Pub Date : 2025-02-26DOI: 10.1016/j.gca.2025.02.026
Yunchao Shu , Chadlin M. Ostrander , Dalton S. Hardisty , Peter K. Swart , Sune G. Nielsen
Thallium isotope ratios (205Tl/203Tl) recovered from ancient marine shales are able to provide novel information about Earth’s ocean oxygenation history. Here we demonstrate the potential to extend this utility to the ancient carbonate record. We present Tl concentration and isotope ratio data for modern and geologically recent carbonates from the Great Bahama Bank that capture initial carbonate deposition to diagenesis on multiple scales. Young carbonates from bank-top cores reveal bulk Tl isotope compositions (ε205Tl) that are either indistinguishable from today’s globally homogenous seawater value (ε205Tl = –6.0 ± 0.3‱) or within 0.4‱. Older carbonates from the deeper and diagenetically altered cores also oftentimes capture seawater ε205Tl values. Carbonates with high dolomite contents are the most reliable archives, revealing with only minor exception ε205Tl values within analytical error of modern seawater. Meteoric diagenesis predictably drives carbonate ε205Tl values higher and toward the average composition of global freshwaters (ε205Tl ≈ –2‱). Our findings suggest that properly screened ancient carbonates can be viable archives of past seawater ε205Tl values. These seawater ε205Tl values are set by past marine Tl isotope mass-balance, which is sensitive to manganese oxide burial on the seafloor and hence past levels of global bottom water ocean oxygenation.
{"title":"Extending the utility of the Tl isotope paleoredox proxy to carbonates","authors":"Yunchao Shu , Chadlin M. Ostrander , Dalton S. Hardisty , Peter K. Swart , Sune G. Nielsen","doi":"10.1016/j.gca.2025.02.026","DOIUrl":"10.1016/j.gca.2025.02.026","url":null,"abstract":"<div><div>Thallium isotope ratios (<sup>205</sup>Tl/<sup>203</sup>Tl) recovered from ancient marine shales are able to provide novel information about Earth’s ocean oxygenation history. Here we demonstrate the potential to extend this utility to the ancient carbonate record. We present Tl concentration and isotope ratio data for modern and geologically recent carbonates from the Great Bahama Bank that capture initial carbonate deposition to diagenesis on multiple scales. Young carbonates from bank-top cores reveal bulk Tl isotope compositions (ε<sup>205</sup>Tl) that are either indistinguishable from today’s globally homogenous seawater value (ε<sup>205</sup>Tl = –6.0 ± 0.3‱) or within 0.4‱. Older carbonates from the deeper and diagenetically altered cores also oftentimes capture seawater ε<sup>205</sup>Tl values. Carbonates with high dolomite contents are the most reliable archives, revealing with only minor exception ε<sup>205</sup>Tl values within analytical error of modern seawater. Meteoric diagenesis predictably drives carbonate ε<sup>205</sup>Tl values higher and toward the average composition of global freshwaters (ε<sup>205</sup>Tl ≈ –2‱). Our findings suggest that properly screened ancient carbonates can be viable archives of past seawater ε<sup>205</sup>Tl values. These seawater ε<sup>205</sup>Tl values are set by past marine Tl isotope mass-balance, which is sensitive to manganese oxide burial on the seafloor and hence past levels of global bottom water ocean oxygenation.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"394 ","pages":"Pages 32-42"},"PeriodicalIF":4.5,"publicationDate":"2025-02-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143547106","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}
This study investigated the cerium (Ce) geochemical composition in the regolith at Tanakami Mountain to assess the effectiveness of using Ce proxies for redox tracing during regolith formation. Based on the in-profile Ce isotope pattern, we divided this regolith into three different layers: I (0–2.0 m), II (2.0–5.0 m), and III layers (5.0–8.0 m). The regolith exhibits Ce anomalies (Ce/Ce∗) ranging from 0.2 to 4.2, with Ce primarily in its tetravalent form (85.3 %). Notably, δ142Ce values range from 0.060 to 0.307 ‰, predominantly heavier than those in the bedrock (∼ − 0.1 to 0 ‰), which is contrary to previous observations in weathering profiles. Eolian deposition has a minor impact on the δ142Ce composition in the regolith, as supported by the εNd pattern. Under weakly acidic conditions (pH: 4.88–6.91), both O2-driven spontaneous oxidation and oxidative adsorption on MnO2 cause preferential retention of isotopically lighter Ce while heavier Ce isotopes migrate downward. We suggest that the pre-existing surface layer (E layer), which is enriched in isotopically lighter Ce, has likely been eroded, while the deeper I layer (δ142Ce: 0.131–0.307 ‰), enriched in heavier Ce isotopes, has been preserved. In addition, the oxidation–reduction cycling of Mn in the II layer promotes the downward migration of isotopically heavier Ce (δ142Ce: 0.139–0.248 ‰) and an increase in δ142Ce value with depth. The reprecipitation of Mn oxides and subsequent oxidative adsorption transforms Ce into its tetravalent form (Bir-Ce4+, Ce4+ adsorbed on birnessite) in the II layer. The bottom III layer, close to the substrate with subtle weathering signals exhibits limited Ce isotope fractionation (δ142Ce: 0.078–0.161 ‰, nearly identical to the bedrock). In summary, the combination of elemental, isotopic, and speciation information of Ce provides a comprehensive picture of terrestrial redox status and fluctuations. Moreover, our findings emphasize the need to consider erosion processes when using redox-sensitive elements, including Ce and other redox-sensitive elements (e.g. S, Fe, Mn, and Mo), for redox tracing in Earth’s surface environment.
