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The dinosaur–bird transition involved several anatomical, biomechanical, and physiological modifications of the theropod bauplan. Non-avian maniraptoran theropods, such as Troodon , are key to better understand changes in thermophysiology and reproduction occurring during this transition. Here, we applied dual clumped isotope (Δ 47 and Δ 48 ) thermometry, a technique that resolves mineralization temperature and other nonthermal information recorded in carbonates, to eggshells from Troodon , modern reptiles, and modern birds. Troodon eggshells show variable temperatures, namely 42 and 29 ± 2 °C, supporting the hypothesis of an endothermic thermophysiology with a heterothermic strategy for this extinct taxon. Dual clumped isotope data also reveal physiological differences in the reproductive systems between Troodon , reptiles, and birds. Troodon and modern reptiles mineralize their eggshells indistinguishable from dual clumped isotope equilibrium, while birds precipitate eggshells characterized by a positive disequilibrium offset in Δ 48 . Analyses of inorganic calcites suggest that the observed disequilibrium pattern in birds is linked to an amorphous calcium carbonate (ACC) precursor, a carbonate phase known to accelerate eggshell formation in birds. Lack of disequilibrium patterns in reptile and Troodon eggshells implies these vertebrates had not acquired the fast, ACC-based eggshell calcification process characteristic of birds. Observation that Troodon retained a slow reptile-like calcification suggests that it possessed two functional ovaries and was limited in the number of eggs it could produce; thus its large clutches would have been laid by several females. Dual clumped isotope analysis of eggshells of extinct vertebrates sheds light on physiological information otherwise inaccessible in the fossil record.

Calcitic valves of non-marine ostracodes are important geochemical archives. Investigations of the relationship between the isotopic ranges of modern ostracode populations and their host water provide important information on local or regional conditions and influences. Here we present the first δ18Oostracode and δ13Costracode dataset of the freshwater ostracode species Cytheridella ilosvayi along with characterization of the precipitating water - chemical composition, δDwater, δ18Owater, δ13CDIC values - covering a large geographical range (Florida to Brazil). With this data we extended a newly developed approach based on the estimation of δ18O values of monthly equilibrium calcites as references for the interpretation of δ18Oostracode values.The expected apparent oxygen isotope fractionation between CaCO3 - and H2O is correlated with temperature with smaller values occurring at higher temperatures as valid at isotope equilibrium (δ18Ocalcite_eq). Additional to a species-specific offset, unusual high deviations of δ18Oostracode vs. δ18Owater values most likely reflect the time lag between valve calcification and sampling. Coincidence between δ18Oostracode and δ18Ocalcite_eq is restricted to few months indicating a seasonal calcification of Cytheridella. There is a characteristic pattern in its difference between mean δ18Oostracode and δ18Ocalcite_eq which implies that Cytheridella provides a synchronous life cycle in its geographical range with two calcification periods in spring (May, June) and autumn (October). This ubiquitous life cycle of Cytheridella in the entire study area is considered to be phylogenetically inherited. It might have originally been adapted to environmental conditions but has been conserved during the migration and radiation of the group over the Neotropical realm.

Green inhibitors (GI) are eco-friendly organic molecules capable of inhibiting the nucleation and precipitation of solids, like CaCO3 minerals. Although increasingly used in technical settings, the...

ZusammenfassungUm notwendige Reinigungsarbeiten zur Aufrechterhaltung der Drainagewirkung von Drainagerohren in Tunneln zu minimieren, wurden im gegenständlichen Projekt Kunststoffe mit verschiedenen aktiven Wirkstoffen modifiziert, welche die Versinterungsneigung an den Rohroberflächen reduzieren sollen. Ausgehend von dieser praktischen Fragestellung wurden sieben verschiedene Rezepturen hinsichtlich ihres Potentials zur Verringerung der karbonatischen Versinterungen und zur industriellen Verarbeitbarkeit bewertet. Die hergestellten Compounds aus Matrix-Kunststoff, einem kommerziell verfügbaren Polyethylen-Rohr Typ und dem jeweiligen Wirkstoff sind zu Prüfkörpern verarbeitet und sowohl in Labor- als auch in Feldversuchen in realen Tunnelbauwerken ausgelagert worden. Anschließend fand die Beurteilung der Probekörper hinsichtlich der aufgewachsenen Versinterungen mittels chemischem Säureaufschluss, sowie optischen Analyseverfahren statt. Hinsichtlich der Verringerung der Versinterung zeigten das Polyethylen-Glykol Copolymer sowie das Compound mit Zeolith die besten Effekte.

