Calcite Layer Research Articles

Dual pathways of aragonite-to-calcite transformation in stalagmites: Implications for paleoclimate reconstructions

Multiple geochemical proxies (e.g., trace elements, δ18O and δ13C) and precise 230Th ages in speleothems are crucial for conducting robust paleoclimatic reconstructions, but the impact of diagenesis on these proxies and 230Th ages is not well-established. In this study, we investigate the petrography and geochemical composition of six aragonite-calcite stalagmites from Shennong Cave in southeastern China to analyze the transformation from aragonite to calcite (primary versus secondary) and its effects on geochemical proxies and 230Th ages. No aragonite relics are observed in columnar calcite in four aragonite-calcite stalagmites (SN55, SN49, SN104 and SNB1), although traces of aragonite exist between the calcite crystals or grow parallel at the aragonite-calcite borders. This is different from the obvious aragonite relics preserved in secondary mosaic calcite in the other two aragonite-calcite stalagmites (SN3 and SN15). Both mosaic and columnar calcite show various changes in geochemical proxies and 230Th ages compared with primary aragonite. The trend in the geochemical proxies analyzed (trace elements, δ18O and δ13C) of columnar calcite remains consistent with those of aragonite, despite significant differences in their absolute values within the overlapping periods. These differences are due to the different fractionation coefficients of isotopes and trace elements in aragonite and calcite formed under the same solution conditions rather than late diagenesis. The 230Th ages of columnar calcite are similar to those of primary aragonite, and the values of subsamples from the same calcite layer are consistent. In contrast, the trace elements and δ13C values of mosaic calcite are similar to those of primary aragonite, while its 230Th age significantly differs from that of primary aragonite, exhibiting no consistent patterns. Therefore, these geochemical characteristics of columnar calcite are significantly different from secondary mosaic calcite, indicating that the columnar calcite in these four aragonite-calcite stalagmites is primary. A comparison of trace elements and δ13C records between aragonite-calcite and pure aragonite stalagmites during the overlapping period further confirms that these columnar calcites are primary. Their geochemical proxies can be used for paleoclimate reconstruction after careful evaluation, and the transformation from aragonite to columnar calcite is caused by increased precipitation. However, due to age and geochemical proxies change, secondary mosaic calcite is unsuitable for paleoclimate reconstruction, unlike columnar calcite. This study provides competent evidence to identify whether calcite in aragonite-calcite stalagmites is primary versus secondary and whether it can be used for paleoclimatic reconstruction.

Elemental Uptake by Different Calcite Crystal Faces: An In Situ Study

This study aims to evaluate relationships between elemental signatures in calcite and the crystallographic orientation of its planes. The ability of calcite (a widespread calcium carbonate mineral) to entrap various trace and minor elements in its structure is the foundation of multiple methods (also called proxies) to reconstruct paleoenvironment conditions (e.g., temperature, pH, and marine chemistry). Although several element-to-calcium ratios (E/Ca) are routinely measured in marine carbonates and are widely used in paleoclimate studies, some of the controls on the incorporation of these elements are still unclear. Here, we examine the effect of crystallography on (E/Ca)calcite by growing thin layers of calcite on differently oriented Iceland Spar substrates immersed in modified seawater solution. Newly grown calcite layers were examined with Laser Ablation Inductivity–Coupled Plasma Mass Spectrometry (LA-ICP-MS), Backscattered Electron Imaging (BSE), and Energy Dispersive X-ray Spectroscopy (EDS). We propose that the crystallographic orientation might slightly influence the incorporation of lithium (Li), sodium (Na), magnesium (Mg), sulfur (S), and barium (Ba) into the studied calcite faces and have no impact on the incorporation of boron (B), potassium (K), and strontium (Sr) at least under the conditions of our experiment.

