La tessitura della micrite nel calcare «Corniola» del Lias medio

Farinacci, Anna

Atti della Accademia nazionale dei Lincei. Rendiconti della Classe di scienze fisiche, matematiche e naturali, Série 8, Tome 44 (1968) no. 2, pp. 284-289

Résumé

Data on typical Middle Lias micrite of «umbro-marchigiana» facies are exposed. They were obtained by electron microscope for the first time. The carbonate grains are of skeletal and diagenetic origin, and the ones due to chemical syndepositional precipitation are exluded. The characteristic texture of the micrite permitted the reconstruction of the grain paragenesis. The sizes of grains vary between $0.5 \mu$ and $8-9 \mu$, with average values of $1-2 \mu$ corresponding to the size of skeletal grains. Here the name nannomicrite is proposed and discussed. Of paleontological interest was the discovery of new organisms with a secreted carbonate test. These new organisms, temporarily called Organism $\alpha$ and Organism $\beta$ are not comparable with any living known form. Besides, with the recovering of Carophyta oogonia in the microfacies with Radiolaria and Sponges spicules, a shallow water environment is verified for the sedimentation of «Corniola» limestone, previously identified, for other features, by the writer (1967).