Analysis Of Rare Earth Elements Research Articles

Validation of McCARD Monte Carlo Calculation Code Against NAA Experiments Using Rare Earth Element Certified Reference Material Activated at JRTR

Rare earth elements (REEs) are widely used in several high-tech modern industries. Quantification of REEs demonstrates a technical challenge that requires the use of special scientific techniques. These techniques commonly introduce uncertainties that may propagate not only during the sample preparation phase but also in subsequent measurement and analysis phases. The Jordan Atomic Energy Commission is starting up a REE investigation program utilizing many of its available physical and chemical analytical capabilities, one of which is the Neutron Activation Analysis Facility (NAAF) at the Jordan Research and Training Reactor (JRTR). The NAAF provides accurate and relatively quick analytical services for better estimations of REEs in the unknown samples of interest without the need for any chemical processing prior to or after sample activation. In this paper, we present analytical results of routinely conducted instrumental neutron activation analysis (NAA) experiments using REE certified samples. To optimize future NAA investigations, first, a time-dependent Monte Carlo code at the JRTR, named Monte Carlo Code for Advanced Reactor Design and Analysis (McCARD), is herein validated via comparing its calculation results of the activation process against the presented results of the NAA experiments. The certified REE samples were activated in a well-thermalized NAA vertical activation hole within the reactor reflector region. Detailed neutronics and burnup calculations as well as transmutations were performed using McCARD. Ultimately, this study aims to assess the accuracy and reliability of the McCARD calculation models as a part of the effort of setting up a dedicated REE analysis laboratory at the JRTR. This study shows very good agreement between both obtained results—NAA experiment and McCARD calculations—with confidence levels noted to be more than 90% for almost all REE elements.

Hydrocarbon Accumulation and Overpressure Evolution in Deep–Ultradeep Reservoirs in the Case of the Guole Area of the Tarim Basin

Usually, deep oil and gas accumulation is often controlled by strike–slip faults. However, in the Tarim Basin, deep Ordovician oil and gas accumulations are also found in areas far from the fault zone. The process of oil and gas accumulation in deep reservoirs far from strike–slip fault zones is still unclear at present. The source and evolution of Ordovician fluids were analyzed using inclusion geochemical methods and the U–Pb dating technique. The analysis of rare earth elements and carbon–oxygen–strontium isotopes in the reservoirs showed that the reservoirs were weakly modified by diagenetic fluid. The fluid was derived from the fluid formation during the same period as the seawater, and no oxidizing fluid invaded the reservoir. The late oil and gas reservoirs had good sealing properties. The U–Pb dating results combined with homogenization temperature data revealed that the first-stage oil was charged during the Late Caledonian Period, and the second-stage natural gas was charged during the Middle Yanshanian Period. The evolution of the paleo-pressure showed that the charging of natural gas in the Middle Yanshanian was the main reason for the formation of reservoir overpressure. The strike–slip fault zone was basically inactive in the Middle Yanshanian. During this period, the charged natural gas mainly migrated to the reservoir along the unconformity surface and the open strike–slip fault zone in the upper part of the Ordovician reservoir. The source of the fluid shows that the reservoir in the late stage had good sealing properties, and there was no intrusion of exogenous fluid. The overpressure in the reservoir is well preserved at present.