The oxygen and clumped isotope signatures of Mg calcites are routinely used as environmental proxies in a broad range of surroundings, where Mg calcite forms either by classical nucleation or via an amorphous calcium magnesium carbonate (ACMC) precursor. Although the (trans)formation of ACMC to Mg calcite has been identified for an increasing number of settings, the behavior of both isotope proxies throughout this stage is still unexplored. In the present study ACMC (trans)formation experiments were carried out at constant pH (8.30 ± 0.03) and temperature (25.00 ± 0.03 °C) to yield high Mg calcite (up to 20 mol% Mg). The experimental data indicate that the oxygen isotope values of the amorphous and/or crystalline precipitate (δ$^{18}$O$_{prec}$, analyzed as Mg calcite) are affected by the (trans)formation pathway, whereas clumped isotopes (Δ$_{47prec}$ = Δ$_{47Mg-calcite}$) are not. The oxygen isotope evolution of the solid phase can be explained by the instantaneous trapping of the isotopic composition of the aqueous (bi)carbonate complexes. This entrapment results in remarkably high 10$^{3}$ln(α$_{prec-H2O}$) values of ∼33‰ at the initial ACMC formation stage. During the ACMC transformation process the oxygen isotope equilibrium is approached rapidly between Mg calcite and water (Δ$^{18}$O$_{Mg calcite-water}$ = 30.3 ± 0.4‰) and no isotopic memory of the initial to the final Mg calcite at the end of the experiment occurs. The implications for oxygen and clumped isotope signatures of Mg calcite formed via ACMC are discussed in the aspects of various scenarios of (trans)formation conditions and their use as environmental proxies.

Barium isotope fractionation during calcite and aragonite inorganic precipitation was studied in mixed flow reactors as a function of precipitation rate at 25 °C and pH = 6.3 ± 0.1. The measured Ba isotope fractionation that occurs between calcite and the forming fluid in the investigated range of calcite growth rates (10-8.0 ≤ Rp(calcite) ≤ 10−7.3 mol/m2/s) is insignificant. Barium isotope fractionation between aragonite and the fluid decreases with increasing precipitation rate from Δ137/134Baaragonite-fluid = +0.25 ± 0.06‰ for Rp(aragonite) ≤ 10−8.7 mol/m2/s to −0.10 ± 0.08‰ for Rp(aragonite) = 10−7.6 mol/m2/s, thus reflecting preferential incorporation of either heavy or light Ba isotopes in aragonite at slow and fast growth rates, respectively. The dependence of Ba isotope fractionation on aragonite growth rate is well described by the surface reaction kinetic model developed by DePaolo (2011) when the values +0.27‰ and −2.0 ± 0.2‰ are used for the equilibrium and kinetic Ba isotope fractionation factor, respectively. The enrichment of aragonite in the heavier Ba isotopes is consistent with the equilibrium fractionation factor of +0.34‰, calculated here between Ba-substituted aragonite and Ba2+ (aq), from first-principles calculations. This positive fractionation is related to a shorter average Ba[sbnd]O bond length in the aragonite structure while the coordination number does not change much (i.e. 9). The lack of isotope fractionation between the Ba aquo ions and the 6-coordinated Ba in calcite likely suggests that the coordination reduction required for the incorporation in the lattice of Ba adsorbed at calcite growing sites proceeds without isotope fractionation with the fluid. Otherwise the precipitated calcite should have been enriched in heavy isotopes by ∼0.17‰, as predicted by first-principles calculations. These results are the first experimental measurements of Ba isotope fractionation during inorganic calcite and aragonite mineral formation and set the basis for understanding the mechanisms controlling Ba isotope composition in CaCO3 minerals that is an essential perquisite for application of this isotopic system in natural samples.

This study aims to differentiate the potential recharge areas and flow mechanisms in the North-eastern Basin, Palestine. The results differentiate the recharge into three main groups. The first is ...

