Marine Calcite Research Articles

Persistent late Tonian shallow marine anoxia and euxinia

The increase in the complexity of eukaryotic life during the Tonian Period (ca. 1000 to 720 Ma) is commonly associated with the oxygenation of the Earth’s ocean–atmosphere system, yet the timing and duration of these redox changes remain uncertain. In particular, it is unclear how shallow marine environments, which were likely crucial habitats for early eukaryotic organisms, responded to Neoproterozoic oxygenation. This study uses trace and rare earth element geochemistry to determine shallow marine redox conditions during the deposition of the late Tonian (ca. 760 Ma) Devede Formation, northern Namibia. In this unit, although carbonate phases (microbialite, former aragonite and high Mg calcite marine cements, and primary dolomite marine cements) generally exhibit no Ce/Ce* anomaly, rare negative values (up to 0.55) are consistent with short-lived periods of oxygenation. In contrast, the dominantly positive Eu/Eu* anomalies of the same phases suggest that basinal conditions were anoxic. These phases also exhibit low concentrations of redox-sensitive (U, V, Mo) and chalcophile (Co, Cu, Cd, Zn, Pb) elements, suggesting that euxinic conditions were predominant during the deposition of the Devede Formation. Integration of this data (Ce/Ce* and Eu/Eu*) with that of analogous late Tonian (ca. 840 to 731 Ma) carbonate strata reveals that shallow marine settings were characterised by persistent anoxia and euxinia, suggesting that any potential increase in atmospheric O2 ca. 800 Ma (e.g. the Bitter Springs Anomaly) was insufficient to facilitate resilient ocean oxygenation. These findings suggest that the late Tonian oceans were likely challenging environments for complex (e.g. eukaryotic) life, and add to a growing body of evidence that the spatially variable redox conditions of late Proterozoic shallow marine settings likely reflect the complex nature of the Neoproterozoic Oxygenation Event.

The representation of alkalinity and the carbonate pump from CMIP5 to CMIP6 Earth system models and implications for the carbon cycle

Abstract. Ocean alkalinity is critical to the uptake of atmospheric carbon in surface waters and provides buffering capacity towards the associated acidification. However, unlike dissolved inorganic carbon (DIC), alkalinity is not directly impacted by anthropogenic carbon emissions. Within the context of projections of future ocean carbon uptake and potential ecosystem impacts, especially through Coupled Model Intercomparison Projects (CMIPs), the representation of alkalinity and the main driver of its distribution in the ocean interior, the calcium carbonate cycle, have often been overlooked. Here we track the changes from CMIP5 to CMIP6 with respect to the Earth system model (ESM) representation of alkalinity and the carbonate pump which depletes the surface ocean in alkalinity through biological production of calcium carbonate and releases it at depth through export and dissolution. We report an improvement in the representation of alkalinity in CMIP6 ESMs relative to those in CMIP5, with CMIP6 ESMs simulating lower surface alkalinity concentrations, an increased meridional surface gradient and an enhanced global vertical gradient. This improvement can be explained in part by an increase in calcium carbonate (CaCO3) production for some ESMs, which redistributes alkalinity at the surface and strengthens its vertical gradient in the water column. We were able to constrain a particulate inorganic carbon (PIC) export estimate of 44–55 Tmol yr−1 at 100 m for the ESMs to match the observed vertical gradient of alkalinity. Reviewing the representation of the CaCO3 cycle across CMIP5/6, we find a substantial range of parameterizations. While all biogeochemical models currently represent pelagic calcification, they do so implicitly, and they do not represent benthic calcification. In addition, most models simulate marine calcite but not aragonite. In CMIP6, certain model groups have increased the complexity of simulated CaCO3 production, sinking, dissolution and sedimentation. However, this is insufficient to explain the overall improvement in the alkalinity representation, which is therefore likely a result of marine biogeochemistry model tuning or ad hoc parameterizations. Although modellers aim to balance the global alkalinity budget in ESMs in order to limit drift in ocean carbon uptake under pre-industrial conditions, varying assumptions related to the closure of the budget and/or the alkalinity initialization procedure have the potential to influence projections of future carbon uptake. For instance, in many models, carbonate production, dissolution and burial are independent of the seawater saturation state, and when considered, the range of sensitivities is substantial. As such, the future impact of ocean acidification on the carbonate pump, and in turn ocean carbon uptake, is potentially underestimated in current ESMs and is insufficiently constrained.