Geochemical Study of the Osumi Granodiorite, Southwestern Japan

The Osumi Granodiorite, located on the Osumi Peninsula in southwest Japan, is an example of outer zone granites that were formed during a limited period (13–15 Ma) in response to the subduction of the Philippine Sea Plate. This event, which is linked to the separation of southwest Japan from continental Asia, resulted in unique igneous activity. The Osumi Granodiorite is the largest Miocene granite body in the region. It intrudes into the Mesozoic to Paleogene accretionary complex of the Shimanto Belt and affects contact metamorphism. Despite considerable research on the Osumi Granodiorite, limited geochemical studies, especially on trace and rare earth element (REE) analyses, have been conducted. Furthermore, there are insufficient data on the Rb–Sr isotopic system, leaving the formation process unclear. This study presents whole-rock geochemical and Rb-Sr isotopic data to investigate the petrogenesis of the Osumi Granodiorite. The results suggest a common magma origin for this pluton, as indicated by linear trends on the Harker diagrams and similar REE patterns. The presence of a relatively large Eu anomaly implies formation under a reducing environment. The AKF diagram indicates predominant contamination by pelitic rocks of the Shimanto Belt during magma formation. The Rb–Sr whole-rock isochron diagram and SrI–1000/Sr diagram suggest that the Osumi Granodiorite body was formed by heterogeneous assimilation of magma into the Shimanto Belt. Furthermore, the whole-rock isochron age is 64.3 Ma, which differs by approximately 50 My from the previously reported biotite K–Ar age (14–22 Ma). This age is considered to be a pseudo-isochron age, rather than the consolidation age. During the middle Miocene, the compressive stress field in the outer zone south of the Butsuzo Tectonic Line made it difficult for magma to rise. As a result, it reacted with the sedimentary rocks of the Shimanto Belt to various degrees. The Osumi Granodiorite underwent magma differentiation upon intrusion into the Shimanto Belt. It subsequently ascended, cooled, and interacted with pelitic rocks under stable geological conditions.

Formation mechanism of carbonate cement in tight sandstone reservoirs in the depression zone of foreland basin and its impact on reservoir heterogeneity: The upper Triassic Xujiahe Formation in Western Sichuan foreland basin, China

The carbonate cements in tight sandstone reservoirs are diverse, complex, and important determinants of reservoir quality. This study provides a comprehensive analysis of the characteristics and formation mechanism of carbonate cement in the tight sandstone reservoirs of the Xu3 Member within the Xujiahe Formation in the depression zone of the Western Sichuan foreland basin. Core samples were examined on thin sections using cathodoluminescence and scanning electron microscopy, fluid inclusion analysis, in situ carbon and oxygen stable isotopes, and rare earth element analysis. The study reveals that the Xu3 Member primarily comprises sublitharenite and litharenite, which has three stages of carbonate cementation within the reservoirs. On average, the reservoirs exhibit a porosity of 3.82% and a permeability of 0.1mD. In the eodiagenetic stage, calcite and dolomite (δ13CPDB = 0‰ to −4.07‰; δ18OPDB = −5.64‰ to −12.69‰) formed, filling both intergranular pores and intragranular dissolution pores. This process is driven by the expulsion of organic acids through compaction from the clay and coal-bearing sections during shallow burial. The carbon sources originate from external organic acids and internal carbonate rock fragments, which combine with Ca2+ and Mg2+ ions released from the dissolution of carbonate rock fragments. During the mesodiagenetic stage A, the predominant formation of ferroan calcite and ankerite (δ13CPDB = −5.98‰ to −7.64‰; δ18OPDB = −14.47‰ to −19.87‰) occurred, filling intergranular residual pores and secondary intragranular dissolution pores. This phenomenon is caused by the expulsion of organic acids formed by the compaction of matured organic matter at greater burial depths. The carbon sources primarily originate from external organic acids and combine with Ca2+, Mg2+, and Fe2+ ions in the sandstone, alongside accompanying organic acids. During the mesodiagenetic stage B, coarse-macro crystalline calcites (δ13CPDB = −1.06‰ to −1.64‰; δ18OPDB = −17.95‰ to −20.36‰) with significant positive Eu anomaly-filled fractures were formed. These calcites are associated with hydrothermal fluids in the deep subsurface, precipitating directly in the fractures due to the presence of hot hydrothermal fluids rich in Ca2+ and CO32−. The Xu3 Member displays two sandstone superimposed types. In the mudstone overlain by sandstone type, carbonate cement is mainly present in the middle of the cycle, and reservoir quality is relatively high at both the bottom and top of the cycle. In the sandstone overlain by sandstone type, carbonate cement is predominantly found in the middle and top sections of the cycle, with higher-quality reservoirs primarily forming at the bottom of the cycle. It resulted in significant heterogeneity observed in the tight sandstone reservoirs of the depression zone in the Western Sichuan foreland basin.