The high-precision analysis of the abundance of the dominant m/z 47 CO2 isotopologue derived from acid digestion of carbonate minerals (13C18O16O; denoted by Δ47) forms the basis for carbonate clumped isotope thermometry. Since the first measurements were published 16 years ago, considerable effort has gone into characterizing the relationship between Δ47 and carbonate precipitation temperature, and in identifying carbonates that do not achieve isotopic equilibrium. Mass spectrometry is now capable of the paired measurement of the primary m/z 47 and m/z 48-isotopologues (Δ47 and Δ48; 12C18O2 is denoted by Δ48), which has the potential to place additional constraints on kinetic isotope effects in carbonate minerals and trace distinct reaction pathways. Here, we explored factors that contribute to calcite mineral equilibrium and disequilibrium in Δ47 and Δ48 using a combination of experiments and theoretical calculations with three types of models. We precipitated calcite at pH 8.3 with carbonic anhydrase (CA) to approach quasi-isotopic equilibrium in the dissolved inorganic carbon pool and report values for Δ47, Δ48, and oxygen isotopes (δ18O) for calcite grown over a temperature range from 5 to 25 oC and compare our findings to predictions from an ion-by-ion model that support equilibrium precipitation. We also compare results to the Devils Hole slow-growing cave calcite, and other published temperature calibration data. We report the following combined equilibrium calibration relationships: Δ48 CDES 90 = (0.429 ± 0.010) Δ47 CDES 90 - (0.006 ± 0.006); r2 = 0.98; Δ47 I-CDES = (0.037 ± 0.001) × 106T-2 + (0.178 ± 0.009); r2 = 0.99; Δ48 CDES 90 = (0.015 ± 0.0005) × 106T-2 + (0.078 ± 0.006); r2 = 0.98. We used paired measurements of Δ47 and Δ48 to constrain kinetic isotope effects in calcite precipitated at pH ranging from 8.3-11 and temperatures from 5 to 25 oC, with and without CA present, and observe kinetic enrichments in Δ47, negative (hyperstochastic) values for Δ48, and depleted values of δ18O, compared to equilibrium values. Experimentally constrained kinetic trajectories, when compared with an ion-by-ion model and IsoDIC theoretical predictions, are consistent with CO2 hydration/hydroxylation. Mixing drives elevated Δ47 and Δ48 values and was assessed using mixing experiments with endmembers of varying isotopic compositions and compared to a Δ47 and Δ48 mixing model that constrains nonlinear mixing trajectories for calcite. While mixing may induce artifacts in two-component mixtures when endmember bulk compositions differ by more than 7 ‰, or if endmember Δ47 and Δ48 differ by more than 0.03 ‰, this should be detectable and potentially correctible using paired clumped isotope measurements and is unlikely to be important for some materials.

Retrograde clay mineral reactions (i.e., reverse weathering), including glauconite formation, are first-order controls on element (re)cycling vs sequestration in modern and ancient marine sediments. Here, we report substantial K–Mg–Fe sequestration by glauconite formation in shallow marine settings from the Triassic to the Holocene, averaging 4 ± 3 mmol K·cm−²·kyr− 1, 4 ± 2 mmol Mg·cm−²·kyr− 1 and 10 ± 6 mmol Fe·cm−²·kyr− 1, which is ~ 2 orders of magnitude higher compared to deep-sea settings. Upscaling of glauconite abundances in shallow-water (− 1, ~ 0.04–0.06 Tmol Mg·yr− 1 and ~ 0.11–0.14 Tmol Fe·yr− 1. We conclude that authigenic clay elemental uptake had a large impact on the global marine K, Mg and Fe cycles throughout Earth`s history, in particular during ‘greenhouse’ periods with sea level highstand. Quantifying authigenic clay formation is key for better understanding past and present geochemical cycling in marine sediments.

Retrograde clay mineral reactions (reverse weathering), including glauconite formation, are first-order controls on element sequestration in marine sediments. Here, we report substantial element sequestration by glauconite formation in shallow marine settings from the Triassic to the Holocene, averaging 3 ± 2 mmol·cm−²·kyr−1 for K, Mg and Al, 16 ± 9 mmol·cm−²·kyr−1 for Si and 6 ± 3 mmol·cm−²·kyr−1 for Fe, which is ~2 orders of magnitude higher than estimates for deep-sea settings. Upscaling of glauconite abundances in shallow-water (0–200 m) environments predicts a present-day global uptake of ~≤ 0.1 Tmol·yr−1 of K, Mg and Al, and ~0.1–0.4 Tmol·yr−1 of Fe and Si, which is ~half of the estimated Mesozoic elemental flux. Clay mineral authigenesis had a large impact on the global marine element cycles throughout Earth’s history, in particular during ‘greenhouse’ periods with sea level highstand, and is key for better understanding past and present geochemical cycling in marine sediments.

