Chemical Geology最新文献

{"title":"Provenance and tectonic intricacies revealed by in situ Rb-Sr dating of detrital micas","authors":"Dheerej H. Sathish Kumar ,&nbsp;Hugo K.H. Olierook ,&nbsp;Milo Barham ,&nbsp;Christopher L. Kirkland ,&nbsp;Kai Rankenburg ,&nbsp;Noreen J. Evans","doi":"10.1016/j.chemgeo.2024.122482","DOIUrl":"10.1016/j.chemgeo.2024.122482","url":null,"abstract":"<div><div>The use of detrital minerals to reconstruct sedimentary provenance is subject to a range of biases, which may reduce the value of the geological information they retain. With the advent of in situ Rb-Sr geochronology, rapid analyses of a representative (&gt;100) number of grains can now be performed on radiogenic Sr-bearing minerals to provide more comprehensive knowledge of source-to-sink processes through more diversified mineral analysis. Here, we test the in situ Rb-Sr technique on detrital white mica and biotite from basin margin and axis samples in a simple rift basin (Perth Basin, Australia) for which previously published detrital zircon U-Pb and Hf isotopic data exist. For the basin margin adjacent to Archean basement, which has unimodal detrital zircon ages at c. 2600 Ma, two mica samples reveal a dominant age mode at c. 500 Ma, reflecting thermal resetting in the craton proximal to the Gondwanan orogenic front, and a subordinate portion of Archean mica detritus that can be interpreted as having been distally sourced (&gt;100 km away). Similarly, a basin axis sample yielded minor c. 1200 Ma apparent mica ages, representing distal sources from the Albany-Fraser-Wilkes Orogen, and c. 500 Ma grains that are likely a resetting product. Whilst obscured in the detrital zircon record, mica samples allow quantification of the relative contributions of distal and proximal sources to the basin. Finally, detrital biotite that was (partially) altered to chlorite yielded partially to fully reset ages between c. 500 and 130 Ma, the latter linked to heating from the c. 137–130 Ma Bunbury Basalt. Ultimately, the use of in situ Rb-Sr geochronology from detrital micas reveal previously unrecognized provenance and tectonic information that is critical to understanding the true complexity of ancient geological histories, but which remains obscured in standard detrital zircon U-Pb geochronology.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"671 ","pages":"Article 122482"},"PeriodicalIF":3.6,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652393","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Intra-grain variability of hydrogen and trace elements in rutile","authors":"Mona Lueder ,&nbsp;Jörg Hermann ,&nbsp;Renée Tamblyn ,&nbsp;Daniela Rubatto ,&nbsp;Pierre Lanari ,&nbsp;Thorsten Andreas Markmann","doi":"10.1016/j.chemgeo.2024.122480","DOIUrl":"10.1016/j.chemgeo.2024.122480","url":null,"abstract":"<div><div>Rutile is a commonly used petrogenetic indicator mineral to determine metamorphic temperatures, ages, host−/source lithologies, geochemical reservoirs, and subduction conditions. However, intra grain variabilities of trace elements in rutile are rarely considered. We performed trace element and hydrogen mapping of rutile to assess zoning and diffusion in natural rutile from various lithologies. Trace element and hydrogen show distinct zoning patterns, with mostly regular zoning in rutile from pegmatites and low-<em>T</em> hydrothermal clefts, and typically irregular zoning in rutile from high-<em>P</em> veins and metamorphic rocks. Whereas no clear patterns of trace element correlations can be identified, hydrogen, tri-, tetra- and pentavalent cations can show the same zoning patterns within single rutile grains, despite different substitution mechanisms. This indicates that hydrogen and trace element incorporation is externally controlled by availability and diffusivity of hydrogen and trace elements within the rock matrix, as well as rutile growth rates. H₂O mapping reveals that hydrogen is retained in rutile at temperatures of up to ∼650 °C. Coupled substitution of hydrogen with divalent and trivalent cations requires coupled diffusion processes for charge balance if hydrogen is diffusively re-equilibrated. Slow diffusion rates and thus relatively high temperatures for diffusive closure in rutile lead to retention of primary hydrogen and trace element zoning. At high-<em>T</em> conditions of &gt;650 °C, diffusive re-equilibration of all trace elements can be observed. Complex zoning patterns of Zr in rutile show that Zr incorporation into rutile is not purely temperature dependent. In this study, Zr-undersaturation can lead to inaccurate Zr-in-rutile temperatures of up to ∼35 °C difference from peak formation temperatures within single rutile grains and might be a useful tool to evaluate rutile growth conditions. Niobium and Ta are highly zoned in rutile, leading to extremely variable Nb/Ta ratios within single rutile grains that cannot be reconstructed from single spot analyses. Overall, mapping offers a novel and promising tool to understanding trace element behavior in rutile.