Evaluating the performance and durability of concrete paving blocks enhanced by bio-cement posttreatment

Concrete pavement often experiences accelerated deterioration due to water and chemical ingress through micro-cracks and surface voids. Particularly, the ingress of aggressive agents into the concrete matrix results in irreversible changes and deterioration on its endurance. Numerous studies unveiled that hydrophobic surface protection could be an inexpensive and effective way of enhancing the durability of concrete. This research work aims to assess the feasibility of bio-cement posttreatment for facilitating hydrophobic surface protection, thus enhancing the performance and durability of concrete blocks. Enzyme induced carbonate precipitation (EICP) is one of the promising bio-cement methods. Concrete blocks casted in four different grades were subjected to EICP treatment with different treatment schemes and recipes of cementation media. The treated blocks were tested for water absorption, ultrasonic pulse velocity (UPV) measurements, unconfined compressive strength (UCS), thermal performance, and scanning electron microscopy (SEM). The results indicated that the concrete blocks subjected to EICP posttreatment showed over a 55% reduction in water absorption, a 15% higher UCS and a 6.7% higher UPV when compared with control blocks. The SEM analysis suggested that the EICP posttreatment could enhance the durability of concrete paving blocks by enabling a layer of calcite on the surface and by plugging the transport pore channels of the concrete. Although most of the posttreatment strategies investigated herein were found to be operative, a better response was seen in the posttreatment by spraying scheme with 0.5 mol/L cementation media (CM). With the successful demonstration, the EICP treatment prior to the use of concrete blocks can be recommended to the pavement construction industry.

Compensatory shell thickening in corrosive environments varies between related rocky-shore and estuarine gastropods

Few studies have considered the capabilities of gastropods living in minerally-deficient acidified coastal waters to compensate for outer shell corrosion or compromised growing edge shell production. We compared inner shell thickening between pristine shells (control) and corroded shells (experiment) of two related intertidal neritid gastropod species from reduced salinity and acidified environments. We predicted that the rocky-shore, Nerita chamaeleon, which has greater access to shell building biomineralization substrates, should better control shell thickness than the estuarine, Neripteron violaceum. Accordingly, N. chameleon was found to compensate perfectly for variation in the thickness of the outer calcitic blocky layer (BL). Optimal shell thickness (OST) was maintained by selective reabsorption of the aperture ridge of the distal shell (aragonitic crossed-lamellar layer, CL) and by increased internal deposition of proximal (older) shell (aragonitic protocrossed lamellar, PCL). Despite greater exposure to acidification and hyposalinity, N. violaceum showed no significant compensatory shell thickening. These findings reveal that shell thickening capability may vary greatly among intertidal gastropods and that this may be constrained by environmental biomineralization substrate availability. Such environmentally-related responses carry implications for predicted future reductions in coastal water pH and salinity.

New genes helped acorn barnacles adapt to a sessile lifestyle.

Barnacles are the only sessile lineages among crustaceans, and their sessile life begins with the settlement of swimming larvae (cyprids) and the formation of protective shells. These processes are crucial for adaptation to a sessile lifestyle, but the underlying molecular mechanisms remain poorly understood. While investigating these mechanisms in the acorn barnacle, Amphibalanus amphitrite, we discovered a new gene, bcs-6, which is involved in the energy metabolism of cyprid settlement and originated from a transposon by acquiring the promoter and cis-regulatory element. Unlike mollusks, the barnacle shell comprises alternate layers of chitin and calcite and requires another new gene, bsf, which generates silk-like fibers that efficiently bind chitin and aggregate calcite in the aquatic environment. Our findings highlight the importance of exploring new genes in unique adaptative scenarios, and the results will provide important insights into gene origin and material development.

