Carbonate Production Research Articles

Effect of operating pressure on design of extractive distillation process separating DMC-MeOH azeotropic mixture

Although dimethyl carbonate is defined as a green chemical, separation of dimethyl carbonate-methanol azeotropic mixture is an important issue for many dimethyl carbonate production processes. Extractive distillation process is considered as a favorable method for separating this mixture, but the recovery of entrainer still results in a significant loss of capital and operating costs. On the other hand, operating pressure is an important design variable for distillation columns since it has an important impact on column temperature and phase equilibrium. In this work, the effect of operating pressure is investigated for an extractive distillation process separating the dimethyl carbonate-methanol mixture using methyl isobutyl ketone as entrainer. It is observed that the increase in the operating pressure of extractive distillation column significantly decreases the amount of required entrainer flowrate. As the result, a process with an extractive distillation column operating at 10 bar reduces total annual cost and carbon dioxide emissions by 34.1% and 29.8%, respectively compared to the conventional process with an extractive distillation column operating at atmospheric pressure.

Decrease in volume and density of foraminiferal shells with progressing ocean acidification

Rapid increases in anthropogenic atmospheric CO2 partial pressure have led to a decrease in the pH of seawater. Calcifying organisms generally respond negatively to ocean acidification. Foraminifera are one of the major carbonate producers in the ocean; however, whether calcification reduction by ocean acidification affects either foraminiferal shell volume or density, or both, has yet to be investigated. In this study, we cultured asexually reproducing specimens of Amphisorus kudakajimensis, a dinoflagellate endosymbiont-bearing large benthic foraminifera (LBF), under different pH conditions (pH 7.7–8.3, NBS scale). The results suggest that changes in seawater pH would affect not only the quantity (i.e., shell volume) but also the quality (i.e., shell density) of foraminiferal calcification. We proposed that pH and temperature affect these growth parameters differently because (1) they have differences in the contribution to the calcification process (e.g., Ca2+-ATPase and Ω) and (2) pH mainly affects calcification and temperature mainly affects photosynthesis. Our findings also suggest that, under the IPCC RCP8.5 scenario, both ocean acidification and warming will have a significant impact on reef foraminiferal carbonate production by the end of this century, even in the tropics.

Calcium carbonate production in the southernmost subtropical Atlantic coral reef

Emerging evidence have been supporting the idea that the better known South Atlantic coral reefs (located between 18°S and 24°S) are now essentially senescent structures that have experienced little or no additional vertical reef growth over the past millennia. This has often coincided with a shift to a dominance of non-coral calcifying organisms becoming the main CaCO3 producers in these high latitude and marginal marine settings. Here, we used Calcification Accretion Units (CAUs) and census-based methods to measure non-coral rates of CaCO3 production on the geologically senescent reef and adjacent rhodolith beds within the southernmost subtropical Atlantic reef (i.e., Queimada Grande Reef, QGR). The reef habitat is currently producing CaCO3 at rates of ∼126 g m−2 yr−1. In contrast, fragments of dead corals skeletons deposited adjacent to the reef over the last ∼2000 years are now colonized by crustose coralline red algae. These form a rhodolith bed that produces CaCO3 at rates of 858 g m−2 yr−1. Our results indicate that, whilst not sufficient to promote active net framework accumulation, CaCO3 production by coralline algae and bryozoans on the QGR appears to be sufficient to at least limit net large-scale erosion of the underlying reef structure, allowing the reef structure to persist in a state close to budgetary stasis. Finally, our results are also of relevance for providing insights regarding the balance of CaCO3 production/dissolution/erosion processes in coral reefs, especially in these less understood marginal reefs.

The role of phosphate on non-skeletal carbonate production in a Cretaceous alkaline lake