Boron isotope fractionation during the formation of amorphous calcium carbonates and their transformation to Mg-calcite and aragonite

The non-classical crystallization pathway of carbonate minerals proceeds through the initial formation of an amorphous precursor phase and commonly takes place during biomineralization. Although the isotopic composition of marine calcifiers is often used to reconstruct paleo-environmental conditions, the impact of the crystallization pathway followed by these organisms on the isotope composition of their skeletons has rarely been quantified. This study presents the first examination of B partitioning and isotope fractionation during CaCO3 formation via an amorphous calcium carbonate phase, which provides new insights into the incorporation of B into marine calcite and aragonite that form via this route. Boron concentrations and isotope compositions of the fluids and the formed solids were characterized during the course of experiments that lasted two years and were performed at 25 °C under controlled pH conditions. The results suggest that during Mg-ACC formation, B distribution coefficients are 1.5–4 orders of magnitude higher than those reported earlier in the literature for calcite and aragonite. Additionally, B isotope fractionation during Mg-ACC formation is strongly affected by the continuous exchange of solutes between the nanoporous solid phase and the bulk fluid. The isotope composition of the transient amorphous phase is not inherited in the crystalline carbonate mineral phase that ultimately forms, because crystallization proceeds via a continuous dissolution/re-precipitation process and/or chemical/isotope exchange between the solid surface and the fluid. Interestingly, the isotope fractionation between the fluid and the final crystalline products is different from those achieved in earlier studies where mineral growth proceeded via the standard mechanism of ion-by-ion addition of solutes to advancing steps. The B isotope fractionations measured in this study are in good agreement with results of equilibrium first principle calculations for calcite and aragonite (Balan et al., 2018) except in the case of calcite formed at pH = 8.9, suggesting that changes in aqueous speciation (i.e. increase of NaB(OH)4° and CO32− concentrations) may be responsible for slight changes of the calcite BO4 environment and isotope composition. It is expected that this study will help to better decipher the mechanisms controlling B isotope fractionation during the non-classical growth of calcium carbonates involving the formation of transient amorphous precursors.

Determinants of Planktonic Foraminifera Calcite Flux: Implications for the Prediction of Intra‐ and Inter‐Annual Pelagic Carbonate Budgets

AbstractPlanktonic foraminifera precipitate calcite shells, which after the death of the organisms are exported to the seafloor. Globally, the resulting calcite flux constitutes up to half of the pelagic calcite flux. Given their importance for the marine calcite budget and for the carbonate counter pump, which counteracts the biological pump in terms of oceanic capacity for CO2 uptake, it is crucial to understand the mechanisms regulating the planktonic foraminifera calcite flux. In principle, variability in individual species calcite flux could be caused by changes in (a) shell flux, (b) shell size, and (c) calcification intensity. Where size and calcification intensity differ among species, variations can be caused by changes in species composition. To assess the importance of these factors in regulating the planktonic foraminifera calcite flux, we investigated two sediment trap time series from the Cape Blanc upwelling area. On intra‐annual timescales, 82% of the variability in the calcite flux can be explained by shell flux alone. Since the intra‐annual flux variability at the study site covers the global range of mean annual shell fluxes, our results indicate that a global prediction of steady‐state planktonic foraminifera calcite flux can be predicted by shell flux variability in combination with species‐specific average shell mass. However, our results show that on inter‐annual timescales, shell mass variability can be as important as shell flux variability. Therefore, this implies that in order to predict temporal changes in the planktonic foraminifera calcite flux variability in shell size and calcification intensity also require considered.

Mg and Sr isotopic evidence for basin wide alteration of early diagenetic dolomite in the Williston Basin by ascending crustal fluids

