Premiers Resultats de l'Observation au M.E.B. de la Lorica des Calpionelles et de quelques Microfossiles qui leur sonst Associes

Abstract

The observation of the loricas of Calpionellae by means of the Scanning Electron Microscope (S.E.M.) shows that their ultrastructure varies with the lithological nature of the fossilizing environment. We posit the hypothesis that - at the starting point - the walls of loricas consist of an only layer of small polyhedric crystals set side by side, uniform in diameter: 0,3 to 0,4 μ and arranged helicoidically. In the course of the diagenesis, three evolutions my occur: 1) in an argillaceous environment, initial crystallites grow into largesized crystals including the components of the surrounding stone (particularly coccolithes); 2) in an calcareous environment, the diagenesis leads to the formation of curved crystalline plates; 3) lastly, instead of growing, crystallites may undergo corrosion and cease to touch one another. They may even disappear