Rapid quantitative analysis of multiple rare earth elements in NdFeB alloys based on laser-induced breakdown spectroscopy (LIBS) and random forest (RF)

NdFeB material has excellent comprehensive magnetic properties, which plays a crucial role in the field of rare earth magnetic materials, and is one of the important basic materials to support modern high-tech industries. In the production of NdFeB alloys, the control of rare earth elements (REEs) is directly related to the quality and resource utilization efficiency of NdFeB materials. Therefore, the prediction of REEs content in NdFeB alloys is of great research significance and application value for the quality control of products, the enhancement of production efficiency and reduction of energy consumption by the rare earth material industry. In this study, a combination of laser-induced breakdown spectroscopy (LIBS) and random forest (RF) was used to investigate the quantitative analysis of four REEs (Nd, Pr, Tb and Dy) in NdFeB alloys. Firstly, the original LIBS spectra were screened by principal component analysis-mahalanobis distance (PCA-MD). Then, the effects of different data processing methods on the screened LIBS spectra were explored, and next, the feature variables were extracted from the preprocessed spectral data by the variable importance measurement (VIM). In order to further verify the prediction performance of the model, the prediction results of the RF models based on the different methods were compared. Finally, a PCA-VIM-RF calibration model was established on the basis of the optimized spectra, selected feature variables and parameters. Leave-one-out cross validation (LOOCV) was used to optimize the parameters of PCA-MD method, spectral preprocessing method and variable importance thresholds during the construction of the calibration model. The results show that the PCA-VIM-RF model has better prediction performance than the RF calibration model based on the raw spectra. For the PCA-VIM-RF calibration method of Nd, Pr, Tb and Dy elements, the values of R2CV are 0.9991, 0.9998, 0.9986, and 0.9984, respectively, the values of RMSECV are 0.06296%, 0.02788%, 0.04647% and 0.05252%, respectively. The values of R2P are 0.9508, 0.9975, 0.9691 and 0.9457, respectively, and the values of RMSEP are 0.6082%, 0.09205%, 0.5776% and 0.2631%, respectively.The above results indicate that LIBS combined with PCA-VIM-RF algorithm is a promising method for rapid quantitative analysis of REEs in NdFeB alloys without complicated sample preparation, which can provide some new ideas or strategies for the future research, development and quality control of rare earth materials.

Eocene to Miocene sediment provenance features and evolution history of the western slope area in the Xihu Sag of the East China Sea Continental Shelf Basin

Rift basins are commonly characterised by multiple sediment sources (e.g. transverse and longitudinal) that change over time during different rifting evolution stages. Therefore, tracing sediment provenance to decipher the sedimentary source-to-sink analyses processes in rift basins is important to predict sandy reservoirs. The Xihu Sag in the East China Sea Shelf Basin, particularly its western slope, features large-scale sand bodies of unclear origin. We used petrography, heavy minerals and geochemistry to study sediment provenance in the Eocene Baoshi to Miocene Longjing formations. Our work suggests there are three distinct areas (namely zones A, B and C) affected by different source areas. Zone A, influenced by the Hupijiao uplift, primarily contains metamorphic rock minerals; Zone B, affected by the Haijiao and Hupijiao uplifts, contains igneous and metamorphic rock minerals; and Zone C, dominated by the Haijiao uplift, features igneous with some metamorphic sources, which increase over time, indicating stronger sediment input from the northern Hupijiao uplift. Rare earth element analysis suggests a continental margin and island arc setting, primarily with intermediate–acid felsic rock sources. However, a Eu negative anomaly in Eocene upper Pinghu Formation to the Miocene Longjing Formation indicates some basic source contributions, possibly from a volcanic belt east of the South Yellow Sea. This intermediate–basic volcanic rock belt is located to the northwest of the Hupijiao uplift and may provide clasts for zones A and B through axial channels. These findings indicate that varied sediment sources in the different zones and basin evolution stages with a growing extra-basinal contribution from the Eocene to Miocene, which align with the tectonic shift from the rifting to post-rift period, are essential for understanding the sedimentary filling in this area.

Rare earth elements sediment analysis tracing anthropogenic activities in the stratigraphic sequence of Alagankulam (India)

A methodological approach based on rare earth elements analysis was developed to observe human activities in the stratigraphic sequence of Alagankulam. The site was one of the main ancient ports in south-eastern India and one of the transoceanic connecting points between East and West during the Classical Period. The sampled sediments where collected from vertical profiles, areas with traces of firing activities and filled deposits. Major, minor and trace element concentrations were measured by the means of spectroscopic and spectrometric techniques. Data from multielemental analysis were then cross-referenced together with archaeological evidence to map the variability within the site and its association with the detected anthropic activities. The matching of the interpretation of the archaeological record and the analytical data has allowed a combined mapping of visible and invisible traces of human activities in the site, giving a deeper insight of the Alagankulam occupational history.

