Geochimica et Cosmochimica Acta最新文献

{"title":"Vacuum-thermal alteration of lunar soil: Evidence from iron whiskers on troilite in Chang’e-5 samples","authors":"Chen Li ,&nbsp;Yang Li ,&nbsp;Kuixian Wei ,&nbsp;Xiumin Chen ,&nbsp;Kairui Tai ,&nbsp;Zhuang Guo ,&nbsp;Rui Li ,&nbsp;Han Yu ,&nbsp;Xiongyao Li ,&nbsp;Wenhui Ma ,&nbsp;Jianzhong Liu","doi":"10.1016/j.gca.2024.10.035","DOIUrl":"10.1016/j.gca.2024.10.035","url":null,"abstract":"<div><div>The formation of a unique microstructure of minerals on the surface of airless bodies is attributed to space weathering. However, it is difficult to distinguish the contributions of meteorite impacts and solar wind to the modification of lunar soil, resulting in limited research on the space weathering mechanism of airless bodies. The thermochemical reactivity of troilite can be used to distinguish the contributions of impact events and solar wind to the modification of lunar soil and provide evidence for space weathering of lunar soil. We examined the structure of troilite particles in the Chang’e-5 lunar soil and determined whether an impact caused the thermal reaction. Microanalysis showed that troilite underwent substantial mass loss during thermal desulfurization, forming a crystallographically aligned porous structure with iron whiskers, an oxygen-rich layer, and other crystallographic and thermochemical evidence. We used an <em>ab initio</em> deep neural network model and thermodynamic calculations to conduct experiments and determine the anisotropy and crystal growth of troilite. The surface microstructure of troilite was transformed by the thermal reaction in the vacuum on the lunar surface. Similar structures have been found in near-Earth objects (NEOs), indicating that small bodies underwent the same impact-induced thermal events. Thus, thermal reactions in a vacuum are likely ubiquitous in the solar system and critical for space weathering alterations of the soil of airless bodies.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"387 ","pages":"Pages 28-37"},"PeriodicalIF":4.5,"publicationDate":"2024-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142662824","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Colloids control the mobilization of released zinc- and cadmium- species in calcite-rich soils","authors":"Xinyang Li ,&nbsp;Jiawen Zhou ,&nbsp;Pengjie Hu ,&nbsp;Tong Zhou ,&nbsp;Zhu Li ,&nbsp;Yongming Luo ,&nbsp;Longhua Wu ,&nbsp;Michael Schindler","doi":"10.1016/j.gca.2024.11.003","DOIUrl":"10.1016/j.gca.2024.11.003","url":null,"abstract":"<div><div>Cadmium (Cd)-bearing sphalerite (SP, ZnS) and smithsonite (SM, ZnCO₃) particulate matter (PM) is deposited on soils near carbonate-hosted Zn ore deposits. Whether and how carbonate rocks such as limestone influence the mobility of Cd and Zn in soils is largely unknown. For this reason, we conducted a soil incubation experiment to investigate the chemical and mineralogical changes in soil–soil solution samples, including the occurrence of Cd- and Zn-bearing colloids and nanoparticles. Here the addition of calcite to SP- and SM-spiked soils promoted the formation of Cd- and Zn- bearing nanoparticles and colloids and thus significantly decreased the concentrations of Cd and Zn in soil solutions. Transmission electron microscope and extended X-ray absorption fluorescence spectroscopy showed that the addition of calcite resulted in the formation of Fe-OM-Ca colloids (OM = organic matter), sequestrating Cd and Zn. Furthermore, the release of Ca²⁺ during the dissolution of calcite promoted the aggregation of colloids and thus decreased the mobility of Cd- and Zn-bearing colloids in the soil column. The addition of calcite also decreased the amount of Cd and Zn released from the dissolution of SP and SM through the formation of calcite nano-layers armoring particles of the SP and SM phases. This study provides new insights into the environmental fate of particulate Cd and Zn in soils around carbonate-hosted Pb-Zn ore deposits. Specifically, it shows that the formation and aggregation of Cd- and Zn-bearing colloids decrease the mobility and bioavailability of both elements.