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Université de Neuchâtel

Bacterially Induced Mineralization of Calcium Carbonate in Terrestrial Environments: The Role of Exopolysaccharides and Amino Acids

Braissant, Olivier ; Cailleau, Guillaume ; Dupraz, Christophe ; Verrecchia, Eric P.

In: Journal of Sedimentary Research, 2003, vol. 73, no. 3, p. 485-490

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...

Université de Neuchâtel

Occurrence and Genesis of Palygorskite and Associated Clay Minerals in a Pleistocene Calcrete Complex, Sde Boqer, Negev Desert, Israel

Verrecchia, Eric P. ; Le Coustumer, M.-N.

In: Clay Minerals, 1996, vol. 31, no. 2, p. 183-202

Palygorskite and associated clay minerals have been studied in a Pleistocene calcrete complex from the Negev desert (Sde Boqer, Israel). This complex is divided into five main parts: the chalky and marly bedrock overlain by its weathered product, a brecciated calcrete hardpan; the laminar crust; loess pockets trapped in the calcrete; and the overlying soft surficial soil. The distribution of clay...

Université de Neuchâtel

Does prism width from the shell prismatic layer have a random distribution?

Verrecchia, Eric P. ; Vancolen, Séverine

In: Geo-Marine Letters, 2008, vol. 28, no. 5-6, p. 383-393

A study of the distribution of the prism width inside the prismatic layer of Unio tumidus (Philipsson 1788, Diss Hist-Nat, Berling, Lundæ) from Lake Neuchâtel, Switzerland, has been conducted in order to determine whether or not this distribution is random. Measurements of 954 to 1,343 prism widths (depending on shell sample) have been made using a scanning electron microscope in...

Université de Neuchâtel

Evidence for an organic origin of pedogenic calcitic nanofibres

Dadras, Massoud ; Abolhassani-Dadras, Sousan ; Braissant, Olivier ; Verrecchia, Eric P.

In: Journal of Crystal Growth, 2009, vol. 311, no. 8, p. 2490-2495

Calcium carbonate nanofibres are found in numerous terrestrial environments, often associated with needle fibre calcite. This study attempts to mimic the natural system and generate comparable crystalline structures. A comparison of natural and synthesized nanofibre structures, using HRTEM as well as electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI), has...

Université de Neuchâtel

The Discrete Cosine Transform, a Fourier-related Method for Morphometric Analysis of Open Contours

Dommergues, Cyril H. ; Dommergues, Jean-Louis ; Verrecchia, Eric P.

In: Mathematical Geology, 2007, vol. 39, no. 8, p. 749-763

The discrete cosine transform (DCT) is described and then tested to see whether it is a suitable Fourier-related method for morphometric analysis of open outlines. While most Fourier methods are mainly effective with closed outlines, the DCT can handle open curves too, making it useful for quantitative descriptions of a broad range of natural objects. Like other Fourier-type methods, the DCT...

Université de Neuchâtel

Use of fractal dimensions to quantify coral shape

Martin-Garin, B. ; Lathuilière, B. ; Verrecchia, Eric P. ; Geister, J.

In: Coral Reefs, 2007, vol. 26, no. 3, p. 541-550

A morphometrical method to quantify and characterize coral corallites using Richardson Plots and Kaye’s notion of fractal dimensions is presented. A Jurassic coral species (Aplosmilia spinosa) and five Recent coral species were compared using the Box-Counting Method. This method enables the characterization of their morphologies at calicular and septal levels by their fractal dimensions...