ZusammenfassungAusgehend von der Problematik aufwändiger Instandhaltungsarbeiten für die Funktionstüchtigkeit von Drainagerohren in Tunnelbauwerken wurde das interdisziplinäre Forschungsprojekt „PolyDrain“ initiiert. Im Rahmen des Forschungsprojekts werden diesbezüglich kritische Bauwerke in Österreich erhoben und vielversprechende Methoden zur Verringerung von zumeist karbonatischen Versinterungen in Drainagerohren untersucht. Durch gezielte Materialmodifikationen der Drainagerohre soll der Instandhaltungsaufwand zukünftiger oder zu sanierender Tunnelbauwerke reduziert werden, indem Reinigungsintervalle gestreckt und/oder Reinigungen rascher durchgeführt werden können. Der gewählte Ansatz umfasst die maßgeschneiderte Modifizierung von Kunststoff-Drainagerohrmaterialien. Dadurch ist es möglich, mechanisch widerstandsfähigere Rohre zu erzeugen und/oder das Versinterungsverhalten im Drainagerohr, inklusive der Drainageschlitze, zu reduzieren. Bevor eine Umsetzung im großtechnischen Maßstab möglich ist, ist es allerdings wichtig, nicht nur die kurzzeitige Wirksamkeit – im Projekt auch im Labor – zu untersuchen.

Lithium (Li) isotopes in marine carbonates have considerable potential as a proxy to constrain past changes in silicate weathering fluxes and improve our understanding of Earth's climate. To date the majority of Li isotope studies on marine carbonates have focussed on calcium carbonates. The determination of the Li isotope fractionation between dolomite and a dolomitizing fluid would allow us to extend investigations to deep times (i.e. Precambrian) when dolostones were the most abundant marine carbonate archives. Dolostones often contain a significant proportion of detrital silicate material, which dominates the Li budget; thus, pretreatment needs to be designed so that only the isotope composition of the carbonate-associated Li is measured. This study aims to serve two main goals: (1) to determine the Li isotope fractionation between Ca–Mg carbonates and solution, and (2) to develop a method for leaching the carbonate-associated Li out of dolostone while not affecting the Li contained within the detrital portion of the rock. We synthesized Ca–Mg carbonates at high temperatures (150 to 220 ∘C) and measured the Li isotope composition (δ7Li) of the precipitated solids and their respective reactive solutions. The relationship of the Li isotope fractionation factor with temperature was obtained: 103ln⁡αprec-sol=-(2.56±0.27)106(1)/T2+(5.8±1.3) Competitive nucleation and growth between dolomite and magnesite were observed during the experiments; however, there was no notable effect of their relative proportion on the apparent Li isotope fractionation. We found that Li isotope fractionation between the precipitated solid and solution is higher for Ca–Mg carbonates than for Ca carbonates. If the temperature of a precipitating solution is known or can be estimated independently, the above equation could be used in conjunction with the Li isotope composition of dolostones to derive the composition of the solution and hence make inferences about the past Li cycle. In addition, we also conducted leaching experiments on a Neoproterozoic dolostone and a Holocene coral. Results show that leaching with 0.05 M hydrochloric acid (HCl) or 0.5 % acetic acid (HAc) at room temperature for 60 min releases Li from the carbonate fraction without a significant contribution of Li from the siliciclastic detrital component. These experimental and analytical developments provide a basis for the use of Li isotopes in dolostones as a palaeo-environmental proxy, which will contribute to further advance our understanding of the evolution of Earth's surface environments.