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"387 ","pages":"Pages 12-27"},"PeriodicalIF":4.5,"publicationDate":"2024-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142662873","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Metabolic imprints in the hydrogen isotopes of Archaeoglobus fulgidus tetraether lipids","authors":"Jeemin H. Rhim ,&nbsp;Sebastian Kopf ,&nbsp;Jamie McFarlin ,&nbsp;Ashley E. Maloney ,&nbsp;Harpreet Batther ,&nbsp;Carolynn M. Harris ,&nbsp;Alice Zhou ,&nbsp;Xiahong Feng ,&nbsp;Yuki Weber ,&nbsp;Shelley Hoeft-McCann ,&nbsp;Ann Pearson ,&nbsp;William D. Leavitt","doi":"10.1016/j.gca.2024.09.032","DOIUrl":"10.1016/j.gca.2024.09.032","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The stable hydrogen isotope composition of archaeal lipids is emerging as a potential paleoenvironmental proxy, adding to the well-established application of plant leaf wax-derived &lt;em&gt;n&lt;/em&gt;-alkanes in paleohydrological reconstruction. A handful of studies reported relatively invariant and depleted hydrogen isotope compositions for archaeal lipids despite the range of different organisms and growth conditions explored. However, how modes of metabolism and physiological state (growth phase) affect the hydrogen isotope signatures of archaeal lipids remains poorly understood, limiting our ability to interpret archaeal lipid biomarker records from the environment. Here we conducted water isotope label experiments with a metabolically flexible and well-studied model archaeon &lt;em&gt;Archaeoglobus fulgidus&lt;/em&gt; and quantified the hydrogen isotope fractionation between lipids and water in response to different carbon substrates and electron donor–acceptor pairs at different growth phases. The &lt;sup&gt;2&lt;/sup&gt;H/&lt;sup&gt;1&lt;/sup&gt;H fractionation between lipids and water (ε&lt;sub&gt;L/W&lt;/sub&gt;) was overall negative. Both carbon metabolism and growth phase affected the magnitude of isotope fractionation in &lt;em&gt;A. fulgidus&lt;/em&gt;; however, the changes in ε&lt;sub&gt;L/W&lt;/sub&gt; values were relatively subtle where they ranged from –283 to –229 ‰ across all tested conditions, overlapping with the ranges observed for other archaea in previous studies. Isotope flux-balance model results suggest that ≥ 80 % and ≥ 50 % of lipid-bound H in &lt;em&gt;A. fulgidus&lt;/em&gt; cultures directly reflect water isotope compositions (i.e., not via organic substrate or H&lt;sub&gt;2&lt;/sub&gt;) during autotrophy and heterotrophy, respectively. The model results also suggest two main mechanisms of consistent &lt;sup&gt;2&lt;/sup&gt;H depletion observed in &lt;em&gt;A. fulgidus&lt;/em&gt; tetraethers as well as other archaeal lipids reported in previous studies: 1) isotopic re-equilibration via upstream isomerization reactions involving C&lt;sub&gt;5&lt;/sub&gt; units and 2) downstream double bond reduction catalyzed by a flavoenzyme geranylgeranyl reductase. These results are consistent with previous isotope flux-balance model results for a different archaeon. Finally, we synthesized available data to compare ε&lt;sub&gt;L/W&lt;/sub&gt; patterns across all three domains of life: Eukarya, Archaea and Bacteria. Because they vary fundamentally in lipid biosynthesis pathways, we present comparative discussions in pairs, focusing on the shared biochemical mechanisms among isoprenoid lipids and potential signals of metabolic adaptations across prokaryotic lipids. Emerging patterns between diverse archaeal and eukaryotic isoprenoid lipids are consistent with the two proposed mechanisms for &lt;sup&gt;2&lt;/sup&gt;H depletion identified (isomerization and final saturation). The patterns between archaeal isoprenoids and bacterial fatty acids suggest that the general state of energy limitation may also contribute to large, negative values of ε&lt;sub&gt;L/W&lt;/sub&gt; observed in prokaryotic lipi","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"386 ","pages":"Pages 196-212"},"PeriodicalIF":4.5,"publicationDate":"2024-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142662968","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Antimony stable isotope fractionation during adsorption onto birnessite: A molecular perspective from X-ray absorption spectroscopy and density functional theory","authors":"Ziyi Zhou ,&nbsp;Guangyi Sun ,&nbsp;Weiqing Zhou ,&nbsp;Jianwei Zhou ,&nbsp;Xinbin Feng ,&nbsp;Y. Zou Finfrock ,&nbsp;Peng Liu","doi":"10.1016/j.gca.2024.09.028","DOIUrl":"10.1016/j.gca.2024.09.028","url":null,"abstract":"<div><div>Sorption of antimony (Sb) onto birnessite significantly influences the fate of Sb in oceanic and terrestrial environments and fractionates Sb isotopes. Nevertheless, little is known about Sb isotopic fractionation during its adsorption on birnessite. Here, we show the value of Δ¹²³Sb_{adsorbed-aqueous} increases from −0.398 to −0.332 ‰ in 1 h and then decreases and stabilizes at −0.384 ‰ in 72 h. The enrichment of the light Sb isotope is predominantly due to the distortion of the octahedral symmetry. X-ray absorption spectroscopy results indicate Sb first forms a double-corner-sharing complex on birnessite and then transforms to a double-edge-sharing complex during adsorption. The optimized bond distances for double-corner-sharing (3.37 Å) and double-edge-sharing (2.90 Å) complexes calculated using density functional theory (DFT) fits well with the structure (3.41 and 3.00 Å) revealed by X-ray absorption spectroscopy, respectively. The fractionation derived from reduced partition function ratios calculated using DFT aligns well with the experimental results. Therefore, the variation in Sb isotopic fractionation during adsorption is attributed to the evolving structure of Sb complexes on birnessite. Our results demonstrate the isotopic fractionation of Sb during adsorption on birnessite and provide a molecular-scale understanding of Sb behavior, contributing to the correct reconstruction of the Sb isotope composition of ancient seawater using ferromanganese crusts and nodules, and efforts to trace Sb migration in epigenetic mining environments.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"386 ","pages":"Pages 173-184"},"PeriodicalIF":4.5,"publicationDate":"2024-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142662977","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Surface complexation of rare earth elements on goethite in sea-floor hydrothermal environment: Insight from first principles simulations","authors":"Yingchun Zhang,&nbsp;Xiandong Liu,&nbsp;Xiancai Lu,&nbsp;Rucheng Wang","doi":"10.1016/j.gca.2024.09.029","DOIUrl":"10.1016/j.gca.2024.09.029","url":null,"abstract":"<div><div>Deep-sea mud shows tremendous resource potential for rare earth elements (REEs) and its formation is closely associated with sea-floor hydrothermal activities. Iron (oxyhydr)oxides link the sources and sinks of REEs in sea-floor hydrothermal systems. However, the complexation mechanisms of REEs on iron (oxyhydr)oxides have not been well understood yet. In this study, by using the first principles molecular dynamics technique, we first calculated the pK_a’s of surface groups on goethite (1<!--> <!-->1<!--> <!-->0) surface at elevated temperatures relevant to sea-floor hydrothermal systems and then evaluated the complexation structures and free energies of REEs on goethite (1<!--> <!-->1<!--> <!-->0) and (0<!--> <!-->1<!--> <!