Dolomite is a predominantly diagenetic mineral that forms by replacing marine calcite and aragonite during burial. Dolomitization requires subsurface fluid flow to deliver Mg and remove product Ca, and only forms abiotically in laboratory experiments at temperatures above ~100°C, equivalent to burial depths of 3 km or greater. Limited sources of Mg at these depths would appear to restrict most dolomite formation to shallow burial depths using seawater as a source of reactive Mg, despite the kinetic limitation imposed by lower temperatures. The Williston Basin is replete with evaporites and dolomites that appear to have formed using Mg from evaporatively concentrated seawater at near surface temperatures. However, two dolomite bodies examined in this study record basin wide gradients in 87Sr/86Sr ratios and δ26Mg values that are inconsistent with dolomitization by seawater. We evaluate the processes that may have created these gradients. We propose a model whereby seepage reflux created early diagenetic protodolomite that was later altered during deep burial by 87Sr and Mg-enriched fluids ascending from the deep structural center of the basin with the degree of alteration decreasing towards the edges. The ascending fluid flow event is tentatively linked to anomalous heating in the Late Devonian / Early Carboniferous. Vertical faults are hypothesized to have behaved as conduits for channeling 87Sr and Mg-enriched crustal fluids upwards into the bottom of the Williston Basin, pressurizing the basal aquifer system and commencing up-dip directed fluid flow through confined aquifers. Clumped isotope and fluid inclusion thermometry indicate that the ascending fluids were hydrothermal with an estimated δ26Mg value of –0.65 ±0.20‰, which is much lower than estimates of early Paleozoic seawater δ26Mg values of +0.09 to +0.23‰. Two sources of crustal Mg are consistent with the low inferred δ26Mg values of the ascending fluid: (1) chlorite, which preferentially releases isotopically light Mg, with literature values in the range of –0.78‰ to –1.8‰, and (2) magnesite, which forms during carbonation of serpentinite with literature values in the range –0.7‰ to –1.1‰. Ultramafic rocks belonging to the Thompson Nickel Belt pass beneath the center of the Williston Basin in North Dakota, indicating that dissolution of both chlorite and magnesite may have contributed reactive Mg to the Williston Basin during the ascending fluid flow event. As dolomite is a mineral that is easily altered during burial, our findings warrant caution in choosing dolomites for reconstructing the 26Mg history of seawater.

Impact of Foliar Application of Various Forms of Silicon on the Chemical Composition of Sugar Beet Plants

The effect of marine calcite, a mixture of ortho- and polysilicic acid as well as orthosilicic acid applied as a foliar spray on the chemical composition of sugar beet leaves in the critical phase of nutrient supply (beginning of July) but also leaves and roots during harvest time in 2015–2016, was studied. The content of silicon in the leaves ranged from 1.24 to 2.36 g kg−1 d.m. at the beginning of July, 3.85–5.34 g kg−1 d.m. during harvest and 2.91–4.20 g kg−1 d.m. in the roots. The foliar application of silicon caused a significant increase in the content of magnesium and calcium in leaves (in July) as compared to the control. The sugar beet consumes approx. 75 kg Si ha−1, which is almost 3.5 times more than P and 20% more than Mg thus proving its importance for its species. About 70% of the silicon taken up by sugar beet is stored in roots and 30% in leaves. The pure sugar yield is most favorably influenced by two- and threefold foliar application of the product containing silicon in the form of orthosilicic acid stabilized with choline, and a threefold mixture of ortho- and polysilicic acid. The increase in the pure sugar yield is not the result of a change in the chemical composition of sugar beet plants, but their more efficient functioning after foliar application of silicon under stress conditions caused by water shortage.

Clumped isotope geothermometry of an Ordovician carbonate mound, Hudson Bay Basin

The Hudson Bay sedimentary basin was overlooked geologically until two decades ago. Recent efforts to understand the palaeogeothermal history of this basin have led to the evaluation of fluid inclusion microthermometry, apatite fission track, organic matter reflectance and Rock–Eval analyses. Although apatite fission track and organic maturity indicators tend to show relatively low maximum burial temperatures (60–80°C), evidence of potential oil slicks on the sea surface and oil and gas shows in offshore wells have been reported across Hudson Bay. Fluid inclusion microthermometry in a carbonate mound sequence suggests homogenization temperatures of 118 ± 25 and 93 ± 10°C for recrystallized synsedimentary marine calcite and late pore-filling burial calcite, respectively. This sequence provides an interesting geological framework to test the application of clumped isotope thermometry against independent geothermometers. Here, we present clumped isotope data acquired on the late calcite cements and diagenetically altered early marine phases. The integration of clumped isotopic data with other thermal indicators allows the reconstruction and refinement of the thermal–diagenetic history of these carbonates by confirming an episode of heating, probably of hydrothermal origin and prior to normal burial diagenesis, that reset both fluid inclusions and the clumped isotope indicators without recrystallization.