Hydrated aluminosilicates were synthesized with and without aqueous heavy metals (Me), such as cobalt (Co), chromium (Cr), and zinc (Zn), by a sol–gel process at different initial molar ratios of Ca/(Si + Al) (0.6–1.6) and Me/Si (0.0–2.0), and constant Al/Si ratio (0.05) using equilibrium-approaching experiments. The chemical composition of the reactive solutions during aluminosilicate precipitation and maturation was monitored by ICP-OES. The mineralogy, nanostructure, and chemical composition of the precipitates were studied by XRD and high-resolution TEM. At Me/Si ratios ≤ 0.2, calcium–aluminium–silicate–hydrates (C–A–S–H) with a defect 14 A tobermorite-like structure formed, whereas at a Me/Si ratio of 2.0, either trioctahedral Co- and Zn-smectite or amorphous Cr gels precipitated, independent of the initial Ca/(Si + Al) ratio used for gel synthesis. The immobilization capacities for $$ {\text{Co}}^{2 + } $$ , $$ {\text{Cr}}^{3 + } $$ , and $$ {\text{Zn}}^{2 + } $$ by C–A–S–H, Cr gel, and trioctahedral smectite are 3–40 mg/g, 30–152 mg/g, and 122–141 mg/g, respectively. The immobilization mechanism of heavy metals is based on a combination of isomorphous substitution, interlayer cation exchange, surface (ad)sorption, and surface precipitation. In engineered systems, such as underground concrete structures and nuclear waste disposal sites, hydrated aluminosilicates should exhibit a high detoxication potential for aqueous heavy metals.

Zur systematischen Erfassung von Isotopendaten osterreichischer Lagerstatten wurden erstmals stabile Mg-Isostope (δ26MgDSM-3) ausgewahlter ostalpiner Spatmagnesitlagerstatten/-vorkommen (Hohentauern/Sunk, Hochfilzen, Breitenau, Radenthein/Millstatter Alpe, Kaswassergraben) und des kryptokristallinen Kraubath Magnesits bestimmt. Zusatzlich wurde aus Vergleichsgrunden und zur Charakterisierung wichtiger Typen von Magnesitlagerstatten auch auslandisches Material (Bela Stena/Serbien, Bushveld/Sudadfrika, Poldasht/NW Iran) untersucht. Dabei wurden fur die global wichtigen Typen von Magnesitlagerstatten signifikat unterschiedliche δ26MgDSM-3-Werte ermittelt: Kraubath-Typ −2.88 ‰ bis −1.80 ‰, Veitsch-Typ −1.54 bis −0.49 ‰, Bela Stena-Typ −1.07 bis −0.42 ‰, Poldasht-Typ −1.04 bis +1.01 ‰. Diese lassen sich weitestgehend auf die unterschiedlichen Bildungsprozesse (z. B. Evaporation, Metasomatose) zuruckfuhren.

The Δ47 (paleo)thermometer has opened a new avenue to determine carbonate formation temperatures independent of the oxygen isotopic composition of the fluid from which the carbonate crystallized. A major limitation of this thermometer is related to kinetic effects if homogeneous isotopic equilibrium is not attained during carbonate precipitation. Dual clumped isotope thermometry – the high-precision analysis of Δ48 along with Δ47 in CO2 evolved from phosphoric acid digestion of carbonates – makes it possible to resolve temperature from the kinetic information recorded in an individual carbonate phase. Therefore, it provides a new opportunity to identify (bio)mineralization pathways and to determine carbonate formation temperatures devoid of a kinetic bias, based solely on isotopic analysis of a single carbonate phase. Identification of the nature and extent of kinetic effects as well as the reconstruction of accurate formation temperatures requires knowledge of the position of equilibrium in Δ47 vs Δ48 space. Here, we present Δ47 and Δ48 data of carbonates that were previously considered as having crystallized closest to equilibrium in a temperature range of 8 to 1100 °C. Across this range, the temperature dependences of Δ47 and Δ48 are best expressed by the following fourth order polynomials of 1/T: Δ47 (CDES 90) (‰) = 1.038 (−5.897 1/T − 3.521 103 1/T2 + 2.391 107 1/T3 − 3.541 109 1/T4) + 0.1856 Δ48 (CDES 90) (‰) = 1.028 (6.002 1/T − 1.299 104 1/T2 + 8.996 106 1/T3 − 7.423 108 1/T4) + 0.1245 with CDES 90 representing the Carbon Dioxide Equilibrium Scale at a reaction temperature of 90 °C. In its entire temperature range, our Δ47 (CDES 90) - T - relationship agrees within 2 ppm with two previous Δ47 (I-CDES) - T - relationships reported by Jautzy et al. (2020) and Anderson et al. (2021). Accuracy of our proposed Δ47 (CDES 90) − Δ48 (CDES 90) equilibrium relationship is independently confirmed by additional dual clumped isotope data of experimental and geothermal carbonates which precipitated from potentially equilibrated dissolved inorganic carbon pools at a temperature range of 25–100 °C. Furthermore, we reprocessed original dual clumped isotope data of natural carbonates (Bajnai et al., 2020) and compared their composition to the position of equilibrium in Δ47 vs Δ48 space. These results corroborate preliminary evidence that the hydration/hydroxylation reactions became rate-limiting during the calcification of a speleothem-like sample, a warm water coral, a cold water coral and a brachiopod, finally evoking significant departures of carbonate-Δ47 and -Δ48 from dual clumped isotope equilibrium. An anti-clumped Δ48 value of −419 (±16) ppm (95% confidence interval level) is obtained for a technical calcite that was precipitated by the injection of CO2 into a Ca(OH)2-saturated solution. Its negative Δ48 value largely arises from a combinatorial effect, i.e. the carbonate oxygen derives from two sources with different bulk isotopic compositions. Besides the identification of the nature and the extent of (bio)mineralization kinetics and the reconstruction of carbonate formation temperatures unbiased by kinetics, dual clumped isotope analysis, therefore, allows tracing the isotopic heterogeneity of oxygen pools contributing to carbonate formation.

