organic matter (Noffke et al. 2008). Likewise, other studies (Bouougri and Porada
2002) provide a detailed description of microbial mats and associated structures
from Neoproterozoic (780 Ma) peritidal siliciclastic sediments and relate them to the
energy environment for their formation and preservation in intertidal and supratidal
zones. Moreover, fossilized sequences of siliciclastic biolaminites that describe the
cyclic interplay between mat growth and sediment trapping have been described
from Ediacaran (~ 545 Ma) fossils (Bouougri and Porada 2007). Often, the fossil
MISS have modern analogues which they may seem easily relatable to (Cuadrado
et al. 2015); yet this comparison needs to be made with caution, as morphological
similarity alone does not constitute scientific proof of a common origin, and the
likelihood of conclusively identifying microbial structures from visual appearance
alone is slim (García Ruiz et al. 2002; Davies et al. 2016). The evidence gathered
with experimental approaches using modern mats and MISS is of paramount importance for such inferences. For instance, studies have experimentally quantified the
forces that microbial mats can withstand when subject to viscoelastic and plastic
deformation (Thomas et al. 2013; Pan et al. 2019) and how they translate to the
establishment of MISS.
Microbial colonization of intertidal sediments may have been favored over other
coastal sedimentary environments such as the supratidal band that is not regularly
inundated by seawater or subtidal deposits permanently covered by seawater for
several reasons. Firstly, it is an absolute truth that most (if not all) microbes rely on
liquid water for their development (Walter and Allwood 2005). In the case of
supratidal environments, the supply of water is not as reliable or steady as it is in
intertidal and subtidal zones, even though there are modern microbial mats that
abound in the supratidal region (e.g., Bolhuis and Stal 2011). Moreover, nutrients
play a significant role in the distribution of autotrophic microbes in intertidal
sediments. Studies on the rate of nutrient transport through tidal advection and
diffusive fluxes between sediment and porewater have shown that the sedimentwater exchange of nutrients attributed to tidal flooding in intertidal microbial
ecosystems is several orders of magnitude larger than any other physical exchange
process such as diffusive fluxes through porewater (Ospina-Alvarez et al. 2014).
Hence autotrophic microbes developing in the intertidal band might exploit this
regular resupply of inorganic nutrients to their advantage.
As stated, the archetypical biogenic structure falling under the MISS classification is the epibenthic microbial mat. Some 3.5 Ga ago, microbial mats covered most
of well-illuminated shallow seas, and their constituent microbes exploited all ecological niches available within a layered biosedimentary structure a few mm thick
(Des Marais 1990). Fossil microbial mats and associated MISS from tidal deposits in
the Barberton belt of South Africa differ fundamentally in appearance and genesis
from early Archean stromatolites and bacterial cell fossils preserved in chert (Noffke
et al. 2006). With a dating of 3.2 Ga, these Barberton fossils are the oldest microbial
mats and MISS recorded from restricted coastal habitats. As the remainder of this
essay will largely deal with microbial mats and MISS from siliciclastic settings, it is
fitting to introduce them with certain depth.
64
J. Pan
2002) provide a detailed description of microbial mats and associated structures
from Neoproterozoic (780 Ma) peritidal siliciclastic sediments and relate them to the
energy environment for their formation and preservation in intertidal and supratidal
zones. Moreover, fossilized sequences of siliciclastic biolaminites that describe the
cyclic interplay between mat growth and sediment trapping have been described
from Ediacaran (~ 545 Ma) fossils (Bouougri and Porada 2007). Often, the fossil
MISS have modern analogues which they may seem easily relatable to (Cuadrado
et al. 2015); yet this comparison needs to be made with caution, as morphological
similarity alone does not constitute scientific proof of a common origin, and the
likelihood of conclusively identifying microbial structures from visual appearance
alone is slim (García Ruiz et al. 2002; Davies et al. 2016). The evidence gathered
with experimental approaches using modern mats and MISS is of paramount importance for such inferences. For instance, studies have experimentally quantified the
forces that microbial mats can withstand when subject to viscoelastic and plastic
deformation (Thomas et al. 2013; Pan et al. 2019) and how they translate to the
establishment of MISS.
Microbial colonization of intertidal sediments may have been favored over other
coastal sedimentary environments such as the supratidal band that is not regularly
inundated by seawater or subtidal deposits permanently covered by seawater for
several reasons. Firstly, it is an absolute truth that most (if not all) microbes rely on
liquid water for their development (Walter and Allwood 2005). In the case of
supratidal environments, the supply of water is not as reliable or steady as it is in
intertidal and subtidal zones, even though there are modern microbial mats that
abound in the supratidal region (e.g., Bolhuis and Stal 2011). Moreover, nutrients
play a significant role in the distribution of autotrophic microbes in intertidal
sediments. Studies on the rate of nutrient transport through tidal advection and
diffusive fluxes between sediment and porewater have shown that the sedimentwater exchange of nutrients attributed to tidal flooding in intertidal microbial
ecosystems is several orders of magnitude larger than any other physical exchange
process such as diffusive fluxes through porewater (Ospina-Alvarez et al. 2014).
Hence autotrophic microbes developing in the intertidal band might exploit this
regular resupply of inorganic nutrients to their advantage.
As stated, the archetypical biogenic structure falling under the MISS classification is the epibenthic microbial mat. Some 3.5 Ga ago, microbial mats covered most
of well-illuminated shallow seas, and their constituent microbes exploited all ecological niches available within a layered biosedimentary structure a few mm thick
(Des Marais 1990). Fossil microbial mats and associated MISS from tidal deposits in
the Barberton belt of South Africa differ fundamentally in appearance and genesis
from early Archean stromatolites and bacterial cell fossils preserved in chert (Noffke
et al. 2006). With a dating of 3.2 Ga, these Barberton fossils are the oldest microbial
mats and MISS recorded from restricted coastal habitats. As the remainder of this
essay will largely deal with microbial mats and MISS from siliciclastic settings, it is
fitting to introduce them with certain depth.
64
J. Pan