-->0) surfaces using the method of constraint by taking Sc³⁺, Y³⁺, and La³⁺ as model REE cations. The results show that REE complexation occurs in mildly acidic to neutral conditions. The most thermodynamically stable complexes of REEs are bidentate complexes on two neighboring <img>FeOH sites on goethite (1<!--> <!-->1<!--> <!-->0) surface and tridentate complexes on two neighboring <img>FeOH sites plus one <img>Fe₂OH site on goethite (0<!--> <!-->1<!--> <!-->0) surface. Sc³⁺ complexes match the goethite lattice and can be incorporated into the lattice. The stabilities of REE complexes increase with the distance from hydrothermal vents. Complexation of Y³⁺ is less favored on goethite compared to other REEs whereas Sc³⁺ prefers complexation on goethite (0<!--> <!-->1<!--> <!-->0) surface and La³⁺ exhibits similar stabilities on both (0<!--> <!-->1<!--> <!-->0) and (1<!--> <!-->1<!--> <!-->0) surfaces. The derived atomic level complexation mechanisms would be helpful for the interpretation of experimental data and the prediction of REEs’ behavior in the sea-floor. The findings presented here provide valuable insights into REEs fractionation and enrichment in deep-sea muds.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"386 ","pages":"Pages 185-195"},"PeriodicalIF":4.5,"publicationDate":"2024-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142662979","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A 187Re-187Os and highly siderophile element study of diamondiferous kimberlite melt-mantle interactions and the inferred age of continental lithosphere","authors":"Taryn Linzmeyer ,&nbsp;James M.D. Day ,&nbsp;Raquel Alonso-Perez ,&nbsp;Theo Phahla ,&nbsp;Anton Wolmarans ,&nbsp;Andrew Rogers","doi":"10.1016/j.gca.2024.09.026","DOIUrl":"10.1016/j.gca.2024.09.026","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The ∼ 1.15-billion-year-old (Ga) Premier kimberlite pipe (Cullinan diamond mine), South Africa, is composed of several distinct kimberlite facies (Grey, Brown, Pale Piebald, Dark Piebald, Black Coherent [Type 3C], Blue/Brown Transitional, and Fawn). We report bulk rock Re-Os isotope data for Premier kimberlite facies, as well as for a suite of entrained peridotite and mafic xenoliths. These data are complemented by bulk rock highly siderophile element (HSE: Re, Pd, Pt, Ru, Ir, Os), major- and trace-element abundances. Measured &lt;sup&gt;187&lt;/sup&gt;Os/&lt;sup&gt;188&lt;/sup&gt;Os for the kimberlite facies range from 0.1223 to 0.1672 (γOs&lt;sub&gt;i&lt;/sub&gt; of −2.5 to + 17.4), peridotite xenoliths range from 0.1096 to 0.1244 (γOs&lt;sub&gt;i&lt;/sub&gt; of −13.3 to −1.1), and pyroxenite xenoliths range from 0.1796 to 0.938 (γOs&lt;sub&gt;i&lt;/sub&gt; of + 27 to + 419). A single measured amphibolite xenolith has the most radiogenic measured &lt;sup&gt;187&lt;/sup&gt;Os/&lt;sup&gt;188&lt;/sup&gt;Os of 2.86 (γOs&lt;sub&gt;i&lt;/sub&gt; of + 43). Harzburgite xenoliths yield time of rhenium depletion model ages (T&lt;sub&gt;RD&lt;/sub&gt;) of ∼ 1.5 to 2.8 Ga, consistent with average T&lt;sub&gt;RD&lt;/sub&gt; ages for Premier peridotites (2.4 ± 0.4 Ga). With these and published data, we considered the relationships between kimberlite and mantle xenoliths, compare estimates of relative peridotite incorporation to sampled diamond grade, and explore recratonization versus refertilization arguments with regards to T&lt;sub&gt;RD&lt;/sub&gt; model ages. Kimberlite melt infiltration into Premier peridotite xenoliths is evident from melt veins accounting for ∼ 2 and ∼ 14 modal % of samples, and has led to incompatible element enrichment, including elevated Re. In turn, kimberlites show geochemical evidence for addition of peridotite xenolith fragments, with Type 3C having &gt; 30 % more peridotite contribution than the Brown volcaniclastic facies. Kimberlites and peridotites plot on a &lt;sup&gt;187&lt;/sup&gt;Re/&lt;sup&gt;188&lt;/sup&gt;Os