The full potential of the dolomite Ca isotope proxy only unfolds when combined with data of the other main elements (C, O, Mg) in the crystal lattice of Mg-carbonates. Data presented here reveal the level of complexity inherent to dolomite precipitation and alteration environments and add new constraints to the understanding of early diagenetic dolomite formation. Well-constrained Precambrian to Pleistocene dolomites were investigated, representing three characteristic formation and alteration environments: (i) sabkha, (ii) altered marine and (iii) lacustrine/palustrine dolomites. Primary sabkha dolomites with typically low cation ordering degree (COD), high d13C and low d44/40Ca values contrast with recrystallized sabkha dolomites with relatively high COD, low d13C and high d44/40Ca values. Both d13C and d44/40Ca values of sabkha dolomite bear witness to the relative effects of kinetic and equilibrium Ca isotope fractionation conditions. Primary sabkha dolomites display D44/40Cadolomite-fluid ranging from −0.4 to −1.30, whereas recrystallized dolomite is approaching isotopic equilibrium (D44/40Cadolomite-fluid ∼ 00). Using the fractionation factor deduced from the sabkha dolomite data set, recrystallized Precambrian dolomite points to a d44/40Caseawater/pore fluid of about 1.20 (SRM 915a), a value that is distinctively lower compared to previously suggested ones and modern seawater. Altered marine dolomites display evidence for meteoric overprint, indicated by d18O values as low as −4.620. Both Mg and Ca isotope signatures correlate with d18O values of altered marine dolomites, whereas d13C values lack correlation with the other isotope systems. We propose that freshwater circulated through silicate aquifers prior to reaching the dolostone units and Ca, Mg and O isotopes of altered marine dolomites reflect variable degrees of this meteoric overprint. Lacustrine/palustrine dolomites display a correlation between the isotope values of C, Mg and Ca. These dolomites are formed during pulses of marine ingression in swamp, playa and lake environments and are thus characterized by water-logged conditions (anaerobic) and saline, sulfate-rich fluids. Bacterial-sulfate reduction induces dolomite formation and leads to lower d13C and d44/40Ca as well as to higher d26Mg values. The Ca isotope proxy acts as a benchmark against which other proxy data can be calibrated or processes tested. Taking COD and dolomite stoichiometry into consideration, the here documented multi-proxy isotope approach is promising and provides benchmarks against which proxy signals can be calibrated and tested. Interestingly, even the limited data sets shown here point to patterns that can be interpreted in a meaningful manner that is of relevance for dolomite research.

