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Study of environmental changes and diagenetic processes by use of structural and chemical characteristics of biominerals

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Biominerals are composite structures in which specific sets of organic macromolecules build templates for crystallisation of mineral ions issued from waters. Thus biominerals are natural records of ancient environmental conditions and are widely used in this respect, mainly when studying isotopic measurements.

There is a striking contrast between the increasing sensibility of the recently designed mass spectrometers, the accuracy of the resulting isotopic ratio measurements and the general failure to appreciate the importance of previous analyses of the biominerals from which the data is produced. Obviously, none of the highly sophisticated modelling processes are able to compensate for the initial defects caused by measurements carried out on adulterated biominerals. The very precise measurements required by studies of environmental evolution during the last ten thousand years necessitate the exclusive use of the best preserved biominerals as records of the climate changes, and the checking of the present status of these materials cannot be carried out by using the usual mineralogical criteria. Only highly specific biochemical and structural features can provide adequate information regarding the diagenetic evolution of biominerals.

Thus methodological developments enabling a better knowledge of the organomineral structure of biominerals are the key to a better understanding of their geological behaviour and precise evaluation of the ability to provide reliable data concerning present and ancient environments. In particular, the sensitivity of biominerals to diverse and very early causes of decay, leading to important and rapid structural or compositional changes at the molecular level, requires a very close association of investigators to define a new standard of preliminary controls to be applied to biominerals used in researches dealing with ancient marine conditions.

After the experiments have been carried out, a first approach of the biochemical method for characterisation of the preservation status of the calcareous environmental records will be presented. The three analytical methods, chromatography and electrophoresis, histochemical characterisation and ultrastructural characterisation will offer a complete overview of the internal organisation of biocrystals and a significant set of biochemical data. Results will be compared from various parts of the selected shells, sponges or corals, with the isotopic measurements carried out on the same specimens.

A chart of the diagnostic processes will be made, based on biochemical changes in calcareous fossils records, and information on the most relevant specimens when high precision measurements are required will be indicated.

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Université de Paris-Sud - Paris XI
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Adresse
Bât.504 - Fac. des Sciences
91405 Orsay
Frankreich

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