{"title":"Abnormally heavy cerium stable isotope composition in regolith: Implications for redox tracing","authors":"Yuanyuan Wang, Wenshuai Li, Ryoichi Nakada, Makoto Nagasawa, Jianxi Zhu, Hongping He, Yoshio Takahashi","doi":"10.1016/j.gca.2025.02.025","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.025","url":null,"abstract":"This study investigated the cerium (Ce) geochemical composition in the regolith at Tanakami Mountain to assess the effectiveness of using Ce proxies for redox tracing during regolith formation. Based on the in-profile Ce isotope pattern, we divided this regolith into three different layers: I (0–2.0 m), II (2.0–5.0 m), and III layers (5.0–8.0 m). The regolith exhibits Ce anomalies (Ce/Ce<ce:sup loc=\"post\">∗</ce:sup>) ranging from 0.2 to 4.2, with Ce primarily in its tetravalent form (85.3 %). Notably, δ<ce:sup loc=\"post\">142</ce:sup>Ce values range from 0.060 to 0.307 ‰, predominantly heavier than those in the bedrock (∼ − 0.1 to 0 ‰), which is contrary to previous observations in weathering profiles. Eolian deposition has a minor impact on the δ<ce:sup loc=\"post\">142</ce:sup>Ce composition in the regolith, as supported by the ε<ce:inf loc=\"post\">Nd</ce:inf> pattern. Under weakly acidic conditions (pH: 4.88–6.91), both O<ce:inf loc=\"post\">2</ce:inf>-driven spontaneous oxidation and oxidative adsorption on MnO<ce:inf loc=\"post\">2</ce:inf> cause preferential retention of isotopically lighter Ce while heavier Ce isotopes migrate downward. We suggest that the pre-existing surface layer (E layer), which is enriched in isotopically lighter Ce, has likely been eroded, while the deeper I layer (δ<ce:sup loc=\"post\">142</ce:sup>Ce: 0.131–0.307 ‰), enriched in heavier Ce isotopes, has been preserved. In addition, the oxidation–reduction cycling of Mn in the II layer promotes the downward migration of isotopically heavier Ce (δ<ce:sup loc=\"post\">142</ce:sup>Ce: 0.139–0.248 ‰) and an increase in δ<ce:sup loc=\"post\">142</ce:sup>Ce value with depth. The reprecipitation of Mn oxides and subsequent oxidative adsorption transforms Ce into its tetravalent form (Bir-Ce<ce:sup loc=\"post\">4+</ce:sup>, Ce<ce:sup loc=\"post\">4+</ce:sup> adsorbed on birnessite) in the II layer. The bottom III layer, close to the substrate with subtle weathering signals exhibits limited Ce isotope fractionation (δ<ce:sup loc=\"post\">142</ce:sup>Ce: 0.078–0.161 ‰, nearly identical to the bedrock). In summary, the combination of elemental, isotopic, and speciation information of Ce provides a comprehensive picture of terrestrial redox status and fluctuations. Moreover, our findings emphasize the need to consider erosion processes when using redox-sensitive elements, including Ce and other redox-sensitive elements (e.g. S, Fe, Mn, and Mo), for redox tracing in Earth’s surface environment.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"179 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-02-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666414","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}
Pub Date : 2025-02-24DOI: 10.1016/j.gca.2025.02.023
Nitzan Yanay , Jay Quade , Zhennan Wang , Muhammed Tahir Waseem , David L. Dettman
Clumped isotope-derived temperatures of various carbonate phases can be powerful tools for reconstructing past environmental signals such as surface and animal body temperatures, as well as calculating the oxygen isotope composition of ancient waters. However, solid-state isotope reordering can alter clumped isotope ordering and calculated temperatures without affecting the bulk carbon and oxygen isotopic composition of the samples. Such alteration can, in theory, be predicted using theoretical models when a thermal history is known. Here, we utilize a new infrared laser spectroscopic system for clumped isotope analysis to produce a large dataset (236 samples) of multiple carbonate phases from Himalayan foreland deposits in Nepal and Pakistan with well-known thermal histories. We use these to 1) establish the conditions required to alter primary clumped isotope composition in these phases, and 2) test whether the two latest theoretical models accurately predict the magnitude of reordering in these phases. Our results indicate that paleosol carbonate temperatures were altered by burial to 80–110 °C in less than 5Myr. Aragonitic shells show a similar extent of alteration to that observed in calcitic soil carbonates even though they were not converted to calcite. Ostrich eggshell and mammal tusk behaved similarly to each other and to soil carbonates. A large and diverse sample of mammalian tooth enamel from Pakistan did not consistently produce realistic body temperatures regardless of depth, species, or section. Carbonate-cemented sandstone and calcite veins either formed at higher-than-surface temperatures or underwent open system recrystallization. Based on soil carbonate samples from the section with the best-constrained thermal history (Surai Khola, Nepal), the two latest models reproduce the general alteration trend in the data, although some discrepancies are evident between the models. These results confirm the results of previous studies based on much smaller and narrower sample sets: the serious challenge of reconstructing primary temperatures using clumped isotope values from some commonly used non-marine carbonates. They also show that preservation of carbon and oxygen isotopic composition does not guarantee preservation of clumped isotope temperatures.