Incorporation of Rare Earths and Yttrium in Calcite: A Critical Re-evaluation

The reported partition coefficients of REE with calcite are reviewed and critically discussed. In some of the reported experimental sets, REE concentrations are found to be supersaturated with respect to individual REE2(CO3)3 but never to REE(OH)3. Although the solutions are unsaturated with respect to individual REY carbonates, REY including Y are incorporated in calcite surfaces, where they are overgrown by calcite. Charge balances may be obtained by building {REY–Na-(CO3)2}n or by exchange of 2Ca2+ against REY3+ + blank space calcite lattice. These surface compounds may either be homogeneously distributed or clustered. Both the size and frequency of clusters increase with [REY]/[Ca] or [ΣREY3+]/[Ca2+] in solution. If these surface precipitates are removed into solutions saturated with respect to ΣREE2(CO3)3, they start growing in the aqueous phase. In this case, the apparent DREY and kREY values decrease with increasing REY concentrations in solution. In previous studies, only the individual distribution coefficients are reported not considering that the entirety of REY determines their behavior in partitioning. Given enough time, these surface clusters equilibrate with the aqueous phase before being overgrown by calcite. In the double logarithmic plots of {REY}/{Ca} versus [REY]/[Ca] or [REY3+]/[Ca2+], two relationships evolve characterizing the REY distribution in marine calcite and experimental calcites grown in Mg2+-free solutions. The double logarithmic plots of partition coefficients of REYi3+ in calcite grown from seawater show a slope exceeding unity, whereas those from fluids without Mg2+ depict slopes less than unity being both in contrast to the Henderson–Kracek rule.

THE ECONOMIC EFFECTS OF FOLIAR FERTILIZATION OF SUGAR BEET WITH MARINE CALCITE

In 2010-2012, in Sahryń (Lubelskie Voivodeship), a field experiment was carried out, the aim of which was to assess the cost-effectiveness of foliar nutrition of sugar beet with marine calcite Herbagreen Basic containing silicon. The fertilizer was applied in two variants: 1) 1 kg/ha at the 4-6 leaf stage of sugar beet (BBCH 14-16) + 2 kg/ha 21 days later; 2) 2 kg/ha at the 4-6 leaf stage of sugar beet (BBCH 14-16) + 2 kg/ha 21 days later; the effects were compared with the control (without foliar nutrition with marine calcite). Additionally, in the years 2011-2012, an identical experiment was carried out with another sugar beet cultivar. For each combination, the gross production value, foliar nutrition costs, the net production value and profitability index were calculated. The total cost of application of foliar calcite was 190 and 240 PLN/ha. The gross production value of sugar beet in experiment 1, on average over three years of research, increased in combination 1 by 24.8% and in combination 2 by 25.6% compared to the control; in experiment 2, on average for 2 years of research, in combination 1 by 15.7%, and in combination 2 by 15.0%. The increase in the net production value in experiment 1 amounted to 22.8 and 23.2% respectively, and in experiment 2 - 13.9 and 12.8%. The indicator of the profitability of foliar nutrition with marine calcite in experiment 1, on average, for the period 2010-2012, amounted to 12.6 in combination 1 and 10.3 in combination 2. In experiment 2, the index of profitability of foliar nutrition, on average, for the period 2011-2012, reached the value of 8.96 for object 1 and 6.77 for object 2.

High-temperature alteration and porosity generation in Upper Ordovician microbial reefs, Hudson Bay intracratonic Basin, Arctic Canada

Upper Ordovician biohermal mounds of the Red Head Rapids River Formation in the Hudson Bay Basin consist of microbial and sponge boundstone and cementstone. The cementstone is made up of isopachous layers and botryoids of former aragonite now calcite. Secondary dissolution porosity and small fractures are cutting through the bioherm. Secondary pore-fillings consist of drusy calcite cement and subsequent bitumen. The δ18OVPDB and δ13CVPDB values of late cements are invariably more negative than those of the marine cements. Fluid inclusion microthermometry documents the presence of two distinct populations of homogenization temperatures, one in secondary pore-filling burial calcite cement (Th average 93 ± 10 °C) and a second one in recrystallized marine calcite cements (Th average 118 ± 25 °C). The combined δ18OVPDB and Th data suggest that burial cements precipitated from a fluid having δ18OSMOW values between +0.5 and −2‰, whereas the marine cement data indicate resetting of the fluid inclusions in the presence of a high temperature, δ18OSMOW heavy brine (+2.5 to +12‰). The lower temperature fluid inclusions of the late pore-filling cement agree with recent Apatite Fission Track data suggesting early oil window temperature at maximum burial. The higher Th values recorded in the marine cement represent resetting of initial or entrapment of new fluid inclusions from fracture-controlled circulation of basement-derived fluids. The petrographic and geochemical data suggest that fracture-controlled high temperature brine circulation occurred after the inception of burial and recrystallization of original marine aragonite to calcite, which resulted in the generation of significant secondary porosity that was later filled by lower temperature burial cements and hydrocarbons.

