relatively complex architecture, such as biofilms or
microbial mats.
In addition to problems related to the interpretation of
the observations, sample preparation itself can introduce
artefacts and abiotic contaminants. It is not surprising that,
given all these constraints, the study of microfossils is the
subject of much controversy.
4.2.3.2 Stromatolites: A Definition
Stromatolites or stromatolitic structures have a particular
place as a biosignature in the rock record and have been
identified in all geological eras (from the Archaean
(4.0–2.5 Ga) to the present). The oldest stromatolitecontaining formations are located in the Archaean greenstone belts in the Pilbara in northwestern Australia
(Hofmann et al. 1999) and at Barberton in eastern South
Africa (Byerly et al. 1986).
A stromatolite is primarily a lithified microbial mat, whose
growth is the result of the trapping of sediment particles and
the precipitation of carbonate by microbial action. A stromatolite is thus essentially composed of a nonliving part
consisting of superimposed organo-sedimentary strata, and
on its surface, it is covered by a complex microbial mat
community whose thickness may reach a few centimetres
(cf. Sect. 9.7.3). Stromatolites can be either two-dimensional
(tabular or stratiform) or three-dimensional (in the form of
columns, domes, tepees) (Krumbein 1983). In the broad sense
of this definition, any microbial mat is a potential stromatolite.
Stromatolites are formed exclusively by photosynthetic
microbial mats growing in shallow water habitats within the
Fig. 4.7 Abiotic structures.
Photomicrographs using scanning
electron microscopy of silica
structures resembling biological
forms. These composite materials
are formed of amorphous silica
and crystalline barium carbonate.
Both phases self-assemble
creating structures that mimic
biological forms. The formation
of these inorganic materials is a
plausible phenomenon in certain
geochemical conditions and
demonstrates that this type of
morphology cannot be used as an
unambiguous criterion of
structures of biological origin
(Photographs courtesy of
Juan-Manuel Garcı ´a-Ruiz Bars:
a: 40 μm; b: 50 μm, c, d
and e: 10 μm; f: 5 μm)
88
J.-C. Bertrand et al.
microbial mats.
In addition to problems related to the interpretation of
the observations, sample preparation itself can introduce
artefacts and abiotic contaminants. It is not surprising that,
given all these constraints, the study of microfossils is the
subject of much controversy.
4.2.3.2 Stromatolites: A Definition
Stromatolites or stromatolitic structures have a particular
place as a biosignature in the rock record and have been
identified in all geological eras (from the Archaean
(4.0–2.5 Ga) to the present). The oldest stromatolitecontaining formations are located in the Archaean greenstone belts in the Pilbara in northwestern Australia
(Hofmann et al. 1999) and at Barberton in eastern South
Africa (Byerly et al. 1986).
A stromatolite is primarily a lithified microbial mat, whose
growth is the result of the trapping of sediment particles and
the precipitation of carbonate by microbial action. A stromatolite is thus essentially composed of a nonliving part
consisting of superimposed organo-sedimentary strata, and
on its surface, it is covered by a complex microbial mat
community whose thickness may reach a few centimetres
(cf. Sect. 9.7.3). Stromatolites can be either two-dimensional
(tabular or stratiform) or three-dimensional (in the form of
columns, domes, tepees) (Krumbein 1983). In the broad sense
of this definition, any microbial mat is a potential stromatolite.
Stromatolites are formed exclusively by photosynthetic
microbial mats growing in shallow water habitats within the
Fig. 4.7 Abiotic structures.
Photomicrographs using scanning
electron microscopy of silica
structures resembling biological
forms. These composite materials
are formed of amorphous silica
and crystalline barium carbonate.
Both phases self-assemble
creating structures that mimic
biological forms. The formation
of these inorganic materials is a
plausible phenomenon in certain
geochemical conditions and
demonstrates that this type of
morphology cannot be used as an
unambiguous criterion of
structures of biological origin
(Photographs courtesy of
Juan-Manuel Garcı ´a-Ruiz Bars:
a: 40 μm; b: 50 μm, c, d
and e: 10 μm; f: 5 μm)
88
J.-C. Bertrand et al.