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"671 ","pages":"Article 122480"},"PeriodicalIF":3.6,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652761","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Pyrite geochemistry and its implications for ore formation in reduced copper skarn systems: A case study of the Saibo deposit, Northwest China","authors":"Qing-Fei Sun ,&nbsp;Ju-Xing Tang ,&nbsp;Shun-Da Li ,&nbsp;Qiu-Ming Pei ,&nbsp;Xin-Hao Sun ,&nbsp;Chuan Chen ,&nbsp;Ling-Ling Gao ,&nbsp;Xiao-Fei Du ,&nbsp;Jin-Ling Xie","doi":"10.1016/j.chemgeo.2024.122478","DOIUrl":"10.1016/j.chemgeo.2024.122478","url":null,"abstract":"<div><div>Copper skarns are the main source of Cu worldwide, and they are classified into two types according to their redox state: oxidized and reduced. Numerous studies have investigated the mineralization processes of oxidized Cu skarn deposits in terms of pyrite trace element compositions. However, it remains unclear how the compositional and micro-textural features of pyrite are linked to specific physicochemical processes in reduced Cu skarn systems. The Saibo deposit in the northern part of the western Tianshan orogenic belt is a typical reduced Cu skarn deposit, characterized by abundant Ti-rich garnet, arsenopyrite, pyrrhotite, and CH₄-rich inclusions. In this study, we examined pyrite geochemical and micro-textural features and related these features to Cu-forming processes at Saibo. Copper skarn mineralization was recognized to occur in the contact zone between the granodiorite porphyry and the Kusongmuqieke Group limestone as veins, bands, massive, and disseminations. Five stages were identified: (I) prograde skarn, (II) retrograde skarn, (III) quartz–pyrite–arsenopyrite (Py1), (IV) quartz–polymetallic sulfides (Py2), and (V) quart–calcite–polymetallic sulfides (Py3).</div><div>Pb, Sb, Ag, Cu, Zn, and Bi were typically present in the host pyrite as micro- and nanoscale mineral inclusions, whereas Co, Ni, Se, Te, and As were mostly present as lattice substitutions for S and Fe. In situ δ³⁴S values of Py1 to Py3b for the Cu skarn ore at Saibo defined a narrow range from 4.86 ‰ to 7.67 ‰, which was well consistent with the published S values of sulfide separates (0.2 to 9.1 ‰). These values are similar to those of Middle–Late Devonian granitoids, such as the Lamasu plagiogranite, and different from those of sediments. This indicates that the dominant source of sulfides in the Saibo deposit is the Middle–Late Devonian granodiorite porphyry. The overall increasing concentrations of As, Sb, Te, Pb, Au, and Bi, and decreasing concentrations of Co, Ni, and Se from Py1 to Py3b indicate that prior to Cu precipitation, ore-forming fluids were in low oxygen fugacity conditions that were associated with fluid-rock interactions and fluid boiling. Furthermore, the main controlling factors during Cu precipitation were sulfur loss, the increase in pH, and the decrease in temperatures of ore-forming fluids, which could be attributed to fluid-rock interactions, later-stage fluid boiling, and mixing with meteoric water, respectively. The PLS-DA results show that pyrite composition varies following skarn redox state. Pyrite from reduced skarns have in common high concentrations of Au, Bi, and Ni, while those from oxidized have in common high As, Sb, and Pb. Pyrite trace element composition is effective in discriminating different redox states of skarns.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"671 ","pages":"Article 122478"},"PeriodicalIF":3.6,"publicationDate":"2024-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652765","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Fore-arc metasomatism by hybrid slab fluids during subduction initiation: Sr–Mg–Ca isotopes of rodingite, western Yarlung Zangbo suture zone","authors":"Gui-Fang Ou ,&nbsp;Song-Jie Wang ,&nbsp;Hao Deng ,&nbsp;Wen-Yong Duan ,&nbsp;Xu-Ping Li ,&nbsp;Hans-Peter Schertl","doi":"10.1016/j.chemgeo.2024.122473","DOIUrl":"10.1016/j.chemgeo.2024.122473","url":null,"abstract":"<div><div>Subduction zone metasomatism is critical for Earth's material exchanges, yet the details of slab dehydration, particularly deserpentinization beneath fore-arcs, remain poorly understood. Here, we present Sr–Mg–Ca isotopic data for Purang rodingites from the western