Diagenetic Origins of the Calcite Microcrystals That Host Microporosity In Limestone Reservoirs

Abstract Micron-size pores are common in limestones, and they host significant hydrocarbon reserves in conventional and unconventional plays worldwide. Previous studies have shown that the vast majority of micropores in limestones occur in the interstices between micron-size calcite crystals that are present in nearly all depositional environments and burial depths throughout the Phanerozoic. In an effort to elucidate the genetic history of these calcite microcrystals, a geochemical study was undertaken to investigate a global dataset collected from seven new subsurface microporous reservoirs as well as data from 21 previous studies. Bulk elemental analyses indicate that the vast majority of microcrystals are composed of low-Mg calcite (average 14 mmol/mol, range 1.6–90, Mg/Ca). Microcrystal Sr/Mg ratios are consistent with abiotic calcite cements, though overall Mg/Ca and Sr/Ca are lower than modern abiotic calcite cements reported in the literature. Higher Sr/Ca observed in depositional chalks implies a biotic, though probably not aragonitic, precursor. Most calcite microcrystals have oxygen isotope compositions that are 0 to 4‰ more negative, and carbon isotope compositions just slightly more negative (< 1‰), than contemporaneous abiotic marine calcite. Most stable oxygen and carbon isotopic data plot either along a burial trend anchored at its most positive end in the age-equivalent marine-calcite composition or parallel to that trend with an offset in δ13C. Assuming that δ13C offsets are due to marine carbon isotopic excursions, the isotopic data are consistent with shallow-burial diagenesis as the dominant diagenetic pathway for most calcite microcrystals. For samples with information on porosity and depth, more negative δ18O (ca. 1–4‰) is associated with increased depth and reduced porosity, implying that progressive overgrowth of calcite microcrystals is modifying bulk chemistry and rock properties of the reservoir during burial diagenesis. A meteoric calcite line was evident only in two datasets. This demonstrates that evidence of meteoric diagenesis can be preserved in the chemistry of calcite microcrystals, but that its occurrence is rare in comparison with evidence for diagenesis during shallow-burial. Geochemical data from calcite microcrystals are bulk samples, i.e., measurements averaged over many, many calcite microcrystals which themselves may have zoned chemistries. As such, microcrystal data require additional interpretation compared to samples from calcite macrocrystals where superposition puts samples into clear chronological order and produces diagenetic trends on, for example, δ18O–δ13C plots. Bulk samples of calcite microcrystals should show mixing between phases on diagenetic trends. With this model in mind, the assembled database suggests that most samples are mixes of primary marine and burial calcite.

Glacial–interglacial changes in H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;&amp;lt;sup&amp;gt;18&amp;lt;/sup&amp;gt;O, HDO and deuterium excess – results from the fully coupled ECHAM5/MPI-OM Earth system model

Abstract. In this study we present the first results of a new isotope-enabled general circulation model set-up. The model consists of the fully coupled ECHAM5/MPI-OM atmosphere–ocean model, enhanced by the JSBACH interactive land surface scheme and an explicit hydrological discharge scheme to close the global water budget. Stable water isotopes H218O and HDO have been incorporated into all relevant model components. Results of two equilibrium simulations under pre-industrial and Last Glacial Maximum conditions are analysed and compared to observational data and paleoclimate records for evaluating the model's performance in simulating spatial and temporal variations in the isotopic composition of the Earth's water cycle. For the pre-industrial climate, many aspects of the simulation results of meteoric waters are in good to very good agreement with both observations and earlier atmosphere-only simulations. The model is capable of adequately simulating the large spread in the isotopic composition of precipitation between low and high latitudes. A comparison to available ocean data also shows a good model–data agreement; however, a strong bias of overly depleted ocean surface waters is detected for the Arctic region. Simulation results under Last Glacial Maximum boundary conditions also fit to the wealth of available isotope records from polar ice cores, speleothems, as well as marine calcite data. Data–model evaluation of the isotopic composition in precipitation reveals a good match of the model results and indicates that the temporal glacial–interglacial isotope–temperature relation was substantially lower than the present spatial gradient for most mid- to high-latitudinal regions. As compared to older atmosphere-only simulations, a remarkable improvement is achieved for the modelling of the deuterium excess signal in Antarctic ice cores. Our simulation results indicate that cool sub-tropical and mid-latitudinal sea surface temperatures are key for this progress. A recently discussed revised interpretation of the deuterium excess record of Antarctic ice cores in terms of marine relative humidity changes on glacial–interglacial timescales is not supported by our model results.

