Carbonate in natural and man-made surroundings

Specific tasks:

Dolomite

Dolomite, CaMg(CO3)2, is a common rock-forming mineral in ancient platform carbonates, but its occurrence in modern environments is rare, despite the ambient seawater is highly supersaturated in respect to this mineral phase. After more than 200 years of ongoing research there is still an active debate in the geoscientific community about the underlying processes causing dolomite formation in sedimentary (low temperature) settings. This enigma is referred to as the dolomite problem.

In this sub-project, we investigate spatial trace element distributions and concentrations (e.g., Na, Sr, S, Fe, Mn), the isotopic signatures (e.g., δ13C, δ18O, δ26Mg, and δ34SCAS) as well as the petrographic and mineralogical features of recent dolomites and ancient dolomitized platform carbonates in order to elucidate the physicochemical conditions and underlying dolomitization pathways operating in modern and past dolomite-forming environments.

Contact: Andre Baldermann

© A. Baldermann

Non-traditional stable isotope fractionation of lacustrine high-Mg calcites and dolomite of Lake Neusiedl

Lacustrine carbonates display an important regional environmental archive, with deposition depending upon lake hydrology and morphology, and hence climatic influences. It is further known that carbonate deposition in lakes is mainly driven by biogenic or bio-induced precipitation, resulting in some places in the enigmatic formation of high-Mg calcite or dolomite.

Lakes, such as Lake Neusiedl are thus ideal large-scale laboratories that permit detailed examination of highly important aspects of authigenic dolomite formation. Calcium and magnesium isotope signatures trace Ca and Mg cycling within the lake and its catchment area in relation to authigenic high-Mg calcite and dolomite formation.

Contact: Dorothee Hippler

© D. Hippler
© D. Hippler

Biomineralisation vs. Bioerosion-induced alteration of biogenic carbonates (CHARON)

The shells of marine calcifiers (e.g. bivalves) are mainly composite materials made of mineralized and organic tissue. This fact makes shell material highly interesting for hard substrate dwellers, such as micro-boring algae or fungi, causing remarkable bioerosion of the original shell material. This study therefore focuses on the impact of bioerosion on the structure, mineralogy and geochemistry of original shell material via the comparision of pristine, bio-eroded and fossil shell material.

Contact: Dorothee Hippler

© D. Hippler
© D. Hippler

Mineral precipitates in geotechnical drainage systems

Rapid deposition of chemical sediments (mostly carbonates and sulfates) is widespread in man-made drainage settings such as artificial (bypassing) river beds and tunnel drainage systems. Pronounced fluid-solid interaction results in dissolution versus precipitation reactions, e.g. concrete linings interacting with stream waters promoting supersaturated aqueous solutions.

Our research focuses on hydrogeochemical and site-specific process understanding with regard to applicable environmental and engineering solutions. This approach comprises detailed mineral and water characterization combined with in-situ monitoring programs and hydrochemical modelling.

Contact: Ronny Boch

© R. Boch
© R. Boch

Carbonate coatings & cements infilling fractures and faults

Brittle tectonic structures such as open fractures, joints and fault zones are occasionally, all or partly refilled with multi-directional secondary coatings across their inner faces. Major proportions of clastic material in these voids might be consolidated by carbonate cements precipitating from the vadose or phreatic supersaturated waters.

From the famous "Erzberg" iron ore mining site (Styria, Austria) densely laminated aragonite-calcite successions (erzbergite) in vertical fractures are studied. Our research focuses on the origin, radiometric dating and growth dynamics of these formations, as well as paleoenvironmental (climate archive) and (neo)tectonic constraints.

Contact: Ronny Boch

© R. Boch
© R. Boch

Geothermal Scaling

Highly mineralized waters of elevated temperature and pressure from deep geothermal wells tend to precipitate various chemical sediments. The solid precipitates in wells, pumps, transport pipes and heat exchangers cause severe problems in thermal water and energy production, i.e. clogging or reduction of inner diameters. Depending on natural and man-made environmental conditions spatiotemporally variable deposition (scaling progress) is common.

We apply high-resolution analytical techniques to study the mechanisms determining the nucleation and growth dynamics of these mineral deposits focusing on forensic tasks and retarding/preventive measures. Detailed solid-phase characterization is complemented by laboratory experiments and computer modelling. The precipitates are also of interest in the context of fundamental research in testing and calibration of stable- and "clumped" isotopic fractionation at the specific but well-constrained (T, P, hydrochemistry) conditions.

Contact: Ronny Boch

© R. Boch
© R. Boch

Speleothems and Caves

Speleothems (dripstones) are increasingly used in paleoenvironmental research based on their capability to archive climate information, their wide (global) distribution in karst areas, high preservation potential underground and precise age control based on uranium-series dating. Our research focuses on site-specific growth dynamics of modern (active) speleothems combining petrographic, chemical and stable isotopic information captured in the actively growing stalagmites with field (cave) monitoring of dripwaters, cave air and carbonate precipitation on artificial substrates, as well as comparison with regional meteorological data.

Understanding the modern solid-fluid environmental interactions is crucial for applying stalagmites of different time intervals as an archive of past climate conditions. Katerloch Cave located north of Graz is well known for its overwhelming speleothem decoration and was selected as an attractive study site.

Contact: Ronny Boch

© R. Boch
© R. Boch

Travertine & Carbonate tufa: Processes & Paleoenvironment

Travertine deposits are mostly laminated, consist of compact aragonite and/or calcite successions and are frequently associated with thermal waters, fault zones and microbial activity. Carbonate tufa, in contrast, is typically porous and calcite precipitates from supersaturated stream waters of ambient temperature.

We study fossil and active sites of such freshwater formations with regard to (paleo)environmental information captured in their chemical composition, inorganic vs. organic processes, as indicators of past or active tectonics and mass movements, and regarding their value as decoration- and building material. Two study sites are currently investigated: A Late Glacial travertine deposit in Eastern Tyrol and an active carbonate tufa stream near Köttmannsdorf, Carinthia.

Contact: Ronny Boch

© R. Boch
© R. Boch

Dissolution of Dolomite in Alkaline Cementitious Media

Chemical alteration of concrete has gained much attention due to sulphate attack, thaumasite formation and alkali silica reactions. However, less is known about the so-called alkali carbonate reaction (ACR). Our results concerning ACR clearly indicate that dolomite aggregates in concrete dissolve incongruently and are replaced by calcite (CaCO3) and brucite (Mg(OH)2). Incongruent dissolution of dolomite is stimulated by high Ca2+ concentration (>500mg/l), high ionic strength, low temperature (< 8°C) and high pH (>10) due to low Mg2+ concentration.

The figure shown below is a BSE image of a chemically altered concrete showing a partly dissolved dolomite aggregate in a matrix of brucite (Bru) and thaumasite (Tha). The sample comes from the shotcrete of an Austrian tunnel. Width of image is 0.5 mm.

Contact: Dietmar Klammer

© TU Graz/IAG

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