Alkaline carbonate-rich systems may, under some circumstances, result in significant accumulation of aqueous phosphorus. Additionally, the geochemistry of modern alkaline lakes, combined with current understanding of CaCO3 precipitation kinetics, indicates that the establishment of high alkalinity, high dissolved inorganic carbon (DIC), and CaCO3 supersaturation require compounds that inhibit or interfere with CaCO3 precipitation. Furthermore, the interplay between these factors may potentially affect fabric development in non-skeletal carbonates. In order to understand how these interlinked processes may have regulated PO4 concentrations and the processes and products of non-skeletal CaCO3 precipitation in the distant past, we conducted a detailed geological and geochemical study in two cores drilled in different portions of the Santos Basin, offshore southeastern Brazil, consisting of lacustrine carbonate rocks from the Lower Cretaceous Barra Velha Formation. We find that phosphorus in the sediments comes from two main products, phosphatic bioclasts and authigenic phosphate (of both primary and diagenetic origins). We also find that phosphorus occurs in concentrations of up to several thousand ppm in some intervals and is preferentially associated with some calcite textures potentially reflecting the primary sedimentary depositional conditions (e.g., upward-radiating aggregates of fibrous calcite, or “shrubs” and spherulitic aggregates of fibrous calcite, or “spherulites”). Microanalytical data from selected samples and high-Mg CaCO3 textures show median P values can be particularly high in crusts, shrubs and spherulitic calcite minerals interpreted here to have formed as primary to early diagenetic deposits, and roughly vary between 1000 and 2000 ppm (10.5–21.1 mmol/kg). The average P/(Ca + Mg) molar ratio values based on the same data for these three calcite textures are 1.45 ± 0.98, 1.13 ± 0.97 and 1.09 ± 0.90 mmol/mol, respectively, being as high as 4.80 mmol/mol in specific spots in “shrubby” textures. Although multiple source-to-sink mechanisms were likely involved in the P budget in lake waters and in the sediments, such as recycling and remobilisation of skeletal- and organic-bound phosphate, high alkalinity may have enhanced its accumulation in the lake’s waters. In light of current understanding of CaCO3 precipitation kinetics, we hypothesise that phosphate may have played a central role in maintaining high calcium carbonate saturation (14–45 < Ωcalcite ≤ 100–180). These conditions would have favoured growth of calcite crystals on pre-existing substrates over nucleation of finely particulate carbonate sediment. By combining these observations with theoretical geochemical considerations, we propose that phosphate inhibition of calcium carbonate precipitation was enhanced by high alkalinity, further sustaining CaCO3 supersaturation and favouring distinctive carbonate growth textures. This unique and relatively well-preserved example of non-skeletal carbonate production implies that similar regulation of CaCO3 precipitation kinetics and PO4 concentrations may have operated across other intervals of time in Earth’s history, both in non-marine and marine environments that pre-date the emergence of skeletal calcification.

Miocene paleoceanographic evolution of the Mediterranean area and carbonate production changes: A review

Miocene is a key interval in the global climate evolution as well as in the geodynamic evolution of the Mediterranean basin. Therefore, global and regional factors controlled Miocene Mediterranean oceanography, which, in turn, affected carbonate production. In this work, we review the Miocene paleocenographic evolution of the Mediterranean starting from its Sr and Nd isotope records. Secondly, we discuss Mediterranean shallow-water carbonate production changes to identify the role of oceanographic conditions in controlling carbonate systems' evolution. During Aquitanian, Sr and Nd isotope records attest an open Mediterranean, mainly fed by the Indian Ocean. From the late Burdigalian, the intermittent connection with the Indian Ocean changed the overall circulation in the basin, leading to higher residence time of waters and smaller water exchanges with the adjacent oceans. In this newly established paleoceanographic framework, regional factors such as volcanism, significantly affected Mediterranean seawater chemistry. Local tectonics led to the development of small sub-basins in the Eastern Mediterranean, characterized by restricted water exchanges from the Tortonian in the easternmost part, to the early Messinian, as attested by the deviation of the Sr isotope record of the proto-Adriatic basin. Larger Benthic Foraminifera (LBF) assemblages dominated carbonate production in the Aquitanian, while they were the most affected by the Indo-Pacific closure, showing a demise after the Burdigalian. With the LBF demise, red algae and bryozoans dominated carbonate ramps from the middle Miocene to the Tortonian. Bryozoans in particular spread during the Monterey Event, favoured by global and regional factors. During early to middle Miocene, corals formed mounds in the oligophotic zone or coral carpets controlled by local conditions. Conversely, in the late Tortonian-early Messinian, they developed as huge reef complexes in the Western and Central Mediterranean, with the exception of small restricted sub-basins, such as the proto-Adriatic basin, where red algae and small benthic foraminifera persisted.

