Microfossils from the Arymas and Debengda formations, the Riphean of the Olenek Uplift: Age and presumable nature

Micropaleontology of the lower Mesoproterozoic Roper Group, Australia, and implications for early eukaryotic evolution

“…Early work in Russia established a broad biostratigraphic framework for organic-walled microfossils in Proterozoic shales, with Satka favosa characterizing early Mesoproterozoic samples and Valeria lophostriata more common in Neoproterozoic successions (summaries in Jankauskas et al, 1989; Sergeev et al, 2010). More recent research shows that both of these morphospecies co-occur with Tappania plana and other Roper taxa in the Kamo Group, Siberia, and in correlative shales of the Debengda Formation (Nagovitsin, 2009; Stanevich et al, 2009; Nagovitsin et al, 2010). The fossiliferous shales are interspersed with stromatolitic carbonates and so represent shallow platform environments.…”

A review of microbial‐environmental interactions recorded in Proterozoic carbonate‐hosted chert

“…shows the coccoidal cyanobacteria that form pustular mats and produce concentric envelopes of EPS around cells and cell clusters (see Moore et al, 2020, andSkoog et al, 2022, for culturing conditions). Oehler , 1977, 1978Schopf, 1968;Schopf & Kudryavtsev, 20091995Stanevich et al, 2009) and the inability of amorphous silica, the precursor to chert, to precipitate abiotically at concentrations below 2 mM silica (Iler, 1979) suggest that the fossil-preserving chert may not have precipitated due to abiotic processes alone. This, and the lack of modern marine analog environments that are both supratidal and contain high concentrations of silica, suggests that different chemical and biological conditions in Proterozoic supratidal environments favored the preservation of marine organisms by silicification.…”

“…This chemical difference likely contributed to the precipitation of chert in Proterozoic tidal environments and the preservation of exquisite body fossils (Manning‐Berg & Kah, 2017 ; e.g., Figure 1 ), a phenomenon that does not generally occur in modern tidal environments, with rare exceptions (e.g., Kremer et al, 2012 ). The localized nature of the marine Proterozoic chert (e.g., Anderson et al, 2020 ; Barghoorn & Schopf, 1965 ; Butterfield, 2000 , 2001 ; Butterfield, 2004 ; Butterfield et al, 1988 , 1990 , 1994 ; Campbell, 1982 ; Croxford et al, 1973 ; Donaldson & Delaney, 1975 ; Green et al, 1987 , 1988 ; Hofmann, 1976 ; Horodyski & Donaldson, 1980 , 1983 ; Kempe et al, 2002 ; Knoll, 1982 ; Knoll et al, 1986 , 1991 ; Knoll et al, 2013 ; Knoll & Golubic, 1979 ; Manning‐Berg et al, 2018 , 2019 ; Muir, 1976 ; Oehler, 1976 , 1977 , 1978 ; Schopf, 1968 ; Schopf & Kudryavtsev, 2009 , 2011 ; 1995 , 1997 ; Sergeev & Schopf, 2010 ; Stanevich et al, 2009 ) and the inability of amorphous silica, the precursor to chert, to precipitate abiotically at concentrations below 2 mM silica (Iler, 1979 ) suggest that the fossil‐preserving chert may not have precipitated due to abiotic processes alone. This, and the lack of modern marine analog environments that are both supratidal and contain high concentrations of silica, suggests that different chemical and biological conditions in Proterozoic supratidal environments favored the preservation of marine organisms by silicification.…”

“…Thus, none are direct analogs for Proterozoic marine carbonate‐hosted fossiliferous chert (Jones et al, 2004 ). The modern large, laterally extensive chert deposits differ in scale, texture, and formation mechanism from the nodules, lenses, and layers of fossiliferous chert that punctuate Proterozoic carbonate deposits from tidal environments (e.g., Anderson et al, 2020 ; Barghoorn & Schopf, 1965 ; Butterfield, 2000 , 2001 ; Butterfield, 2004 ; Butterfield et al, 1988 , 1990 , 1994 ; Campbell, 1982 ; Croxford et al, 1973 ; Donaldson & Delaney, 1975 ; Green et al, 1987 , 1988 ; Hofmann, 1976 ; Horodyski & Donaldson, 1980 , 1983 ; Kempe et al, 2002 ; Knoll, 1982 ; Knoll et al, 1986 , 1991 ; Knoll et al, 2013 ; Knoll & Golubic, 1979 ; Manning‐Berg et al, 2018 , 2019 ; Muir, 1976 ; Oehler, 1976 , 1977 , 1978 ; Schopf, 1968 ; Schopf & Kudryavtsev, 2009 , 2011 ; 1995 , 1997 ; Sergeev & Schopf, 2010 ; Stanevich et al, 2009 ). This underscores the need to explain the more localized precipitation of silica as nodules and lenses in tidal environments, where silica concentrations were likely below 2 mM as evidenced by the lack of large‐scale, laterally extensive chert deposits that might be expected from consistently supersaturated waters like those in hydrothermal systems.…”

“…These fossils first appear in the rock record in the ~2 Ga Belcher Island Group [(Hofmann, 1974 , 1975 , 1976 ) Figures 1 and 6 ] and are reported in many younger Proterozoic deposits (Table 1 ). These fossils of pustular mat‐forming organisms are always preserved in chert nodules and lenses within supratidal carbonate deposits (Hofmann, 1974 , 1976 ; Horodyski & Donaldson, 1983 ; Knoll et al, 2013 ; Knoll & Golubic, 1979 ; Manning‐Berg et al, 2018 , 2019 ; Manning‐Berg & Kah, 2017 ; Oehler, 1978 ; Seong‐Joo & Golubic, 1999 ; Sergeev et al, 1995 , 1997 ; Stanevich et al, 2009 ) or in rip‐up clasts and other grains that were transported and deposited in subtidal deposits [e.g., Svanbergfjellet Formation (Butterfield et al, 1994 ; Eleonore Bay Group; Green et al, 1988 )]. In contrast to simpler coccoidal fossils, Eoentophysalis mats exhibit a distinct macroscopic pustular texture that arises from the division of the cells along multiple planes and the thick, multilayered envelopes interpreted as EPS that surround cells and clusters of cells (Figure 6 ).…”