versus &lt;sup&gt;187&lt;/sup&gt;Os/&lt;sup&gt;188&lt;/sup&gt;Os mixing line (R&lt;sup&gt;2&lt;/sup&gt; = 0.92), with kimberlites having older apparent ages than the true age of crystallization. This mixing line provides estimates of lithospheric incorporation into the kimberlites, where the units with higher peridotite incorporation do not correlate with diamond grade. This is likely due to lithological and post-emplacement alteration heterogeneity within the kimberlite units, perhaps also reflecting the eclogitic paragenesis of many Premier diamonds. The peridotites provide evidence for the nature of the lithosphere beneath Premier prior to ∼ 1.15 Ga. Metasomatism of the peridotites is possibly linked to the Bushveld Igneous Event at ∼ 2 Ga, as well as to other magmatic events that affected the Kaapvaal craton from the Archean to the Mesoproterozoic. Premier peridotites do not suggest that the cratonic lithosphere beneath the region was completely replaced. Samples with Proterozoic T&lt;sub&gt;RD&lt;/sub&gt; eruption model ages may represent Archean lithosphere that experienced alteration by metasoma","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"386 ","pages":"Pages 157-172"},"PeriodicalIF":4.5,"publicationDate":"2024-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142662976","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On the origin and evolution of deuterium enrichment in type 1 and 2 chondritic organic solids","authors":"George D. Cody ,&nbsp;Conel M. O’D. Alexander ,&nbsp;Dionysis I. Foustoukos ,&nbsp;Yoko Kebukawa ,&nbsp;Ying Wang","doi":"10.1016/j.gca.2024.09.023","DOIUrl":"10.1016/j.gca.2024.09.023","url":null,"abstract":"<div><div>Rotationally resonant Deuterium Nuclear Magnetic Resonance spectroscopy (D MAS NMR) was applied to IOM isolated from a CR1 chondrite Grosvenor Mountains (GRO) 95577 and a CM2 chondrite (Murchison). It is shown that in IOM D strongly prefers the aliphatic hydrogen reservoir over the aromatic hydrogen reservoir. For GRO 95577, that has a bulk δD of 3303 ‰ (Alexander et al., 2010), the average δD value of the aromatic reservoir is 1740 ± 128 ‰ and the aliphatic reservoir is 4477 ± 105 ‰, i.e., D/H enrichments of 1.27 and 0.64, respectively, relative to the bulk. For Murchison IOM, that has a bulk δD of 811 ‰ (Alexander et al., 2010), the average δD of the aromatic reservoir is 512 ± 88 ‰ and the aliphatic reservoir is 1033 ± 64 ‰ i.e., D/H enrichments of 1.12 and 0.82, respectively, relative to the bulk. D-H exchange between D-enriched water and a type III kerogen reveals nearly equivalent D up take by both aromatics and aliphatics. Laboratory synthesis of IOM-like material in the presence of D₂O reveals a high degree of deuteration with a strong preferential deuteration of the aliphatic hydrogen reservoir indicating that the δD of the water during IOM synthesis is the primary determinant of syn-IOM’s δD. The IOM in GRO 95577 and Murchison (FA and H/C × 100) lie on the molecular evolution line as defined by the IOM of the Tagish Lake clasts and Murchison IOM has experienced more molecular evolution relative to that exhibited by GRO 95577 IOM. A forward prediction derived from the D/H ratios for the aliphatic and aromatic hydrogen reservoirs in Murchison and GRO 95577, relative to their bulk D/H ratios, derived from D MAS NMR, is applied to explain the origin of the Tagish Lake trend of δD vs molecular evolution (H/C × 100). The results of this forward prediction suggest that the Tagish Lake isotopic trend results from a combination of molecular evolution (loss of predominantly aliphatic H and D) and partial D-H exchange with D depleted chondritic water during a short-term hydrothermal alteration event. Such events may be faithfully identified in chondritic organic solids and be a common occurrence, but not necessarily revealed in the mineralogy of type 1 and 2 carbonaceous chondrites.