Seagrass development in terrigenous‐influenced inner ramp settings during the middle Eocene (Urbasa–Andia Plateau, Western Pyrenees, North Spain)

AbstractSince their first occurrence in the late Cretaceous, seagrasses have played a major role in carbonate production and sedimentation across shallow‐water and nearshore environments, sustaining a prolific carbonate factory and contributing to sediment accumulation through the combination of baffling and trapping effects. Most reported Palaeogene seagrass occurrences developed in oligo−mesotrophic shallow warm‐water habitats and are characterized by distinct associations of small and larger benthic foraminifers adapted to low terrigenous influence. This study describes a number of seagrass episodes interbedded in the Bartonian (middle Eocene) of San Fausto–Lazkua area (Navarra region, North Spain), within a nearshore to inner‐ramp succession that, in spite of being deposited under general transgressive conditions, was highly influenced by terrigenous supply from the adjacent land. Up to twelve different seagrass bed intervals occur interbedded in a cyclical manner with high‐energy nearshore siliciclastics and inner ramp bioclastic carbonates rich in mesophotic−oligophotic foraminifers and heterozoan biota (red algae, echinoderms, bryozoans). Seagrass deposits exhibit typical unsorted textures, abundant bioturbation and moderate to high terrigenous content, and comprise a characteristic skeletal association of epiphytic foraminifers, red algae and, most particularly, of abundant encrusting acervulinids, commonly with distinct hooked and tubular growth forms. This abundance of suspension‐feeders relative to autotrophs and mixotrophs may be indicative of temperate waters, although the taxonomic diversity of the foraminiferal assemblages in both seagrass and non‐seagrass embedding deposits supports the interpretation of shallow, warm‐water conditions. The studied seagrass deposits provide evidence that high siliciclastic supply and associated nutrient input may determine the occurrence of temperate‐like seagrass deposits in warm‐water settings, analogous to extensive heterozoan carbonate production in modern shallow‐tropical environments. Thus, the identification and correct interpretation of past seagrass‐vegetated environments are crucial for reconstructing palaeoecological conditions in ancient shallow‐marine environments. Therefore, in comparison with carbonate‐dominated environments, the mixed terrigenous−carbonate seagrass deposits are volumetrically less important, presenting a more irregular, patchy distribution, and a skeletal assemblage dominated by heterotrophs, regardless of the water temperature.

Inferring time averaging and hiatus durations in the stratigraphic record of high‐frequency depositional sequences

AbstractA sequence stratigraphic framework predicts that time averaging and hiatus durations will be long at times of fastest sea‐level rise. This prediction does not necessarily apply to environments where carbonate production keeps up with sea‐level rise and where undetected hiatuses decouple short‐term from long‐term sedimentation rates. The taphonomic clock, however, which measures the residence time of skeletal particles in the mixed layer, can estimate the duration of hiatuses if the rate of skeletal alteration is slow and if skeletal particles endure long‐term exposure in the mixed layer. Here, time averaging is calibrated by using evidence from alteration of bivalves in a metre‐scale Holocene sequence in the Adriatic Sea. In this sequence, transgressive molluscan lags, a maximum‐flooding zone shell bed with bivalves, and highstand bryomol assemblages were all deposited under similar long‐term sedimentation rates (ca0.01 to 0.03 cm year−1) and exhibit millennial time averaging. Median ages of valves stained by pyrite and cemented by high‐magnesium calcitic micritic envelopes exceedingca1000 years indicate that: (i) these authigenic processes are slow in subsurface zones with reducing conditions (with prolonged sulphate reduction and carbonate ions sourced from dissolved shells in the surface zones); and (ii) subsurface micrite precipitation prolongs the disintegration half‐lives of valves exhumed to surface zones from decades to millennia. The high abundance of stained valves, valves with micrite envelopes, and valves with composite alteration (encrusters and borers colonizing stained and cemented grains) thus identifies hiatuses and skeletal concentrations time‐averaged to &gt;1000 years. The upcore decrease in abundance of valves with composite alteration, coupled with temporally‐constant long‐term sedimentation rates and time averaging, indicates that a temporal decline in sediment exhumation was compensated by a decline in burial of skeletal carbonate produced by molluscs.

