Tracking Organomineralization Processes from Living Microbial Mats to Fossil Microbialites

Abstract

<jats:p>Geneses of microbialites and, more precisely, lithification of microbial mats have been studied in different settings to improve the recognition of biogenicity in the fossil record. Living microbial mats and fossil microbialites associated with older paleoshorelines have been studied in the continental Maquinchao Basin in southernmost South America. Here, we investigate carbonate crusts from a former pond where active mineralizing microbial mats have been previously studied. Petrographic observations revealed the presence of abundant erect and nonerect microfilaments and molds with diameters varying from 6 to 8 micrometers. Additionally, smaller pores and organic matter (OM) remains have been identified in areas containing less filaments and being dominated by carbonate. A Mg, Al and Si-rich phase has also been identified in the carbonate matrix associated with the dominant micritic calcite. Moreover, mineralized sheaths contain mixed carbonate (calcite) with Mg, Al and Si, where the latter elements are associated with authigenic clays. The presence of mineralized sheaths further attests to biologically induced processes during the uptake of CO2 by photosynthetic microorganisms. Additionally, the high density of the micritic phase supports the subsequent mineralization by nonphotosynthetic microorganisms and/or physicochemical processes, such as evaporation. Since the micritic filament microstructure of these recent crusts is very similar to that observed in fossil microbialites, they can be used to bridge the gap between living mats and fossil buildups.</jats:p>

The influence of microbial mats on travertine precipitation in active hydrothermal systems (Central Italy)

“…Among the microbial metabolic pathways that appear to play a key role in carbonate precipitation by modifying the microenvironment, driving increased alkalinity and carbonate supersaturation, the most significant appear to be: (a) photosynthesis by autotrophic oxygenic cyanobacteria (Bissett et al, 2008; Castanier et al, 1999; Eymard et al, 2020; Golubic et al, 2000; Merz, 1992; Merz‐Preiß, 2000; Merz‐Preiß & Riding, 1999; Obst et al, 2009; Pentecost & Riding, 1986; Plée et al, 2010; Robbins & Blackwelder, 1992), with eventually carbonate encrustation of microbial cells in settings with low dissolved inorganic carbon (DIC) and high calcium (Arp et al, 2001, 2003, 2010; Défarge et al, 1996; Kamennaya et al, 2012; Merz, 1992; and (b) ammonification of amino‐acids and sulphate reduction by heterotrophic bacteria (Andres et al, 2006; Baumgartner et al, 2006; Castanier et al, 1999; Dupraz & Visscher, 2005; Dupraz et al, 2004, 2009; Knorre & Krumbein, 2000; Pace et al, 2016; Visscher et al, 2000).…”

Biomineralization processes in modern calcareous tufa: Possible roles of viruses, vesicles and extracellular polymeric substances (Corvino Valley – Southern Italy)

“…Tufa is a calcium carbonate precipitate that forms in freshwater settings under cool to near‐ambient temperatures rich in microphytes and macrophytes, leaves and woody tissue (Pedley, 1990; Ford & Pedley, 1996). The structure and composition of tufa depend on physicochemical and biological interactions (Pedley, 1990; Ford & Pedley, 1996; Manzo et al ., 2012; Capezzuoli et al ., 2014; Rogerson et al ., 2014; Eymard et al ., 2020) leading to purely abiotic and/or biotic mechanisms being advanced as responsible for the tufa formation. For instance, abiotic mineral precipitation can be driven by CO 2 degassing resulting from turbulence in the water body, leading to calcite precipitation upon organic and inorganic substrates (Kano et al ., 2003; Kawai et al ., 2006), whereas biotically‐mediated mineral precipitation can be driven by cyanobacterial take‐up of CO 2 through the process of photosynthesis (Pedley, 2000; Shiraishi et al ., 2008).…”

A 571 million‐year‐old alkaline volcanic lake photosynthesizing microbial community, the Anti‐atlas, Morocco

“…Microbialites are lithified bio‐sedimentary deposits formed through the trapping and binding of sediment grains by benthic microbial communities and/or in situ mineral precipitation and organomineralization (Eymard et al., 2020; Riding, 1991). These biologically derived organo‐sedimentary structures vary in shape, including columnar, sheet‐like and domal structures, dependent upon the microbial community involved in their construction, the environment, physicochemical conditions, and the level of overlay.…”

“…In the modern setting, great environmental diversification has enabled our understanding of the relationships existing between depositional setting, microbial remains, and extant communities as analogues of fossilized microbialites (Eymard et al., 2020). Present‐day examples of alkaline lake microbialites include Shark Bay and Lee Stocking Island microbialites (Chagas et al., 2016; Kaźmierczak et al., 2011; Kremer et al., 2019).…”