{"title":"Alteration of carbonate clumped isotope composition by burial heating in foreland sediments of the Himalaya","authors":"Nitzan Yanay , Jay Quade , Zhennan Wang , Muhammed Tahir Waseem , David L. Dettman","doi":"10.1016/j.gca.2025.02.023","DOIUrl":"10.1016/j.gca.2025.02.023","url":null,"abstract":"<div><div>Clumped isotope-derived temperatures of various carbonate phases can be powerful tools for reconstructing past environmental signals such as surface and animal body temperatures, as well as calculating the oxygen isotope composition of ancient waters. However, solid-state isotope reordering can alter clumped isotope ordering and calculated temperatures without affecting the bulk carbon and oxygen isotopic composition of the samples. Such alteration can, in theory, be predicted using theoretical models when a thermal history is known. Here, we utilize a new infrared laser spectroscopic system for clumped isotope analysis to produce a large dataset (236 samples) of multiple carbonate phases from Himalayan foreland deposits in Nepal and Pakistan with well-known thermal histories. We use these to 1) establish the conditions required to alter primary clumped isotope composition in these phases, and 2) test whether the two latest theoretical models accurately predict the magnitude of reordering in these phases. Our results indicate that paleosol carbonate temperatures were altered by burial to 80–110 °C in less than 5Myr. Aragonitic shells show a similar extent of alteration to that observed in calcitic soil carbonates even though they were not converted to calcite. Ostrich eggshell and mammal tusk behaved similarly to each other and to soil carbonates. A large and diverse sample of mammalian tooth enamel from Pakistan did not consistently produce realistic body temperatures regardless of depth, species, or section. Carbonate-cemented sandstone and calcite veins either formed at higher-than-surface temperatures or underwent open system recrystallization. Based on soil carbonate samples from the section with the best-constrained thermal history (Surai Khola, Nepal), the two latest models reproduce the general alteration trend in the data, although some discrepancies are evident between the models. These results confirm the results of previous studies based on much smaller and narrower sample sets: the serious challenge of reconstructing primary temperatures using clumped isotope values from some commonly used non-marine carbonates. They also show that preservation of carbon and oxygen isotopic composition does not guarantee preservation of clumped isotope temperatures.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"394 ","pages":"Pages 15-31"},"PeriodicalIF":4.5,"publicationDate":"2025-02-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143527018","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}
Pub Date : 2025-02-22DOI: 10.1016/j.gca.2025.02.022
Svetlana Demidova, Alexander Nemchin, Renaud Merle, Yue Guan, James Head, Katherine Helen Joy, Clive R. Neal, Martin Whitehouse, Mikhail Ivanov, Xiao-Lei Wang, Xiaochao Che, Cyril Lorenz, Theodoros Ntaflos, Sofia Tetroeva, Natalia Kononkova, Gavin Kenny, Lanlan Tian, Wenli Xie, Zengsheng Li, Yiyi Ban, Wenxiao Peng, Chen-Long Ding
Two types of mare basalt have been previously reported in the Luna-16 returned soil samples: dominant Intermediate-Ti basalts and minor Very-Low-Ti (VLT) basalts. The crystallization age of the main group of Intermediate-Ti basalts determined for 14 fragments by the Pb-Pb isochron approach is 3590.3 ± 9.4 Ma. Intermediate-Ti basalts are likely to represent the late episode of volcanism that occupies the largest part of the Mare Fecunditatis surface. The VLT group Pb-Pb isochron obtained from 3 fragments corresponds to an age 3919 ± 27 Ma. The VLT basalts may represent an initial underlying basaltic filling of Mare Fecunditatis, at least in some parts of the basin.
{"title":"Two episodes of lunar basaltic volcanism in Mare Fecunditatis as revealed by Luna-16 soil samples","authors":"Svetlana Demidova, Alexander Nemchin, Renaud Merle, Yue Guan, James Head, Katherine Helen Joy, Clive R. Neal, Martin Whitehouse, Mikhail Ivanov, Xiao-Lei Wang, Xiaochao Che, Cyril Lorenz, Theodoros Ntaflos, Sofia Tetroeva, Natalia Kononkova, Gavin Kenny, Lanlan Tian, Wenli Xie, Zengsheng Li, Yiyi Ban, Wenxiao Peng, Chen-Long Ding","doi":"10.1016/j.gca.2025.02.022","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.022","url":null,"abstract":"Two types of mare basalt have been previously reported in the Luna-16 returned soil samples: dominant Intermediate-Ti basalts and minor Very-Low-Ti (VLT) basalts. The crystallization age of the main group of Intermediate-Ti basalts determined for 14 fragments by the Pb-Pb isochron approach is 3590.3 ± 9.4 Ma. Intermediate-Ti basalts are likely to represent the late episode of volcanism that occupies the largest part of the Mare Fecunditatis surface. The VLT group Pb-Pb isochron obtained from 3 fragments corresponds to an age 3919 ± 27 Ma. The VLT basalts may represent an initial underlying basaltic filling of Mare Fecunditatis, at least in some parts of the basin.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"67 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143547107","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}
Pub Date : 2025-02-22DOI: 10.1016/j.gca.2025.02.014
Soumendu Sarkar, Hayden Dalton, Andrea Giuliani, David Phillips, D. Graham Pearson, Geoff M. Nowell, Jon D. Woodhead, Janet Hergt, Roland Maas, A. Lynton Jaques, N.V. Chalapathi Rao, Yaakov Weiss, Sujoy Ghosh
Cratonic lamproites are rare ultrapotassic rocks that occur in every continent and were emplaced over the last 2 billion years. Owing to their highly radiogenic Sr and unradiogenic Nd-Hf isotopic compositions along with enrichment in K and incompatible trace elements (e.g., Ba, Sr, Ti, Zr), lamproites are believed to be formed by melting geochemically enriched regions in the sub-continental lithospheric mantle (SCLM). In contrast, olivine compositions indistinguishable from those of kimberlites and the occurrence of diamonds containing inclusions of majorite-bearing garnet in some cratonic lamproites, suggest that primary lamproitic (or proto-lamproitic) melts may originate in the convecting mantle. Here we re-evaluate the different source component(s) responsible for the genesis of cratonic lamproites worldwide using major-, trace-element and radiogenic isotope geochemistry.