Yarlung Zangbo suture zone (YZSZ), a remnant of the Neo-Tethys Ocean that was subducted during the collision between the Indian and Eurasian Plates. The rodingites, occurring as centimeter- to meter-sized veins and blocks in serpentinized harburgite, are dominated by amphibolite- to greenschist-facies minerals like tremolite, magnesiohornblende, and chlorite. Their cumulate textures and rare earth element patterns resemble troctolite or gabbronorite, presumably formed beneath a seafloor spreading center. The rodingites are enriched in large ion lithophile elements and depleted in high field strength elements, with higher Sr/Nb and Ba/La and lower Nb/U and Ce/Pb ratios than mid-ocean ridge basalts (MORB) and rodingites formed through seawater or serpentinizing fluid alteration of MORB-like protoliths. They also exhibit higher initial ⁸⁷Sr/⁸⁶Sr ratios (0.7067–0.7075) and elevated δ²⁶Mg values (−0.22 ± 0.07 ‰ to −0.13 ± 0.02 ‰) compared to unaltered oceanic basalts, while their δ^44/40Ca values (0.72 ± 0.02 ‰ to 0.87 ± 0.03 ‰) remain similar to MORB. These signatures point to a metasomatic process beyond seafloor alteration, suggesting modification of a MOR-derived protolith in the fore-arc mantle at slab depths of &lt;40 km, driven by Sr- and Mg-rich fluids from clay-rich sediments and serpentinized mantle. The measured Sr, Mg and Ca isotope compositions can be reproduced by mixing a MORB-like protolith with hybrid fluids derived from varying proportions of sedimentary clays and serpentinized peridotite. Combined with previous studies on YZSZ metamorphic soles, we propose that this fore-arc metasomatism occurred during the early Cretaceous, concurrent with the incipient subduction of the Neo-Tethys oceanic rocks. These results highlight the significance of deserpentinization at shallow fore-arc mantle settings during subduction initiation, suggesting that slab dehydration is more complex than previously recognized.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"671 ","pages":"Article 122473"},"PeriodicalIF":3.6,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652392","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Unveiling the paleosalinity constraints on southern peri-Pannonian Lower Miocene lacustrine systems in Serbia and Bosnia and Herzegovina: Lopare (Dinaride Lake System) versus Toplica basin (Serbian Lake System)","authors":"Nikola Burazer ,&nbsp;Aleksandra Šajnović ,&nbsp;Darko Spahić ,&nbsp;Pavle Tančić ,&nbsp;Nenad Grba ,&nbsp;Branimir Jovančićević","doi":"10.1016/j.chemgeo.2024.122475","DOIUrl":"10.1016/j.chemgeo.2024.122475","url":null,"abstract":"<div><div>Early Neogene saline lakes were widely developed across Central Paratethys, particularly across its „Dinaride-Anatolide“ landbridge (area of Dinarides, Balkans). The constraints on Lopare (western part of Jadar block; eastern Bosnia and Herzegovina) and Toplica (Jastrebac Mt., central Serbia) Neogene paleolakes provide a better understanding of deep-time climate evolution. The study focused on early Neogene paleolacustrine configuration, paleogeography, and the factors affecting a considerable paleosalinity increase. The study integrated available records on the predominantly Lower Miocene sedimentary sequence by analyzing and interpreting several paleosalinity markers (inorganic geochemical proxies, mineralogical data). The constraints on paleosalinity markers are afterward coupled with rather complex tectonic inferences. The two wellbores drilled in the Lopare and Toplica basins expose Neogene sections from which the critical paleosalinity markers are extracted (drillhole depths up to 350 and 1000 m, respectively). The mineral searlesite (NaBSi₂O₅(OH)₂), and high B/Ga, markers of alkaline and arid paleoenvironmental lacustrine conditions, suggested intense evaporation (frequent drought periods). The evaporation was associated with paleoclimatic conditions during the Miocene Climatic Optimum. The Early Neogene arid climate and frequent evaporation episodes resulted in significant salinization of the Lower Miocene Lopare lacustrine sequence. The salinity in the Lopare sequence changed its character between brackish and saline, as evidenced by S/TOC and Ca/(Ca + Fe) ratios (TOC—Total Organic Carbon). At the same time, the salinity in the early Toplica basin was significantly lower and characterized by freshwater and brackish environments. The salinity variations between Toplica and Lopare were further exposed by Fe/(Ca + Mg), (Al + Fe)/(Ca + Mg), and C-value, yielding the change in the (paleo)water column. These markers further indicated the influence of warm climate conditions, consistent with the Miocene paleoclimatic record. Regarding paleogeography and Early Neogene tectonics, the results showed that before the Middle Miocene Badenian transgression, the Paratethyan Sea had no interference with the investigated intramontane lacustrine basins.