Machine learning-based design optimization of aperiodic multilayer coatings for enhanced solar reflection

Multilayered coatings are promising and successful for applications in semiconductors, optical mirrors, and energy harvesting technologies. Amongst these, optical mirrors are essential for passive radiative cooling. Building upon the multilayer radiative cooling systems observed in snails and drawing from previous research, this study showcases the efficacy of machine learning algorithms in optimizing and gaining insights into multilayer structures. Due to the constraint of low sky window emissivity in biologically found calcite shells, focusing on solar reflectance becomes crucial to maximize the biological phenomenon found in snails. The manual search of the periodic multilayer design space for calcite with air gaps points to the maximum solar reflectance of ∼89% at 170 nm layer thickness for 20 μm coating. To unlock the full potential of these multilayers, we then employ machine learning-based evolutionary optimization method - a genetic algorithm. The optimized aperiodic coating shows a significant enhancement of solar reflectance to ∼99.8% for a 20 μm coating. Interestingly, the same average layer thickness of 170 nm provides maximum solar reflectance in 20 μm periodic and aperiodic calcite multilayer. Investigation of the spectral reflectance shows that layer thickness is crucial in tuning the solar reflectance. For small coatings, wavelengths with higher solar intensity are prioritized. Increasing the coating thickness allows inclusion of thicker layers to reflect longer wavelengths, leading to increasing trend of average calcite layer thickness. Further work exploring radiative cooling materials shows that calcite and barium sulfate reflect sunlight significantly better than silicon dioxide due to their refractive index contrast. Our findings and insights using bio-inspired design can provide superior solar reflectance utilizing thin coatings with modern manufacturing technology.

Morphological features of the cuticle of hatching eggs of chickens and turkeys subjected to pre-incubation treatment

Improving the productivity of poultry, especially egg crosses, depends on the quality of the bioceramic calcite (CaCO3) layers and surface glycoprotein film of the egg (cuticle). These are the barriers that control the flow of gases and water vapor. Any disruptions in the transport process can lead to a significant reduction in egg hatchability. It has been proven that treatment of chicken and turkey eggs with acid solutions (acetic acid or hydrochloric acid) and sodium hypochlorite prior to hatching has increased egg hatchability compared to the control. In view of this, the aim of this study was to investigate the protective structures of incubation eggs of chickens and turkeys using non-destructive electron microscopic methods and computer processing of digital images of the cuticle coatings of these eggs for reliable prediction of the degree of increase in gas permeability of the cuticle-shell system due to the destructive effect of various chemicals, including disinfectants, for pre-hatching egg treatment. In the experiments, hatching eggs of Leghorn White hens (n = 90) 15–20 weeks of laying and Broad Breasted White turkeys (n = 80) were used. The antimicrobial agents used in the experiments were a 0.6% solution (0.08 mol/L) of sodium hypochlorite, a 2.5% solution (0.4 mol/L) of acetic acid, and a 5.0% solution (1.40 mol/L) of hydrochloric acid. Using the computer analysis of digital electron microscopic images of the egg surface with the software packages Visilog and FemtoScan Online, it was experimentally proved that the destructive effect of these substances on the cuticle-shell system increases in the range of sodium hypochlorite < hydrochloric acid < acetic acid, which positively correlates with the gas permeability of hatching eggs of chickens and turkeys and the egg hatchability index. The presence of fundamentally different morphological features and correlations of the cuticle of chicken and turkey eggs in response to the action of acids and oxidants used for pre-hatching treatment was shown. The digital markers of the cuticle-shell system state, obtained from analytical programs of digital images, have been established, which makes it possible to reliably predict the indicators of increasing the hatchability of chicken and turkey eggs under the conditions of using certain chemicals. The prospect of further research is to study the effect of modern complex antimicrobial agents on the hatchability of poultry eggs of different species.