Thermal stress reduces carbonate production of benthic foraminifera and changes the material properties of their shells

Abstract In shallow marine environments, benthic foraminifera are important foundation species and carbonate producers. Understanding their response to future climate is often drawn from their acclimation potential in short laboratory experiments, thereby limiting our understanding of migration, species replacement, and adaptive potential. To overcome this challenge, we examine two species of benthic foraminifera from a thermally polluted field site mimicking future warming. This site and a control station cover 13–36°C causing both warm and cold stress to the local species. Computer Tomography reveals that under heat stress, even with acclimation, Lachlanella significantly reduced its shell volume. In contrast, Pararotalia calcariformata did not reduce its shell volume but reduced the relative amount of calcite with respect to shell volume and changed its reproduction cycle from twice to once per year. Raman spectroscopy indicates that thermal conditions alter the chemical composition of the calcite shells of both species. Calcification during thermal stress creates alterations in the crystal structure that are unexpectedly more prominent under cold stress than warm stress indicating warming might positively affect the shell's protective function. Supported by previous laboratory experiments and observations from the geological record, our results provide new perspective to the effect of warming on benthic foraminifera.

Performance of supported metal catalysts in the dimethyl carbonate production by direct synthesis using CO2 and methanol

CO2 chemical transformation is an exciting way to reduce CO2 concentration in the atmosphere. The use of CO2 to produce dimethyl carbonate (DMC), a linear, biodegradable, low toxicity carbonate via direct synthesis, is one of the most promising routes from the environmental point of view. However, DMC direct synthesis presents obstacles such as unfavorable thermodynamics and catalytic deactivation due to the water produced as a by-product. Therefore, the development and optimization of a catalytic system that can overcome these obstacles are crucial. This study investigated the catalytic activity of iron nitrate (AC-Fe), copper nitrate (AC-Cu), magnesium nitrate (AC-Mg), and nickel nitrate (AC-Ni) impregnated in activated carbon for DMC direct synthesis. Catalysts were synthesized by the impregnation method and characterized by several techniques. Simulation results evidenced the major reaction steps and simplified models of a complex involving metallic catalysts and reactants. The optimization of the catalyst amount, pressure, temperature, and recyclability of the best catalyst under optimized conditions and in the presence of different dehydrating agents was also performed. Results showed that the AC-Fe catalyst is the most efficient in the DMC direct synthesis, with a yield of 23.5 % and a selectivity of 100 % (80 °C, 40 bar, and 24 h). Reaction optimization (120 °C, 40 bar, and 24 h) using (AC-Fe) as catalyst resulted in a DMC yield of approximately 30 %. The catalytic systems recycling proved that using the dehydrating agent right combination (molecular sieve) and catalyst (AC-Fe) can maintain selectivity at 100 %, slightly decreasing yield.

Low calcification rate, structural complexity, and calcium carbonate production of Pocillopora corals in a biosphere reserve of the central Mexican Pacific

AbstractThe capacity of coral reefs to provide ecosystem services is widely recognized, but this ability depends on continued carbonate production within the coral community. The Islas Marías archipelago (21° 29.5′ N–106° 15′ W) is subject to minimal anthropic pressures. This archipelago serves as a model to study the influence of environmental variables [e.g., sea surface temperature (SST), upwelling periods, El Niño‐Southern Oscillation (ENSO) events, and pH] on the structure of the coral community. The aim of this study was to evaluate the growth parameters, ecological volume, and CaCO3 production of Pocillopora corals, which comprise the dominant genus in the Eastern Tropical Pacific (ETP). During an annual period (2016–2017), 10 colonies were stained with alizarin red and height, major diameter, and minor diameter measurements were recorded. Live coral cover, the annual extension rate (cm/year), skeletal density (g/cm3), the calcification rate (g/cm2 year−1), ecological volume (cm−3), and carbonate production (kg m−2 year−1) were also calculated. The average extension rate (± SD), skeletal density, and the calcification rate were 1.86 ± 0.31 cm/year, 2.28 ± 0.34 g CaCO3 cm−3, and 4.34 ± 1.28 g CaCO3 cm−2 year−1, respectively. The average live coral coverage was 3.19 ± 3.17%, and the relative cover of Pocillopora corals was 65%. Ecological volume increased 140.6 ± 84.28% with respect to the initial volume, and the average production of CaCO3 was 0.46 ± 0.41 kg CaCO3 m−2 year−1. This study shows evidence of low growth rates, low generation of three‐dimensionality, and low CaCO3 production in the study area when compared to other sites in the ETP. These results are relevant because they indicate compromised long‐term maintenance and reef development in Islas Marías, which may result in low reef functionality and compromise the stability of reef‐associated biodiversity and ecosystem services.

