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Frollini, Eleonora, Daniele Parrone, Stefano Ghergo, Rita Masciale, Giuseppe Passarella, Maddalena Pennisi, Matteo Salvadori i Elisabetta Preziosi. "An Integrated Approach for Investigating the Salinity Evolution in a Mediterranean Coastal Karst Aquifer". Water 14, nr 11 (27.05.2022): 1725. http://dx.doi.org/10.3390/w14111725.
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Coastal areas are characterized by considerable demographic pressure that generally leads to groundwater overexploitation. In the Mediterranean region, this situation is exacerbated by a recharge reduction enhanced by climate change. The consequence is water table drawdown that alters the freshwater/seawater interface facilitating seawater intrusion. However, the groundwater salinity may also be affected by other natural/anthropogenic sources. In this paper, water quality data gathered at 47 private and public wells in a coastal karst aquifer in Apulia (southern Italy), were interpreted by applying disparate methods to reveal the different sources of groundwater salinity. Chemical characterization, multivariate statistical analysis, and mixing calculations supplied the groundwater salinization degree. Characteristic ion ratios, strontium isotope (87Sr/86Sr), and pure mixing modelling identified the current seawater intrusion as a main salinity source, also highlighting the contribution of water–rock interaction to groundwater composition and excluding influence from Cretaceous paleo-seawater. Only the combined approach of all the methodologies allowed a clear identification of the main sources of salinization, excluding other less probable ones (e.g., paleo-seawater). The proposed approach enables effective investigation of processes governing salinity changes in coastal aquifers, to support more informed management.
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Hohl, Simon V., Shao-Yong Jiang, Sebastian Viehmann, Wei Wei, Qian Liu, Hai-Zhen Wei i Stephen J. G. Galer. "Trace Metal and Cd Isotope Systematics of the Basal Datangpo Formation, Yangtze Platform (South China) Indicate Restrained (Bio)Geochemical Metal Cycling in Cryogenian Seawater". Geosciences 10, nr 1 (19.01.2020): 36. http://dx.doi.org/10.3390/geosciences10010036.
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The behaviour of bioavailable trace metals and their stable isotopes in the modern oceans is controlled by uptake into phototrophic organisms and adsorption on and incorporation into marine authigenic minerals. Among other bioessential metals, Cd and its stable isotopes have recently been used in carbonate lithologies as novel tracer for changes in the paleo primary productivity and (bio)geochemical cycling. However, many marine sediments that were deposited during geologically highly relevant episodes and which, thus, urgently require study for a better understanding of the paleo environment are rather composed of a mixture of organic matter (OM), and detrital and authigenic minerals. In this study, we present Cd concentrations and their isotopic compositions as well as trace metal concentrations from sequential leachates of OM-rich shales of the Cryogenian basal Datangpo Formation, Yangtze Platform (South China). Our study shows variable distribution of conservative and bioavailable trace metals as well as Cd isotope compositions between sequential leachates of carbonate, OM, sulphide, and silicate phases. We show that the Cd isotope compositions obtained from OM leachates can be used to calculate the ambient Cryogenian surface seawater of the restricted Nanhua Basin by applying mass balance calculations. By contrast, early diagenetic Mn carbonates and sulphides incorporated the residual Cd from dissolved organic matter that was in isotopic equilibrium with deep/pore waters of the Nanhua Basin. Our model suggests that the Cd isotopic composition of surface seawater at that time reached values of modern oxygenated surface oceans. However, the deep water Cd isotope composition was substantially heavier than that of modern fully oxygenated oceans and rather resembles deep waters with abundant sulphide precipitation typical for modern oxygen minimum zones. This argues for incomplete recycling of Cd and other bioavailable metals shortly after the Sturtian glaciation in the redox stratified Cryogenian Nanhua Basin. Our study highlights the importance of sequential leaching procedures when dealing with impure authigenic sediments such as OM-rich carbonates, mudstones, or shales to achieve reliable trace metal concentrations and Cd isotope compositions as proxies for (bio)geochemical metal cycling in past aquatic systems.
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Nehrke, G., N. Keul, G. Langer, L. J. de Nooijer, J. Bijma i A. Meibom. "A new model for biomineralization and trace-element signatures of Foraminifera tests". Biogeosciences 10, nr 10 (29.10.2013): 6759–67. http://dx.doi.org/10.5194/bg-10-6759-2013.
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Abstract. The Mg/Ca ratio of Foraminifera calcium carbonate tests is used as proxy for seawater temperature and widely applied to reconstruct global paleo-climatic changes. However, the mechanisms involved in the carbonate biomineralization process are poorly understood. The current paradigm holds that calcium ions for the test are supplied primarily by endocytosis of seawater. Here, we combine confocal-laser scanning-microscopy observations of a membrane-impermeable fluorescent marker in the extant benthic species Ammonia aomoriensis with dynamic 44Ca-labeling and NanoSIMS isotopic imaging of its test. We infer that Ca for the test in A. aomoriensis is supplied primarily via trans-membrane transport, but that a small component of passively transported (e.g., by endocytosis) seawater to the site of calcification plays a key role in defining the trace-element composition of the test. Our model accounts for the full range of Mg/Ca and Sr/Ca observed for benthic Foraminifera tests and predicts the effect of changing seawater Mg/Ca ratio. This places foram-based paleoclimatology into a strong conceptual framework.
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Nehrke, G., N. Keul, G. Langer, L. J. de Nooijer, J. Bijma i A. Meibom. "A new model for biomineralization and trace-element signatures of foraminifera tests". Biogeosciences Discussions 10, nr 6 (18.06.2013): 9797–818. http://dx.doi.org/10.5194/bgd-10-9797-2013.
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Abstract. The Mg / Ca ratio of foraminifera calcium-carbonate tests is used as proxy for seawater temperature and widely applied to reconstruct global paleo-climatic changes. However, the mechanisms involved in the carbonate biomineralization process are poorly understood. The current paradigm holds that calcium ions for the test are supplied primarily by endocytosis of seawater. Here, we combine confocal-laser scanning-microscopy observations of a membrane-impermeable fluorescent marker in the extant benthic species Ammonia aomoriensis with dynamic 44Ca-labeling and NanoSIMS isotopic imaging of its test. We infer that Ca for the test in A. aomoriensis is supplied primarily via trans-membrane transport, but that a small component of passively transported (e.g. by endocytosis) seawater to the site of calcification plays a key role in defining the trace-element composition of the test. Our model accounts for the full range of Mg / Ca and Sr / Ca observed for benthic foraminifera tests and predicts the effect of changing seawater Mg / Ca ratio. This places foram-based paleoclimatology into a strong conceptual framework.
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Hall, Jenney M., L. H. Chan, William F. McDonough i Karl K. Turekian. "Determination of the lithium isotopic composition of planktic foraminifera and its application as a paleo-seawater proxy". Marine Geology 217, nr 3-4 (czerwiec 2005): 255–65. http://dx.doi.org/10.1016/j.margeo.2004.11.015.
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Frei, Robert, Cora Paulukat, Sylvie Bruggmann i Robert M. Klaebe. "A systematic look at chromium isotopes in modern shells – implications for paleo-environmental reconstructions". Biogeosciences 15, nr 16 (20.08.2018): 4905–22. http://dx.doi.org/10.5194/bg-15-4905-2018.
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Abstract. The chromium isotope system (53Cr ∕ 52Cr, expressed as δ53Cr relative to NIST SRM 979) in marine biogenic and non-biogenic carbonates is currently being evaluated as a proxy for the redox state of the ocean. Previous work has concentrated on using corals and foraminifera for this purpose, but investigations focusing on the behavior of Cr in bivalves as potential archives are lacking. Due to their often good preservation, fossil marine biogenic carbonates have the potential to serve as useful archives for the reconstruction of past ocean redox fluctuations and eventually link those to climatic changes throughout Earth's history. Here, we present an evaluation of the Cr isotope system in shells of some modern bivalves. Shell species from Lucidinadae, Cardiidae, Glycimerididae and Pectenidae, collected systematically from one Mediterranean location (Playa Poniente, Benidorm, Spain) over a 3-year period reveal δ53Cr values ranging from 0.15 ‰ to 0.65 ‰, values that are systematically below the local seawater δ53Cr value of 0.83±0.05 ‰. This attests to a significant reduction of dissolved seawater chromium in the process leading to calcification and thus for control of Cr isotope fractionation during biological routes. A similar, constant offset in δ53Cr values relative to surface seawater is observed in shells from Mytilius edulis from an arctic location (Godhavn, Disko Bay, Greenland). Chromium concentrations in the studied shells are significantly controlled by organic matter and typically range from 0.020 to 0.100 ppm, with some higher concentrations of up to 0.163 ppm recorded in Pectenidae. We also observe subtle, species-dependent differences in average Cr isotope signatures in the samples from Playa Poniente, particularly of Lucidinadae and Cardiidae, with considerably depressed and elevated δ53Cr values, respectively, relative to the other species investigated. Intra-species heterogeneities, both in Cr concentrations and δ53Cr values, are favorably seen to result from vital effects during shell calcification rather than from heterogeneous seawater composition. This is because we observe that the surface seawater composition in the particular Playa Poniente location remained constant during the month of July of the 3 years we collected bivalve samples. Intra-shell heterogeneities – associated with growth zones reflecting one to several years of growth, both in δ53Cr and Cr concentrations – are observed in a sample of Placuna placenta and Mimachlamys townsendi. We suspect that these variations are, at least partially, related to seasonal changes in δ53Cr of surface seawaters. Recognizing the importance of organic substances in the bivalve shells, we propose a model whereby reduction of Cr(VI) originally contained in the seawater as chromate ion and transported to the calcifying space, to Cr(III), is effectively adsorbed onto organic macromolecules which eventually get included in the growing shell carbonates. This study, with its definition of statistically sound offsets in δ53Cr values of certain bivalve species from ambient seawater, forms a base for future investigations aimed at using fossil shells as archives for the reconstruction of paleo-seawater redox fluctuations.
