HR: 14:10h
AN: V23D-03    [Abstracts]
TI: 3-D Crystal Tectonics of Red Coral (Corallium Rubrum)
AU: * Vielzeuf, D
EM: vielzeuf@crmcn.univ-mrs.fr
AF: CRMCN, Campus de Luminy, Marseille, 13288, France
AU: Garrabou, J
EM: joaquim.garrabou@com.univmed.fr
AF: COM, rue Batterie des Lions, Marseille, 13007, France
AU: Baronnet, A
EM: baronnet@crmcn.univ-mrs.fr
AF: CRMCN, Campus de Luminy, Marseille, 13288, France
AU: Grauby, O
EM: grauby@crmcn.univ-mrs.fr
AF: CRMCN, Campus de Luminy, Marseille, 13288, France
AU: Marschal, C
EM: christian.marschal@com.univmed.fr
AF: COM, rue Batterie des Lions, Marseille, 13007, France
AB: A combination of analytical techniques (petrographic microscopy, SEM, TEM, and EMP) has been used to characterize the internal physico-chemical structure of the red coral (corallium rubrum) skeleton. A section normal to the skeleton axis shows an inner medullar zone with a bulbous-tip cross shape, surrounded by a large circular domain composed of concentric rings (width of each ring ca 150 microns). Growth rings are revealed by the cyclic variation of concentration of the organic matter (OM) and oscillations of the Mg/Ca ratio. Experiments carried out in natural environment show that the detected growth rings are annual. Thus, both oscillations of concentration of OM and Mg/Ca ratio can be used to determine the age of the red coral colonies, some of which can be as old as a few tens (or even a few hundreds) of years. Concentric ring are riddled and display a succession of wavelets (wavelength ca 300 microns). The internal structure of each wavelet is complex, both physically and chemically: it is formed by the accumulation of strata with locally tortuous interfaces due to the presence of micro protuberances (ca 30 microns). This interlocked structure confers an exceptional stiffness on the red coral skeleton. Interfaces between strata sometimes display sharp discontinuities indicating interruption of the mineralizing process. This fact has important consequences on the ability of the whole structure to register external forcings with accuracy. SEM and TEM studies show that each stratum is made of submicron crystalline units (ca 200 nm) organized or not in polycrystalline fibers or blades (ca 1 to 10 microns). Porosity can be observed at all scales between the various structural units. HRTEM studies show that in spite of displaying single crystal scattering behavior, the submicron crystalline units are made of 2-5 nm nanodomains with intercalated nanopores. We interpret the nanodomains as nanograins aggregated by a mechanism of oriented attachment. The red coral skeleton is an example of hierarchically organized organic-inorganic composite material, with five levels of organization. This complex material exhibits structural and compositional order on length scales from the nm to the cm. It is an example of nanoparticles as building blocks for the bottom-up fabrication of complex superstructures with exceptional mechanical properties.
DE: 0400 BIOGEOSCIENCES
DE: 0419 Biomineralization
DE: 0424 Biosignatures and proxies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting