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Nanotextures of aragonite in stromatolites from the quasi-marine
Satonda crater lake, Indonesia
KARIM BENZERARA
1
*, ANDERS MEIBOM
2
, QUENTIN GAUTIER
1
,
J
´
ZEF KA
´
MIERCZAK
3
, JAROSŁAW STOLARSKI
3
, NICOLAS MENGUY
1
&
GORDON E. BROWN, JR
4,5
1
Equipe G´obiosph`re Actuelle et Primitive, IMPMC & IPGP, UMR 7590, CNRS,
Universit´s Paris 6 et IPGP. 140, rue de Lourmel, 75015 Paris, France
2
Mus´um National d'Histoire Naturelle, Laboratoire de Min´ralogie et Cosmochimie du
Mus´um (LMCM), UMR 7202, Paris, France
3
Institute of Paleobiology, Polish Academy of Sciences, Twarda 51/55, 00818 Warsaw, Poland
4
Surface & Aqueous Geochemistry Group, Department of Geological & Environmental
Sciences, Stanford University, Stanford, CA 94305-2115, USA
5
Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory,
Menlo Park, CA 94025, USA
*Corresponding author (e-mail: karim.benzerara@impmc.jussieu.fr)
Abstract: Stromatolites have been extensively used as indicators of ancient life on Earth.
Although much work has been done on modern stromatolites, the extent to which biological
processes control their structure, and the respective contributions of biological and abiotic pro-
cesses in their formation are, however, still poorly constrained. A better description of the miner-
alogical textures of these formations at the submicrometre scale may help improve our
understanding of how carbonates nucleate and grow in stromatolites. Here, we used a combination
of microscopy and microspectroscopy techniques to study the chemical composition and the
texture of aragonite in lacustrine stromatolites from the alkaline crator lake in Satonda, Indonesia.
Several textural features are described, including morphological variations of aragonite from
nanosized grains to micrometre-sized fibres, the presence of striations in the aragonite laminae
showing a striking similarity with growth bands in corals, and clusters of small aragonite crystals
sharing a common crystallographic orientation. These nanotextural features are compared with
those observed in scleractinian corals, and possible processes involved in their formation
are discussed.
Stromatolites are laminated sedimentary growth
structures, usually composed of calcium carbonates,
with growth initiated from a point or a limited
surface (Semikhatov et al. 1979). They have been
found throughout the geological record as far back
as 3.5 Ga ago (e.g. Hofmann 2000). As modern
stromatolites are systematically and intimately
associated with microbial communities, ancient
stromatolites have often been considered to be one
of the oldest traces of life on Earth (Hofmann
2000; Altermann et al. 2006; Schopf et al. 2007).
The biogenicity of many ancient stromatolites has,
however, been questioned in particular because
very few microfossils have been found in these
samples (e.g. Lowe 1994; Grotzinger & Rothman
1996; Lepot et al. 2008) and similar morphological
patterns can be produced abiotically (Grotzinger &
Rothman
macroscopic morphology (e.g. Allwood et al.
2006) as well as the mesostructure (Shapiro 2000)
of stromatolites are important tools presently used
to infer the biogenicity of ancient stromatolites.
New numerical models allowing exploration of the
various possible morphologies of stromatolites and
assessment of the respective roles of environmental
and biological processes in their formation have
been proposed by Dupraz et al. (2006). These
authors note that a detailed mechanistic description
of how stromatolites are formed is still warranted.
Such a description may benefit from a more detailed
characterization of the mineral and organic building
units of stromatolites and their arrangement at the
submicrometre-scale, that is, the scale at which
nucleation and mineral growth take place. However,
one difficulty is that this approach requires the use of
specialized analytical tools, as the building units of
1996;
McLoughlin
et
al.
2008).
The
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