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"386 ","pages":"Pages 139-156"},"PeriodicalIF":4.5,"publicationDate":"2024-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142662970","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Establishing the content in trace and minor elements of magnetite as a biosignature of magnetotactic bacteria","authors":"François P. Mathon ,&nbsp;Matthieu Amor ,&nbsp;François Guyot ,&nbsp;Nicolas Menguy ,&nbsp;Christopher T. Lefevre ,&nbsp;Vincent Busigny","doi":"10.1016/j.gca.2024.09.020","DOIUrl":"10.1016/j.gca.2024.09.020","url":null,"abstract":"<div><div>Magnetotactic bacteria (MTB) produce intracellular magnetite (Fe₃O₄) nanoparticles in a genetically controlled manner. They may represent some of the oldest biomineralizing organisms available in the geological record, but identification of their fossils remains highly debated. While organic molecules are degraded during diagenesis and metamorphic processes, MTB magnetite nanocrystals can be efficiently preserved in the rock record and are referred to as magnetofossils. Experimental work on the freshwater bacterium <em>Magnetospirillum magneticum</em> strain AMB-1 has demonstrated specific minor and trace element patterns distinct from those of abiotic magnetite, and were proposed as a tool for magnetofossil identification. These promising geochemical signatures need to be validated in diverse MTB strains to be used for paleontological reconstruction. Here, we cultivated a marine MTB (<em>Magnetovibrio blakemorei</em> strain MV-1) under various chemical conditions to test possible generalization of this new proxy. MV-1 was grown under various Fe concentrations (50, 100 and 150 μM) and redox states using either Fe(II)-ascorbate or Fe(III)-citrate as Fe sources. The chemical compositions of the growth media and extracted magnetite crystals were determined by ICP-MS analyses to quantify the partitioning of trace and minor elements between magnetite and solution. Results show that partition coefficients do not depend at first order on the Fe concentration and redox state, a crucial conclusion for potential application to natural systems. A comparison of the two strains shows that MV-1 magnetite generally contains higher concentrations of impurities than AMB-1 magnetite. However, a number of elements possess similar partition coefficients and may represent useful chemical proxies for testing the biological origin of magnetite. These consistent elements can be separated into three groups. The first group is composed of elements (Co, Mn, Pb, Sr) highly depleted in MTB magnetite relative to abiotic magnetite. The second group contains elements with similar partitioning in MTB and abiotic magnetite, including Ca and Li. This group may serve as a reference for constraining a paleo-fluid composition. The last group contains elements (Mo, Sn, Se) enriched in MTB magnetite relative to abiotic magnetite. Such enrichments might be related to biological function of those elements. Chemical patterns determined from laboratory experiments therefore represent promising chemical proxies to identify MTB magnetite in the rock record but now need to be tested in modern natural environments, where MTB and surrounding solution can be jointly collected.