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"671 ","pages":"Article 122475"},"PeriodicalIF":3.6,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652391","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Uranium-series isotopes as tracers of physical and chemical weathering in glacial sediments from Taylor Valley, Antarctica","authors":"Graham Harper Edwards ,&nbsp;Gavin G. Piccione ,&nbsp;Terrence Blackburn ,&nbsp;Slawek Tulaczyk","doi":"10.1016/j.chemgeo.2024.122463","DOIUrl":"10.1016/j.chemgeo.2024.122463","url":null,"abstract":"<div><div>The McMurdo Dry Valleys of Antarctica formed by extensive glacial erosion, yet currently exhibit hyperarid polar conditions canonically associated with limited chemical and physical weathering. Efficient chemical weathering occurs when moisture is available, and polythermal subglacial conditions may accommodate ongoing mechanical weathering and valley incision. Taylor Valley, one of the MDV, hosts several Pleistocene glacial drift deposits that record prior expansions of Taylor Glacier and sediment redistribution, if not sediment production. We present U-series isotopics of fine-grained sediments from these drifts to assess the timescales of physical weathering and subsequent chemical alteration. The isotopes ²³⁸U, ²³⁴U, and ²³⁰Th are sensitive to both chemical and physical fractionation processes in sedimentary systems, including the physical fractionation of daughter isotopes by energetic recoil following radioactive decay. By comparing U-series isotopic measurements with models of U-series response to chemical weathering and physical fractionation processes, we show that Pleistocene drift sediments record histories of significant chemical alteration. However, fine-grained sediments entrained in the basal ice of Taylor Glacier record only minor chemical alteration and U-series fractionation, indicating comparatively recent sediment comminution and active incision of upper Taylor Valley by Taylor Glacier over the Pleistocene. In addition, the results of this study emphasize the utility of U-series isotopes as tracers of chemical and physical weathering in sedimentary and pedogenic systems, with particular sensitivity to radionuclide implantation by <span><math><mi>α</mi></math></span>-recoil from high-U authigenic phases into lower-U detrital phases. This process has occurred extensively in <span><math><mrow><mo>&gt;</mo><mn>200</mn></mrow></math></span> ka drifts but to a lesser degree in younger deposits. U-series <span><math><mi>α</mi></math></span>-recoil implantation is an important physicochemical process with chronometric implications in other hyperarid and saline sedimentary systems, including analogous Martian environments.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"671 ","pages":"Article 122463"},"PeriodicalIF":3.6,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652748","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"A zircon petrochronologic perspective on raising the central Tibetan crust","authors":"Shu-Hui Ren ,&nbsp;Yun-Chuan Zeng ,&nbsp;Roberto Weinberg ,&nbsp;Ji-Feng Xu ,&nbsp;Jian-Lin Chen ,&nbsp;Bao-Di Wang ,&nbsp;Feng Huang ,&nbsp;Xi-Jun Liu ,&nbsp;Hong-Xia Yu ,&nbsp;Ming-Jian Li","doi":"10.1016/j.chemgeo.2024.122472","DOIUrl":"10.1016/j.chemgeo.2024.122472","url":null,"abstract":"<div><div>Being the most commonly dated accessory mineral, the geochemical makeup of zircon has increasingly been recognized as a promising indicator of the parent magma composition, providing a means to reconstruct the paleo-crustal thickness of orogenic belts where whole-rock records are limited. However, the robustness of zircon approaches in paleo-crustal thickness reconstruction remains controversial. Here, we report on U<img>Pb age, trace element and Hf isotope data for zircon in sedimentary rocks of central Tibet, aiming to reconstruct the central Tibetan paleo-crustal thickness evolution from Meso-Tethyan subduction to the India–Asia collision, and test the results by comparing against geological evidence. The consistent variations of different pressure-sensitive geochemical proxies over time, e.g., (La/Yb)_N, (Sm/Yb)_N, MREE/HREE, Eu anomaly, and Y values, indicate that pressure is the first-order control on zircon compositional changes. Using southern Tibet as a reference and comparing the results from various geochemical proxies, we find that zircon Eu geochemical proxy yields relatively reasonable estimates of