The geochemistry of germanium in deep-sea cherts

doi:10.1016/0016-7037(88)90135-4

Geochimica et Cosmochimica Acta

Volume 52, Issue 9, September 1988, Pages 2333-2336

https://doi.org/10.1016/0016-7037(88)90135-4 Get rights and content

Abstract

Nineteen chert samples from a continuous core of the DSDP (Leg 17, Hole 167) were analysed for Ge; in addition we analysed five samples from other cores. The ages range between Late Jurassic, and Late Eocene. The concentration of Ge changes with age from 0.87 ppm in the oldest samples to 0.23 ppm in the youngest (equivalent to a $Ge Si$ decrease from 0.72 × 10⁻⁶ to 0.19 × 10⁻⁶). The decrease in $Ge Si$ is well correlated with the $^{87} Sr^{86} Sr$ ratio in sea water of the relevant age. The interpretation of this trend may reflect: (a) different levels of $Ge Si$ in sea water as a result of a different ratio between hydrothermal and riverine input, (b) a diagenetic trend in siliceous sediments, (c) recording (by radiolaria) a transition between a radiolaria dominated ocean (with relatively high $Ge Si$ ratios in sea water) and diatom domination or (d) a combination of the above.

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Cited by (15)

The Ediacaran-Cambrian rise of siliceous sponges and development of modern oceanic ecosystems
2019, Precambrian Research
Citation Excerpt :
Ge/Si ratio, which is commonly used to distinguish the different sources of silica in cherts (Tribovillard et al., 2011), was calculated (Fig. 12B; see Fig. 13 for stratigraphic plot). Although the preservation of the Ge/Si ratio during diagenesis has been discussed, multiproxy analyses indicated that Ge/Si in chert is a robust proxy for origin of silica (Kolodny and Halicz, 1988; Tribovillard, 2013). Ge and Si share similar geochemical characters and are closely related in oceanic cycling.
The lack of unequivocal sponge fossils before the Cambrian despite their probable deep origin during the Cryogenian period has been a conundrum to geologists. Their impact on the dramatic evolution of ecosystems and the seawater silica cycle during the Ediacaran-Cambrian (E-C) transition is also speculative. In this study, abundant sponge spicules and spicule-like structures that probably represent original sponge fossils were recovered from four sections of the E-C boundary interval in the Yangtze Gorges, South China. The paleontological and geochemical data presented herein provides evidence for a continuous distribution of relatively abundant sponge spicules, some even forming spiculites, as well as the earliest biogenic deposition of silica by metazoans in the Ediacaran-Cambrian boundary interval. These results further confirm that a biological takeover of oceanic dissolved Si co-occurred with the evolution of silica biomineralization in the E-C interval, resulting in the widespread deposition of biogenic chert. Hydrothermal input in spicule-bearing cherts is also observed. Such hydrothermal activity might have favored the blooming of sponges through significant nutrient supply. These results provide the first conjunction of geochemical and paleontological proxies in support of previous models considering that sponges, by ventilation, filtration and oxygenation of seawater, were important ecosystem engineers of the E-C bioradiation event and of the related establishment of modern-type ecosystems.
Germanium-silicon fractionation in a river-influenced continental margin: The Northern Gulf of Mexico
2016, Geochimica et Cosmochimica Acta
Citation Excerpt :
The sedimentary record of Ge/Siopal therefore holds information on past changes in the Si cycle. The Ge/Siopal recorded in opal-rich marine sediments has varied significantly over time (Kolodny and Halicz, 1988; Murnane and Stallard, 1988; Froelich et al., 1989, 1992; Shemesh et al., 1989; Mortlock et al., 1991; Bareille et al., 1998; Lin and Chen, 2002). Both Si and Ge exhibit oceanic residence times of approximately 10 ky or less (Hammond et al., 2000; Tréguer and De La Rocha, 2013), allowing changes in their cycles on these timescales to be examined.