'Ten Years After'-a long-term settlement and bioerosion experiment in an Arctic rhodolith bed (Mosselbukta, Svalbard).

Rhodolith beds and bioherms formed by ecosystem engineering crustose coralline algae support the northernmost centres of carbonate production, referred to as polar cold-water carbonate factories. Yet, little is known about biodiversity and recruitment of these hard-bottom communities or the bioeroders degrading them, and there is a demand for carbonate budgets to include respective rates of polar carbonate build-up and bioerosion. To address these issues, a 10-year settlement and bioerosion experiment was carried out at the Arctic Svalbard archipelago in and downslope of a rhodolith bed. The calcifiers recorded on experimental settlement tiles (56 taxa) were dominated by bryozoans, serpulids and foraminiferans. The majority of the bioerosion traces (30 ichnotaxa) were microborings, followed by attachment etchings and grazing traces. Biodiversity metrics show that calcifier diversity and bioerosion ichnodiversity are both elevated in the rhodolith bed, if compared to adjacent aphotic waters, but these differences are statistically insignificant. Accordingly, there were only low to moderate dissimilarities in the calcifier community structure and bioerosion trace assemblages between the two depth stations (46 and 127m), substrate orientations (up- and down-facing) and substrate types (PVC and limestone), in that order of relevance. In contrast, surface coverage as well as the carbonate accretion and bioerosion rates were all significantly elevated in the rhodolith bed, reflecting higher abundance or size of calcifiers and bioerosion traces. All three measures were highest for up-facing substrates at 46m, with a mean coverage of 78.2% (on PVC substrates), a mean accretion rate of 24.6gm-2 year-1 (PVC), and a mean bioerosion rate of -35.1gm-2 year-1 (limestone). Differences in these metrics depend on the same order of factors than the community structure. Considering all limestone substrates of the two platforms, carbonate accretion and bioerosion were nearly in balance at a net rate of -2.5gm-2 year-1 . A latitudinal comparison with previous settlement studies in the North Atlantic suggests that despite the harsh polar environment there is neither a depletion in the diversity of hard-bottom calcifier communities nor in the ichnodiversity of grazing traces, attachment etchings and microborings formed by organotrophs. In contrast, microborings produced by phototrophs are strongly depleted because of limitations in the availability of light (condensed photic zonation, polar night, shading by sea ice). Also, macroborings were almost absent, surprisingly. With respect to carbonate production, the Svalbard carbonate factory marks the low end of a latitudinal gradient while bioerosion rates are similar or even higher than at comparable depth or photic regime at lower latitudes, although this might not apply to shallow euphotic waters (not covered in our experiment), given the observed depletion in bioeroding microphytes and macroborers. While echinoid grazing is particularly relevant for the bioerosion in the rhodolith bed, respective rates are far lower than those reported from tropical shallow-water coral reefs. The slow pace of carbonate production but relatively high rates of bioerosion (both promoted by low carbonate supersaturation states in Arctic waters), in concert with high retention of skeletal carbonates on the seafloor and no calcite cements forming in open pore space created by microborers, suggest a low fossilisation potential for polar carbonates, such as those formed in the Mosselbukta rhodolith beds.

Mechanism of CaO catalyst deactivation with unconventional monitoring method for glycerol carbonate production via transesterification of glycerol with dimethyl carbonate