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Dissard, D., E. Douville, S. Reynaud, A. Juillet-Leclerc, P. Montagna, P. Louvat i M. McCulloch. "Light and temperature effect on δ<sup>11</sup>B and B/Ca ratios of the zooxanthellate coral <i>Acropora</i> sp.: results from culturing experiments". Biogeosciences Discussions 9, nr 5 (25.05.2012): 5969–6014. http://dx.doi.org/10.5194/bgd-9-5969-2012.
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Abstract. The boron isotopic composition (δ11B) of marine carbonates (e.g. corals) has been established as a reliable proxy for paleo-pH, with the strong correlation between δ11B of marine calcifiers and seawater pH being now well documented. However, further investigations are needed in order to better quantify other environmental parameters potentially impacting boron isotopic composition and boron concentration into coral aragonite. To achieve this goal the tropical scleractinian coral Acropora sp. was cultured under 3 different temperature (22, 25 and 28 °C) and two light conditions (200 and 400 μmol photon m−2 s−1). The δ11B indicates an internal increase in pH from ambient seawater under both light conditions. Changes in light intensities from 200 to 400 μmol photon m−2 s−1 could bias pH reconstructions by about 0.05 units. For both light conditions, a significant impact of temperature on δ11B can be observed between 22 and 25 °C corresponding to enhancements of about 0.02 pH-units, while no further δ11B increase can be observed between 25 and 28 °C. This non-linear temperature effect complicates the determination of a correcting factor. B/Ca ratios decrease with increasing light, confirming the decrease in pH at the site of calcification under enhanced light intensities. When all the other parameters are maintained constant, boron concentrations in Acropora sp. increase with increasing temperature and increasing carbonate ions concentrations. These observations contradict previous studies where B/Ca in corals was found to vary inversely with temperature suggesting that the controlling factors driving boron concentrations have not yet been adequately identified and might be influenced by other seawater variables and species specific responses.
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Li, Shilei, Weiqiang Li, Brian L. Beard, Maureen E. Raymo, Xiaomin Wang, Yang Chen i Jun Chen. "K isotopes as a tracer for continental weathering and geological K cycling". Proceedings of the National Academy of Sciences 116, nr 18 (15.04.2019): 8740–45. http://dx.doi.org/10.1073/pnas.1811282116.
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The causal effects among uplift, climate, and continental weathering cannot be fully addressed using presently available geochemical proxies. However, stable potassium (K) isotopes can potentially overcome the limitations of existing isotopic proxies. Here we report on a systematic investigation of K isotopes in dissolved load and sediments from major rivers and their tributaries in China, which have drainage basins with varied climate, lithology, and topography. Our results show that during silicate weathering, heavy K isotopes are preferentially partitioned into aqueous solutions. Moreover, δ41K values of riverine dissolved load vary remarkably and correlate negatively with the chemical weathering intensity of the drainage basin. This correlation allows an estimate of the average K isotope composition of global riverine runoff (δ41K = −0.22‰), as well as modeling of the global K cycle based on mass balance calculations. Modeling incorporating K isotope mass balance better constrains estimated K fluxes for modern global K cycling, and the results show that the δ41K value of seawater is sensitive to continental weathering intensity changes. Thus, it is possible to use the δ41K record of paleo-seawater to infer continental weathering intensity through Earth’s history.
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Huang, Hao, Xiaochi Jin i Yukun Shi. "AVerbeekinaassemblage (Permian fusulinid) from the Baoshan Block in western Yunnan, China". Journal of Paleontology 89, nr 2 (marzec 2015): 269–80. http://dx.doi.org/10.1017/jpa.2014.24.
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AbstractA newly discoveredVerbeekinaassemblage from the Xiaoxinzhai Section in the Baoshan Block in western Yunnan, China, provides additional data for better understanding fusulinid biostratigraphy and the thermal condition of middle Permian (Guadalupian) seawater of this block. This assemblage comprises 11 species of six genera, includingVerbeekina,Pseudodoliolina,Sumatrina,Yangchienia,Xiaoxinzhaiella, and ?Rugosochusenella. The age of this assemblage is considered to be Midian (approximately Capitanian), based on combined evidence of stratigraphic position and specific composition. Furthermore, this assemblage bears two unusual attributes: overwhelming dominance ofVerbeekinaand relatively low total diversity, compared with coeval fusulinids from South China, which represents a paleo-tropical setting during the middle Permian. These features indicate that the Baoshan Block was probably located in a subtropical setting with warm water during the Midian time; however, its water temperature was still not as optimal as the tropical area (e.g., South China) for the diversification of fusulinids.
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Wang, J. X., C. L. Zhang, W. Xie, Y. G. Zhang i P. Wang. "Contribution of Marine Group II <i>Euryarchaeota</i> to cyclopentyl tetraethers in the Pearl River estuary and coastal South China Sea: impact on the TEX<sub>86</sub> paleothermometer". Biogeosciences Discussions 12, nr 15 (7.08.2015): 12455–84. http://dx.doi.org/10.5194/bgd-12-12455-2015.
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Abstract. TEX86 (TetraEther indeX of glycerol dialkyl glycerol tetraethers (GDGTs) with 86 carbon atoms) has been widely applied to reconstruct (paleo-) sea surface temperature (SST). While Marine Group I (MG I) Thaumarchaeota have been commonly believed to be the source for GDGTs, Marine Group II (MG II Euryarchaeota) have recently been suggested to contribute significantly to the GDGT pool in the ocean. However, little is known how the MG II Euryarchaeota-derived GDGTs may influence TEX86 in marine sediment record. In this study, we characterize MG II Euryarchaeota-produced GDGTs and assess the likely effect of these tetraether lipids on TEX86. Analyses of core lipid (CL-) and intact polar lipid (IPL-) based GDGTs, 454 sequencing and quantitative polymerase chain reaction (qPCR) targeting MG II Euryarchaeota were performed on suspended particulate matter (SPM) and surface sediments collected along a salinity gradient from the lower Pearl River (river water) and its estuary (mixing water) to the coastal South China Sea (seawater). The results showed that the community composition varied along the salinity gradient with MG II Euryarchaeota as the second dominant group in the mixing water and seawater. qPCR data indicated that the abundance of MG II Euryarchaeota in the mixing water was three to four orders of magnitude higher than the river water and seawater. Significant linear correlations were observed between the gene abundance ratio of MG II Euryarchaeota vs. total archaea and the relative abundance of GDGTs-1, -2, -3, or -4 as well as the ring index based on these compounds, which collectively suggest that MG II Euryarchaeota may actively produce GDGTs in the water column. These results also show strong evidence that MG II Euryarchaeota synthesizing GDGTs with 1–4 cyclopentane moieties may bias TEX86 in the water column and sediments. This study highlights that valid interpretation of TEX86 in sediment record, particularly in coastal oceans, needs to consider the contribution from MG II Euryarchaeota.
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Kurahashi-Nakamura, Takasumi, André Paul, Guy Munhoven, Ute Merkel i Michael Schulz. "Coupling of a sediment diagenesis model (MEDUSA) and an Earth system model (CESM1.2): a contribution toward enhanced marine biogeochemical modelling and long-term climate simulations". Geoscientific Model Development 13, nr 2 (2.03.2020): 825–40. http://dx.doi.org/10.5194/gmd-13-825-2020.
