An early ecosystem of Archean tidal microbial mats (Moodies Group, South Africa, ca. 3.2 Ga)

Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in theca.3.48 Billion-Year-Old Dresser Formation, Pilbara, Western Australia

“…To date, the oldest microbial mat communities that formed MISS are from the 3.2 Ga Moodies Group, South Africa (Noffke et al, 2006b;Heubeck, 2009) wrinkle structures and one roll-up structure were detected in tidal deposits. The 2.9 Ga Ntombe Formation, Pongola Supergroup, South Africa, includes eight wrinkle structures that record fossil microbial mats on shallow shelf settings (Noffke et al, 2003).…”

Morphological adaptations of 3.22 Ga-old tufted microbial mats to Archean coastal habitats (Moodies Group, Barberton Greenstone Belt, South Africa)

“…In the strata of the BGB, a variety of microbial traces are preserved, e.g., carbonaceous chert containing filamentous, coccoidal and spindle-shaped microfossils (Walsh andLowe, 1985, 1999;Walsh, 1992;Westall et al, 2006), planar microbial mats (Tice et al, 2004;Tice and Lowe, 2006;Tice, 2009), pseudocolumnar, stromatolite-like structures (Byerly et al, 1986;Walsh and Westall, 2003 and references therein), and organic-walled, spheroidal microfossils (Javaux et al, 2010). Moreover, the BGB includes the world's oldest known regionally mappable record of microbial mats in a siliciclastic tidal setting, exposed in the 3.22 Ga, and remarkably well-preserved Moodies Group (Noffke et al, 2006;Heubeck, 2009;Gamper et al, 2012).…”

Iron formations: A global record of Neoarchaean to Palaeoproterozoic environmental history

“…until precipitation of Rapitan-type IF, associated with the Sturtian glaciation and extensional magmatism linked to the breakup of Rodinia (Isley and Abbott, 1999;Huston and Logan, 2004;Klein, 2005;Slack and Cannon, 2009). This gap has been explained by a shift to fully oxic (Holland, 1984), sulfidic (Canfield, 1998), or suboxic (Slack et al, 2007;2009) deep-ocean conditions. The earlier suggestion of oxic deep-ocean conditions after ca.…”

“…The filamentous bacteria, typically cyanobacteria or chemotrophic sulfide-oxidising bacteria, such as Beggiatoa, that comprise the mats, trap and bind sediments with their exopolysaccharide (EPS) secretions as they grow upward; this biostabilisation method allows them to withstand erosion by waves and currents. MRS are one of the oldest forms of fossil evidence, having been found in rocks as old as the 3.2 Ga Moodies Group, South Africa (Noffke et al, 2006;Heubeck, 2009) and the 2.9 Ga Pongola Supergroup, South Africa (Noffke et al, 2003). In the case of the Moodies Group, recent stratigraphic and depositional facies analysis have documented the association of three principal mat morphotypes representing different environmental settings: (1) planar-type in coastal floodplains, (2) wavy-type in intertidal zones, and (3) tufted-type in upper inter-to supratidal zones.…”

“…In the Archaean and Proterozoic oceans, ε Nd (t) values (which describe the deviation of the 143 Nd/ 144 Nd ratio measured in a sample relative to the 143 Nd/ 144 Nd ratio in a chondritic uniform reservoir at time t and in parts per 10 4 ) are estimated to have been +1 to +2 for deep waters dominated by hydrothermal sources, whereas values down to -3 would have been typical of shallow-waters dominated by terrestrial sources (Miller and O'Nions, 1985;PimentelKlose, 1988a, 1988b;Alexander et al, 2008). The relative contribution of continentally-sourced versus mantle-sourced REE+Y, discussed in more detail in the next section, has been estimated using Ce and Nd isotope compositions Wasserburg, 1980, Bau et al, 1997;Shimizu et al, 1990;Alexander et al, 2008;2009;Viehmann et al, 2015). In some cases, 138 Ce systematics show that Ce anomalies in IFs are a feature produced by recent hydrothermal events and are not intrinsic to ancient seawater (Hayashi et al, 2004).…”