Glycerol carbonate (GC) was synthesized by transesterification of glycerol with dimethyl carbonate (DMC) using calcium oxide (CaO) derived from eggshell as a catalyst. The best results of 96% glycerol conversion and 94% GC yield were achieved under the following reaction conditions: 0.08 mole ratio of CaO to glycerol, 1:2.5 mole ratio of glycerol to DMC, 60°C reaction temperature, and 3 hours reaction time. As expected, CaO showed deteriorated catalytic performance when recycling as observed by a rapid decrease in GC yield. This research showed that the active CaO phase first was converted to calcium methoxide (Ca[OCH3]2) and calcium diglyceroxide (Ca[C3H7O3]2) and finally to carbonate phase (CaCO3) which can be confirmed by XRD patterns. According to the phase transformation, the basicity decreased from 0.482 mmol/g to 0.023 mmol/g, and basic strength altered from strong basic strength (15.0 < H_ < 18.4) to weak basic strength (7.2 < H_ < 9.8), resulting in the lower catalytic activity of the consecutive runs. Despite the fact that the GC selectivity was almost 100%, the reaction products (methanol and GC) were not obtained in their stoichiometric ratio and their extents corresponded with that of the catalyst phase transformation to CaCO3. The mechanism of CaO catalyzed transesterification based on the condensation reaction of glycerol and catalyst was proposed, and in situ formation of water-derivative species was hypothesized as a cause of CaO transformation. CaO could react with DMC and water, generating methanol and CaCO3. This enabled unconventional monitoring of catalyst deactivation by checking if the mole ratio of methanol to GC was higher than 2:1 of its reaction stoichiometric ratio. It was also demonstrated that calcination of post-run catalyst at 900°C to CaO exhibited almost constant catalytic activity, and the mole ratio of methanol to GC was constant at its reaction stoichiometry (2:1) for at least 4 times use.

Investigation and characterization of high purity and nano-sized SrCO3 production by mechanochemical synthesis process

In this study, the production of strontium carbonate (SrCO3) from concentrated celestite ore (SrSO4) by mechanochemical synthesis process was investigated. Different proportions of ammonium carbonate ((NH4)2CO3) were used to convert the celestite ore to strontium carbonate. The effects of SrSO4: (NH4)2CO3 stoichiometric ratio and synthesis time on the purity of the produced strontium carbonate were examined. In the mechanochemical synthesis experiments, the stoichiometric ratios of 1:1, 1:1.5 and, 1:2 between SrSO4 and (NH4)2CO3, and synthesis times of 10, 100, and 200 min were applied. Impurities and contaminations in concentrated celestite ore were removed by acid leaching and calcination processes. DTA, TGA, XRD, SEM, EDX, TEM, and FT-IR analyzes were performed throughout the strontium carbonate production process. Experimental studies have revealed that the 1:2 stoichiometric ratio between SrSO4 and (NH4)2CO3 and 200 min synthesis time are the most suitable process parameters for the production of high purity strontium carbonate.

Enzyme-mediated biocalcification by a novel alkaliphilic Bacillus psychrodurans LC40 and its eco-friendly application as a biosealant for crack healing

Biocalcification is a natural biochemical process, which has been regarded as a promising method for sequestering heavy metals or carbon dioxide in the environment, healing cracks in concrete structures, and stabilizing soil. One of the key factors in this process is calcium carbonate-producing bacteria. The purpose of this study was to maximize the production of calcium carbonate by alkaliphilic Bacillus psychrodurans LC40 isolated from a limestone cave, by manipulating the medium composition for fast and non-detrimental crack healing, and to investigate the mechanism of its production. Strain LC40 could grow well in the strongly alkaline region (pH 9.5–11), indicating its alkaliphilic nature. The optimal medium for calcium carbonate production contained 2% tryptone, 1.5% urea, 0.15% NaHCO3, and 150 mM calcium formate (pH 6). Using this medium, the yield of calcium carbonate at 72 h was approximately 8.6-fold higher than that obtained through Urea-CaCl2 medium. In this culture, the urease and carbonic anhydrase activities were observed simultaneously, and the pH of the medium was found to have increased to 9.4, leading to maximum calcium carbonate production. This suggests that this pH value is achieved by the synergistic action of the two enzymes, resulting in a high calcium carbonate yield. The crystals were characterized by FESEM, EDS and XRD, which confirmed the production of rhombohedral and spherical calcium carbonate crystals containing vaterite and calcite. Strain LC40 completely healed a 0.75 mm wide crack in a very short time of 3 days using the optimized medium as a cementation solution. Our findings indicate that B. psychrodurans LC40 could be a promising candidate for the development of eco-friendly biosealant applicable to environmentally stressed concrete structures.