In this study we have sampled the water column and sediments of the Gulf of Mexico to investigate the effects of high riverine terrigenous load and sediment redox conditions on the cycling of Ge and Si. Water column Ge/Si ratios across the Gulf of Mexico continental shelf range from 1.9 to 25 μmol/mol, which is elevated compared to the global ocean value of 0.7 μmol/mol. The Ge enrichment in the Gulf of Mexico seawater is primarily due to anthropogenic contamination of the Mississippi river, which is the main Ge and Si source to the area, and to a smaller extent due to discrimination against Ge during biogenic silica (bSi) production (Ge/Si = 1.2–1.8 μmol/mol), especially by radiolarians and siliceous sponges (Ge/Si = 0.6–1.1 μmol/mol). Most sediment pore waters (Ge/Si = 0.3–4.5 μmol/mol) and sediment incubation experiments (benthic flux Ge/Si = 0.9–1.2 μmol/mol) indicate precipitation of authigenic phases that sequester Ge from pore waters (non-opal sink). This process appears to be independent of oxidation–reduction reactions and suggests that authigenic aluminosilicate formation (reverse weathering) may be the dominant Ge sink in marine sediments. Compilation of previously published data shows that in continental margins, non-opal Ge burial flux is controlled by bSi supply, while in open ocean sediments it is 10–100 times lower and most likely limited by the supply of lithogenic material. We provide a measurement-based estimate of the global non-opal Ge burial flux as 4–32 Mmol yr⁻¹, encompassing the 2–16 Mmol yr⁻¹ needed to keep the global marine Ge cycle at steady state.
Germanium isotope fractionation during Ge adsorption on goethite and its coprecipitation with Fe oxy(hydr)oxides
2014, Geochimica et Cosmochimica Acta
Citation Excerpt :
In this regard, Ge isotopes may provide useful geochemical tracers for the study of oceanic systems as well as continental weathering environments (Galy et al., 2003; Rouxel et al., 2006; Siebert et al., 2006; Qi et al., 2011; Escoube et al., 2012). Despite significant research efforts in deciphering Ge behaviour in natural systems such as hydrothermal systems (Mortlock et al., 1993; Evans and Derry, 2002; Wheat and McManus, 2008), iron-rich oceanic margin sediments (Kolodny and Halicz, 1988; King et al., 2000; Hammond et al., 2000; McManus et al., 2003), soils (Kurtz et al., 2002; Opfergelt et al., 2010; Cornelis et al., 2010), rivers (Murname and Stallard, 1990; Froelich et al., 1992; Derry et al., 2006) and biogenic minerals (Shemesh et al., 1989; Rouxel et al., 2006), the exact physical–chemical mechanisms controlling Ge at the Earth’s surface remain poorly characterized. One of the main results of previous studies of Ge isotope fractionation is that Ge is tightly linked to the Fe redox cycle and Fe mineral formation in contemporary and past Earth surface environments.
Isotopic fractionation of Ge was studied during Ge adsorption on goethite and its coprecipitation with amorphous Fe oxy(hydr)oxides. Regardless of the pH, surface concentration of adsorbed Ge or exposure time, the solution–solid enrichment factor for adsorption (Δ^74/70Ge_{solution–solid}) was 1.7 ± 0.1‰. The value of the Δ⁷⁴Ge_{solution–solid} in Fe–Ge coprecipitates having molar ratio 0.1 < (Ge/Fe)_solid < 0.5 remained constant at 2.0 ± 0.4‰. For (Ge/Fe)_solid ratio < 0.1, the Δ⁷⁴Ge_{solution–solid} increased with the decrease of Ge concentration in the solid phase, with the value as high as 4.4 ± 0.2‰ at (Ge/Fe)_solid < 0.001, corresponding to the majority of natural settings. These results can be interpreted based on available structural data for adsorbed and coprecipitated Ge. It follows that Ge(OH)₄° adsorption occurring as bidentate binuclear complexes at the goethite surface is characterised by an enrichment factor of ∼1.7‰, likely related to the distortion of the GeO₄ tetrahedron and the formation of Ge–O–Fe bonds at the goethite surface as compared to aqueous