paleo-crustal thickness for this orogen, which is thereby employed to explore the evolution of paleo-crustal thickness in central Tibet. A history of multi-stage thickening crust separated by episodes of thinning for central Tibet is revealed by zircon multi-proxy approach, and supported by multiple lines of independent evidence, including whole-rock geochemical proxies, structural geology, low-temperature thermochronology, and paleo-altimetry. We propose that a thick crust similar to the current one was likely formed in central Tibet by the Late Eocene (∼40–35 Ma), predominantly due to crustal shortening as a consequence of the India–Asia collision. Our study strengthens the applicability of zircon petrochronologic data in delineating the paleo-crustal thickness evolution of specific regions when supported by rigorous and comprehensive regional geological evidence.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"670 ","pages":"Article 122472"},"PeriodicalIF":3.6,"publicationDate":"2024-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142572250","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Evolution of continental inputs and watermass during cretaceous oceanic anoxic event 2 in the Neo-Tethyan region: Evidence from Nd-isotopes in southern Tibet","authors":"Xiaofeng Cheng ,&nbsp;Biao Chang ,&nbsp;Zhaoyu Zeng ,&nbsp;Lian Zhou ,&nbsp;Junhua Huang ,&nbsp;William F. Defliese ,&nbsp;Shucheng Xie","doi":"10.1016/j.chemgeo.2024.122462","DOIUrl":"10.1016/j.chemgeo.2024.122462","url":null,"abstract":"<div><div>During the mid-Cretaceous extreme greenhouse (∼ 90 to 125 Ma), changes in continental inputs and water-mass circulation influenced nutrient distribution and set the stage for ocean anoxia. Investigation of these changes is critical for an understanding of contemporaneous global-ocean evolution. Previous studies on δ⁶⁶Zn, δ¹⁵N, δ¹³C and ¹⁸⁷Os/¹⁸⁸Os isotopes in the Neo-Tethyan Ocean inferred both of these changes might be responsible for the continuous nutrient supply required to cause expansion of carbon burial during Oceanic Anoxic Event 2 (OAE2). Here, we applied the hydroxylamine hydrochloride (HH) extraction procedure to the analysis of Nd isotopic compositions of sediments collected from the mid-Cretaceous Dongshan and Lengqingre formations in southern Tibet. Our Nd isotope [ε_Nd(t)] records exhibit a large negative excursion (from −9.8 to −6.1) during the Cenomanian-Turonian period, but little variation (−6.5 to −5.2) during the Aptian period. Major and trace elements as well as ε_Nd(t) of residues indicate that the HH-extracted Nd in this study is mainly sourced from authigenic Fe<img>Mn oxides. To evaluate the robustness of our ε_Nd(t) records, we examined the potential influences of the detrital fraction. Our ɛ_Nd(t) records reflect a mixing signal of surface currents from the Central Pacific and continental weathering inputs, and the corresponding negative excursion is triggered by the changes of continental weathering inputs in the Neo-Tethyan region, which was synchronous with the change of riverine systems during the drift of the Greater Indian Plate in the mid-Cretaceous greenhouse. Further, the enhanced continental weathering inputs, which supplied continuous nutrients to the Neo-Tethyan ocean, have likely caused OAE2 and extended the duration of OAE2. Our ε_Nd(t) records shed new lights on our understanding of OAE2 during the mid-Cretaceous.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"671 ","pages":"Article 122462"},"PeriodicalIF":3.6,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652750","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Validating the rhenium proxy for rock organic carbon oxidation using weathering profiles","authors":"Katherine E. Grant ,&nbsp;Mathieu Dellinger ,&nbsp;Alexander J. Dickson ,&nbsp;Mateja Ogric ,&nbsp;Kate Horan ,&nbsp;Steven Petsch ,&nbsp;Robert G. Hilton","doi":"10.1016/j.chemgeo.2024.122464","DOIUrl":"10.1016/j.chemgeo.2024.122464","url":null,"abstract":"<div><div>Chemical weathering over geological timescales acts as a source or sink of atmospheric carbon dioxide (CO₂), while influencing long-term redox cycling and atmospheric oxygen (O₂) at Earth's surface. There is a growing recognition that the oxidative weathering of rock organic carbon (OC_petro) can release more CO₂ than is locally drawn down by silicate weathering, and may vary due to changes in erosion and climate. The element rhenium (Re) has emerged as a proxy to track the oxidative weathering of OC_petro, yet uncertainties in its application remain namely that we lack a systematic assessment of the comparative mobility of Re and OC_petro during sedimentary rock weathering. Here