea pool presented here, rare CaCO 3 concretions found in the As‐rich layer of the mat do not contain As (Figure 3).…”

“…Interestingly, Mg-Si enrichment have been commonly described in (mineralizing) microbial mats (e.g., Arp et al, 2003;Kazmierczak & Kempe, 2003;Kempe et al, 2011) where a transitional Mg-Si phase, often referred to as "amorphous Mg-Si phase", precedes the formation of carbonate minerals (Bontognali et al, 2010;Pace et al, 2018;Zeyen et al, 2015). This enrichment has been interpreted as a transitional phase that enhances biofilm mineralization by CaCO 3 precipitation (Pace et al, 2018;Suosaari, Lascu, et al, 2022). In the Dead Sea, heavy Mg enrichment (up to 152,000 ppm) is expected given the extreme concentration of Mg 2+ in the environment (Ionescu et al, 2012) and in the pond water (Table 1).…”

Combined genomic and imaging techniques show intense arsenic enrichment caused by detoxification in a microbial mat of the Dead Sea shore

“…Arp et al, 2003;Kazmierczak & Kempe, 2003;Kempe et al, 2011) where a transitional Mg-Si phase, often referred to as "amorphous Mg-Si phase" precedes the formation of carbonate minerals (Bontognali et al, 2010;Pace et al, 2018;Zeyen et al, 2015). This enrichment has been interpreted as a transitional phase that enhances biofilm mineralization by CaCO3 precipitation (Pace et al, 2018;Suosaari, Lascu, et al, 2022). In the Dead Sea, heavy Mg enrichment (up to 152,000 ppm) is to be expected given the extreme concentration of Mg 2+ in the environment (Ionescu et al, 2012) and in the pond water (Table 1).…”