International audience; Diagenesis of carbonate minerals is ubiquitous throughout the geologic record. Alteration is initiated immediately after deposition, or takes place in the endo- and exoskeletons as early as during the lifetime of a given carbonate-secreting biota, and can continue throughout the burial history of carbonate sediments and rocks. Variations in the diagenetic response of carbonate archives pose challenges for the reconstruction of past environmental conditions based on proxy data. This paper comparatively assesses alteration features of different aragonitic materials by experimentally-induced diagenesis. A multitude of factors lead to different reactivity and responses of a given aragonite archive, and provide insight to the interpretation of diagenetically altered material in the rock record. Chosen materials used in this study include relatively organic-rich samples such as coral skeletons and bivalve shells, and organic-lean abiotic carbonates such as speleothems and aragonite single crystals. Obtained datasets include distributions of elements, organics, carbon and oxygen isotope ratios, and crystallographic features. Observed variations in diagenetic responses include mineralogy of the diagenetic phases, rate and extent of mineral transformation, distribution of foreign ions in the crystal lattice (primarily Sr, Mg, and S), and the number of specific processes and products along diagenetic pathways. Alteration is shown to be primarily controlled by the initial diagenetic susceptibility of the sample (including porosimetry and structural characteristics, concentrations of organic material, and primary amounts of trace elements in the carbonate, such as Mg). Structural characteristics lead to initial internally “fluid-” or “rock-buffered” conditions, with low porosity and permeability resulting in a greater effect of internal fluids and organics. Differences in the amount of organic content and internal fluids affect transformation rates, secondary mineralogy, and isotope equilibria. Samples with relatively high porosity, high mineral transformation rates, and high primary Mg/Ca, may preferentially form secondary aragonite during fast equilibration with the diagenetic environment. Our results suggest that the degree and nature of diagenetic alteration of aragonite materials are strongly controlled by the micro- to nano-scale internal architecture governing the availability and transfer of aqueous fluids. Results of this study provide significant implications for the interpretation of diagenetic signals in carbonate archives, and have direct significance for the mechanistic understanding of carbonate diagenesis and (paleo)environmental conditions.

The origin of Quaternary dolomites in continental environments (e.g. karst and lakes) is barely constrained compared to marine dolomites in sedimentary records. Here we present a study of dolomite and aragonite formations infilling young fractures of the ‘Erzberg’ iron ore deposit, Austria, under continental-meteoric and low temperature conditions. Two dolomite generations formed shortly after the Last Glacial Maximum (~20 kyr BP): dolomite spheroids and matrix dolomite. Clumped isotope measurements and U/Th disequilibrium ages reveal formation temperatures of 0–3 °C (±6 °C) and 3–20 °C (±5 °C) for the both dolomite types, and depositional ages around 19.21 ± 0.10 kyr BP and 13.97 ± 0.08 kyr BP or younger, respectively. Meteoric solution and carbonate isotope compositions (δ18O, δ13C and 87Sr/86Sr) indicate the dolomites formed via aragonite and high-Mg calcite precursors from CO2-degassed, Mg-rich solutions. Our study introduces low temperature dolomite formations and their application as a sedimentary-chemical archive., Communications Earth & Environment, 1 (1), ISSN:2662-4435

The transition from the Proterozoic to the Phanerozoic Eon was accompanied by the rise of metazoan life, a key and unique biogeochemical milestone in Earth's history. Concomitant continental re-organization and collision were associated with enhanced continental reworking and changes in global ocean currents, with profound impacts on continental weathering rates, riverine run-off and associated changes in the ocean nutrient budget. The causal relationship between the geological re-organisation of continents and the biologic evolution of marine life, however, remains elusive. In this study, we investigate phosphatic shallow-water sedimentary successions from Kazakhstan, which host key marker horizons from the Precambrian-Cambrian (Pc-C) boundary. We show that a rapid change (over ca. 3 Myrs) towards heavier stable Mg isotope compositions of the phosphatic sedimentary deposits in Kazakhstan, which we consider representative for contemporaneous ocean chemistry, co-varies with changes in radiogenic Sr isotope signatures. We propose that ocean chemistry at the Pc-C boundary, represented through this co-variation, was strongly affected by continental re-organization and associated weathering, which, in analogy, would have affected ocean nutrient levels. A rapid reversal of isotope compositions towards signatures similar to those prior to the isotope excursion likely reflects the fading influence of weathering and a buffering of water-rock interactions during oceanic spreading. We conclude that, based on the positive, coupled 87Sr/86Sr- δ26Mg isotope spike in ocean water chemistry, a link between Gondwana re-organization at the Pc-C boundary and the marked change in marine fauna seems plausible.

