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Verrecchia, Eric

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Verrecchia, Eric
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https://libra.unine.ch/handle/123456789/143

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  • Publication
    Accès libre
    Translation of energy into morphology : Simulation of stromatolite morphospace using a stochastic model
    (2006)
    Dupraz, Christophe
    ;
    Pattisina, R.
    ;
    Verrecchia, Eric 
    Stromatolites are examples of an iterative system involving radiate accretive growth of microbial mats, biofilm and/or minerals that result from interaction between intrinsic and extrinsic factors, which progressively shape the final morphology. These interactions can neither be easily described by simple mathematical equations, nor by simple physical laws or chemical reactions. Therefore, a holistic approach that will reduce the system to a set of variables (which are combinations of natural variables) is proposed in order to create virtual morphologies which will be compared with their natural counterparts. The combination of both Diffusion Limited Aggregation (DLA) and cellular automata (CA) allows the exploration of the stromatolite morphological space and a representation of the intrinsic and extrinsic factors responsible for natural stromatolite morphogenesis. The holistic approach provides a translation in simple parameters of (1) the way that energy, nutrients and sedimentary particles reach the active surface of a future build-up, (2) how these elements are distributed and used in order to create morphology, and (3) how simple environmental parameters, such as sedimentation, can disturb morphogenesis. In addition, most Precambrian stromatolite morphologies that are impossible to produce with numerical modeling such as the Kardar–Parisi–Zhang (KPZ) equation can be simulated with the DLA–CA model and this, with a minimum set of variables.
  • Publication
    Accès libre
    Biologically induced accumulations of CaCO3 in orthox soils of Biga, Ivory Coast
    (2005)
    Cailleau, Guillaume 
    ;
    Braissant, Olivier
    ;
    Dupraz, Christophe
    ;
    Aragno, Michel 
    ;
    Verrecchia, Eric 
    Biologically induced accumulations of calcium carbonate have been found inside orthox soils, under and around the native iroko tree Milicia excelsa (Moraceae) in Biga (Ivory Coast). The nature of these accumulations and their origin were studied in two soil profiles, directly under the tree and at a distance of 30 cm from the trunk. Microscale forms of CaCO3 include: (1) wood pseudomorphic structures such as parenchyma cells, cellulose fibers, and calcitic vessel infillings; (2) three types of rhombohedra; and (3) needle fiber calcite (NFC). In addition, large scale blocks exhibit three types of textures: (1) micritic calcite, which seems to be the original material; (2) light-colored sparite in moldic voids; and (3) asymmetrical radiaxial laminated fibrous cement. Some micritic aggregates and hemi-spherulites (vaterite) were found in the sap on the trunk as well as in soils on silica grains and the wood itself. The mineralogy of all these carbonate forms is mainly a stoichiometric calcite or a moderately enriched Mg calcite. However, some samples contain monohydrocalcite, as well as two polymorphs of calcium oxalate (weddellite and whewellite). Calcite precipitation is facilitated by the oxidation of oxalate by soil bacteria that contributes to the increase in pH in Biga soils. This is in contrast to conventional orthox soils. Therefore, three conditions are necessary for biologically induced precipitation of calcium carbonate in orthox soils associated with iroko trees: the presence of a large amount of oxalate (originating from the tree and fungi), the existence of an oxalotrophic flora for oxalate oxidation into carbonate, and a dry season.
  • Publication
    Métadonnées seulement
    Translation of energy into morphology: Simulation of stromatolite morphospace using a stochastic model
    (: Elsevier Science Bv, 2004)
    Dupraz, Christophe
    ;
    Pattisina, Ronny
    ;
    Verrecchia, Eric 
    Stromatolites are examples of ail iterative system involving radiate accretive growth of microbial mats, biofilm and/or minerals that result from interaction between intrinsic and extrinsic factors, which progressively shape the final morphology. These interactions call neither be easily described by simple mathematical equations, nor by simple physical laws or chemical reactions. Therefore, a holistic approach that will reduce the system to a set of variables (which are combinations of natural variables) is proposed in order to create virtual morphologies which will be compared with their natural counterparts. The combination of both Diffusion Limited Aggregation (DLA) and cellular automata (CA) allows the exploration of the stromatolite morphological space and a representation of the intrinsic and extrinsic factors responsible for natural stromatolite morphogenesis. The holistic approach provides a translation in simple parameters of (I) the way that energy, nutrients and sedimentary particles reach the active surface of a future build-up, (2) flow these elements are distributed and used in order to create morphology, and (3) how simple environmental parameters, such as sedimentation, can disturb morphogenesis. In addition, most Precambrian stromatolite morphologies that are impossible to produce with numerical modeling such as the Kardar-Parisi-Zhan (KPZ) equation can be simulated with the DLA-CA model and this, with a minimum set of variables. (c) 2005 Elsevier B.V. All rights reserved.
  • Publication
    Accès libre
    La classification des premiers organismes vivants
    (2004)
    Verrecchia, Eric 
    ;
    Dupraz, Christophe
    ;
    Pattisina, Ronny
    Les stromatolithes fossiles sont les témoins des plus anciens organismes de la planète. Leur nomenclature était fondée, à tort, sur des différences de formes qui pouvaient résulter, l’analyse moderne le montre, d’une même espèce.
  • Publication
    Accès libre
    Bacterially Induced Mineralization of Calcium Carbonate in Terrestrial Environments: The Role of Exopolysaccharides and Amino Acids
    (2003)
    Braissant, Olivier
    ;
    Cailleau, Guillaume 
    ;
    Dupraz, Christophe
    ;
    Verrecchia, Eric 
    This study stresses the role of specific bacterial outer structures (such as glycocalix and parietal polymers) on calcium carbonate crystallization in terrestrial environments. The aim is to compare calcium carbonate crystals obtained in bacterial cultures with those obtained during abiotically mediated synthesis to show implications of exopolysaccharides and amino acids in the mineralogy and morphology of calcium carbonate crystals produced by living bacteria. This is done using various amounts of purified exopolysaccharide (xanthan EPS) and L-amino acids with a range of acidities. Amino acids and increasing xanthan content enhance sphere formation in calcite and vaterite. Regarding calcite, the morphology of crystals evolves from rhombohedral to needle shape. This evolution is characterized by stretching along the c axis as the amino acid changes from glutamine to aspartic acid and as the medium is progressively enriched in EPS. Regarding vaterite, the spherulitic habit is preserved throughout the morphological sequence and starts with spheres formed by the agglomeration of short needles, which are produced in a xanthan-free medium with glutamine. Monocrystals forming spheres increase in size as xanthan is added and the acidity of amino acids (glutamic and aspartic acids) is increased. At high xanthan concentrations, amino acids, and mainly aspartic and glutamic acids, induce vaterite precipitation. The role of the carboxyl group is also probably critical because bacterial outer structures associated with peptidoglycan commonly contain carboxyl groups. This role, combined with the results presented here, clearly demonstrate the influence of bacterial outer structure composition on the morphology and mineralogy of bacterially induced calcium carbonate. This point should not be neglected in the interpretation of calcite cements and carbonate accumulations in terrestrial environments.