Novel heterococcolithophores, holococcolithophores and life cycle combinations from the families Syracosphaeraceae and Papposphaeraceae and the genus &amp;lt;i&amp;gt;Florisphaera&amp;lt;/i&amp;gt;

Abstract. Coccolithophores are a diverse group of calcifying phytoplankton, which are responsible for a large part of the modern oceanic carbonate production. Here, we describe novel or poorly known coccolithophores and novel life cycle combination coccospheres detected in samples collected either in the Gulf of Aqaba in the northern Red Sea or in the Gulf of Naples in the western Mediterranean. These include Syracosphaera winteri, for which detached coccoliths have previously been recorded but both a formal description and taxonomic affiliation were lacking, and five undescribed sets of combination cells linking HET and HOL forms for S. pulchra, S. mediterranea, S. azureaplaneta, S. lamina and S. orbicula. We also propose the replacement name S. kareniae for the fossil species Deutschlandia gaarderae. We describe a new species of the genus Ophiaster, O. macrospinus, displaying a unique morphological and ecological distribution as well as putative combination cells of two variants of the deep-dwelling Florisphaera profunda, which provide new insights on the affiliation of this genus within the Calcihaptophycideae. Additionally, in the family Papposphaeraceae we detected a new species, Pappomonas vexillata, and combination cells of Picarola margalefi and of a species resembling Papposphaera arctica. Finally, we detected three novel, unpaired holococcolithophore forms (Calyptrosphaera lluisae, Calicasphaera bipora and one form designated as Holococcolithophore A). Overall, this set of novel observations and ensuing discussions provide further insights into the diversity, evolution and life cycle complexity of coccolithophores in the oceans.

Episodes of seabed rise and rapid drowning controlling the development of regressive and transgressive rhodolithic limestones in a tectonically-active subduction setting (Early Miocene, Wairarapa region, New Zealand)

ABSTRACT Early Miocene limestones from the Wairarapa region of New Zealand were deposited on thrust-bounded margins of trench-slope basins, and consist of two superposed stratal units, namely units A and B, interpreted as forced regressive and forced transgressive foralgal and rhodolith-bearing deposits, respectively. Unit A is floored by a regressive surface of marine erosion cut into shelfal to bathyal siliciclastic successions, and is overlain across a transgressive surface of erosion by Unit B. A drowning surface abruptly places the latter deposits in contact with deeper hemipelagites and turbidites. The succession is explainable within a tectono-eustatic based framework as follows: (1) Structurally controlled rapid relative sea-level fall, (i.e. sea-bed rise), from upper bathyal to shelfal depths promoted development of regressive (‘lowstand’) mixed carbonate–siliciclastic deposits. Continuation of seabed rise resulted in deposition of pure carbonate sediments, which are represented by channel-fill rhodolithic rudstones; (2) early stage of relative sea-level rise (i.e. seabed drowning) caused emplacement of transgressive glauconitic limestones, consisting of either foralgal deposits, or incised rhodolithic limestones; (3) continued relative sea-level rise terminated carbonate production. The present study documents carbonate production and termination in a tectonically active and confined intra-slope setting, reflected in the development and distribution of unusual forced regressive, and transgressive rhodolithic-heterozoan carbonates.

Variations in carbonate-evaporite shoreline and ramp facies trends: Middle Miocene Fatha Formation, Kurdistan Region, NE Iraq

A sedimentological investigation of Miocene deposits at the periphery of the Zagros foreland basin, Kurdistan Region, NE Iraq, reveals a cyclical arrangement of carbonate-evaporite ramp facies. The study aims to provide rare insight into the lateral variability of microfacies and environments of such systems' inner ramp and shoreline. Between 10 and 40 depositional cycles are preserved, separated by a flooding surface, and recording an overall basinward progradation. In each cycle, a shallowing-upward trend from a lower-energy calcareous mudstone and mudstone-wackestone carbonate microfacies at the base to a higher-energy packstone-grainstone-rudstone or low-energy algal mat/stromatolitic carbonate microfacies above is evident. Evaporite deposits of supratidal sabkha origin cap each carbonate deposit. Red clastic sediments that advanced south-westward into the basin from the adjacent Zagros hinterland overlie each evaporite deposit. A flooding surface and return to calcareous mudstones mark the start of the next cycle. Outcrop and thin-section analysis of the carbonate deposits of each cycle reveals a shoaling-up to inner-ramp facies with varied environmental settings that developed under a range of hydrodynamic conditions. Microfacies analysis indicates that these environments included normal marine salinity open lagoons, hypersaline lagoons, restricted and shallow lagoons, sand shoals, intertidal and supratidal flats, supratidal ponds, and a coastal alluvial plain that included channelised deposits and palaeosols. The cyclical facies trend changes toward the top of the succession in that the relative rate of siliciclastic supply markedly increased, whereas the rate of carbonate and evaporite production decreased. Progradation and shoreline migration through time caused lateral and vertical facies changes and thickness variations over the succession. Repeated relative sea-level changes, associated changes in climate, and variations in sediment supply from the hinterlands during the collision of the Arabian and Iranian plates, combined with a variable rate of accommodation generation, are inferred to have controlled the preserved cyclicity.