Neutron Activation Analysis of Rare Earth Elements (Sc, La, Ce, Nd, Sm, Eu, Tb, Dy, Yb) in the Diagnosis of Ecosystems of Donbass

Neutron Activation Analysis of Rare Earth Elements (Sc, La, Ce, Nd, Sm, Eu, Tb, Dy, Yb) in the Diagnosis of Ecosystems of Donbass

Organic matter accumulation as a convergence response to astronomical forcing: Insights from Milankovitch periods and sea-level fluctuations during the early Cambrian

The accumulation of organic matter (OM) in marine sediments is a vital part of the global carbon cycle today and on ancient Earth, and is driven by a cumulative shift of organic carbon flux through oceans to marine sediments. This shift is a complicated process that is known to be influenced by the biological pump, diagenesis, and thermal alteration, so is affected by oceanic conditions and palaeo-climate, but less attention has been paid to the triggers of OM accumulation. Here, a set of marine sedimentary rocks from the early Cambrian in the southwestern part of the Yangtze Platform in China was used to search for clues to the triggers of OM accumulation. The effect of astronomical forcing, which potentially is a major control on Earth's oceanic conditions, was assessed via frequency analysis based on a high-resolution log dataset from a borehole in Yunnan Province. An astronomical time scale was constructed based on a 405,000 year-tuned filter. Palaeo-oceanic sedimentary conditions and palaeo-climate, which were recorded in the sedimentary rocks, were determined through geochemical analyses of major, trace, and rare earth elements. The mutual influence of astronomical forcing and the early Earth oceanic sedimentary conditions and paleoclimate were examined though Pearson Correlation analyses to provide evidence for the intensity of alteration of sedimentary conditions and the forces impacting the shift of organic carbon in the marine ecosystem. The results show that two convergence responses of OM accumulation were associated with ca. 1.5 and 2.4 million year (Myr) Milankovitch cycles. Fluctuations in sea level establish a connection between Milankovitch forcings and changes in sedimentary conditions, thereby providing evidence for the triggering of a cumulative shift of OM flux to sediments, and the effect of astronomical forcing on the organic carbon cycle.

Neodymium isotope composition and rare earth element distribution of East Antarctic continental shelf and deep waters

Circumpolar Deep Water (CDW) and Antarctic Bottom Water (AABW) play key roles in the Earth's climate system. Both water masses form critical components of the Antarctic Circumpolar Current and Meridional Overturning Circulation and therefore directly influence the large-scale redistribution of heat, nutrients and carbon. Reconstruction of past CDW transport and AABW production and export has been a key target in palaeoceanography. One promising proxy to achieve this has been the neodymium (Nd) isotope composition of seawater. The biogeochemical processes controlling Nd in the ocean, however, remain underconstrained, and modern observations of Nd isotopes in the Southern Ocean are still geographically limited.To overcome this limitation, 61 seawater samples were collected for Nd isotope and rare earth element (REE) analysis at nine stations along the Wilkes Land continental margin and in the Australian-Antarctic Basin (65°S 125°E) near East Antarctica. The results show that the different water masses have the following Nd isotope characteristics: Antarctic Surface Water (AASW), εNd = −9.0 ± 1.0 (2SD; n = 22); Modified CDW (MCDW), εNd = −8.8 ± 0.8 (2SD; n = 22); AABW, εNd = −8.3 ± 0.5 (2SD; n = 17).There is no evidence of continental REE inputs to surface waters on the Wilkes Land margin. Observed zonal variability of Nd isotope composition in AASW can be attributed to seasonal competition between the poleward flow of warm AASW from the AAG and the westward export of cold surface shelf waters by the Antarctic Slope Current.In terms of deep and bottom waters, mixing of upwelled CDW with AASW and AABW exclusively controls the Nd isotope composition of MCDW, with no indication of boundary processes modifying the Nd isotope composition of MCDW as it encroaches the shelf or slope. The regional Nd isotope signature for AABW is intermediate between published data for the Atlantic sector AABW (εNd = −9.1 ± 0.7) and Pacific sector AABW (εNd = −7.4 ± 0.9). In the absence of active convection, this Nd isotope signature can be explained by a mixture of advected AABW from the Adélie Land coast with a more dominant component of local MCDW and CDW.The data presented in this study constitute the first Nd isotope data set in this part of the Southern Ocean and suggest conservative behaviour of Nd in proximity to the old East Antarctic continent.

