Transfer of germanium to marine sediments: Insights from its accumulation in radiolarites and authigenic capture under reducing conditions. Some examples through geological ages

Abstract

In the geosphere, germanium (Ge) has a chemical behavior close to that of silicon (Si), and Ge commonly substitutes for Si (in small proportions) in silicates. Studying the evolution of the respective proportions of Ge and Si through time allows us to better constrain the global Si cycle. The marine inventory of Ge present as dissolved germanic acid is facing two main sinks known through the study of present sediments: 1) incorporation into diatom frustules and transfer to sediments by these "shuttles", 2) capture of Ge released to pore water through frustule dissolution by authigenic mineral phases forming within reducing sediments. Our goals are to determine whether such a bioinduced transfer of Ge is also achieved by radiolarian and whether Ge could be trapped directly from seawater into authigenic phases with no intervention of opal-secreting organisms (shuttles). To this end, we studied two Paleozoic radiolarite formations and geological formations dated of Devonian, Jurassic and Cretaceous, deposited under more or less drastic redox conditions. Our results show that the Ge/Si values observed for these radiolarites are close to (slightly above) those measured from modern diatoms and sponges. In addition, our results confirm what is observed with some present-day reducing sediments: the ancient sediments that underwent reducing depositional conditions are authigenically enriched in Ge. Furthermore, it is probable that at least a part of the authigenic Ge came directly from seawater. The recurrence and extent (through time and space) of anoxic conditions affecting sea bottoms have been quite important through the geological times; consequently, the capture of Ge by reducing sediments must have impacted Ge distribution and in turn, the evolution of the seawater Ge/Si ratio.

On the Lower Cambrian biotic and geochemical record of the Hetang Formation (Yangtze Platform, south China): evidence for biogenic silica and possible presence of Radiolaria

“…These values fall within the range corresponding to the opalsecreting organisms and plot far from the value attributed to the average clastic supply ( Fig. 5; Tribovillard et al, 2011). We interpret these results as an indication that the cherts originate from biogenic silica, implying either sponges alone or both sponges and radiolarians.…”

“…5. values of the Ge/Si ratio (expressed in μg g -1 ) for the studied samples compared to those of biogenic origin, seawater and average land-derived clastic fluxes (Tribovillard et al, 2011).…”

Syndepositional glauconite as a paleoenvironmental proxy - the lower Cenomanian Chalk of Cap Blanc Nez (N-France)

“…However, by comparing the contents of the glauconite studied and those of seawater, we observe that, in the glauconite, Mo is absent, U is depleted, and finally, V is enriched compared to seawater of a factor close to x47. Germanium (Ge), which is also an element sensitive to redox conditions (Tribovillard et al, 2011), is weakly present in seawater (0.0055 µg/g) but it is highly enriched in the glauconite of this study (x900). Germanium being an element possibly substituting for silicium, it might be instructive to compare the Ge/SiO2 ratios of seawater and glauconite.…”

Ge/Si Partitioning in Igneous Systems: Constraints From Laser Ablation ICP‐MS Measurements on Natural Samples

“…Ge can be enriched in sulfide minerals (e.g., argyrodite, briartite, renierite, and germanite), sometimes to levels high enough to form Ge ore (Bernstein, 1985;Höll et al, 2007). Ge is also known to form complexes with organic molecules, which may decouple it from Si in some parts of the marine environment (Bareille et al, 1998;Dong et al, 2015;Shen et al, 2011;Tribovillard et al, 2011). Ge compounds are more volatile than Si compounds at high pressures in hot water vapor (Höll et al, 2007), which leads to the enrichment of Ge in hydrothermal minerals, such as topaz (Breiter et al, 2013).…”