we measure Re and OC_petro loss across gradients in rock weathering at 9 global sites, spanning a range of initial OC_petro values from ∼0.2 % to &gt;10 %. We use titanium to account for volume changes during weathering and assess Re and OC_petro loss alongside major elements that reflect silicate (Na, Mg), carbonate (Ca, Mg) and sulfide (S) weathering. Across the dataset, Re loss is correlated with OC_petro loss but not with loss of any other major element. Across the weathering profiles, the average molar ratio of OC_petro to Re loss was 0.84 ± 0.15, with 8 out of 9 sites having a ratio &gt;0.74. At one site (Marcellus Shale), the average ratio was lower at 0.58 ± 0.11. The excess loss of Re matches expectations that, typically, between ∼0 and 20 % of the Re liberated by sedimentary rock weathering derives from silicate or sulfide phases, while some OC_petro may be physically or chemically protected from weathering. Overall, our measurements provide validation for the Re proxy of OC_petro oxidation and allow future work to further improve our knowledge of regional and global-scale rates of this important source of CO₂ in the geochemical carbon cycle.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"671 ","pages":"Article 122464"},"PeriodicalIF":3.6,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652749","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Land snail Δ47 thermometry using cultured and European natural populations of Clausilia pumila, Succinella oblonga and Trochulus hispidus","authors":"Gábor Újvári ,&nbsp;László Rinyu ,&nbsp;Anna Sulikowska-Drozd ,&nbsp;Barna Páll-Gergely ,&nbsp;Stefano M. Bernasconi","doi":"10.1016/j.chemgeo.2024.122461","DOIUrl":"10.1016/j.chemgeo.2024.122461","url":null,"abstract":"<div><div>Clumped isotope composition (Δ₄₇) of aragonitic shells of terrestrial molluscs allow the quantitative reconstructions of continental paleotemperatures from loess-paleosol records of the last 2.5 million years, but it needs testing the method under controlled laboratory conditions and using natural populations. In this study the stable carbon, oxygen and clumped isotope compositions of cultured individuals and field-collected specimens of three species (<em>Clausilia pumila</em>, <em>Succinella oblonga</em> and <em>Trochulus hispidus</em>), widespread in Quaternary loess deposits in Europe, were measured in the Debrecen (ATOMKI) and ETH Zürich laboratories. Our data of cultured snails demonstrate that shells of the three species record Δ₄₇ signatures close to equilibrium conditions with mostly positive (<em>C. pumila</em>), both positive/negative (<em>T. hispidus</em>), and mostly negative (<em>S. oblonga</em>) offsets on the order of 0.0158 ± 0.0105 ‰ (mean offset±1 SD) compared to the Anderson et al. (2021) unified calibration. Calcification temperatures (T_Δ47) derived from <em>C. pumila</em> shells were found to be in excellent agreement with chamber temperatures of 12, 18 and 24 °C, especially in the ATOMKI laboratory (mean T offset: 2.1 ± 2.2 °C, 1 SD), while the other two species exhibited larger discrepancies on the order of 5–8 °C (mean offset). Single shell-based mean T_Δ47 values of field-collected molluscs indicated growth temperatures spanning values from the frost-free period to summer season, or even above summer maxima. The sites of natural populations, characterized by different climate conditions, could be grouped using the aridity index (AI) with values of 0.96–1.06 representing mean temperature of the frost-free period (T_FFP), and AI ranging either from 0.85 to 0.91 or 1.14 to 1.51 reflecting mean summer season or July temperatures (T_JJA/T_J). Multi-shell T_Δ47, obtained by homogenizing the material of 3–5 shells of <em>C. pumila</em> and <em>T. hispidus</em>, reflect T_JJA in most cases. We observed a dependence of the shell oxygen isotope compositions of the three species on oceanity/continentality with more negative/positive values characteristic for more continental/oceanic sites, likely due to moisture source distance and depletion of rainfall in ¹⁸O towards the continental interior. In addition, deviation of body fluid δ¹⁸O values (derived from δ¹⁸O_shell and Δ_47shell) from seasonal precipitation δ¹⁸O is also controlled by an additional temperature effect, being independent of the climate zone of the collection site, but co-varying with the site-specific difference between single shell T_Δ47 and T_JJA.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"670 ","pages":"Article 122461"},"PeriodicalIF":3.6,"publicationDate":"2024-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142661988","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}