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Abstract. We developed a coupling scheme for the Community Earth System Model version 1.2 (CESM1.2) and the Model of Early Diagenesis in the Upper Sediment of Adjustable complexity (MEDUSA), and explored the effects of the coupling on solid components in the upper sediment and on bottom seawater chemistry by comparing the coupled model's behaviour with that of the uncoupled CESM having a simplified treatment of sediment processes. CESM is a fully coupled atmosphere–ocean–sea-ice–land model and its ocean component (the Parallel Ocean Program version 2; POP2) includes a biogeochemical component (the Biogeochemical Elemental Cycling model; BEC). MEDUSA was coupled to POP2 in an offline manner so that each of the models ran separately and sequentially with regular exchanges of necessary boundary condition fields. This development was done with the ambitious aim of a future application for long-term (spanning a full glacial cycle; i.e. ∼105 years) climate simulations with a state-of-the-art comprehensive climate model including the carbon cycle, and was motivated by the fact that until now such simulations have been done only with less-complex climate models. We found that the sediment–model coupling already had non-negligible immediate advantages for ocean biogeochemistry in millennial-timescale simulations. First, the MEDUSA-coupled CESM outperformed the uncoupled CESM in reproducing an observation-based global distribution of sediment properties, especially for organic carbon and opal. Thus, the coupled model is expected to act as a better “bridge” between climate dynamics and sedimentary data, which will provide another measure of model performance. Second, in our experiments, the MEDUSA-coupled model and the uncoupled model had a difference of 0.2 ‰ or larger in terms of δ13C of bottom water over large areas, which implied a potentially significant model uncertainty for bottom seawater chemical composition due to a different way of sediment treatment. For example, an ocean model that does not treat sedimentary processes depending on the chemical composition of the ambient water can overestimate the amount of remineralization of organic matter in the upper sediment in an anoxic environment, which would lead to lighter δ13C values in the bottom water. Such a model uncertainty would be a fundamental issue for paleo model–data comparison often relying on data derived from benthic foraminifera.
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Delsman, J. R., K. R. M. Hu-a-ng, P. C. Vos, P. G. B. de Louw, G. H. P. Oude Essink, P. J. Stuyfzand i M. F. P. Bierkens. "Paleo-modeling of coastal saltwater intrusion during the Holocene: an application to the Netherlands". Hydrology and Earth System Sciences 18, nr 10 (2.10.2014): 3891–905. http://dx.doi.org/10.5194/hess-18-3891-2014.
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Abstract. Coastal groundwater reserves often reflect a complex evolution of marine transgressions and regressions, and are only rarely in equilibrium with current boundary conditions. Understanding and managing the present-day distribution and future development of these reserves and their hydrochemical characteristics therefore requires insight into their complex evolution history. In this paper, we construct a paleo-hydrogeological model, together with groundwater age and origin calculations, to simulate, study and evaluate the evolution of groundwater salinity in the coastal area of the Netherlands throughout the last 8.5 kyr of the Holocene. While intended as a conceptual tool, confidence in our model results is warranted by a good correspondence with a hydrochemical characterization of groundwater origin. Throughout the modeled period, coastal groundwater distribution never reached equilibrium with contemporaneous boundary conditions. This result highlights the importance of historically changing boundary conditions in shaping the present-day distribution of groundwater and its chemical composition. As such, it acts as a warning against the common use of a steady-state situation given present-day boundary conditions to initialize groundwater transport modeling in complex coastal aquifers or, more general, against explaining existing groundwater composition patterns from the currently existing flow situation. The importance of historical boundary conditions not only holds true for the effects of the large-scale marine transgression around 5 kyr BC that thoroughly reworked groundwater composition, but also for the more local effects of a temporary gaining river system still recognizable today. Model results further attest to the impact of groundwater density differences on coastal groundwater flow on millennial timescales and highlight their importance in shaping today's groundwater salinity distribution. We found free convection to drive large-scale fingered infiltration of seawater to depths of 200 m within decades after a marine transgression, displacing the originally present groundwater upwards. Subsequent infiltration of fresh meteoric water was, in contrast, hampered by the existing density gradient. We observed discontinuous aquitards to exert a significant control on infiltration patterns and the resulting evolution of groundwater salinity. Finally, adding to a long-term scientific debate on the origins of groundwater salinity in Dutch coastal aquifers, our modeling results suggest a more significant role of pre-Holocene groundwater in the present-day groundwater salinity distribution in the Netherlands than previously recognized. Though conceptual, comprehensively modeling the Holocene evolution of groundwater salinity, age and origin offered a unique view on the complex processes shaping groundwater in coastal aquifers over millennial timescales.
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Walter, Rachel M., Hussein R. Sayani, Thomas Felis, Kim M. Cobb, Nerilie J. Abram, Ariella K. Arzey, Alyssa R. Atwood i in. "The CoralHydro2k database: a global, actively curated compilation of coral δ18O and Sr ∕ Ca proxy records of tropical ocean hydrology and temperature for the Common Era". Earth System Science Data 15, nr 5 (24.05.2023): 2081–116. http://dx.doi.org/10.5194/essd-15-2081-2023.
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Abstract. The response of the hydrological cycle to anthropogenic climate change, especially across the tropical oceans, remains poorly understood due to the scarcity of long instrumental temperature and hydrological records. Massive shallow-water corals are ideally suited to reconstructing past oceanic variability as they are widely distributed across the tropics, rapidly deposit calcium carbonate skeletons that continuously record ambient environmental conditions, and can be sampled at monthly to annual resolution. Climate reconstructions based on corals primarily use the stable oxygen isotope composition (δ18O), which acts as a proxy for sea surface temperature (SST), and the oxygen isotope composition of seawater (δ18Osw), a measure of hydrological variability. Increasingly, coral δ18O time series are paired with time series of strontium-to-calcium ratios (Sr/Ca), a proxy for SST, from the same coral to quantify temperature and δ18Osw variability through time. To increase the utility of such reconstructions, we present the CoralHydro2k database, a compilation of published, peer-reviewed coral Sr/Ca and δ18O records from the Common Era (CE). The database contains 54 paired Sr/Ca–δ18O records and 125 unpaired Sr/Ca or δ18O records, with 88 % of these records providing data coverage from 1800 CE to the present. A quality-controlled set of metadata with standardized vocabulary and units accompanies each record, informing the use of the database. The CoralHydro2k database tracks large-scale temperature and hydrological variability. As such, it is well-suited for investigations of past climate variability, comparisons with climate model simulations including isotope-enabled models, and application in paleodata-assimilation projects. The CoralHydro2k database is available in Linked Paleo Data (LiPD) format with serializations in MATLAB, R, and Python and can be downloaded from the NOAA National Center for Environmental Information's Paleoclimate Data Archive at https://doi.org/10.25921/yp94-v135 (Walter et al., 2022).
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Mikhailova, Vasileva, Fedorov, Ershova, Vereshchagin, Rogov i Pokrovsky. "Glendonite-Like Carbonate Aggregates from the Lower Ordovician Koporye Formation (Russian Part of the Baltic Klint): Detailed Mineralogical and Geochemical Data and Paleogeographic Implications". Minerals 9, nr 9 (29.08.2019): 524. http://dx.doi.org/10.3390/min9090524.
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Stellate and plate-like carbonate bodies, traditionally called anthraconites, are found throughout the Baltic-Ladoga Klint in bituminous shale of the Koporye Formation (Tremadocian, Lower Ordovician). Although this time interval is usually considered as a greenhouse, there is some evidence for the existence of at least temporary cold conditions during the Cambrian–Ordovician. However, the origin of anthraconites is still strongly debated. We studied the mineralogical, petrographic, cathodoluminescence, geochemical, and isotopic characteristics of anthraconites from five sections of the Russian part of the Baltic paleobasin. A close similarity between the morphological, petrographic, cathodoluminescence, and isotopic characteristics of the studied anthraconites with those of glendonites allow us to suggest that these bodies formed in a similar paleo-environment and should be considered as pseudomorphs of the mineral ikaite. The oxygen and carbon isotope ratios reveal that ikaite precipitation occurred in low-temperature conditions on the seafloor. The carbon isotopic values reveal influence of inorganic seawater carbon along with organic matter decomposition and/or methane oxidation during ikaite-glendonite transformations. The oxygen isotopic composition significantly changed after deposition due to meteoric diagenesis. We propose that the studied Tremadocian anthraconites formed under a region of upwelling, where cold phosphate-rich deep waters rose to the relatively shallow part of the Baltic paleobasin, providing favorable conditions for ikaite precipitation. Based on our cathodoluminescence study, we suggest that ikaite was transformed to calcite over several stages during diagenesis. Mineralogical studies also reveal that primary calcite was transformed to sulfate (gypsum) or dolomite during late superimposed processes.
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Dissard, D., E. Douville, S. Reynaud, A. Juillet-Leclerc, P. Montagna, P. Louvat i M. McCulloch. "Light and temperature effects on δ<sup>11</sup>B and B / Ca ratios of the zooxanthellate coral <i>Acropora</i> sp.: results from culturing experiments". Biogeosciences 9, nr 11 (20.11.2012): 4589–605. http://dx.doi.org/10.5194/bg-9-4589-2012.