Geochemical signatures of the early Campanian belemnite Belemnellocamax mammillatus from the Kristianstad Basin in Scania, Sweden

article Macrofossil calcite plays a central role for palaeoenvironmental reconstructions because its preservation state and geochemical signatures can be checked using a variety of screening techniques. Reconstructions of the ecology and seawater composition from such data require knowledge about species-specific compositions of well-preserved calcitic fossils. Comprehensive datasets, recording averages, intraspecimen and intraspecific variability of geochemical proxies in fossil calcite, however, are still largely lacking. Here we report δ 13 C and δ 18 O values, as well as Mg/Ca, Sr/Ca and Mn/Ca ratios of 204 aliquots sampled along transectsthroughthree rostraof thelate earlyCampanianbelemnite speciesBelemnellocamax mammillatus. Geo- chemical signatures of partially altered samples are consistent to those reported for early marine calcite cemen- tationandshowtrendstowardsmoderatelyhigherMn/Ca,heavier δ 13 CandlowerSr/Ca.Incontrast,Mg/Caratios and δ 18 O values remain similar to projected original values. Median δ 18 Ov alues of−0.3 to 0.0‰ are comparable to the heaviest values of coeval oysters from the same localities, and internal variability of the well-preserved parts of the rostra is low. These findings suggest that B. mammillatus lived mostly in the deep part of the basin where seasonal changes were low and water temperatures cool. The δ 13 C is offset from oysters and most coeval

THE EFFECT OF SILICON FOLIAR FERTILIZATION IN SUGAR BEET – Beta vulgaris (L.) ssp. vulgaris conv. crassa (Alef.) prov. altissima (Döll)

ABSTRACT Presented results are extended continuation study of earlier research (2010–2012) on silicon fertilization effect and comes from the research that was conducted in 2013–2014 in the southeastern region of Poland, in Sahryn (50°41' N and 23°46' E). Two variants of silicon foliar fertilization were tested in sugar beet, Danuśka KWS variety. Two kinds of silicon fertilizers (Herbagreen Basic and Optysil) in 3 stages (in the stage of 4-6 sugar leaf, than a week and two weeks later). One of the silicon fertilizer contained marine calcite and silicon (Ca+Si) and the second one contained silicon (Si) only. Seven variants of foliar fertilization including control variant were tested as total. Foliar fertilization regardless of the kind of fertilizer resulted in increases of: 1) the root yield (for Ca+Si variant 10.4–16.2% and for Si variant 13.7–15.9%), 2) biological sugar yield (respectively 11.4–18.1% and 13.7–15.9%), 3) technological sugar yield (respectively 12.2–17.7% and 12.2–15.6%) compared with the control variant. However the tested variants had no effect for technological root quality compared with the control. A tendencies to decrease content of sodium as a result of foliar fertilizations were observed only. Keywords: Beta vulgaris L.; Biological sugar yield; Roots yield; Sugar content; Technological quality of roots.

Enigmatic carbonates of the Ombombo Subgroup, Otavi Fold Belt, Namibia: A prelude to extreme Cryogenian anoxia?

The Ombombo Subgroup of the Otavi Fold Belt, Kaokoveld, Namibia preserves a succession of clastic and carbonate sediments with unusual sedimentary features. The stratigraphy of these units is discussed here in detail for the first time since their initial definition, with particular emphasis on the sedimentology of carbonate units. Early Neoproterozoic shales of the Beesvlakte Formation, equivalent to the Zambian Katangan Copperbelt's Lower Roan Formation, host evaporitic lithologies and minor copper mineralisation. The overlying, dolomitic ~760Ma Devede Formation contains carbonate platformal lithologies which are in many ways dissimilar to Phanerozoic shallow-water carbonates. This includes unusual “curl breccias”, sheet cavities, carbonate shrubs, and tepee carbonate lithologies which contain large quantities of fibrous cements. “Curl breccias” are defined here as distinctive, curled intraclasts of laminated dolomite that often have shrinkage cracks in their margins, and are cemented by fibrous dolomite cements. Fibrous cements take on two forms: an early, length-fast fascicular-optic dolomite and a later length-slow phase with unit extinction. The presence of overlying internal sediments, the fibrous habit of these first-generation cements, as well as their preserved cathodoluminescent and optical character, suggests that these cements originally precipitated as calcite and dolomite marine cements respectively. After this initial marine calcite precipitation, all components of Devede Formation carbonates have been mimetically dolomitised, preserving original depositional fabrics. Combined with the presence of marine dolomite cements, this style of dolomitisation is suggested to be syn-sedimentary, similar to that of some Cryogenian dolomites, suggesting unusual ocean conditions during the Early Neoproterozoic. In particular, the presence of dolomite marine cements, which have been linked to ocean anoxia and high seawater Mg/Ca conditions, suggests that the onset of marine anoxia in the Neoproterozoic may have occurred during the growth of the Devede Formation carbonate platforms, prior to the Sturtian glaciation. This implies that glaciation may not be the sole cause for the development of marine anoxia during the Neoproterozoic. It is possible that marine anoxia in this southern African ocean basin may have contributed to a build-up of metals in seawater, perhaps pre-enriching basinal fluids for large-scale stratabound copper mineralisation.