Rare earth element geochemistry of reef carbonates in the South China Sea since the Miocene: Insights into paleoclimatic significance

Seawater chemistry critically affects the functioning of ocean ecosystems. However, the evolution of the seawater chemistry in the South China Sea (SCS) since the Miocene is not fully resolved, and its links to tectonic and climate changes remain unclear. In-situ, shallow marine carbonates can provide insights into long-term changes in seawater chemistry and associated environmental processes. In this study, we conducted the rare earth element (REE) analysis of the NK-1 core in the southern SCS since the Miocene. The results reveal poor relationships between siliciclastic/diagenetic indicators (mineralogical, isotopic, and elemental data) and REE proxies, which demonstrate that the REE compositions are insensitive to non-carbonate contaminations and diagenesis. The results exhibit seawater-like REE patterns with LREE depletion, positive La anomaly, superchondritic Y/Ho ratio, and negative Ce anomaly, which demonstrate that this core has preserved a signal of the primary seawater REE composition. The Y/Ho ratios range from 45 to 80 and La anomalies range from 1.0 to 2.3 during ∼23–13 Ma, and they then decrease after ∼13 Ma, with the Y/Ho ratios ranging from 30 to 52 and La anomalies ranging from 0.6 to 1.5. Considering that seawater REE components are mainly sourced from terrigenous sources which exhibit lower La anomalies and Y/Ho ratios, our results indicate an enhanced terrigenous input since ∼13 Ma. We consider that the climate cooling and aridity since ∼13 Ma might be responsible for the phenomenon.

The depositional characteristics of turbidity current in Manila Trench: sediment provenance, geochemical elements and organic carbon burial

Turbidity currents play a significant role in sediment transport in deep ocean, profoundly impacting sedimentation in the abyssal sea. This study focused on a 375 cm long sediment core collected from the Manila Trench, revealing a distinctive 15 cm turbidite layer characterized by coarse sediment, an upward fining pattern, and a basal erosion surface. Analysis of rare earth elements and Nd isotope indicates that this turbidite layer originated from Taiwan Island. Initiated in the estuarine shelf region of southwestern Taiwan Island, the turbidity current transported substantial biogenic debris and marine fresh organic carbon into the Manila Trench. Consequently, the turbidite layer exhibited an elevated CaO content and more positive δ13C values. Despite lower TOC content in the turbidite layer due to coarse particle size, the mixture of marine fresh organic matter significantly lowered the carbon age of this layer compared to the strata both below and above it. The rapid sedimentation of the turbidite deposit led to an organic carbon burial flux comparable to the rate at which normal deep-sea sediment buries organic carbon over seven hundred years. Notably, finer sediment overlaying the turbidite layer acted as a cap, enhancing carbon sequestration within the trench. In contrast to nearby core GEO6, which documented over 11 turbidity currents, core S02 recorded only one event. Detailed bathymetric analysis highlights the crucial role of local topography in detecting and preserving turbidity currents. The insights gained from this study would advance our understanding of how turbidity currents shape and influence the deep ocean sedimentation.

Rare-earth Element-based Electrocatalysts Designed for CO2 Electro-reduction.