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Abstract. The boron isotopic composition (δ11B) of marine carbonates (e.g. corals) is increasingly utilised as a proxy for paleo-pH, with the strong correlation between δ11B of marine calcifiers and seawater pH now well documented. However, the potential roles of other environmental parameters that may also influence both the boron isotopic composition and boron concentration into coral aragonite are poorly known. To overcome this, the tropical scleractinian coral Acropora sp. was cultured under 3 different temperatures (22, 25 and 28 °C) and two light conditions (200 and 400 μmol photon m−2 s−1). The δ11B indicates an increase in internal pH that is dependent on the light conditions. Changes in light intensities from 200 to 400 μmol photon m−2 s−1 seem to indicate an apparent decrease in pH at the site of calcification, contrary to what is expected in most models of light-enhanced calcification. Thus, variations in light conditions chosen to mimic average annual variations of the natural environments where Acropora sp. colonies can be found could bias pH reconstructions by about 0.05 units. For both light conditions, a significant impact of temperature on δ11B can be observed between 22 and 25 °C, corresponding to an increase of about 0.02 pH-units, while no further δ11B increase can be observed from 25 to 28 °C. This non-linear temperature effect complicates the determination of a correction factor. B / Ca ratios decrease with increasing light, consistent with the decrease in pH at the site of calcification under enhanced light intensities. When all the other parameters are constant, boron concentrations in Acropora sp. increase with increasing temperatures and increasing carbonate ion concentrations. These observations contradict previous studies where B / Ca in corals was found to vary inversely with temperature, suggesting that the controlling factors driving boron concentrations have not yet been adequately identified and might be influenced by other environmental variables and/or species-specific responses.
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Brinkmann, Inda, Christine Barras, Tom Jilbert, Tomas Næraa, K. Mareike Paul, Magali Schweizer i Helena L. Filipsson. "Drought recorded by Ba∕Ca in coastal benthic foraminifera". Biogeosciences 19, nr 9 (16.05.2022): 2523–35. http://dx.doi.org/10.5194/bg-19-2523-2022.
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Abstract. Increasing occurrences of extreme weather events, such as the 2018 drought over northern Europe, are a concerning issue under global climate change. High-resolution archives of natural hydroclimate proxies, such as rapidly accumulating sediments containing biogenic carbonates, offer the potential to investigate the frequency and mechanisms of such events in the past. Droughts alter the barium (Ba) concentration of near-continent seawater through the reduction in Ba input from terrestrial runoff, which in turn may be recorded as changes in the chemical composition (Ba/Ca) of foraminiferal calcium carbonates accumulating in sediments. However, so far the use of Ba/Ca as a discharge indicator has been restricted to planktonic foraminifera, despite the high relative abundance of benthic species in coastal, shallow-water sites. Moreover, benthic foraminiferal Ba/Ca has mainly been used in open-ocean records as a proxy for paleo-productivity. Here we report on a new geochemical data set measured from living (CTG-labeled) benthic foraminiferal species to investigate the capability of benthic Ba/Ca to record changes in river runoff over a gradient of contrasting hydroclimatic conditions. Individual foraminifera (Bulimina marginata, Nonionellina labradorica) were analyzed by laser-ablation ICP-MS over a seasonal and spatial gradient within Gullmar Fjord, Swedish west coast, during 2018–2019. The results are compared to an extensive meteorological and hydrological data set, as well as sediment and pore-water geochemistry. Benthic foraminiferal Ba/Ca correlates significantly to riverine runoff; however, the signals contain both spatial trends with distance to Ba source and species-specific influences such as micro-habitat preferences. We deduce that shallow-infaunal foraminifera are especially suitable as proxy for terrestrial Ba input and discuss the potential influence of water-column and pore-water Ba cycling. While distance to Ba source, water depth, pore-water geochemistry, and species-specific effects need to be considered in interpreting the data, our results demonstrate confidence in the use of Ba/Ca of benthic foraminifera from near-continent records as a proxy for past riverine discharge and to identify periods of drought.
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Huang, Keke, Xiaoning Li, Zuowei Hu i Yijiang Zhong. "Oxygen and Carbon Isotopic Composition of Carbonate Rocks of the Permian Qixia Formation, Sichuan Basin: Thermal Effects of Emeishan Basalt". Earth Sciences Research Journal 20, nr 1 (30.04.2016): 1–9. http://dx.doi.org/10.15446/esrj.v20n1.52403.
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<p>The late Permian thermal events related to Emeishan Basalt has made a great impact on the underlying carbonate rock properties in the western margin of the Yangtze Platform. In this paper, we investigate the carbon and oxygen isotopic composition of the Qixia Formation carbonates from two sections: the Qiaoting Section in the northeastern part of the Sichuan Basin and the Changjianggou Section at the northwestern edge of the Basin. The data reveal that: (i) Samples from Qiaoting section show a relatively narrow range of δ<sup>13</sup>C and δ<sup>18</sup>O, varying from 2.7‰ to 5.2‰ with an average of 4.2‰, and -3.8‰ to -7.8‰ with an average of -5.4‰, respectively. In contrast, Samples from Changjianggou section exhibit larger magnitude of variation in δ<sup>13</sup>C and δ<sup>18</sup>O, ranging from -1‰ to 3.8‰ with an average of 1.5‰, and -2.1 to -9.2‰, with an average of -6.0‰ respectively; (ii) δ<sup>13</sup>C and δ<sup>18</sup>O records in carbonates from Qiaoting section are similar to those of Middle Permian seawater whereas carbonates from the Changjianggou section are depleted in <sup>13</sup>C and <sup>18</sup>O compared to contemporary seawater; (iii) On the basis of combined petrographic and paleo-heat flow evidence, the lower carbon and oxygen isotopic composition of the carbonates from the Changjianggou section are interpreted to be the results of thermal effects of Emeishan Basalt because of its proximity to the eruption center of the basalt. The high temperature reduced the δ<sup>18</sup>O values of the carbonates and forced the organic matter to mature at an early stage, thus producing <sup>13</sup>C-enriched carbon dioxide to participate in the formation of carbonates. </p><p> </p><p><strong>Composición Isotópica de Oxígeno y Carbón en Rocas de Carbonato de la Formación de Edad Pérmica Qixia, en la Cuenca de Sichuan: Efectos Térmicos del Basalto Emeishan </strong></p><p><strong><br /></strong></p><p><strong>Resumen</strong></p><p>Los eventos térmicos del Pérmico tardío relacionados con el Basalto Emeishan han tenido un gran impacto en las propiedades de las rocas de carbonato subyacentes en el margen occidental de la plataforma Yangtze. En este artículo se investiga la composición isotópica de carbonatos de la formación Qixia en dos secciones: la sección de Qiaoting en la parte nororiental de la cuenca Sichuan y la sección Changjianggou, en el noroccidente de la cuenca. La información evidencia que, (i) las muestras de la sección Qiaoting tienen un espectro más angosto que va de δ<sup>13</sup>C a δ<sup>18</sup>O, con variación de 2.7 ‰ a 5,2 ‰, con un promedio de 4.2 ‰, y -3.8 ‰ a -7.8 ‰, con una media de -5.4 ‰, respectivamente. En contraste, las muestras de la sección Changjianggou tienen una variación de mayor magnitud en δ<sup>13</sup>C a δ<sup>18</sup>O que va desde -1 ‰ hasta 3.8 ‰, con un promedio de 1.5 ‰, y de -2.1 a -9.2 ‰, con una media de -6.0 ‰, respectivamente; (ii) los registros de δ<sup>13</sup>C y δ<sup>18</sup>O en carbonatos son similares a los de agua marina del pérmico medio, mientras que los carbonatos de la sección Changjianggou se ven empobrecidos en 13C y 18O comparados al agua marina de esta edad; con base en la petrografía combinada y la evidencia del flujo paleotérmico, la baja composición isotópica de oxígeno y carbón de los carbonatos en la sección de Changjianggou se interpretó como resultado de los efectos térmicos del Basalto Emeishan debido a la proximidad con el centro de erupción. La alta temperatura redujo los valores de δ<sup>18</sup>O de los carbonatos y llevó a la maduración temprana de la materia orgánica, lo que produjo dióxido de carbono enriquecido en <sup>13</sup>C durante la formación de los carbonatos.</p>
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Li, Fei, Jiaxin Yan, Robert V. Burne, Zhong-Qiang Chen, Thomas J. Algeo, Wen Zhang, Li Tian, Yuanlu Gan, Ke Liu i Shucheng Xie. "Paleo-seawater REE compositions and microbial signatures preserved in laminae of Lower Triassic ooids". Palaeogeography, Palaeoclimatology, Palaeoecology 486 (listopad 2017): 96–107. http://dx.doi.org/10.1016/j.palaeo.2017.04.005.
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Xiao, J., Y. K. Xiao, C. Q. Liu i Z. D. Jin. "Boron isotope fractionation during brucite deposition from artificial seawater". Climate of the Past 7, nr 3 (6.07.2011): 693–706. http://dx.doi.org/10.5194/cp-7-693-2011.