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"386 ","pages":"Pages 127-138"},"PeriodicalIF":4.5,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142662969","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Oxygen isotope fractionation during amorphous to crystalline calcium carbonate transformation at varying relative humidity and temperature","authors":"Maria P. Asta ,&nbsp;Sarah Bonilla-Correa ,&nbsp;Aurélie Pace ,&nbsp;Martin Dietzel ,&nbsp;Antonio García-Alix ,&nbsp;Torsten Vennemann ,&nbsp;Anders Meibom ,&nbsp;Arthur Adams","doi":"10.1016/j.gca.2024.09.005","DOIUrl":"10.1016/j.gca.2024.09.005","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Crystalline calcium carbonate isotope compositions have been widely used to reconstruct past environments. However, if their isotopic compositions are modified because of crystallization from an amorphous precursor, their reliability as paleo-geochemical proxies can be compromised. This study explored the changes in the oxygen isotope compositions during the transformation of amorphous calcium carbonate (ACC) into crystalline carbonate under different conditions of relative humidity (RH of 33–95 %), temperature (T of 5 °C and 20 °C) and in the presence/absence of atmospheric CO&lt;sub&gt;2&lt;/sub&gt;. The data showed that at low RH and T (e.g., RH ≤ 45 % and 5 °C) when a complete ACC-crystalline carbonate transformation did not take place then the original ACC δ&lt;sup&gt;18&lt;/sup&gt;O values (δ&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;CaCO3&lt;/sub&gt; = −15.9 ± 1.0 ‰, VPDB) were preserved throughout the experimental runtime (up to 144 days). In contrast, in fully crystallized CaCO&lt;sub&gt;3&lt;/sub&gt; (e.g., at RH ≥ 60 %) the δ&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;CaCO3&lt;/sub&gt; values increased rapidly over the first few days, followed by a slower and gradual increase. By the end of the experiments (i.e., after 103–144 days) the crystalline δ&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;CaCO3&lt;/sub&gt; values ranged from −10.4 ‰ to −8.1 ‰ in the presence of atmospheric CO&lt;sub&gt;2&lt;/sub&gt; and from −12.6 ‰ to −9.5 ‰ in the CO&lt;sub&gt;2&lt;/sub&gt;-free experiments. These changes in oxygen isotope compositions of the CaCO&lt;sub&gt;3&lt;/sub&gt; reaction products (calcite and/or vaterite) were mainly driven by exchange with H&lt;sub&gt;2&lt;/sub&gt;O from the hydrated ACC i.e. the synthesis fluid. In CO&lt;sub&gt;2&lt;/sub&gt;-present experiments, oxygen isotope fractionation factors between the CaCO&lt;sub&gt;3&lt;/sub&gt; reaction products and the synthesis fluid (&lt;sup&gt;18&lt;/sup&gt;α&lt;sub&gt;c–w&lt;/sub&gt;) approached or exceeded oxygen isotope equilibrium values. This could be explained by a decrease in the initially high pH of the aqueous fluid released from ACC dissolution during CO&lt;sub&gt;2&lt;/sub&gt; hydration/hydroxylation, which would have increased the oxygen isotope exchange kinetics between H&lt;sub&gt;2&lt;/sub&gt;O and dissolved inorganic carbon (DIC). In some experiments, the hydration/hydroxylation of &lt;sup&gt;18&lt;/sup&gt;O-enriched CO&lt;sub&gt;2&lt;/sub&gt;, due to isotopic salt-effects, might have also resulted in &lt;sup&gt;18&lt;/sup&gt;O-enriched calcium carbonates and calculated fractionation factors that exceeded equilibrium values. In the CO&lt;sub&gt;2&lt;/sub&gt;-free experiments, isotopic equilibrium between the crystalline phase and the synthesis fluid was not reached. This oxygen isotope disequilibrium suggests that without the pH lowering effect of the hydroxylation/hydration of CO&lt;sub&gt;2&lt;/sub&gt;, the CO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;2−&lt;/sup&gt; released during ACC/calcite dissolution-reprecipitation may have not isotopically equilibrated with the high pH synthesis fluid due to the long equilibration times required to reach isotope equilibrium at high pH values, leading to the self-buffering of δ&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;CaCO3&lt;/sub&gt; values. The results suggest that the oxygen iso","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"386 ","pages":"Pages 96-109"},"PeriodicalIF":4.5,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142321642","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Absolute 230Th/U chronologies and Δ47 thermometry paleoclimate reconstruction from soil carbonates