Electrochemical CO2 reduction presents a promising approach for synthesizing fuels and chemical feedstocks using renewable energy sources. Although significant advancements have been made in the design of catalysts for CO2 reduction reaction (CO2RR) in recent years, the linear scaling relationship of key intermediates, selectivity, stability, and economical efficiency are still required to be improved. Rare earth (RE) elements, recognized as pivotal components in various industrial applications, have been widely used in catalysis due to their unique properties such as redox characteristics, orbital structure, oxygen affinity, large ion radius, and electronic configuration. Furthermore, RE elements could effectively modulate the adsorption strength of intermediates and provide abundant metal active sites for CO2RR. Despite their potential, there is still a shortage of comprehensive and systematic analysis of RE elements employed in the design of electrocatalysts of CO2RR. Therefore, the current approaches for the design of RE element-based electrocatalysts and their applications in CO2RR are thoroughly summarized in this review. The review starts by outlining the characteristics of CO2RR and RE elements, followed by a summary of design strategies and synthetic methods for RE element-based electrocatalysts. Finally, an overview of current limitations in research and an outline of the prospects for future investigations are proposed.

Geochemistry of Bled El Hadba phosphorites (NE Algeria): Glauconitization process versus REE-enrichment

Rare earth element (REE) enrichment in Algerian phosphorites has been evoked recently by a number of authors and are considered among the richest Paleocene-Eocene phosphorites worldwide. The Bled El Hadba deposit belongs to the giant Djebel Onk phosphorite complex in northeast Algeria. The deposit was subject to many geological studies that were focused on P2O5 contents for commercial purposes. The upper Thanetian phosphorite layer is about 30 m thick, and subdivided into three sub-layers (lower, main and upper sub-layer), based on P2O5 contents, where the main sub-layer is considered to be the richest. Despite this, few detailed geochemical investigations were carried out on this deposit thus far. In this work, major, trace and REE analyses were conducted on phosphate particles (pellets, coprolites and glauconites) using ‘in situ’ LA-ICP MS, and on whole-rock samples using XRF technique. The results show that the main sub-layer displays the highest whole-rock P2O5 contents, varying between 19.65 and 21.32 wt% compared to the lower (10.47–16.87 wt%) and upper (9.43–13.87 wt%) sub-layers. Among the phosphate particles, glauconites display the lowest P2O5 contents in the three sub-layers (17.45–19.35 wt%) compared to pellets (21.14–24.33 wt%) and coprolites (21.75–24.12 wt%), and largely the highest Al2O3, SiO2, MgO and Fe2O3(t). Glauconites also show higher ΣREE contents (764–2050 ppm) compared to pellets (221–910 ppm) and coprolites (214–909 ppm). Within the glauconite particles, the ΣREE, along with Al2O3, SiO2, MgO, and Fe2O3(t) contents, increase from core to the rim, whereas P2O5 contents decrease, which suggests that glauconitization postdates phosphatization processes. Also, the glauconitization process increase from the lower to the upper sub-layer; this is shown by the positive correlations between Al2O3 contents and those of MgO and SiO2 in one hand, and negative correlations between Al2O3 and P2O5 on the other hand. Ce, Eu, Y anomalies, along with La/Nd ratios and Nd contents, all point towards phosphatization under oxic conditions as a result of warm water upwelling, whereas glauconitization started under more reduced (sub-oxic) conditions; i.e., during early diagenesis, the peak of REE uptake from porewater, and under slow sedimentation rates.Despite their relatively low P2O5 concentrations, the ΣREE contents of the Bled El Hadba phosphate particles record the highest concentrations in all Algerian and north African phosphorites. The main sub-layer is considered to be the most glauconite-rich phosphorite in Algeria. Therefore, more extensive REE analyses are recommended to better evaluate its economic potential in terms of critical raw materials.

Rare Earth Element Characteristics of Shales from Wufeng-Longmaxi Formations in Deep-Buried Areas of the Northern Sichuan Basin, Southern China: Implications for Provenance, Depositional Conditions, and Paleoclimate.

