Silicates/Oxides formation and weathering

Understanding the important role of clay minerals – the by far most abundant silicates on the Earth`s surface –as (trace) element sources and sinks in modern and past sedimentary and marine-diagenetic environments provides substantial information about fluid-rock interactions, paleoclimate, global element cycling, and fundamental biogeochemical processes at water-mineral interfaces.

The experimental synthesis and/or dissolution of redox- and climate-sensitive clay minerals such as glauconite, interstratified illite-smectite, Fe-Mg-saponite, sepiolite and (amorphous) aluminosilicates are powerful tools to trace the underlying reaction pathways and kinetics of clay mineral reactions at low temperatures. Herein, we use latest-state-of-the-art solid-phase and fluid-phase characterization methods as well as hydrogeochemical modeling in order to link our novel experimental work with processes occurring in our dynamic system Earth.

Specific tasks can be seen in the following sections.


Glauconite

Green-clay authigenesis is a worldwide occurring phenomenon, covering huge areas of shelf and ocean floor sediments. We investigate the environmental conditions and reaction paths of the so-called Fe-smectite to glauconite reaction in shallow- and deep-water settings during early diagenesis using a multi-method approach that comprises various solid-phase and fluid-phase analysis as well as hydrogeochemical and kinetic modeling.

The quantification of ultimate iron sequestration related to green-clay authigenesis in modern, deep sea environments is a major task of our ongoing research affecting a variety of biogeochemical processes in the low-temperature cycle of iron.

Contact: Andre Baldermann

© A. Baldermann

Experimental synthesis of ferruginous clay minerals

Ferrous saponite and nontronite are the major alteration products of submarine basalt formed at mid-oceanic ridge sites. The precipitation and deposition of ferruginous clay minerals on the ocean floor is well-known to limit the supply of dissolved iron to the overlying oceanic water masses, which affects a variety of biogeochemical processes in deep-sea sediments and in the deep biosphere environment in general. Thus, an improved understanding of the ambient environmental controls affecting the distribution and abundance of authigenic ferruginous clay minerals in the sedimentary record may provide substantial information about the processes operating the modern and past biogeochemical cycle of iron.

In this project, we synthesize ferrous saponite and nontronite in Teflon-lined, stainless steel autoclaves at diagenetic temperatures, alkaline pH, reducing conditions, and using experimental solutions with varying molar Si:Fe:Mg ratios in order to investigate the effect of these key parameters on the mineralogy, structure, stability, and chemical composition of laboratory grown ferrous clay minerals. Measurements of stable Fe, Si, and Mg isotopes are planned to resolve the underlying reaction mechanisms linked to the formation of saponite and nontronite.

Contact: Andre Baldermann

© A. Baldermann

Experimental synthesis of sepiolite

The formation of Mg-silicates and modulated Mg-phyllosilicates at Earth`s surface conditions has been used successfully for the reconstruction of sedimentary facies in modern and ancient lacustrine, peri-marine, and diagenetic environments. To our current knowledge, sepiolite – a hydrous Mg-rich clay mineral with a modulated structure – is the only Mg-silicate which forms by direct precipitation from seawater.

Using a novel experimental approach, we precipitate sepiolite under nature-near conditions at ambient temperatures in order to experimentally derive the apparent growth rates of fibrous sepiolite crystals. Mg and Si isotope analysis of synthetic and naturally occurring sepiolite is used to trace the underlying mineral-forming processes that are associated with the co-precipitation of Mg2+ ions and silica.

Contact: Andre Baldermann


Chert formation and proxy development (Si/Al, Si-isotopes)

The deposition of widespread phosphorites at the Precambrian-Cambrian boundary is often associated with the deposition of abundant bedded chert sequences in shallow and deeper water environments. However, so far, neither the source of silica nor the formational mechanisms are known with certainty. We therefore investigate how the remarkable retrieval and concentration of dissolved Si can be achieved, how weathering, hydrothermal activity and/or bio-engineering influenced the oceanic and depositional system. This is achieved by applying state-of –the-art geochemical methods, such as trace element ratios, REE, light stable (Δ17O) and Si isotopes.

Contact: Dorothee Hippler

© D. Hippler
© M. Stuff

Dissolution behavior of gibbsite

Contact: Martin Dietzel


Behaviour and occurrence of polymeric and monomeric silicic acid - silicate weathering and adsorption

Contact: Martin Dietzel


Amorphous Silica and HydroxyAluminosilicate Formation

Contact: Martin Dietzel

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