solution. In contrast, coprecipitation yields more distorted edge-sharing GeO₄ tetrahedra and, in the case of the most diluted samples, part of the Ge is found in coordination 6, replacing Fe(III) in octahedral positions. This produces a greater enrichment of the solid phase in lighter isotopes, mostly due to the increase in Ge–O bond distances and coordination number compared to aqueous solution, which is in line with the basic principles of isotope fractionation. Discharge of hydrothermal fluids, leading to massive Fe(OH)₃ precipitation in the vicinity of the springs should, therefore, represent an isotopically-heavy source of dissolved Ge to the ocean. Similarly, groundwater discharge and Fe(OH)₃ precipitation at the Earth’s surface, Fe oxy(hydr)oxide formation in soils and riverine organo-ferric colloids coagulation, leading to iron hydroxide precipitation in estuaries, should produce an isotopically heavy Ge aqueous flux to the ocean compared to bedrock sources and particulate fluxes.
Germanium isotopic systematics in Ge-rich coal from the Lincang Ge deposit, Yunnan, Southwestern China
2011, Chemical Geology
Citation Excerpt :
When this remaining aqueous solution interacted with coal samples in the middle part of the coal seam, those coal samples will consequently show lower Ge concentrations and elevated δ74Ge values as shown in Fig. 5c and d. Germanium concentrations in hydrothermal chert and limestone samples from the LGD are two orders of magnitude higher than those in sedimentary carbonate rocks (0.09 ppm on average, Bernstein, 1985) and in deep-sea cherts (0.23–1.02 ppm, Kolodny and Halicz, 1988; 0.39–1.08 ppm, Rouxel et al., 2006). The distinct correlation between LOI and Ge concentration of limestone samples indicate the addition of Ge-rich organic matter.
Organic matter plays an important role in the transport and precipitation of germanium (Ge) in coal-hosted Ge deposits. In this paper, Ge isotopes of coal samples and their combustion products were analyzed in order to investigate the potential use of Ge isotopes as tracers of Ge sources and enrichment mechanisms in coal. Germanium isotopic composition of various samples (mainly Ge-rich lignite) from the Lincang Ge deposit, Yunnan, Southwest China was analyzed using a continuous flow hydride generation system coupled to a Multi Collector Inductively Coupled Plasma Mass Spectrometer (MC-ICP-MS) and the standard-sample bracketing approach. Variations of ^⁷⁴Ge/^⁷⁰Ge ratios are expressed as δ^⁷⁴Ge values relative to NIST SRM 3120a Ge standard solution. Ge-rich lignite samples show large Ge isotopic fractionation (δ^⁷⁴Ge values range from − 2.59‰ to 4.72‰), and their δ^⁷⁴Ge values negatively correlate with Ge concentrations. Lignite samples with low Ge concentrations (< 500 ppm) tend to show positive δ^⁷⁴Ge values, while δ^⁷⁴Ge values of lignite samples with high Ge concentrations (> 1000 ppm) are close to zero or negative. Along stratigraphic sections, Ge is mainly concentrated in the top or the bottom of the coal seam, such that high values of δ^⁷⁴Ge are usually found in the middle part of the coal seam. Interlayered hydrothermal chert and limestone samples in Ge-rich coal seams also show moderate fractionation (δ^⁷⁴Ge values range from − 0.14‰ to 2.89‰ and from 0.55‰ to 1.87‰, respectively). The overall variations of δ^⁷⁴Ge values of Ge-rich lignite and organic-rich chert samples can be well described by a Rayleigh fractionation model, indicating that preferential enrichment of light Ge isotopes in coal in an open system might be the main factor controlling Ge fractionation in Ge-rich lignite. The germanium isotopic composition of hydrothermal chert (and possibly limestone) might also record the competitive fractionation produced by precipitation of quartz and sorption of coal. Elevated Ge concentrations and/or δ^⁷⁴Ge values of some chert, limestone, sandstone, and claystone samples may be attributed to the mixing with Ge-rich organic matter. Furthermore, similar to the fractionation of