To explore the sedimentary environment and the background of the source area of organic-rich shales in the Wufeng-Longmaxi Formations in the northern Sichuan Basin, samples from Well XX1 in the area were subjected to geochemical testing and analysis of organic carbon content, trace elements, and rare earth elements (REEs). The results show that the total content of REE (ΣREE) of the shale in the Wufeng-Longmaxi Formations varied from 183.08 to 234.66 μg/g with an average of 212.59 μg/g, which is significantly higher than the content of the North American shale composite. The fluctuations in the total amount of REEs in the shale of the Wufeng-Longmaxi Formations reflect certain differences in the geochemical conditions of the Upper Ordovician-Lower Silurian shale. The ratios of LREE/HREE, LaN/YbN, LaN/SmN, and GdN/YbN and the distribution of normalized REE patterns indicate that the source supply or sedimentary structural background may have changed during the shale deposition period of the Wufeng Formation, while the shale deposition period of the Longmaxi Formation may be in a relatively stable source supply and sedimentary structural background. There is no significant correlation between δCe and ΣREE, and the obviously negative Eu abnormity and the weak Ce abnormity indicated that the diagenesis had a limited impact on REEs. Geochemical parameters such as values of ∑REE, δEu, δCe, Ceanom, and LaN/YbN indicate that the climate during the Wufeng-Longmaxi Formation shale deposition period was warm and humid, and the shale was deposited mainly in the suboxic-anoxic water environment. The deposition rate was stable and slow, providing good conditions for the production and preservation of organic matter. At the same time, this shows that the water environment of Wufeng Formation is more anoxic and reductive than that of Longmaxi Formation, which is more conducive to the preservation of organic matter. The correlation between ΣREE and the content of Sc, Ti, Cr, Co, Zr, Nb, Th, Hf, Ta, and other elements indicates that the sources of REEs in the shale of Wufeng and Longmaxi Formations in the study area are similar, mainly terrestrial clasts, and some may come from the sea. The REE distribution pattern shows that the shale provenance of the Wufeng-Longmaxi Formations mainly comes from the upper crust. The La/Yb-∑REE diagram shows that the sediment-parent rocks are mainly early sedimentary rocks and these sediment-parent rocks have granite provenance characteristics. Compared to La/Yb, LREE/HREE, LaN/YbN, and other REE characteristic parameters, it is inferred that the tectonic background of the study area is dominated by passive continental margin.

Paleoenvironmental, Paleoclimatic, and Tectonic Implications of the Yanghugou Formation in the Western Margin of the Ordos Basin, China: Evidence from Palynology and Elemental Geochemical Characteristics

This study explores the sedimentary environment and tectonic implications of the Upper Carboniferous Yanghugou Formation on the western margin of the Ordos Basin through the analysis of major elements, trace elements, and rare earth elements in 23 mudstone samples. The results indicate moderate chemical weathering conditions, as reflected in the Chemical Alteration Index (CIA) and Component Variability Index (ICV) values. Warm and humid paleoclimatic conditions are suggested by Rb/Sr, Sr/Cu, spore, and pollen fossil samples. The paleosalinity of the water is identified as a transitional phase of a brackish water environment based on Sr/Ba and Th/U ratios. Additionally, V/(V + Ni) and δU values imply a transitional phase of a weak oxidation–reduction environment for the water. In accordance with the La-Th-Sc, Th-Sc-Zr, Th-Co-Zr, (La/Yb)-∑REE, and (La/Th)-Hf discrimination diagrams, it is inferred that the study area is part of a continental marginal tectonic setting. The sediments are primarily derived from an upper-crust felsic source area. The sedimentary period of the Yanghugou Formation in the western margin of the basin is considered a marginal rift basin characterized by north–south compression and western rift extension. This setting is influenced by the active continental margin of the Alxa block and the passive continental margin of the Qilian–north Qinling orogenic belt.

Metamorphic evolution of high-pressure and ultrahigh-temperature granulites from the Alxa Block, North China Craton: Implications for the collision and exhumation of Paleoproterozoic orogenic belts