Evidence of a Scheduled End for Prism Growth in the Shell of Pinctada margaritifera: Closure of the Calcite Biomineralization Area by a Specific Organic Membrane

The shell of the pearl oyster Pinctada margaritifera is made up of two layers: an outer layer of calcite prisms and an inner layer of aragonite tablets. Recent studies have shown that the calcite layer develops in a series of steps. We found that the end of prism growth and the start of aragonite deposition are also complex processes. Contrary to the common belief that prism growth is interrupted by the expansion of the aragonite layer, we found that a specific membrane covers the calcite surface before aragonite deposition starts. The earliest aragonite depositions occur as granular spots located only on the surfaces covered by this organic membrane This membrane appears to be the final stage of the calcite biomineralization cycle. This new understanding of calcite development has implications for shell biomineralization research and the production of pearls.

Ubiquitous occurrence of organogenic dolomite in a late Ediacaran limestone-dominated succession from the Eastern Yangtze Gorges area of South China

The widespread occurrence of dolostones in Paleozoic and Precambrian sequences stands in stark contrast to the difficulty of precipitating dolomite in experiments at low temperature under abiotic conditions. The discoveries of dolomite within modern microbial mats and the successful synthesis of proto-dolomite under ambient conditions catalyzed by various microorganisms and organic molecules lend support to the development of organogenic dolomite models. Despite this, convincing evidence for ancient primary dolomite precipitation is rare, mainly due to post-depositional modifications of original textures and mineralogy. Here we present petrographic, mineralogical and C-isotopic data of carbonates preserving primary sedimentary textures in the late Ediacaran Shibantan Member of the Dengying Formation from the eastern Yangtze Gorges area, South China. These carbonates are characterized by calcite layers intercalated with millimeter-thick, organic-rich layers that contain up to 50 % dolomite. Petrographic observations and Raman imaging show that the dolomite occurs preferentially in microbial mats and is closely associated with organic matter. Scanning electron microscopy also revealed the presence of Mg-rich nanoscopic carbonate aggregates and ribbon-like microstructures akin to mineralized extracellular polymeric substances (EPS) in mat layers. These observations are inconsistent with replacive origins but instead support an organogenic origin for the Shibantan dolomite. The relatively high TOC (total organic carbon) contents and consistently positive δ13Ccarb values (up to +4.8 ‰) suggest enhanced burial of organic carbon produced in microbial mats during the Shibantan deposition. Subsequent organic degradation by microorganisms in anoxic, early diagenetic environments likely promoted the ubiquitous formation of organogenic dolomite in Shibantan microbial mats. Our study highlights the important roles of organogenic dolomites in interpreting the wide occurrence of Paleozoic and Precambrian dolostones.

Multitechnique characterization of secondary minerals near HI-SEAS, Hawaii, as Martian subsurface analogues

Secondary minerals in lava tubes on Earth provide valuable insight into subsurface processes and the preservation of biosignatures on Mars. Inside lava tubes near the Hawaii-Space Exploration and Analog Simulation (HI-SEAS) habitat on the northeast flank of Mauna Loa, Hawaii, a variety of secondary deposits with distinct morphologies were observed consisting of mainly sodium sulphate powders, gypsum crystalline crusts, and small coralloid speleothems that comprise opal and calcite layers. These secondary deposits formed as a result of hydrological processes shortly after the formation and cooling of the lava tubes and are preserved over long periods of time in relatively dry conditions. The coralloid speleothem layers are likely related to wet and dry periods in which opal and calcite precipitates in cycles. Potential biosignatures seem to have been preserved in the form of porous stromatolite-like layers within the coralloid speleothems. Similar secondary deposits and lava tubes have been observed abundantly on the Martian surface suggesting similar formation mechanisms compared to this study. The origin of secondary minerals from tholeiitic basalts together with potential evidence for microbial processes make the lava tubes near HI-SEAS a relevant analog for Martian surface and subsurface environments.