The effect of foliar fertilization with marine calcite in sugar beet

The effect of marine calcite (containing calcium and silicon mainly) foliar fertilization on the sugar beet root yield and technological quality relative to the control (treatment 0) was investigated. Study was conducted in 2011&amp;ndash;2012 in the southeastern region of Poland, in Sahryń (50&amp;deg;41'N, 23&amp;deg;46'E). The cultivar of sugar beet was Danuśka KWS. Two treatments of foliar fertilization: (1) treatment (in the stage of 4&amp;ndash;6 sugar leaves &amp;ndash; 262.0 g Ca/ha, 79.9 g Si/ha, and three weeks later &amp;ndash; 524.0 g Ca/ha, 159.8 g Si/ha); and (2) treatment (in the stage of 4&amp;ndash;6 sugar leaves &amp;ndash; 524.0 gCa/ha, 159.8 g Si/ha, three weeks later &amp;ndash; 524.0 g Ca/ha, 159.8 g Si/ha). Calcium and silicon foliar fertilization resulted in increases of: (1) the root yield (average for both treatments about 13.1%; (2) the leaf yield (about 21.0%); (3) the biological sugar yield (about 15.5%), and (4) technological yield of sugar (about 17.7%) compared with the control treatment. At the same time a positive effect on the roots technological quality was found. It was a significant reduction of alpha-amino-nitrogen content and tended to reduce the content of potassium and sodium.

Recognition of Early Eocene global carbon isotope excursions using lipids of marine Thaumarchaeota

The Paleocene–Eocene Thermal Maximum (PETM; ∼56Ma) and Eocene Thermal Maximum 2 (ETM2; ∼53Ma) are geological short (<200,000 years) episodes of extreme global warming and environmental change. Both the PETM and ETM2 are associated with the injection of 13C-depleted carbon into the ocean–atmosphere system as revealed through a globally recognized carbon isotope excursion (CIE) and massive dissolution of deep sea carbonate. However, the magnitude of these CIEs vary with the type of fossil matter, i.e. multiple carbonate phases, bulk organic matter, and terrestrial and marine biomarker lipids, making it difficult to constrain the actual CIE in atmospheric and oceanic carbon pools. Here we analyzed the stable carbon isotopic composition (δ13C) of glycerol dibiphytanyl glycerol tetraether lipids (GDGTs) derived from marine Thaumarchaeota in sediments deposited during the PETM in the North Sea Basin and ETM2 in the Arctic Ocean. The δ13C values of these lipids are potentially directly recording variations in δ13C dissolved inorganic carbon (DIC) and can thus provide a record of marine δ13C DIC across both these Eocene carbon cycle perturbations. Reconstructed pre-CIE δ13CDIC values are slightly lower (0.5–1‰) than modern day values, possibly because Thaumarchaeotal lipids are not only derived from surface waters but also from 13C-depleted subsurface waters. Their values decrease by ∼3.6 (±0.3) ‰ and ∼2.5 (±0.7)‰ during the PETM and ETM2, respectively. The CIE in crenarchaeol for ETM2 is higher than that in marine calcite from other locations, possibly because of the admixture of deep water 13C-depleted CO2 generated by the euxinic conditions that developed occasionally during ETM2. However, the reconstructed PETM CIE lies close to the CIE inferred from marine calcite, suggesting that the δ13C record of crenarchaeol may document changes in marine DIC during the PETM in the North Sea Basin. The δ13C of thaumarchaeotal lipids may thus be a novel tool to reconstruct the δ13C of DIC in sediments that are devoid of carbonates, but relatively rich in organic matter, such as shallow marine coastal settings.

Stable-Isotope Geochemistry of Vertisols Formed On Marine Limestone and Implications for Deep-Time Paleoenvironmental Reconstructions