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Abstract. Experiments involving boron incorporation into brucite (Mg(OH)2) from magnesium-free artificial seawater with pH values ranging from 9.5 to 13.0 were carried out to better understand the incorporation behavior of boron into brucite and the influence of it on Mg/Ca-SST proxy and δ11B-pH proxy. The results show that both the concentration of boron in deposited brucite ([B]d) and its boron partition coefficient (Kd) between deposited brucite and final seawater are controlled by the pH of the solution. The incorporation capacity of boron into brucite is almost the same as that into corals, but much stronger than that into oxides and clay minerals. The isotopic compositions of boron in deposited brucite (δ11Bd) are higher than those in the associated artificial seawater (δ11Bisw) with fractionation factors ranging between 1.0177 and 1.0569, resulting from the preferential incorporation of B(OH)3 into brucite. Both boron adsorptions onto brucite and the precipitation reaction of H3BO3 with brucite exist during deposition of brucite from artificial seawater. The simultaneous occurrence of both processes determines the boron concentration and isotopic fractionation of brucite. The isotopic fractionation behaviors and mechanisms of boron incorporated into brucite are different from those into corals. The existence of brucite in corals can affect the δ11B and Mg/Ca in corals and influences the Mg/Ca-SST proxy and δ11B-pH proxy negatively. The relationship between δ11B and Mg/Ca in corals can be used to judge the existence of brucite in corals, which should provide a reliable method for better use of δ11B and Mg/Ca in corals to reconstruct paleo-marine environment.
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Jeong, Chan-Ho, Byeong-Dae Lee, Jae-Ha Yang, Keisuke Nagao, Kyu-Han Kim, Sang-Won Ahn, Yong-Cheon Lee, Yu-Jin Lee i Hyeon-Woo Jang. "Geochemical and Isotopic Compositions and Geothermometry of Thermal Waters in the Magumsan Area, South Korea". Water 11, nr 9 (26.08.2019): 1774. http://dx.doi.org/10.3390/w11091774.
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The Magumsan thermal waters of the southeastern Korean Peninsula are pumped out of six deep wells (average depth, 300 m) at temperatures of 30.8–49 °C. The thermal waters are chemically classified into two groups: NaHCO3 type (<31 °C) and NaCl (HCO3, SO4) type (>40 °C), both of which have chemical compositions that are distinct from local groundwater (Ca–HCO3 type). δ18O and δD values suggest that the thermal waters originate from meteoric water and they are isotopically fractionated by silicate hydration or H2S exchange. δ34S values (+7.0 to +15%) of dissolved sulfate in the thermal waters reflect enrichment in 34S through kinetically controlled oxidation of magmatic pyrite in the thermal aquifer and mixing with paleo-seawater. On the 3He/4He vs. 4He/20Ne diagram, the thermal waters plot along a single air mixing line of dominant crustal He, which indicates that the heat source for the thermal waters is non-volcanogenic thermal energy that is generated from the decay of radioactive elements in crustal rocks. Chalcedony geothermometry and thermodynamic equilibrium calculations using the PHREEQC program indicate a reservoir temperature for the immature thermal waters of 54–86 °C and 55–83 °C, respectively.
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Jasechko, S., A. Lechler, F. S. R. Pausata, P. J. Fawcett, T. Gleeson, D. I. Cendón, J. Galewsky i in. "Late-glacial to late-Holocene shifts in global precipitation δ<sup>18</sup>O". Climate of the Past 11, nr 10 (14.10.2015): 1375–93. http://dx.doi.org/10.5194/cp-11-1375-2015.
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Abstract. Reconstructions of Quaternary climate are often based on the isotopic content of paleo-precipitation preserved in proxy records. While many paleo-precipitation isotope records are available, few studies have synthesized these dispersed records to explore spatial patterns of late-glacial precipitation δ18O. Here we present a synthesis of 86 globally distributed groundwater (n = 59), cave calcite (n = 15) and ice core (n = 12) isotope records spanning the late-glacial (defined as ~ 50 000 to ~ 20 000 years ago) to the late-Holocene (within the past ~ 5000 years). We show that precipitation δ18O changes from the late-glacial to the late-Holocene range from −7.1 ‰ (δ18Olate-Holocene > δ18Olate-glacial) to +1.7 ‰ (δ18Olate-glacial > δ18Olate-Holocene), with the majority (77 %) of records having lower late-glacial δ18O than late-Holocene δ18O values. High-magnitude, negative precipitation δ18O shifts are common at high latitudes, high altitudes and continental interiors (δ18Olate-Holocene > δ18Olate-glacial by more than 3 ‰). Conversely, low-magnitude, positive precipitation δ18O shifts are concentrated along tropical and subtropical coasts (δ18Olate-glacial > δ18Olate-Holocene by less than 2 ‰). Broad, global patterns of late-glacial to late-Holocene precipitation δ18O shifts suggest that stronger-than-modern isotopic distillation of air masses prevailed during the late-glacial, likely impacted by larger global temperature differences between the tropics and the poles. Further, to test how well general circulation models reproduce global precipitation δ18O shifts, we compiled simulated precipitation δ18O shifts from five isotope-enabled general circulation models simulated under recent and last glacial maximum climate states. Climate simulations generally show better inter-model and model-measurement agreement in temperate regions than in the tropics, highlighting a need for further research to better understand how inter-model spread in convective rainout, seawater δ18O and glacial topography parameterizations impact simulated precipitation δ18O. Future research on paleo-precipitation δ18O records can use the global maps of measured and simulated late-glacial precipitation isotope compositions to target and prioritize field sites.
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Chaves, Hernani Aquini Fernandes, René Rodrigues i Marcus Vinicius Berao Ade. "GEOCHEMICAL CHARACTERIZATION OF COAL DEPOSITS OF CANDIOTA COALFIELD RIO BONITO FORMATION (EO-PERMIAN) OF PARANÁ BASIN, SOUTH BRAZIL / CARACTERIZAÇÃO GEOQUÍMICA DOS DEPOSITOS DE CARVÃO DA FORMAÇÃO RIO BONITO (EOPERMIANO DA BACIA DO PARANÁ) NA ÁREA DE SEIVAL, RS (BRASIL)". Journal of Sedimentary Environments 3, nr 1 (19.03.2018): 19–35. http://dx.doi.org/10.12957/jse.2018.33240.
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This work analyses organic geochemistry (total organic carbon - TOC, total Sulphur - S and Rock Eval pyrolysis data) and detailed organic petrography results of the Eo-Permian interval (Rio Bonito Formation, Paraná Basin) in the Grande Candiota area, Rio Grande do Sul State (RS), where the largest Brazilian coalfield is located. Samples were collected along the SVH-07 well and in front of the open-pit mine at Seival. The organic petrography analysis allowed to characterize the coals composition and to classify the stage of coalification. The results reveal that the Grande Candiota coals were deposited in a stormy coastal environment. As the samples present high percentage of inorganic material, the Seival coals must be considered more appropriately as coaly shales. The highest percentage of TOC was observed at the base of the coal Seams. The Upper Seam 7(US7) presents the highest average organic matter content and the Lower Candiota Seam (LCS) the lowest one. The sampled coals can be classified as humic coal due to the predominance of vitrinite, followed by liptinite and inertinite maceral groups. Analyzing each coal Seam individually, it is observed that vitrinite and organic carbon contents are higher in the base of Rio Bonito Formation, whereas inertinite and liptinite contents increase upwards. These variations encompassed a parasequence scale whose base is represented by the carbon Seam deposited at higher humidity conditions, whereas the top paleo soils are associated to longer dry periods. Considering the coal Seams as a whole, it is observed an upward decreasing of the vitrinite content and an increase of inertinite and liptinite, as well as the Hydrogen Index values. These data should be related to a retro gradational system in a transgressive context of the Rio Bonito Formation. The significant increase of sulfur content in Banco Louco Seam also suggests a greater influx of seawater into the depositional system. The Hydrogen Index values show that the coal of US7 has the highest volatile ratio. This behavior is related to the higher liptinite group content in these strata, diminishing the calorific power of this coal. Data from the organic petrography analyzes of the Seival coals were compared with those of the Candiota coalfields, for Lower Candiota and Upper Candiota Seams; it is observed that they have a certain similarity. In addition, the Seival coal organic composition was compared with other South Hemisphere Gondwanan coals, for which they have significant differences related to the higher proportions of liptinite and smaller of inertinite. The coalification stage (rank) for the Seival coals, on the basis of the vitrinite reflectance, ranged from peat to a sub-bituminous B type. ResumoEste estudo apresenta os resultados e interpretação de análises geoquímicas do intervalo eopermiano (Formação Rio Bonito) na área de Seival, Estado do Rio Grande do SuI, onde se encontra a maior reserva brasileira de carvão. As amostras foram coletadas no poço SVH-07 e na frente da mina a céu aberto de Seival, Rio Grande do Sul. Foram realizadas análises de petrografia orgânica e classificação do estágio de carbonificação dos carvões, além