in Central Asian loess over the past 1 million years","authors":"Gábor Újvári ,&nbsp;Ramona Schneider ,&nbsp;Thomas Stevens ,&nbsp;László Rinyu ,&nbsp;Gabriella Ilona Kiss ,&nbsp;Jan-Pieter Buylaert ,&nbsp;Andrew Sean Murray ,&nbsp;Amélie J.M. Challier ,&nbsp;Redzhep Kurbanov ,&nbsp;Farhad Khormali ,&nbsp;Judit Benedek ,&nbsp;Marjan Temovski ,&nbsp;Danny Vargas ,&nbsp;László Palcsu","doi":"10.1016/j.gca.2024.09.008","DOIUrl":"10.1016/j.gca.2024.09.008","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Pleistocene loess records of the Khovaling Loess Plateau (KLP) in Tajikistan provide rich collections of lithic artifacts demonstrating past human presence in the region. To understand the timing of human activity and environmental conditions prevailing at that time U–Th dating and clumped/stable C/O isotope measurements have been applied to modern and Pleistocene soil carbonates (SCs) collected at several sites on the KLP and surroundings. U–Th ages were corrected by two methods: 1) assuming an initial [&lt;sup&gt;230&lt;/sup&gt;Th/&lt;sup&gt;232&lt;/sup&gt;Th] activity ratio of 0.85 ± 0.25 based on gamma spectrometry of loess/paleosol samples, and 2) the isochron technique using leachates and fully dissolved subsamples. Diagenetic alteration and potential U/Th mobilization and related isotope fractionation due to alpha-recoil was also modelled and found to be minor in the studied soil carbonates. Compared to model ages as references, uncorrected &lt;sup&gt;230&lt;/sup&gt;Th ages are only acceptable if measured [&lt;sup&gt;230&lt;/sup&gt;Th/&lt;sup&gt;232&lt;/sup&gt;Th] activity ratios of leachates are high (&gt;30), while &lt;sup&gt;230&lt;/sup&gt;Th ages derived using method 1 are mostly overcorrected. It appears that SCs can be reliably dated by the U-series disequilibrium method in this sedimentary setting, but isochron dating cannot be spared. Application of the isochron method is required to derive &lt;sup&gt;230&lt;/sup&gt;Th&lt;sub&gt;model&lt;/sub&gt; ages, which ensures that the non-zero initial &lt;sup&gt;230&lt;/sup&gt;Th and possible U–Th gain/loss due to alpha-recoil can be simultaneously corrected and reliable U–Th ages obtained. U–Th ages of Pleistocene SCs clearly demonstrate post-pedogenic ingrowth of multiple, non-contemporaneous populations of SCs within loess/paleosol units, and that SC formation happened in many cases under cold, presumably dry glacial climate conditions. Considering that U–Th ages of SCs provide minimum ages of the sediment in which they form, these ages can be useful in developing loess stratigraphic models and for correlation of paleosols with marine isotope stages. This implies that the age of a given paleosol and any lithic artifacts it may contain, indicating human activity, cannot be younger than the age of SCs formed in that paleosol. This is due to the nature of soil carbonates, which can be the product of both syn- and post-depositional processes.&lt;/div&gt;&lt;div&gt;Clumped isotope thermometry of SCs collected from modern soils at three sites in Tajikistan provide evidence for SCs dominantly recording summer season soil temperatures, while the calculated soil water oxygen isotope signatures reflect annual signals and carbonate precipitation from source waters incorporating rainfall from prior to and during SC formation. In contrast, some Pleistocene SCs record soil temperatures and stable isotope compositions more appropriate to glacial conditions, confirming the findings of U–Th ages, and highlighting the primary role of aridity-driven soil moisture changes in SC precipitation in this setting. Conside","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"386 ","pages":"Pages 110-126"},"PeriodicalIF":4.5,"publicationDate":"2024-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142245682","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}