Preparation of infiltrating calcium carbonate layer in gypsum substrate using novel calcium precursor: The implication for the protection of the surface weathered carbonate heritages from water erosion damage

Surface gypsification is a common problem for calcium carbonate historic construction materials. In this paper, a calcium carbonate protective layer was prepared in gypsum substrate using alcohol solution of calcium hydroxy glycolate. The concentration and penetration depth of alcohol solution of calcium hydroxy glycolate are as high as 2.0 M and 18.0 mm, respectively, which guarantees the sufficient introduction of calcium precursor at single treatment. Additionally, after introducing into gypsum substrate, calcium hydroxy glycolate can be transformed into calcium carbonate layer in the open air only when water was introduced subsequently, indicating that the calcium hydroxy glycolate is completely controllable in application. The results of FT-IR, SEM-EDX, XRD, IC and conductivity demonstrate that the prepared stable calcite layer can prevent the gypsum substrate from water corrosion efficiently. This exploring study provides a new solution for the protection of surface gypsification carbonate materials in the ancient constructions and relics.

Two-layer reconstruction of Raman spectra in diffusive media based on an analytical model in the time domain.

We derive and validate an analytical model that describes the migration of Raman scattered photons in two-layer diffusive media, based on the diffusion equation in the time domain. The model is derived under a heuristic approximation that background optical properties are identical on the excitation and Raman emission wavelengths. Methods for the reconstruction of two-layer Raman spectra have been developed, tested in computer simulations and validated on tissue-mimicking phantom measurements data. Effects of different parameters were studied in simulations, showing that the thickness of the top layer and number of detected photon counts have the most significant impact on the reconstruction. The concept of quantitative, mathematically rigorous reconstruction using the proposed model was finally proven on experimental measurements, by successfully separating the spectra of silicone and calcium carbonate (calcite) layers, showing the potential for further development and eventual application in clinical diagnostics.

Mineralogical and chemical composition of Arctic gastropods shells

Assessment of environmental controls and natural variability of shell chemistry is inevitable to understand the future of marine calcifiers functioning under the climate change and acidification scenarios. Here we document mineralogical and chemical composition (Al/Ca, Ba/Ca, Fe/Ca, Mg/Ca, Mn/Ca, Na/Ca, P/Ca, S/Ca, Sr/Ca and Zn/Ca ratios) of shells of 27 gastropod species collected in four Arctic and sub-Arctic coastal localities. Most examined gastropods had purely aragonitic shells, although three species were characterized by bimineralic mineralogy, with calcite forming the external shell layer. Positive relationship between shell size and proportion of calcite in bimineralic gastropods indicated that older specimens could possess a thicker outer shell layer of calcite than did younger individuals. Statistically significant differences in shell chemical composition were found among species irrespective of the sampling location, suggesting that organisms exerted a biological control on elements uptake and retention. Extrinsic factors (mostly seawater temperature, seawater and sediment metals concentrations) contributed to elements uptake to a lesser degree. Thus, the observed differences in shell elements’ concentrations among gastropod species can be driven by both factors: species-specific selective incorporation of elements into shells and bioavailability of those elements in the ambient environment.

Preparation of a new calcite layer from calcium glycolate for the conservation of sulfated limestone artifacts

AbstractA novel preparation method of calcite layer was explored for the conservation purpose of the surface sulfation limestone artifacts. In this method, the alcoholic solution of calcium glycolate was used as a precursor of calcite layer. After application on the surface of gypsum crust on limestone by spraying, calcium glycolate can combine with the carbon dioxide spontaneously and form a compact calcite layer. The obtained calcite layer can act as a shelter and can prevent the gypsum crust from the dissolution damage of the natural precipitation. The protective properties of the calcite layer were investigated by scanning electron microscopy with energy dispersive X‐ray spectroscopy (SEM/EDS), X‐ray diffraction (XRD), infrared spectroscopy (FTIR), water erosion resistance, water absorption, colour difference, surface strength, and hardness test. The results revealed that the water erosion resistance, surface strength, and hardness of the treated sample were increased remarkably. Meanwhile, the intrinsic physical properties such as porosity, capillary absorption, and appearance were not affected obviously, indicating a good compatibility of the proposed protection method.