de análises geoquímicas para determinação dos teores de carbono orgânico total, enxofre total e pirólise "Rock Eval". Os resultados destas análises foram relacionados com o modelo deposicional em ambiente costeiro tempestítico para os carvões de Grande Candiota.Os resultados relevam que os intervalos carbonosos de Seival devem ser, de modo geral, considerados mais apropriadamente como folhelhos carbonosos, uma vez que as amostras apresentam um alto teor de material inorgânica, fruto de intercalações pelíticas carbonosas com lentes de carvão. Os maiores teores de carbono orgânico encontram-se na base das camadas dos carvões. A camada Superior 7 apresenta o teor médio mais elevado de matéria orgânica, enquanto que o menor teor está na camada Candiota inferior. Os carvões foram classificados como húmicos devido à predominancia do grupo maceral da vitrinita, seguindo-se os grupos da liptinita e da inertinita. Considerando-se cada camada de carvão individualmente, observa-se que, normalmente, os teores de carbono orgânico e de vitrinita são mais elevados na base das camadas, enquanto que, em direção ao topo, há um enriquecimento nos conteúdos relativos de inertinita e liptinita. Estas variações enquadram-se numa escala de parassequência, cuja base é representada pela camada de carvão depositada em condições de maior umidade, e o topo contituido por paleossolos, indica a ocorrência de períodos mais secos. Considerando-se as camadas de carvão em seu conjunto, constatou-se que, em direção ao topo, ocorre um decrescimo no conteúdo de vitrinita e uma elevação nos teores relativos de inertinita e liptinita, assim como, nos valores do índice de hidrogênio. Estes resultados estão relacionados com um sistema retrogradacional condizente com o contexto transgressivo da Formação Rio Bonito. Neste sentido, a elevação substancial dos teores de enxofre, a partir da camada Banco Louco, também sugere um maior influxo da água do mar no sistema deposicional. Os valores do índice de hidrogênio mostram que a camada de carvão com a maior proporção de voláteis é a Superior 7, associados aos macerais do grupo da liptinita, o que, consequentemente, diminuiria o poder calorifico deste carvão. Os dados das anáIises organo-petrográficas dos carvões de Seival foram comparados com os da Jazida de Candiota (RS) para as camadas Candiota inferior, Candiota superior; verifica-se que estes apresentam uma certa similaridade principalmente com as duas primeiras camadas. Além disto, a composição orgânica dos carvões de Seival também foi comparada com a de alguns outros carvões gondwânicos do Hemisfério SuI, apresentando diferenças significativas relacionadas a proporções mais elevadas de liptinita e menores de inertinita. A classificação do grau de carbonificação (rank) para os carvões de Seival, com base no poder refletor médio da vitrinita variou de Turfa a sub-betuminoso B.
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Basu, Pallabi, C. Ishwar-Kumar, Shipra Chaudhary, Ramananda Chakrabarti, M. Satish-Kumar i K. Sajeev. "Major, trace element, and Nd isotopic compositions of banded iron formation and shales from the Sirsi shelf, Dharwar Craton, India: Implications for paleo-seawater chemistry, post-depositional alteration, and provenance". Precambrian Research 382 (listopad 2022): 106882. http://dx.doi.org/10.1016/j.precamres.2022.106882.
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Szynkiewicz, Anna, i Janice L. Bishop. "Assessment of Sulfate Sources under Cold Conditions as a Geochemical Proxy for the Origin of Sulfates in the Circumpolar Dunes on Mars". Minerals 11, nr 5 (11.05.2021): 507. http://dx.doi.org/10.3390/min11050507.
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Determining aqueous sulfate sources in terrestrial cold environments can provide an insight into the surface hydrological conditions and sulfur cycle on Mars. In this study, we analyzed sulfur and oxygen isotope compositions of secondary sulfate salts (e.g., gypsum, thenardite) in the surficial sediments and soils of the McMurdo Dry Valleys (MDV), Antarctica to determine contributions of sulfate from bedrock chemical weathering and atmospheric deposition under persistent dry polar conditions. The sulfate showed wider variation of δ34S (+15.8‰ to +32.5‰) compared to smaller ranges of δ18O (−8.9‰ to −4.1‰). In contrast, the δ34S of bedrock sulfide showed significantly lower and consistent values across the studied area (−0.6‰ to +3.3‰). Based on the δ34S trends, sulfide weathering may contribute up to 20–50% of secondary sulfate salts in the MDV. While the remaining 50–80% of sulfate inputs may originate from atmospheric deposition (e.g., sea aerosols, dimethulsulfide oxidation), the subglacial brines derived by relicts of seawater and/or lake/pond water influenced by microbial sulfate reduction could also be important sulfate endmembers particularly in the Antarctic lowland thaw zones. Additional field observations of frost, ponding water, and thin gypsum crusts on the terrestrial gypsum dunes at White Sands supports reactivity of gypsum on the surface of these dunes during cold winter conditions. Combined with our improved geochemical model of the sulfur cycle for cold Antarctic settings, we propose that transient liquid water or frost was available in near-surface environments at the time of gypsum formation in the north polar region on Mars. Ice and/or water interaction with basaltic sand of the basal unit (paleo-erg) would have enhanced leaching of sulfate from both sulfide oxidation and atmospheric deposition and resulted in formation of secondary gypsum salts.
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Li, Yuan, Wenhui Huang, Bo Jiu, Qilong Sun i Qingsong Che. "Modes of Occurrence and Origin of Minerals in Permian Coals from the Huainan Coalfield, Anhui, China". Minerals 10, nr 5 (29.04.2020): 399. http://dx.doi.org/10.3390/min10050399.
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Minerals in coal provide useful information for not only paleo-environments of peat accumulation, but also for geological evolution during later diagenesis and/or epigenesis. This paper reports new data on coal quality and the mineralogical and geochemical compositions of 17 unaltered (by intrusion) coal samples collected from the Huainan coalfield, providing new insight into the origins and modes of occurrence of the minerals in coal and their geological evolution. The results showed that the studied coal samples were low rank bituminous coal, with low ash yield (11.92–38.31%, average 24.80%) and high volatile content (25.13–43.43%, average 37.29%). Minerals in the coal mainly included kaolinite and quartz; varying proportions of calcite, siderite, ankerite, and pyrite; and traces of chlorite, zircon, strontianite, apatite, and gorceixite. Typical modes of mineral occurrence could be used to determine the formation stage of minerals. The detrital mineral, occurring as sub-angular to rounded discrete fragments or thin layers intimately admixed with organic matter at particular horizons, was of terrigenous origin, deposited during peat accumulation. Cell infillings, as well as nodule siderites and polycrystalline aggregates of pyrite, precipitated during the syngenetic to early diagenetic stages. Cleat infillings, compressed cell infillings, and fracture infillings precipitated in the epigenetic stage. However, the stage of mineral formation of the pore infilling was difficult to determine. Combined with coal quality, mineralogy, and geochemical analysis, the sedimentary environment of Shanxi Formation was affected by seawater, and Fe-rich hydrothermal fluids filled into the No. 3 coal seam in the epigenetic stage. The sedimentary environment of the No. 8 coal seam had widespread reduction and acid conditions due to basin subsidence, and sulfate-rich hydrothermal fluids may have been formed during the peat deposition stage. In contrast, the peat accumulation environment of the Upper Shihezi Formation was oxidized with a low pH condition. Alkaline fluid then flowed into the No. 13-1 coal seam in the epigenetic stage.
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Cisneros-Lazaro, Deyanira, Arthur Adams, Jinming Guo, Sylvain Bernard, Lukas P. Baumgartner, Damien Daval, Alain Baronnet i in. "Fast and pervasive diagenetic isotope exchange in foraminifera tests is species-dependent". Nature Communications 13, nr 1 (10.01.2022). http://dx.doi.org/10.1038/s41467-021-27782-8.
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AbstractOxygen isotope compositions of fossil foraminifera tests are commonly used proxies for ocean paleotemperatures, with reconstructions spanning the last 112 million years. However, the isotopic composition of these calcitic tests can be substantially altered during diagenesis without discernible textural changes. Here, we investigate fluid-mediated isotopic exchange in pristine tests of three modern benthic foraminifera species (Ammonia sp., Haynesina germanica, and Amphistegina lessonii) following immersion into an 18O-enriched artificial seawater at 90 °C for hours to days. Reacted tests remain texturally pristine but their bulk oxygen isotope compositions reveal rapid and species-dependent isotopic exchange with the water. NanoSIMS imaging reveals the 3-dimensional intra-test distributions of 18O-enrichment that correlates with test ultra-structure and associated organic matter. Image analysis is used to quantify species level differences in test ultrastructure, which explains the observed species-dependent rates of isotopic exchange. Consequently, even tests considered texturally pristine for paleo-climatic reconstruction purposes may have experienced substantial isotopic exchange; critical paleo-temperature record re-examination is warranted.