Zn, Cd and Hg isotopes observed between refinery dust or gas and slag, high temperature coal combustion also fractionates Ge isotopes, with the Ge isotopic compositions of soot being distinctly lighter (up to 2.25 per mil) than those of cinder. The distinct enrichment of potential hazardous elements (i.e., Pb, Cd, and As) and Ge in soot after coal combustion, as well as the common enrichment of Ge in sulfide minerals (e.g. sphalerite), highlights the possibility of using Ge isotopes as useful tracers of sources of heavy metal pollution caused by high temperature industrial processes (coal combustion and Pb-Zn refining) in the environment.
Transfer of germanium to marine sediments: Insights from its accumulation in radiolarites and authigenic capture under reducing conditions. Some examples through geological ages
2011, Chemical Geology
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 bio-induced 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.
Germanium isotopic variations in igneous rocks and marine sediments
2006, Geochimica et Cosmochimica Acta
A new technique for the precise and accurate determination of Ge stable isotope compositions has been developed and applied to silicate rocks and biogenic opal. The analyses were performed using a continuous flow hydride generation system coupled to a MC-ICPMS. Samples have been purified through anion- and cation-exchange resins to separate Ge from matrix elements and eliminate potential isobaric interferences. Variations of ⁷⁴Ge/⁷⁰Ge ratios are expressed as δ⁷⁴Ge values relative to our internal standard and the long-term external reproducibility of the data is better than 0.2‰ for sample size as low as 15 ng of Ge. Data are presented for igneous and sedimentary rocks, and the overall variation is 2.4‰ in δ⁷⁴Ge, representing 12 times the uncertainty of the measurements and demonstrating that the terrestrial isotopic composition of Ge is not unique. Co-variations of ⁷⁴Ge/⁷⁰Ge, ⁷³Ge/⁷⁰Ge and ⁷²Ge/⁷⁰Ge ratios follow a mass-dependent behaviour and imply natural isotopic fractionation of Ge by physicochemical processes. The range of δ⁷⁴Ge in igneous rocks is only 0.25‰ without systematic differences among continental crust, oceanic crust or mantle material. On this basis, a Bulk Silicate Earth reservoir with a δ⁷⁴Ge of 1.3 ± 0.2‰ can be defined. In contrast, modern biogenic opal such as marine sponges and authigenic glauconite displayed higher δ⁷⁴Ge values between 2.0‰ and 3.0‰. This suggests that biogenic opal may be significantly enriched in light isotopes with respect to seawater and places a lower bound on the δ⁷⁴Ge of the seawater to +3.0‰.This suggests that seawater is isotopically heavy relative to Bulk Silicate Earth and that biogenic opal may be significantly fractionated with respect to seawater. Deep-sea sediments are within the range of the Bulk Silicate Earth while Mesozoic deep-sea cherts (opal and quartz) have δ⁷⁴Ge values ranging from 0.7‰ to 2.0‰. The variable values of the cherts cannot be explained by binary mixing between a biogenic component and a detrital component and are suggestive of enrichment in the light isotope of diagenetic quartz. Further work is now required to determine Ge isotope fractionation by siliceous organisms and to investigate the effect of diagenetic processes during chert lithification.

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LetterThe geochemistry of germanium in deep-sea cherts

Abstract

Geochim. Cosmochim. Acta

Chem. Geol. (Isotope Geoscience Sect.)

Geochim. Cosmochim. Acta

Determination of germanium in natural waters by graphite furnace atomic absorption spectrometry with hydride generation

Anal. Chem.

Cretaceous and Cenozoic sediments from the Atlantic ocean

Init. Repts. DSDP

Marine diatoms

Principles of Isotope Geology

The marine geochemistry of germanium: ekasilicon

Science

Geochemical behavior of inorganic germanium in an unperturbed estuary

Geochim. Cosmochim. Acta

Letter
The geochemistry of germanium in deep-sea cherts