Taxonomic revision of the canaliculate radiolitid (rudist, bivalve) genus Lattenbergites Lupu, 1987 from the Upper Cretaceous of the central and eastern Mediterranean Tethys: palaeobiogeographic distribution

Lattenbergites Lupu was previously considered to be a new genus of canaliculate radiolitid from the middle–upper Coniacian of Lattenberg, Germany. The re-examination of the holotype and paratypes of the type species L. hermi Lupu of this genus reveals diagnostic characters of Joufia milovanovici (Slišković), including the presence in the left valve of a single ring of radial canals in the calcitic outer shell layer, the canals having sub-rectangular cross-sectional shape flanking the myocardinal apparatus in the originally aragonitic inner shell layer, and a pair of tubular structures in its postero-ventral part, opposing the ‘pseudopillar’-like structures of the right valve. Therefore, we propose that Lattenbergites Lupu, is a junior synonym of Joufia milovanovici. J. milovanovici from the Malatya, Haymana-Polatlı Basins and eastern Pontides of Türkiye, as well as the Roşia Basin of Romania is also described and compared to Lattenbergites. The presence of J. milovanovici in the Northern Calcareous Alps during the middle–late Coniacian, Romania during the late Santonian to early–middle Campanian, and Türkiye during the late Maastrichtian, allows us to reconsider the palaeobiogeographic distribution of this species within the Mediterranean Tethys during Late Cretaceous time, as well as for the genus Joufia.

Organic-rich bimineralic ooids record biological processes in Shark Bay, Western Australia.

Marine ooids have formed in microbially colonized environments for billions of years, but the microbial contributions to mineral formation in ooids continue to be debated. Here we provide evidence of these contributions in ooids from Carbla Beach, Shark Bay, Western Australia. Dark 100-240 μm diameter ooids from Carbla Beach contain two different carbonate minerals. These ooids have 50-100 μm-diameter dark nuclei that contain aragonite, amorphous iron sulfide, detrital aluminosilicate grains and organic matter, and 10-20 μm-thick layers of high-Mg calcite that separate nuclei from aragonitic outer cortices. Raman spectroscopy indicates organic enrichments in the nuclei and high-Mg calcite layers. Synchrotron-based microfocused X-ray fluorescence mapping reveals high-Mg calcite layers and the presence of iron sulfides and detrital grains in the peloidal nuclei. Iron sulfide grains within the nuclei indicate past sulfate reduction in the presence of iron. The preservation of organic signals in and around high-Mg calcite layers and the absence of iron sulfide suggest that organics stabilized high-Mg calcite under less sulfidic conditions. Aragonitic cortices that surround the nuclei and Mg-calcite layers do not preserve microporosity, iron sulfide minerals nor organic enrichments, indicating growth under more oxidizing conditions. These morphological, compositional, and mineralogical signals of microbial processes in dark ooids from Shark Bay, Western Australia, record the formation of ooid nuclei and the accretion of magnesium-rich cortical layers in benthic, reducing, microbially colonized areas.

Effect of curing temperatures and additional activators on chloride ingress and its induced mineralogical alteration of ground granulated blast furnace slag activated by Ca(OH)2

The impact of additional activators (sodium sulfate, sodium nitrite, and calcium nitrite) and curing temperature (20 and 35 °C) on chloride binding and ingress resistance of ground granulated blast furnace slag activated by Ca(OH)2 was studied using X-ray diffraction, scanning electron microscopy, thermogravimetric and thermodynamic modeling. The outcomes of the study indicated that the difference in the chloride binding capacity at low chloride concentrations was primarily affected by the types of the AFm phase. The solid solution formed between Friedel's salt and various types of AFm phases resulted in a decrease in the chloride binding capacity. At a curing temperature of 35 °C, the chloride binding capacity reduced due to the leaching of calcium ions and carbonation induced by the coarse pore structure. It was found that the chloride ingress resistance was significantly related to the leaching of calcium and carbonation, and the denser calcite layer formed at the exposure layer had a positive impact on the chloride ingress resistance.

