2026-06-27T23:35:12Zhttps://docta.ucm.es/rest/oai/requestoai:docta.ucm.es:20.500.14352/879072023-09-30T01:25:30Zcom_20.500.14352_14col_20.500.14352_15
Docta Complutense
author
Sanz Montero, María Esther
author
Rodríguez Aranda, Juan Pablo
author
García del Cura, María Ángeles
2023-09-25T06:07:01Z
2023-09-25T06:07:01Z
2008
1365-3091
10.1111/j.1365-3091.2007.00919.x
https://hdl.handle.net/20.500.14352/87907
https://onlinelibrary.wiley.com/doi/10.1111/j.1365-3091.2007.00919.x
This research provides an ancient analogue for biologically mediated dolomite
precipitation in microbial mats and biofilms, and describes the involvement of
highly structured extracellular polymeric secretion (EPS) templates in
dolomite nucleation. The structure of EPS is shown to match the hexagonal–
trigonal lattice geometry of dolomite, which favoured the epitaxial
crystallization of dolomite on the organic substrate. This structure of EPS
also matches the arrangement of silica nanospheres in opal, which further
accounts for the organically-templated formation of opal enabling the nonreplacive
co-existence of dolomite and silica. The study is focused on a 50 m
thick dolomite succession that is exposed in central areas of the Tertiary Duero
Basin and was deposited in a mudflat-saline lake sedimentary complex during
the Middle to Late Miocene (9 to 15 Ma). In the intermediate intervals of the
succession, poorly indurated dolomite beds pass gradually into silica beds. On
the basis of sedimentological, compositional, geochemical and petrographic
data, silica and dolomite beds have been interpreted as mineralized microbial
mats. The silica beds formed in marginal areas of the lake in response to
intense evaporative concentrations; this resulted in the rapid and early
precipitation of opal. Silicification accounted for the exceptional preservation
of the microbial mat structure, including biofilms, filamentous and coccoid
microbes, and EPS. Extracellular polymeric secretions have a layered
structure, each layer being composed of fibres which are arranged in
accordance with a reticular pattern, with frequent intersection angles at 120
and 60 . Therefore, the structure of EPS matches the lattice geometry of
dolomite and the arrangement of silica nanospheres in opal. Additionally, EPS
binds different elements, with preference to Si and Mg. The concurrence of
suitable composition and surface lattice morphologies in the EPS favoured the
crystallization of dolomite on the substrate. In some cases, dolomite nucleation
took place epicellularly on coccoid micro-organisms, which gave way to
spheroid crystals. Organic surfaces enable the inorganic mineral precipitation
by lowering the free energy barrier to nucleation. Most of the microbial mats
probably developed on the lake floor, under sub-aqueous conditions, where
the decomposition of organic matter took place. The subsequent formation of
openly packed dolomite crystals, with inter-related Si-enriched fibrils
throughout, is evidence for the pre-existence of fibrillar structures in the
mats. Miocene dolomite crystals are poorly ordered and non-stoichiometric, with a slight Ca-excess (up to 5%), which is indicative of the low diagenetic
potential the microbial dolomite has towards a more ordered and
stoichiometric structure; this confirms that microbial imprints can be
preserved in the geological record, and validates their use as biosignatures.
eng
Attribution-NonCommercial-NoDerivatives 4.0 International
Dolomite–silica stromatolites in Miocene lacustrine deposits from the Duero Basin, Spain: the role of organotemplates in the precipitation of dolomite
journal article
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