Deep-sea biogenic silica: new structural and analytical data from infrared analysis - geological implications

The main parameters of infrared spectra have been investigated for marine siliceous skeletons and for silica polymorphs. From infrared (IR) data, the mean values for the Si-O bond length (1.62 angstrom) and for the Si-O-Si angle (about 142 degrees 6) are inferred for biogenic silica. A model is proposed for the molecular structure of biogenic, amorphous silica, which consists of a discontinuous, three-dimensional framework of short chains of [SiO4] tetrahedra, bounded with apical hydroxyls. According to the relationship between the structure of the silica polymorphs and their infrared spectra, it is shown that a quantitative analysis of biogenic silica seems to be possible in quartz-rich sediments. Some geological implications of these data are emphasized, including the processes of siliceous skeleton sedimentation and diagenetic evolution.