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Grasse, Patricia, Kristin Haynert, Kristin Doering, Sonja Geilert, Janice L. Jones, Mark A. Brzezinski i Martin Frank. "Controls on the Silicon Isotope Composition of Diatoms in the Peruvian Upwelling". Frontiers in Marine Science 8 (23.07.2021). http://dx.doi.org/10.3389/fmars.2021.697400.
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The upwelling area off Peru is characterized by exceptionally high rates of primary productivity, mainly dominated by diatoms, which require dissolved silicic acid (dSi) to construct their frustules. The silicon isotope compositions of dissolved silicic acid (δ30SidSi) and biogenic silica (δ30SibSi) in the ocean carry information about dSi utilization, dissolution, and water mass mixing. Diatoms are preserved in the underlying sediments and can serve as archives for past nutrient conditions. However, the factors influencing the Si isotope fractionation between diatoms and seawater are not fully understood. More δ30SibSi data in today’s ocean are required to validate and improve the understanding of paleo records. Here, we present the first δ30SibSi data (together with δ30SidSi) from the water column in the Peruvian Upwelling region. Samples were taken under strong upwelling conditions and the bSi collected from seawater consisted of more than 98% diatoms. The δ30SidSi signatures in the surface waters were higher (+1.7‰ to +3.0‰) than δ30SibSi (+1.0‰ to +2‰) with offsets between diatoms and seawater (Δ30Si) ranging from −0.4‰ to −1.0‰. In contrast, δ30SidSi and δ30SibSi signatures were similar in the subsurface waters of the oxygen minimum zone (OMZ) as a consequence of a decrease in δ30SidSi. A strong relationship between δ30SibSi and [dSi] in surface water samples supports that dSi utilization of the available pool (70 and 98%) is the main driver controlling δ30SibSi. A comparison of δ30SibSi samples from the water column and from underlying core-top sediments (δ30SibSi_sed.) in the central upwelling region off Peru (10°S and 15°S) showed good agreement (δ30SibSi_sed. = +0.9‰ to +1.7‰), although we observed small differences in δ30SibSi depending on the diatom size fraction and diatom assemblage. A detailed analysis of the diatom assemblages highlights apparent variability in fractionation among taxa that has to be taken into account when using δ30SibSi data as a paleo proxy for the reconstruction of dSi utilization in the region.
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Wang, Xiaolei, Ming Tang, Jeff Moyen, Di Wang, Alfred Kröner, Chris Hawkesworth, Xiaoping Xia i in. "The onset of deep recycling of supracrustal materials at the Paleo-Mesoarchean boundary". National Science Review, 30.07.2021. http://dx.doi.org/10.1093/nsr/nwab136.
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Abstract Recycling of supracrustal materials, and in particular hydrated rocks, has profound impacts on mantle composition and thus on the formation of continental crust because water modifies the physical properties of lithological systems and the mechanisms of partial melting and fractional fractionation. On the modern Earth, plate tectonics offers an efficient mechanism for mass transport from the Earth's surface to its interior, but how far this mechanism dates back in the Earth's history is still uncertain. Here, we use zircon O isotopes to track recycling of supracrustal materials into the magma sources of early Archean igneous suites from the Kaapvaal craton, southern Africa. The mean δ18O values of zircon from TTG (tonalite–trondhjemite–granodiorite) rocks abruptly increase at the Paleo-Mesoarchean boundary (ca. 3230 million years ago; Ma), from mantle zircon values of 5–6‰ to approaching 7.1‰, and this increase occurs in the ≤ 3230 Ma rocks with elevated Dy/Yb ratios. The 18O enrichment is a unique signature of low temperature water-rock interaction on the Earth's surface. Because the later phase was emplaced into the same crustal level as the older one and TTG magmas would derive from melting processes in the garnet stability field (>40 km depth), we suggest that this evident shift in TTG zircon O isotopic compositions records the onset of recycling of the mafic oceanic crust that underwent the seawater hydrothermal alteration at low temperature. The onset of enhanced recycling of the supracrustal materials may also develop elsewhere in other Archean cratons and reflects a significant change in tectonic realm during craton formation and stabilization, which may be important processes for the operation of plate tectonics on early Earth.
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Wang, Wenhao, Heather Goring-Harford, Korinna Kunde, E. Malcolm S. Woodward, Maeve C. Lohan, Douglas P. Connelly i Rachael H. James. "Biogeochemical cycling of chromium and chromium isotopes in the sub-tropical North Atlantic Ocean". Frontiers in Marine Science 10 (26.05.2023). http://dx.doi.org/10.3389/fmars.2023.1165304.
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Chromium (Cr) is a redox-sensitive element and because Cr isotopes are fractionated by redox and/or biological processes, the Cr isotopic composition of ancient marine sediments may be used to infer changes in past seawater oxygenation or biological productivity. While there appears to be a ‘global correlation’ between the dissolved Cr concentration and Cr isotopic composition of seawater, there is ongoing debate about the relative importance of external sources and internal cycling on shaping the distribution of dissolved Cr that needs to be resolved to validate the efficacy of using Cr isotopes as a paleo proxy. Here, we present full water column depth profiles of total dissolved Cr (Cr(VI)+Cr(III)) and dissolved Cr isotopes (δ53Cr), together with ancillary data, for three stations along a transect (GEOTRACES GApr08) across the sub-tropical North Atlantic. Concentrations of dissolved Cr ranged between 1.84 and 2.63 nmol kg-1, and δ53Cr values varied from 1.06 to 1.42‰. Although atmospheric dust, hydrothermal vents and seabed sediments have the potential to modify the distribution of Cr in the oceans, based on our observations, there is no clear evidence for substantial input of Cr from these sources in our study region although benthic inputs of Cr may be locally important in the vicinity of hydrothermal vents. Subsurface waters (below the surface mixed layer to 700 m water depth) were very slightly depleted in Cr (by up to ~0.4 nmol kg-1), and very slightly enriched in heavy Cr isotopes (by up to ~0.14‰), relative to deeper waters and the lowest Cr concentrations and highest δ53Cr values coincided with lowest concentrations of colloidal (0.02 to 0.2 μm size fraction) Fe. We found no direct evidence for biological uptake of dissolved Cr in the oligotrophic euphotic zone or removal of Cr in modestly oxygen depleted waters (O2 concentrations ~130 μmol kg-1). Rather, we suggest removal of Cr (probably in the form of Cr(III)) in subsurface waters is associated with the formation of colloid aggregates of Fe-(oxyhydr)oxides. This process is likely enhanced by the high lithogenic particle load in this region, and represents a previously unrecognized export flux of Cr. Regeneration of Cr in deeper waters leads to subtly increased levels of Cr alongside decreased δ53Cr values at individual sites, but this trend is more obvious at the global scale, with δ53Cr values decreasing with increasing radiocarbon age of deep waters, from 1.16 ± 0.10‰ (1SD, n=11) in deep Atlantic waters to 0.77 ± 0.10‰ (1SD, n=25) in deep Pacific waters. Removal of relatively isotopically light Cr from subsurface waters onto particulate material and regeneration of this Cr back into the dissolved phase in deep waters partly accounts for the systematic relationship between δ53Cr and Cr concentrations in seawater discussed by other studies.
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Herlambang, Adhipa, Ardiansyah I. Koeshidayatullah, Abduljamiu O. Amao, Abdulwahab M. Bello, Faisal Al-Ghamdi, Muhammad H. Malik i Khalid A. H. Al-Ramadan. "Structural diagenesis and dolomitization of Cenozoic post-rift carbonates in the Red Sea rift basin: A multiproxy approach". Frontiers in Earth Science 10 (17.11.2022). http://dx.doi.org/10.3389/feart.2022.1037126.
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Middle Miocene post-rift sediments are considered prolific subsurface reservoirs, representing one of the thickest sequences in the Red Sea rift basin. In the Umm Luj Basin of the eastern Red Sea, post-rift sediments are well exposed and represented by a carbonate-dominated system of the Raghama Formation. This formation was intensely fractured, following the rifting trend of the Red Sea. Such fractures and their associated diagenetic products could provide a significant archive of past tectonic fluid evolution. However, little is known about the origin and timing of the different fluid flows and diagenetic processes in the area. This study aims to resolve this issue by integrating fracture and multiproxy geochemical analyses of calcite precipitated in veins, fault breccia, and dolomitized host rock. The δ18O and δ13C isotopic compositions of calcite veins show tight clustering, varying between −10.6 and −9.5‰ and between −7.9 and −7.2‰, respectively. Meanwhile, the precipitated calcite along the fault breccia exhibited a closer to host rock isotopic composition (δ18O = −6.8‰; δ13C = −4.8‰). The δ18OVPDB of the dolomitized host rock shows a heavier average value, closer to the expected range of Miocene seawater. X-ray diffraction analysis shows that the veins have a high magnesium calcite content (up to 79.5%). In contrast, all the host rock samples, except samples 1-1BH, have dolomite contents of up to 94.3%, as well as breccia fragments. Thus, we argue that the structural diagenesis history of the study area comprises two distinct fluid members and tectonic events. The first member is the deposition of heavier isotopic composition related to dolomitization at slightly higher temperatures of up to 42.2°C. The second fluid flow member corresponded to a depleted isotopic calcite member with a temperature of 33°C. Compared with the Midyan Peninsula, the study area shares the same regional tectonic events, but the local tectonic and depositional settings could act as the determining factors of the dolomitization mechanism and meteoric alteration in each location. Hence, our results provide a new understanding of paleo-fluid circulation related to the evolution of tectonic events and highlights the value of integrating fracture and multiproxy geochemical analysis for structural diagenetic studies.