Abstract Carbon and oxygen isotope compositions of pedogenic carbonate preserved in paleosols have been used extensively to reconstruct ancient environmental conditions. One concern is that pedogenic carbonate precipitated in association with a limestone parent material may include a contribution from inherited detrital (lithogenic) marine calcite, thus compromising interpretations of stable-isotope compositions. To investigate the impact of lithogenic calcite on environmental interpretations using paleosols, we measured stable-isotope ratios in pedogenic carbonates and coexisting soil organic matter (SOM) in modern Vertisols (fine, smectitic, thermic, Udic Haplusterts) from Riesel, Texas (Heiden series) and Zabcikville, Texas (Houston Black series) forming on Cretaceous chalk deposits. The pedogenic and lithogenic components in the Heiden series soil at Riesel were identified using micromorphology and cathodoluminescence (CL), which showed incorporation of luminescent marine allochems (i.e., foraminifera, mollusks) into hard nodules and soft powdery pedogenic masses. Additionally, micromorphology showed evidence of meteoric recrystallization of the allochems. Despite the presence of these inherited carbonates into hard nodules and soft powdery masses, the stable-isotope compositions recorded a partial pedogenic signal. Recrystallization of the marine allochems resulted in overprinting of primary marine isotope ratios with ratios that are more similar to those expected for pedogenic carbonates in these soils. This study demonstrates that incorporation of parent material into pedogenic carbonates does not necessarily compromise the pedogenic signal that is useful for paleoenvironmental reconstructions. However, overprinting of marine allochems, if present, can be important and needs to be identified using micromorphology and cathodoluminescence, before using stable-isotope ratios of pedogenic carbonates for paleoenvironmental reconstructions.

Integrated diagenesis and sequence stratigraphic study of tidal sandstones: the Adedia Formation (Cambro-Ordovician), Sinai, Egypt

This work examines the different effects meteoric versus marine diagenesis had on Cambro-Ordovician tidal sandstones during episodes of fluctuating sea level. The distribution of diagenetic fabrics was compared to a sequence stratigraphic framework. Initially, a rise in relative sea level (RSL) resulted in deposition of transgressive systems tract sands directly onto crystalline basement. These sandstones display evidence of limited cementation by marine, grain-fringing dogtooth-like and fibrous calcite. A fall in RSL resulted in the progradation of a tidal flat complex and deposition of highstand systems tract (HST) and lowstand systems tract (braided fluvial) sandstones. Contemporaneous meteoric-water flux into sands of all the systems tracts occurred. Sequence boundaries (SB) are marked by fluvial incision of tidal sands and by the development of palaeosols. Meteoric incursion during sea-level lowstands resulted in the dissolution and kaolinitization of feldspars, micas and mud intraclasts in all systems tracts, but is most extensive in HST sandstones below the SB. The effect of meteoric-water flux on the dissolution of marine calcite cements is poorly known. Mesogenetic alterations include intergranular pressure dissolution and formation of variable amounts of syntaxial quartz overgrowths in all systems tracts. Telogenetic alteration (i.e. weathering) in the sandstones includes the formation of goethite and calcite. Thus, the integration of diagenesis with sequence stratigraphy provides a useful tool with which to understand reservoir-quality distribution in sand-dominated, tidal sediments.

Stable carbon isotopic ratios of CH 4–CO 2-bearing fluid inclusions in fracture-fill mineralization from the Lower Saxony Basin (Germany) – A tool for tracing gas sources and maturity

The stable carbon isotopic ratios (δ 13C) of methane (CH 4) and carbon dioxide (CO 2) of gas-rich fluid inclusions hosted in fracture-fill mineralization from the southern part of the Lower Saxony Basin, Germany have been measured online using a crushing device interfaced to an isotopic ratio mass spectrometer (IRMS). The data reveal that CH 4 trapped in inclusions seems to be derived from different source rocks with different organic matter types. The δ 13C values of CH 4 in inclusions in quartz hosted by Carboniferous rocks range between −25 and −19‰, suggesting high-maturity coals as the source of methane. Methane in fluid inclusions in minerals hosted by Mesozoic strata has more negative carbon isotope ratios (−45 to −31‰) and appears to represent primary cracking products from type II kerogens, i.e., marine shales. There is a positive correlation between increasing homogenization temperatures of aqueous fluid inclusions and less negative δ 13C(CH 4) values of in co-genetic gas inclusions probably indicating different mtaturity of the potential source rocks at the time the fluids were released. The CO 2 isotopic composition of CH 4–CO 2-bearing inclusions shows slight negative or even positive δ 13C values indicating an inorganic source (e.g., water–rock interaction and dissolution of detrital, marine calcite) for CO 2 in inclusions. We conclude that the δ 13C isotopic ratios of CH 4–CO 2-bearing fluid inclusions can be used to trace migration pathways, sources of gases, and alteration processes. Furthermore, the δ 13C values of methane can be used to estimate the maturity of the rocks from which it was sourced. Results presented here are further supported by organic geochemical analysis of surface bitumens which coexist with the gas inclusion-rich fracture-fill mineralization and confirm the isotopic interpretations with respect to fluid source, type and maturity.