We undertook 87Sr/86Sr analyses for a range of carbonate bearing geological reference materials, and combined these with δ26Mg for a subset of samples. Following chemical purification in a series of chromatographic extractions, isotope ratios were measured by Multi-Collector-ICP-MS using a Plasma II (Nu instruments, Wrexham, UK). To validate efficient sample digestion procedures of carbonate fractions, total samples were treated with either 3 mol l−1 HNO3 and 0.5 mol l−1 HCl, respectively. Results of both leaching procedures are identical within reproducibility. Reference values for SRM 88A (formerly NBS 88A), SRM 1B (formerly NBS 1B), SARM 40, SARM 43, JDo-1, JLs-1, and San Carlos olivine range from 0.70292 to 0.73724 in 87Sr/86Sr and from -2.80 to -0.41 ‰ for δ26Mg, respectively. This set of geological reference materials can be used for sedimentary rock material with different carbonate mineral and matrix composition as quality control measurements of combined stable Mg and radiogenic Sr isotope analyses.•We present a protocol that facilitates the chemical separation of Mg and Sr in carbonate bearing geological reference materials including 87Sr/86Sr and δ26Mg of certified reference materials., Graphical abstract Image, graphical abstract

Mineral scale deposits in water drainage and supply systems are a common and challenging issue, especially by clogging the water flow. The removal of such unwanted deposits is cost intensive arguing for case-specific and sustainable prevention strategies. In the present study, a novel on-site approach to prevent calcium carbonate (CaCO3) scale formation was assessed in two road tunnel drainages: Application of the eco-friendly green inhibitor polyaspartate (PASP) caused (i) a significant inhibition of CaCO3 precipitation, (ii) a more porous or even unconsolidated consistence of the deposits, and (iii) a shift from calcite to the metastable aragonite and vaterite polymorphs. Even relatively low PASP concentrations (1–33 mg/l) can significantly decrease CaCO3 scale deposition, removing up to ∼7 t CaCO3/year at an efficiency up to 84%. Application of PASP for water conditioning should also consider case-specific microbial activity effects, where consumption of PASP, e.g. by Leptothrix ochracea, can limit inhibition effects.

A luminescent sensor technique for pH analyses has been tested in cementitious media. The optical sensors monitor in-situ pH every 5 s during early hydration reactions over a period of 100 h from initial fluid up to consolidated stage. The pH development was analysed in calcium aluminate, calcium sulfoaluminate and OPC/slag cements up to a pH level of 13.3 and directly correlated with the heat of hydration. Thus tracing the dissolution and formation processes of solid phases via pH sensor monitoring is possible. This measurement technique enables the recording of continuous and highly reproducible pH data sets from slurries, pastes, and hardening materials leading to new vistas for individual (trans)formation pathways of solids, hydration and consolidation reactions in high alkaline cementitious systems.

Consolidation of MgO castables by organic acids is a common technique for various applications, but the distinct hardening mechanisms of caste stone formation are still poorly constrained. In this study, the individual hardening behavior was experimentally investigated by intermixing of (i) active fine-grained magnesia (MgO_A), (ii) dead-burned coarse magnesia (MgO_D) or inert quartz sand aggregates, (iii) citric acid, malic acid or acetic acid, and (iv) water. The effects of MgO purity, MgO reactivity and the type of organic additive on the evolution of hardening, Mg-organo salt formation, mineralogy and microstructure of the MgO intermixes were assessed by sound velocity measurements, XRD, FTIR spectroscopy, and electron microscopy. The reactivity of MgO_A controls the overall hardening behavior of the MgO intermixes but is strongly affected by the type and spatial distribution of the solid Mg-organo binder. MgO intermixes prepared with citric and malic acid result in stronger hardening compared to those based on acetic acid, which is caused by the interconnecting Mg-Hcitrate and Mg-malate binders vs spatially restricted and compact Mg-acetate encapsulation in micropores. MgO_D with low purity degree yields in stronger hardening, which is due to the high reactivity of accessory solid phases, such as merwinite, magnesioferrite and larnite, forming additional Ca-Fe-Mg-organo binder phases. Systematics in the above MgO-H2O-organo systems are discussed in the scope of hardening reaction mechanisms of castables inferred by type and compositions of distinct MgO and carboxylic acids.