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Jones, Simon M., Jonathan Cloutier, Anthony R. Prave, Timothy D. Raub, Eva E. Stüeken, Holly J. Stein, Gang Yang i Adrian J. Boyce. "Fluid Flow, Alteration, and Timing of Cu-Ag Mineralization at the White Pine Sediment-Hosted Copper Deposit, Michigan, USA". Economic Geology, 1.08.2023. http://dx.doi.org/10.5382/econgeo.5013.
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Abstract White Pine, located in Michigan’s Upper Peninsula, is an archetypal sediment-hosted stratiform copper deposit. The Midcontinent rift system is one of only seven basins globally that host a giant sediment-hosted stratiform copper deposit. Despite many similarities with other deposits of this type, White Pine displays some important differences, including the late Mesoproterozoic age, a thick basalt sequence, an apparent lack of evaporites, and a lacustrine depositional setting. This study analyzes paleofluid flow related to the formation of White Pine and places a particular emphasis on structural and diagenetic fluid pathways. Most of the ore is located in a 30-m-wide zone spanning the Copper Harbor Formation red beds and the overlying Nonesuch Formation shales. Sedimentation of these units was accompanied by subtle synsedimentary faulting. Premineralization phases include calcite concretions and nodules, illite and hematite grain coatings, isopachous chlorite rims, emplacement of liquid petroleum (now pyrobitumen), and bleaching. Mineralization introduced native copper into the footwall sandstones and a zoned suite of native copper and sulfur-poor copper sulfide minerals across a migrating redox front in the overlying shales where copper minerals nucleated on authigenic and detrital chlorite grains. Postmineralization phases include quartz cement, calcite cement, and calcite veins that partially overlapped inversion of synsedimentary faults. Contrary to previous studies, we identified evidence for only one phase of mineralization. An Re-Os chalcocite age of 1067 ± 11 Ma places mineralization 11 to 17 m.y. after host-rock deposition. Sulfide δ34S values of –14.0 to 29.9‰ suggest an important contribution from sour gas and thermochemical sulfate reduction of seawater. Carbon (δ13C) and oxygen (δ18O) isotope compositions of five calcite generations range from –15.1 to –1.3‰ and 10.4 to 41.3‰, respectively, and record early meteoric pore water displaced by later seawater. White Pine is both a sediment-hosted stratiform copper deposit and a paleo-oil field. Synsedimentary faults controlled the sedimentological character of the upper Copper Harbor Formation, and together these imparted a strong control on fluid flow and later diagenetic processes. Early oxidized meteoric fluids were displaced by liquid petroleum and sour gas, which were in turn succeeded by metal-rich but sulfate-poor oxidized seawater. Burial compaction during deposition of the overlying Freda Formation drove fluids through White Pine due to its situation on a paleotopographic high near the basin margin. Mineralization occurred at ~125°C at depths of ~2.0 km and spanned incipient basin inversion related to the distal effects of Grenvillian orogenesis. The hightenor copper mineral assemblage is the product of an abundant supply of metal from basaltic volcanic detritus in the Copper Harbor Formation and low seawater sulfate concentrations in late Mesoproterozoic oceans. This demonstrates that viable sediment-hosted stratiform copper systems can form when a readily leachable metal source rock is present, even if hypersaline and sulfate-rich brines are not.
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Bai, Ying, Zhenyu Zhao, Zhe Zhao i Jianrong Gao. "Multiphase dolomitization mechanisms of the Cambrian upper Changping Formation, North China Platform, China". Frontiers in Earth Science 11 (8.02.2023). http://dx.doi.org/10.3389/feart.2023.1091424.
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The Cambrian dolomite reservoirs of the North China Platform offer good exploration prospects, but their occurrence and the impacts of dolomitization on reservoir quality are not yet clearly understood. The study herein assesses outcrop samples in the Cambrian upper Changping Formation, Dingjiatan area, and highlights the important role of multiphase dolomitization in the formation of paleo-reservoirs of acceptable porosity, where oil pools and fields may be discovered. A combination of petrology, fluid inclusion microthermometry, isotopes, and trace element compositions has been used to explain multiphase dolomitization mechanisms and their impacts on dolomite reservoirs. Five types of dolomites are identified through outcrop observation, thin section identification via transmitted light, and cathodoluminescence. The following geochemical analyses reveal various dolomitization mechanisms. In the (pene) contemporaneous stage, microbial dolomite is commonly related to microbial metabolic activities with significant carbon isotopic depletion compared to the Cambrian seawater values. With the influence of microbial dolomitization, dolomicrite corresponds to the sabkha dolomitization mode in a low-salinity seawater environment and early-stage dolomitization. The structureless dolomite (ssD) in the early highstand systems tract (EHST), characterized by elevated 87Sr/88Sr ratios and low oxygen isotopic values, forms from stratum brine water in the shallow-middle burial stage rather than in the (pene) contemporaneous stage. In contrast, ssD in the late highstand systems tract (LHST) undergoes (pene) contemporaneous dolomitization at salinities between 6% and 28% before later pore water transformation, with the participation of atmospheric freshwater through faults and unconformities exhibiting the lowest inclusion temperature and salinity values. The medium to coarse crystalline dolomite (MCD) in the LHST and the saddle dolomite (SD) in the EHST with low REE values are atypical hydrothermal dolomites caused by a combined superposition of middle-deep burial hydrothermal fluids at temperatures >150°C and stratigraphic brines. The MCD is also influenced by terrigenous water characterized by relatively low Eu anomaly values. Finally, the mechanisms of porosity increase are investigated, and it is concluded that the pore increase caused by the (pene) contemporaneous reflux interaction and the later pore retention both lead to better ssD reservoirs in the LHST than in the EHST.
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Edwards, Cole T., Clive M. Jones, Page C. Quinton i David A. Fike. "Oxygen isotope (δ18O) trends measured from Ordovician conodont apatite using secondary ion mass spectrometry (SIMS): Implications for paleo-thermometry studies". GSA Bulletin, 3.05.2021. http://dx.doi.org/10.1130/b35891.1.
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The oxygen isotopic compositions (δ18O) of minimally altered phosphate minerals and fossils, such as conodont elements, are used as a proxy for past ocean temperature. Phosphate is thermally stable under low to moderate burial conditions and is ideal for reconstructing seawater temperatures because the P-O bonds are highly resistant to isotopic exchange during diagenesis. Traditional bulk methods used to measure conodont δ18O include multiple conodont elements, which can reflect different environments and potentially yield an aggregate δ18O value derived from a mixture of different water masses. In situ spot analyses of individual elements using micro-analytical techniques, such as secondary ion mass spectrometry (SIMS), can address these issues. Here we present 108 new δ18O values using SIMS from conodont apatite collected from four Lower to Upper Ordovician stratigraphic successions from North America (Nevada, Oklahoma, and the Cincinnati Arch region of Kentucky and Indiana, USA). The available elements measured had a range of thermal alteration regimes that are categorized based on their conodont alteration index (CAI) as either low (CAI = 1−2) or high (CAI = 3−4). Though individual spot analyses of the same element yield δ18O values that vary by several per mil (‰), most form a normal distribution around a mean value. Isotopic variability of individual spots can be minimized by avoiding surficial heterogeneities like cracks, pits, or near the edge of the element and the precision can be improved with multiple (≥4) spot analyses of the same element. Mean δ18O values from multiple conodonts from the same bed range between 0.0 and 4.3‰ (median 1.0‰), regardless of low or high CAI values. Oxygen isotopic values measured using SIMS in this study reproduce values similar to published trends, namely, δ18O values increase during the Early−Middle Ordovician and plateau by the mid Darriwilian (late Middle Ordovician). Twenty-two of the measured conodonts were from ten sampled beds that had been previously measured using bulk analysis. SIMS-based δ18O values from these samples are more positive by an average of 1.7‰ compared to bulk values, consistent with observations by others who attribute the shift to carbonate- and hydroxyl-related SIMS matrix effects. This offset has implications for paleo-temperature model estimates, which indicate that a 4 °C temperature change corresponds to a 1‰ shift in δ18O (‰). Although this uncertainty precludes precise paleo-temperature reconstructions by SIMS, it is valuable for identifying spatial and stratigraphic trends in temperature that might not have been previously possible with bulk approaches.