{"title":"Extreme enriched-mantle (EM) compositions recorded by the Sr-Nd-Hf isotopes of global cratonic lamproites","authors":"Soumendu Sarkar, Hayden Dalton, Andrea Giuliani, David Phillips, D. Graham Pearson, Geoff M. Nowell, Jon D. Woodhead, Janet Hergt, Roland Maas, A. Lynton Jaques, N.V. Chalapathi Rao, Yaakov Weiss, Sujoy Ghosh","doi":"10.1016/j.gca.2025.02.014","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.014","url":null,"abstract":"Cratonic lamproites are rare ultrapotassic rocks that occur in every continent and were emplaced over the last 2 billion years. Owing to their highly radiogenic Sr and unradiogenic Nd-Hf isotopic compositions along with enrichment in K and incompatible trace elements (e.g., Ba, Sr, Ti, Zr), lamproites are believed to be formed by melting geochemically enriched regions in the sub-continental lithospheric mantle (SCLM). In contrast, olivine compositions indistinguishable from those of kimberlites and the occurrence of diamonds containing inclusions of majorite-bearing garnet in some cratonic lamproites, suggest that primary lamproitic (or proto-lamproitic) melts may originate in the convecting mantle. Here we re-evaluate the different source component(s) responsible for the genesis of cratonic lamproites worldwide using major-, trace-element and radiogenic isotope geochemistry.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"34 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666393","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}
The origin of hydrocarbons is a central question in climate science, biogeochemistry, and astrobiology. Carbon and hydrogen isotopic ratios have been used to constrain hydrocarbon sources; however, studies based on these parameters alone are lacking. The recent development of a doubly substituted (“clumped”) ethane isotopologue (13C2H6) is expected to be useful in distinguishing between thermogenic and abiotic ethane owing to the specific signature of the former. However, the mechanistic determinants of clumped 13C–13C isotopologue signatures in thermogenic ethane remain insufficiently understood. In this study, we conducted pyrolysis experiments over ∼ 2 years under controlled temperatures and pressures, with lignin, docosane (C22H46), and marine sediments used as reagents. All ethane samples exhibited clumped 13C–13C isotopologue signatures with similarly nearly absent or slight 13C–13C enrichment against a stochastic distribution. The 13C–13C clumping of thermally produced ethane from organic matter was similar to that of natural thermogenic ethane and different from that of putatively abiotic ethane of Kidd Creek and the Dingo gas field in the Amadeus Basin, which showed a significantly lower abundance of 13C–13C relative to stochastic distribution. The abundances of 13C–13C in ethane suggest that the signature of thermogenic ethane is inherited from a C–C bond in the precursor molecule and altered by a combinatorial effect during thermal cracking. Post-genetic ethane decomposition via heating might alter the 13C–13C signature in ethane, although the effects are difficult to observe. Thermogenic ethane should exhibit a positive clumped isotopologue signature regardless of thermal maturity; therefore, clumped isotopologue signatures may serve as key indicators to distinguish between thermogenic and abiotic ethane.