Exceptionally preserved calcified sponge assemblagesin Upper Jurassic carbonates of the eastern Getic Carbonate Platform (Southern Carpathians, Romania)

A rich poriferan assemblage was identified within the easternmost part of the Getic Carbonate Platform of Romania (Grădiștei Gorges). The excellent preservation state of most poriferans here led to the discovery of a new species (Neuropora gigantea Pleș &amp; Schlagintweit, n. sp.) and to the identification of previously unknown diagnostic features in some species (Sarsteinia babai Schlagintweit &amp; Gawlick, 2006 emend., Neuropora lusitanica Termier, 1985, Sphaeractinia steinmanni Canavari, 1893). Calciagglutispongia yabei Reitner, 1992, Sarsteinia babai and Sphaeractinia steinmanni are reported for the first time from the Upper Jurassic carbonates of the Getic Carbonate Platform. The sedimentary input fluctuations and the nutrient competition had an important role in understanding the morphological adaptations of the analysed species. The existing palaeoecological and palaeoenvironmental conditions generated different distribution patterns towards the reef profile and also preferential adaptations to a specific Tethyan domain. As opposed to the poriferan assemblages from the northern Tethyan shelves, these organisms formed sponge-coral-microencruster boundstones at the margins and fore-reefal zones of isolated carbonate platforms within the intra-Tethyan realm. The importance of calcified sponges in reef-zonation is highlighted by the establishment of a general zonation model. Three zones can be distinguished: 1) Cladocoropsis-Milleporidium zone (back-reef area); 2) Bauneia-Chaetetopsis-Parastromatopora zone (central reef area); and 3) Sphaeractinia/Ellipsactinia-Neuropora zone for the fore-reef area. In the absence of a true reef framework these calcified sponges developed typical morphologies, environmental adaptations and partnerships with other biotic groups which strongly influenced the carbonate production throughout the intra-Tethyan domain.

Contribution of bacterial cells as nucleation centers in microbiologically induced CaCO3 precipitation-A mathematical modeling approach.

The microbiologically induced calcite precipitation (MICP) has been extensively studied for geotechnical engineering through simultaneous action of natural phenomena and engineering processes. The focus of bacterial contribution to the MICP has been directed to calcium carbonate productivity, while the additional bacterial role as a crystal nucleation center was not explained especially from a mathematical prediction modeling point of view. Therefore, this study provides explanations and a mathematical modeling approach of bacterial influence on the MICP induced by newly-isolated ureolytic Bacillus strains and Sporosarcina pasteurii DSM 33. Using the obtained results of low-cost, rapid, and simple assays, artificial neural network modeling was applied for cell surface predispositions, pH changes as well as calcium-involved function in biofilm formation during the MICP, for the first time. Based on the obtained contribution of the alkalophilic/alkaloresistant bacteria, calcite precipitation can be significantly directed by the presence, of ureolytic bacterial cells as nucleation centers during CaCO3 precipitation as well as their morphology, surface characteristics, potential to form a biofilm, and/or generate pH changes.

Current and sea level control the demise of shallow carbonate production on a tropical bank (Saya de Malha Bank, Indian Ocean)

AbstractCarbonate platforms are built mainly by corals living in shallow light-saturated tropical waters. The Saya de Malha Bank (Indian Ocean), one of the world's largest carbonate platforms, lies in the path of the South Equatorial Current. Its reefs do not reach sea level, and all carbonate production is mesophotic to oligophotic. New geological and oceanographic data unravel the evolution and environment of the bank, elucidating the factors determining this exceptional state. There are no nutrient-related limitations for coral growth. A switch from a rimmed atoll to a current-exposed system with only mesophotic coral growth is proposed to have followed the South Equatorial Current development during the late Neogene. Combined current activity and sea-level fluctuations are likely controlling factors of modern platform configuration.