Factors determining persistent asymmetry and egg shape in birds: A hypothesis

The shape of birds' eggs has fascinated scientists for many years. It is now possible mathematically to describe shape accurately, allowing exploration of the physical and ecological factors driving the evolution of egg shape. However, there has been relatively little consideration of how egg shape is established in the oviduct or, given that even without an external calcitic layer eggs retain their shape, how shape is fixed in the isthmus. This paper proposes a hypothesis that attempts to explain how egg shape is established and fixed in the oviduct. The hypothesis suggests that as the egg mass (i.e. yolk and albumen) moves from the magnum into the isthmus, it is squeezed by the physical restriction imposed by the isthmus lumen and cannot easily move into the isthmus. As the leading edge of the egg mass enters the isthmus, the egg mass in the distal magnum is forced to bulge outwards, resulting in an asymmetrical shape. The various egg shapes observed in birds are, hence, produced by the interaction between the size of the egg mass relative to female body mass, and the degree of the restriction of the isthmus. Thus, a large egg mass, i.e. relative to female body mass, entering a narrow isthmus will produce a pointed egg shape. If the egg mass is relatively small, and the isthmus lumen wide, more of the egg mass could enter the isthmus and the degree of asymmetry would be reduced. It is further proposed that egg shape is fixed during the formation of the shell membranes in the isthmus because the constituent protein fibres permanently stick together as they are deposited. For the first time this hypothesis helps explain the pattern of deposition and characteristics of the calcitic egg in relation to the diversity of egg shapes in birds and reptiles.

Late Quaternary carbonate microbialite complex on the west shore of Great Salt Lake, Utah, USA

ABSTRACTA Late Pleistocene carbonate microbialite complex at Death Point on the western shore of Great Salt Lake, UT, USA, coats Paleozoic bedrock over an area 70 × 40 m. The complex largely formed while Lake Bonneville flooded the basin. Three distinct stratigraphic units separated by minor unconformities have been identified. The oldest unit (Unit 1) occurs over the entire outcrop area and ranges from 10 cm to 2.5 m in thickness. It precipitated as aragonite in the wave‐agitated shoreline environment during the early transgressive phase of Lake Bonneville and was subsequently pervasively dolomitized. Some near‐vertical faces of Unit 1 are overlain by an 8‐cm‐thick calcite microbialite (Unit 2) precipitated in deeper water of the regressive phase of Lake Bonneville. The youngest microbialite unit (Unit 3) overlies the calcite layer and precipitated as aragonite when the lake had dropped to levels similar to those of modern Great Salt Lake. The elevation, stratigraphy, distinct mineralogical layers, diagenetic history and long depositional span distinguish the Death Point microbialite complex from other microbialites in the Lake Bonneville/Great Salt Lake lacustrine system. The geochronology of Death Point microbialite will lead to modifications of the Lake Bonneville hydrograph, showing significantly lower lake levels in the early‐transgression stage.

Inhibition of Mg corrosion in physiological fluids by carbonate coating

Corrosion protective coatings were grown on pure magnesium in naturally carbonated mineral water containing Ca2+ using a simple, green conversion method. Dissolution of the native corrosion product, Mg(OH)2, mediates the surface nucleation of hydroxycarbonates. The pH increase due to CO2 degassing to atmospheric pressure leads to calcium carbonate nucleation and lateral growth by the incorporation of nanoparticles in a continuous layer of calcite -Ca(Mg)CO3- microcrystals. The coated surfaces have a much improved corrosion resistance in physiological fluids, measured by EIS, weight loss, corrosion rates and hydrogen release. Cell viability/morphology assessment demonstrates that the coating is non-toxic and promotes the proliferation of osteoblastic cells.