{"title":"Clumped 13C–13C isotopologue signatures of thermogenic ethane","authors":"Koudai Taguchi, Yuichiro Ueno, Alexis Gilbert, Yohei Matsui, Takazo Shibuya, Shinsuke Kawagucci","doi":"10.1016/j.gca.2025.02.017","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.017","url":null,"abstract":"The origin of hydrocarbons is a central question in climate science, biogeochemistry, and astrobiology. Carbon and hydrogen isotopic ratios have been used to constrain hydrocarbon sources; however, studies based on these parameters alone are lacking. The recent development of a doubly substituted (“clumped”) ethane isotopologue (<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">2</ce:inf>H<ce:inf loc=\"post\">6</ce:inf>) is expected to be useful in distinguishing between thermogenic and abiotic ethane owing to the specific signature of the former. However, the mechanistic determinants of clumped <ce:sup loc=\"post\">13</ce:sup>C–<ce:sup loc=\"post\">13</ce:sup>C isotopologue signatures in thermogenic ethane remain insufficiently understood. In this study, we conducted pyrolysis experiments over ∼ 2 years under controlled temperatures and pressures, with lignin, docosane (C<ce:inf loc=\"post\">22</ce:inf>H<ce:inf loc=\"post\">46</ce:inf>), and marine sediments used as reagents. All ethane samples exhibited clumped <ce:sup loc=\"post\">13</ce:sup>C–<ce:sup loc=\"post\">13</ce:sup>C isotopologue signatures with similarly nearly absent or slight <ce:sup loc=\"post\">13</ce:sup>C–<ce:sup loc=\"post\">13</ce:sup>C enrichment against a stochastic distribution. The <ce:sup loc=\"post\">13</ce:sup>C–<ce:sup loc=\"post\">13</ce:sup>C clumping of thermally produced ethane from organic matter was similar to that of natural thermogenic ethane and different from that of putatively abiotic ethane of Kidd Creek and the Dingo gas field in the Amadeus Basin, which showed a significantly lower abundance of <ce:sup loc=\"post\">13</ce:sup>C–<ce:sup loc=\"post\">13</ce:sup>C relative to stochastic distribution. The abundances of <ce:sup loc=\"post\">13</ce:sup>C–<ce:sup loc=\"post\">13</ce:sup>C in ethane suggest that the signature of thermogenic ethane is inherited from a C–C bond in the precursor molecule and altered by a combinatorial effect during thermal cracking. Post-genetic ethane decomposition via heating might alter the <ce:sup loc=\"post\">13</ce:sup>C–<ce:sup loc=\"post\">13</ce:sup>C signature in ethane, although the effects are difficult to observe. Thermogenic ethane should exhibit a positive clumped isotopologue signature regardless of thermal maturity; therefore, clumped isotopologue signatures may serve as key indicators to distinguish between thermogenic and abiotic ethane.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"91 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-02-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143547108","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}
Pub Date : 2025-02-15DOI: 10.1016/j.gca.2025.02.018
Genevieve M. Pugsley, Thomas P. Guilderson, Danielle S. Glynn, Yuan Shen, Matthew D. McCarthy
Decadal-scale climate variability drives important fluctuations in nutrient availability and productivity in highly productive eastern boundary current upwelling ecosystems, but the relatively brief duration of most monitoring efforts limits understanding of these dynamics. When applied to high-resolution paleoarchives such as deep-sea proteinaceous coral skeletons, stable carbon and nitrogen isotope (δ13C and δ15N) analysis can provide useful new insight into biogeochemical and ecological changes beyond the instrumental record. However, interpretation of bulk δ13C and δ15N records is often complicated by multiple possible drivers of variability. Here, we addressed these challenges by applying both bulk and compound-specific amino acid δ15N and δ13C analysis to two bamboo coral specimens from Sur Ridge on the central California margin, generating sub-decadal resolution records spanning c. 1810 to present. Our overarching goals were to first test amino acid δ13C and δ15N proxies in proteinaceous deep-sea bamboo coral archives, and second to investigate links between climate forcing and biogeochemical responses on the California margin over the Anthropocene.
{"title":"Proteinaceous deep sea coral amino acid isotope records reveal climate-driven decadal-scale planktic ecosystem fluctuations","authors":"Genevieve M. Pugsley, Thomas P. Guilderson, Danielle S. Glynn, Yuan Shen, Matthew D. McCarthy","doi":"10.1016/j.gca.2025.02.018","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.018","url":null,"abstract":"Decadal-scale climate variability drives important fluctuations in nutrient availability and productivity in highly productive eastern boundary current upwelling ecosystems, but the relatively brief duration of most monitoring efforts limits understanding of these dynamics. When applied to high-resolution paleoarchives such as deep-sea proteinaceous coral skeletons, stable carbon and nitrogen isotope (δ<ce:sup loc=\"post\">13</ce:sup>C and δ<ce:sup loc=\"post\">15</ce:sup>N) analysis can provide useful new insight into biogeochemical and ecological changes beyond the instrumental record. However, interpretation of bulk δ<ce:sup loc=\"post\">13</ce:sup>C and δ<ce:sup loc=\"post\">15</ce:sup>N records is often complicated by multiple possible drivers of variability. Here, we addressed these challenges by applying both bulk and compound-specific amino acid δ<ce:sup loc=\"post\">15</ce:sup>N and δ<ce:sup loc=\"post\">13</ce:sup>C analysis to two bamboo coral specimens from Sur Ridge on the central California margin, generating sub-decadal resolution records spanning c. 1810 to present. Our overarching goals were to first test amino acid δ<ce:sup loc=\"post\">13</ce:sup>C and δ<ce:sup loc=\"post\">15</ce:sup>N proxies in proteinaceous deep-sea bamboo coral archives, and second to investigate links between climate forcing and biogeochemical responses on the California margin over the Anthropocene.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"8 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143547109","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}
Pub Date : 2025-02-14DOI: 10.1016/j.gca.2025.02.011
Baoliang Wang, Frederic Moynier, Matthew G. Jackson, James M.D. Day
Ocean island basalts (OIB) offer valuable insights into the chemical composition of Earth’s mantle. Distinct radiogenic isotope compositions recorded in OIB have been used to characterize diverse mantle sources, indicating the presence of recycled crustal components within plume sources. Rubidium isotopes have the potential to trace crustal recycling, given the significant enrichment of Rb in the crust relative to the mantle, and the inherent variability of Rb isotopes among crustal materials. Here we present Rb isotope data of twenty-eight OIB and two peridotite xenoliths representing EM1, EM2, HIMU, and FOZO mantle, with locations spanning the Pacific, Atlantic, and Indian Oceans. Except for one sample from Mangaia, which was affected by low-temperature alteration, the Rb isotopic compositions of remaining samples reflect the characteristics of their mantle source, exhibiting a δ87Rb range of variations from −0.19 to +0.01 ‰. To a first order, the Rb isotopic similarity between OIB, peridotite xenoliths, and previously reported mid-ocean ridge basalts (MORB) suggests a relatively homogeneous Rb isotope composition of the mantle, displaying an average δ87Rb value of −0.12 ± 0.09 ‰ (2SD, n = 52). Nevertheless, a discernible difference exists in primary lava compositions from Mangaia, with their Rb isotopic compositions (−0.02 ± 0.06 ‰, 2SD, n = 3) being 0.1 ‰ heavier than other OIB samples and the Bulk Silicate Earth (BSE) estimate. The heavy Rb isotope enrichment in Mangaia, the most extreme (highest 206Pb/204Pb) HIMU-type OIB examined in this study, is attributed to incorporation of high δ87Rb signal within the mantle source, potentially due to the deep recycling of ancient altered oceanic crust.
{"title":"Rubidium isotopic compositions of the mantle sources of ocean island basalts","authors":"Baoliang Wang, Frederic Moynier, Matthew G. Jackson, James M.D. Day","doi":"10.1016/j.gca.2025.02.011","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.011","url":null,"abstract":"Ocean island basalts (OIB) offer valuable insights into the chemical composition of Earth’s mantle. Distinct radiogenic isotope compositions recorded in OIB have been used to characterize diverse mantle sources, indicating the presence of recycled crustal components within plume sources. Rubidium isotopes have the potential to trace crustal recycling, given the significant enrichment of Rb in the crust relative to the mantle, and the inherent variability of Rb isotopes among crustal materials. Here we present Rb isotope data of twenty-eight OIB and two peridotite xenoliths representing EM1, EM2, HIMU, and FOZO mantle, with locations spanning the Pacific, Atlantic, and Indian Oceans. Except for one sample from Mangaia, which was affected by low-temperature alteration, the Rb isotopic compositions of remaining samples reflect the characteristics of their mantle source, exhibiting a δ<ce:sup loc=\"post\">87</ce:sup>Rb range of variations from −0.19 to +0.01 ‰. To a first order, the Rb isotopic similarity between OIB, peridotite xenoliths, and previously reported mid-ocean ridge basalts (MORB) suggests a relatively homogeneous Rb isotope composition of the mantle, displaying an average δ<ce:sup loc=\"post\">87</ce:sup>Rb value of −0.12 ± 0.09 ‰ (2SD, n = 52). Nevertheless, a discernible difference exists in primary lava compositions from Mangaia, with their Rb isotopic compositions (−0.02 ± 0.06 ‰, 2SD, n = 3) being 0.1 ‰ heavier than other OIB samples and the Bulk Silicate Earth (BSE) estimate. The heavy Rb isotope enrichment in Mangaia, the most extreme (highest <ce:sup loc=\"post\">206</ce:sup>Pb/<ce:sup loc=\"post\">204</ce:sup>Pb) HIMU-type OIB examined in this study, is attributed to incorporation of high δ<ce:sup loc=\"post\">87</ce:sup>Rb signal within the mantle source, potentially due to the deep recycling of ancient altered oceanic crust.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"51 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143496185","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}
Potassium-rich basalts provide valuable information about mantle heterogeneity and crust-mantle interaction because of their distinctive geochemical features. One of the long-standing issues regarding the origin of K-rich basalts is the nature of the K-rich mantle component required to generate such lavas. To provide further constraints on this issue, we present combined analyses of Mg, Zn and Fe isotopic compositions in the Cenozoic intraplate K-rich basalts from northeast China. The samples include both potassic and ultrapotassic basalts with K2O/Na2O ratios up to 3.42 and have typical Enriched Mantle-I Sr-Nd isotopic signatures. The ultrapotassic basalts have lighter Mg isotopic compositions than those of mid-ocean ridge basalts (MORB), but their Zn isotopic compositions are similar to or slightly higher than those of MORB, defining a strong Mg-Zn isotopic decoupling that suggests a dominant role of recycled carbonate-poor siliciclastic sediments in their sources. These rocks have Fe isotopic compositions (δ56Fe) identical with those of MORB, indicating a peridotite-dominant source that has not been oxidized by the recycled sediments. Along with the high Fo (molar Mg2+/(Mg2++Fe2+) × 100) of olivine phenocrysts, we suggest that the ultrapotassic basalts originated from the metasomatized (K-rich) sub-continental lithospheric mantle. Compared with ultrapotassic basalts, the potassic basalts have heavier Zn isotopic compositions at similar δ26Mg, defining a weaker Mg-Zn isotopic decoupling that suggests a large proportion of carbonates in the recycled siliciclastic sediments (i.e., carbonate-rich sediments). In addition, the potassic basalts have higher δ56Fe and lower Fo of olivine phenocrysts, pointing to a deeper, fertile mantle source that may have been oxidized by recycled carbonates, most likely at the mantle transition zone (MTZ). These results collectively suggest that both the potassic and ultrapotassic lavas in northeast China were formed via partial melting of the mantle hybridized by recycled siliciclastic sediments containing different proportions of carbonates. Therefore, the K-rich mantle component required for generating the extreme K enrichment in some intraplate lavas was primarily produced by recycled carbonate-bearing siliciclastic sediments in different mantle domains.
{"title":"Mg, Zn and Fe isotope evidence for derivation of K-rich basalts from the mantle hybridized by recycled carbonate-bearing silicate sediments","authors":"Zhao-Xue Wang, Sheng-Ao Liu, Dejan Prelević, Shuguang Li, Ze-Zhou Wang, Tianhao Wu, Jingao Liu","doi":"10.1016/j.gca.2025.02.016","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.016","url":null,"abstract":"Potassium-rich basalts provide valuable information about mantle heterogeneity and crust-mantle interaction because of their distinctive geochemical features. One of the long-standing issues regarding the origin of K-rich basalts is the nature of the K-rich mantle component required to generate such lavas. To provide further constraints on this issue, we present combined analyses of Mg, Zn and Fe isotopic compositions in the Cenozoic intraplate K-rich basalts from northeast China. The samples include both potassic and ultrapotassic basalts with K<ce:inf loc=\"post\">2</ce:inf>O/Na<ce:inf loc=\"post\">2</ce:inf>O ratios up to 3.42 and have typical Enriched Mantle-I Sr-Nd isotopic signatures. The ultrapotassic basalts have lighter Mg isotopic compositions than those of mid-ocean ridge basalts (MORB), but their Zn isotopic compositions are similar to or slightly higher than those of MORB, defining a strong Mg-Zn isotopic decoupling that suggests a dominant role of recycled carbonate-poor siliciclastic sediments in their sources. These rocks have Fe isotopic compositions (δ<ce:sup loc=\"post\">56</ce:sup>Fe) identical with those of MORB, indicating a peridotite-dominant source that has not been oxidized by the recycled sediments. Along with the high Fo (molar Mg<ce:sup loc=\"post\">2+</ce:sup>/(Mg<ce:sup loc=\"post\">2+</ce:sup>+Fe<ce:sup loc=\"post\">2+</ce:sup>) × 100) of olivine phenocrysts, we suggest that the ultrapotassic basalts originated from the metasomatized (K-rich) sub-continental lithospheric mantle. Compared with ultrapotassic basalts, the potassic basalts have heavier Zn isotopic compositions at similar δ<ce:sup loc=\"post\">26</ce:sup>Mg, defining a weaker Mg-Zn isotopic decoupling that suggests a large proportion of carbonates in the recycled siliciclastic sediments (i.e., carbonate-rich sediments). In addition, the potassic basalts have higher δ<ce:sup loc=\"post\">56</ce:sup>Fe and lower Fo of olivine phenocrysts, pointing to a deeper, fertile mantle source that may have been oxidized by recycled carbonates, most likely at the mantle transition zone (MTZ). These results collectively suggest that both the potassic and ultrapotassic lavas in northeast China were formed via partial melting of the mantle hybridized by recycled siliciclastic sediments containing different proportions of carbonates. Therefore, the K-rich mantle component required for generating the extreme K enrichment in some intraplate lavas was primarily produced by recycled carbonate-bearing siliciclastic sediments in different mantle domains.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"42 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143496184","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}
Pub Date : 2025-02-13DOI: 10.1016/j.gca.2025.02.013
Antonia Klatt, Cindy De Jonge, Daniel B. Nelson, Marta Reyes, Carsten J. Schubert, Nathalie Dubois, S. Nemiah Ladd
Reconstructions of past changes in algal community composition provide important context for future alterations in biogeochemical cycling. However, many existing phytoplankton proxies are indicative of individual algal groups and are not fully representative of the whole community. Here, we evaluated hydrogen isotope ratios of algal lipids (δ<ce:sup loc="post">2</ce:sup>H<ce:inf loc="post">Lipid</ce:inf>) as a potential proxy for phytoplankton community composition. We sampled the water column of Rotsee, a small eutrophic lake in Switzerland, every second week from January 2019 to February 2020 and analyzed distributions and the relative offsets between δ<ce:sup loc="post">2</ce:sup>H<ce:inf loc="post">Lipid</ce:inf> values (δ<ce:sup loc="post">2</ce:sup>H<ce:inf loc="post">Lipid1/Lipid2</ce:inf>) from short-chain fatty acids, phytosterols and phytol. Comparing these data with phytoplankton cell counts, we found that δ<ce:sup loc="post">2</ce:sup>H<ce:inf loc="post">C16:0 Acid/Sterol</ce:inf> and δ<ce:sup loc="post">2</ce:sup>H<ce:inf loc="post">Sterol/Phytol</ce:inf> values reflect shifts within the eukaryotic algal community. To assess whether the selected phytoplankton groups were the main sources of the selected lipids, we further modeled algal δ<ce:sup loc="post">2</ce:sup>H<ce:inf loc="post">Lipid1/Lipid2</ce:inf> values based on δ<ce:sup loc="post">2</ce:sup>H<ce:inf loc="post">C16:0 Acid</ce:inf>, δ<ce:sup loc="post">2</ce:sup>H<ce:inf loc="post">Sterol</ce:inf> and δ<ce:sup loc="post">2</ce:sup>H<ce:inf loc="post">Phytol</ce:inf> values from batch cultures of individual algal groups and their biovolume in Rotsee and evaluated the role of heterotrophy on δ<ce:sup loc="post">2</ce:sup>H<ce:inf loc="post">Lipid1/Lipid2</ce:inf> values using a model incorporating δ<ce:sup loc="post">2</ce:sup>H<ce:inf loc="post">C16:0 Acid</ce:inf> and δ<ce:sup loc="post">2</ce:sup>H<ce:inf loc="post">Sterol</ce:inf> values from microzooplankton. Annually-integrated and amount-weighted δ<ce:sup loc="post">2</ce:sup>H<ce:inf loc="post">Lipid1/Lipid2</ce:inf> values measured in Rotsee were within 2 to 20 ‰ of the mean of modeled algal δ<ce:sup loc="post">2</ce:sup>H<ce:inf loc="post">Lipid1/Lipid2</ce:inf> values, demonstrating a strong link with the phytoplankton community composition, while δ<ce:sup loc="post">2</ce:sup>H<ce:inf loc="post">Lipid1/Lipid2</ce:inf> values including microzooplankton lipids had a larger offset. Additionally, cyanobacterial biovolume was positively correlated with the ratio of phytol and phytosterols (phytol:sterol ratio) as well as the ratio of unsaturated C18 and C16:0 fatty acids (C18:C16 ratio). Our results support the application of sedimentary δ<ce:sup loc="post">2</ce:sup>H<ce:inf loc="post">Lipid1/Lipid2</ce:inf> values in eutrophic lakes as a proxy for past phytoplankton community assemblages. Moreover, the calculation of sedimentary phytol:sterol and C18:C16 ratios provides an additional proxy for reconstructing cyanobac
{"title":"Algal lipid distributions and hydrogen isotope ratios reflect phytoplankton community dynamics","authors":"Antonia Klatt, Cindy De Jonge, Daniel B. Nelson, Marta Reyes, Carsten J. Schubert, Nathalie Dubois, S. Nemiah Ladd","doi":"10.1016/j.gca.2025.02.013","DOIUrl":"https://doi.org/10.1016/j.gca.2025.02.013","url":null,"abstract":"Reconstructions of past changes in algal community composition provide important context for future alterations in biogeochemical cycling. However, many existing phytoplankton proxies are indicative of individual algal groups and are not fully representative of the whole community. Here, we evaluated hydrogen isotope ratios of algal lipids (δ<ce:sup loc=\"post\">2</ce:sup>H<ce:inf loc=\"post\">Lipid</ce:inf>) as a potential proxy for phytoplankton community composition. We sampled the water column of Rotsee, a small eutrophic lake in Switzerland, every second week from January 2019 to February 2020 and analyzed distributions and the relative offsets between δ<ce:sup loc=\"post\">2</ce:sup>H<ce:inf loc=\"post\">Lipid</ce:inf> values (δ<ce:sup loc=\"post\">2</ce:sup>H<ce:inf loc=\"post\">Lipid1/Lipid2</ce:inf>) from short-chain fatty acids, phytosterols and phytol. Comparing these data with phytoplankton cell counts, we found that δ<ce:sup loc=\"post\">2</ce:sup>H<ce:inf loc=\"post\">C16:0 Acid/Sterol</ce:inf> and δ<ce:sup loc=\"post\">2</ce:sup>H<ce:inf loc=\"post\">Sterol/Phytol</ce:inf> values reflect shifts within the eukaryotic algal community. To assess whether the selected phytoplankton groups were the main sources of the selected lipids, we further modeled algal δ<ce:sup loc=\"post\">2</ce:sup>H<ce:inf loc=\"post\">Lipid1/Lipid2</ce:inf> values based on δ<ce:sup loc=\"post\">2</ce:sup>H<ce:inf loc=\"post\">C16:0 Acid</ce:inf>, δ<ce:sup loc=\"post\">2</ce:sup>H<ce:inf loc=\"post\">Sterol</ce:inf> and δ<ce:sup loc=\"post\">2</ce:sup>H<ce:inf loc=\"post\">Phytol</ce:inf> values from batch cultures of individual algal groups and their biovolume in Rotsee and evaluated the role of heterotrophy on δ<ce:sup loc=\"post\">2</ce:sup>H<ce:inf loc=\"post\">Lipid1/Lipid2</ce:inf> values using a model incorporating δ<ce:sup loc=\"post\">2</ce:sup>H<ce:inf loc=\"post\">C16:0 Acid</ce:inf> and δ<ce:sup loc=\"post\">2</ce:sup>H<ce:inf loc=\"post\">Sterol</ce:inf> values from microzooplankton. Annually-integrated and amount-weighted δ<ce:sup loc=\"post\">2</ce:sup>H<ce:inf loc=\"post\">Lipid1/Lipid2</ce:inf> values measured in Rotsee were within 2 to 20 ‰ of the mean of modeled algal δ<ce:sup loc=\"post\">2</ce:sup>H<ce:inf loc=\"post\">Lipid1/Lipid2</ce:inf> values, demonstrating a strong link with the phytoplankton community composition, while δ<ce:sup loc=\"post\">2</ce:sup>H<ce:inf loc=\"post\">Lipid1/Lipid2</ce:inf> values including microzooplankton lipids had a larger offset. Additionally, cyanobacterial biovolume was positively correlated with the ratio of phytol and phytosterols (phytol:sterol ratio) as well as the ratio of unsaturated C18 and C16:0 fatty acids (C18:C16 ratio). Our results support the application of sedimentary δ<ce:sup loc=\"post\">2</ce:sup>H<ce:inf loc=\"post\">Lipid1/Lipid2</ce:inf> values in eutrophic lakes as a proxy for past phytoplankton community assemblages. Moreover, the calculation of sedimentary phytol:sterol and C18:C16 ratios provides an additional proxy for reconstructing cyanobac","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"30 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143547111","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}
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