High-pressure (HP) and ultrahigh-temperature (UHT) granulites with a high geothermal gradient (greater than 500 °C/GPa) are prominent features of Paleoproterozoic orogenic belts and may represent paired metamorphic belts present during the early stages of plate tectonics. Understanding their pressure−temperature−time (P-T-t) paths and metamorphic evolutionary relationships could provide valuable constraints on the tectonic processes of Paleoproterozoic orogenic belts. Here, we describe garnet mafic and clinopyroxene-orthopyroxene (Cpx-Opx) granulites from the Diebusige area of the Alxa Block in the western part of the Khondalite Belt, North China Craton. Through detailed petrographic, phase equilibrium modeling, and Ti-in-amphibole thermometric studies, we obtained the preserved peak mineral assemblages of two types of mafic granulites: garnet + clinopyroxene + amphibole + plagioclase + quartz + ilmenite, and clinopyroxene + orthopyroxene + plagioclase + amphibole + garnet (rare) + ilmenite. The preserved peak P-T conditions were determined to be 850−890 °C/11.4−13.2 kbar (HP granulite-facies) and 950−970 °C/8.2−9.2 kbar (UHT conditions), with thermal gradients of ∼70 °C/kbar (moderate differential temperature/differential pressure, dT/dP) and ∼110 °C/kbar (high dT/dP), respectively. Using sensitive high-resolution ion microprobe U-Pb dating and rare earth element analysis of zircons, we found that the garnet mafic granulite recorded an HP granulite-facies metamorphic age of ca. 1.95 Ga and a retrograde cooling age of ca. 1.8 Ga, while the Cpx-Opx granulite recorded a consistent retrograde cooling age of ca. 1.8 Ga. By combining these results with the metamorphic evolution and timing (ca. 1.92−1.91 Ga) of UHT rocks from the Khondalite Belt, we suggest that the garnet (HP) mafic and Cpx-Opx (UHT) granulites may represent different stages of the same metamorphic event, shedding light on the processes involved in the collision and subsequent exhumation of Paleoproterozoic orogenic belts.

PROVENANCE AND DISTRIBUTION OF MIDDLE BAONG SAND IN THE MALACCA STRAIT AND ITS SURROUNDING

The Middle Baong Sand Formation has long been ascribed to the Malay Peninsula. However, this contradicts the results of chronostratigraphic correlation and rare earth element (REE) analysis, which indicate another source from the south. This research was conducted in North Sumatra, especially in Pertamina's onshore and offshore work areas. The comparison area is located in Kutacane-Karo and the Malay Peninsula. The objective of the study is to understand the provenance of the Middle Baong Sand Formation in North Sumatra. Data from four wells and 32 outcrops are used to evaluate the provenance and distribution of Middle Baong Sand in the study area. Besides that, secondary data from three outcrops are also used to support the analysis. The methods used in this study are chronostratigraphic correlation and REE analysis. The results showed that the provenance of the Middle Baong Sand onshore is estimated to originate from southwest Sumatra, contrary to general assumptions. Validation was carried out by comparing Malay Peninsula data with Kutacane research data and wells using REE analysis. The analysis results showed that the Middle Baong Sand Formation in the onshore area has a different provenance from the Middle Baong Sand Formation in the offshore area, which contradicts other research conducted so far. Based on this study, it is concluded that the paleogeography of the North Sumatra basin undergoes deepening symmetrically in the central basin since 10.46 million years ago (Mya).

Origins and paleoclimatic and paleoceanographic significance of laminated sediments of middle Pleistocene age from the southern Bering Sea

Laminated diatomaceous sediments occur intermittently in the Bering Sea over the past 5 million years. A varve (annually deposited) origin for the laminae has been suggested, but there is currently no consensus. Here, we report results of a study of two laminated intervals dating from ∼528 ka and ∼ 782 ka from IODP Site U1340 on the Bowers Ridge. We combine conventional micropaleontological methods with scanning electron microscope analysis that resolves the seasonal cycle of flux events recorded and demonstrates an annual origin for the laminae. Resting spores of Chaetoceros spp., and more rarely of Thalassiosira antarctica represent early spring blooms with the latter likely due to increased meltwater input. Diatom laminae containing concentrations of Shionodiscus trifultus, Thalassiosira spp., Actinocyclus curvulatus, and Neodenticula seminae, represent flux from the main spring-summer bloom episodes, with the latter indicating influx of seed populations from the North Pacific Alaskan Stream. Concentrations of Coscinodiscus spp. in the uppermost part of the diatom laminae represent “Fall Dump” sedimentation of these stratified-adapted diatoms in response to break down of summer stratification in autumn/early-winter storms. The lithogenic laminae represent mainly winter deposition and rare earth element analysis suggests provenance from the southern Bering Sea shelf and the Aleutian Arc. Productivity was high in the studied intervals with total mass fluxes around 5 times higher than modern values. Variation in lamina thickness and diatom composition contain periodicities of 2–8 years, as well as a bi-decadal variability likely related to influence of the Pacific Decadal Oscillation.

Petrography and geochemistry of sandstones of the Ash Shumaysi Formation in the Jeddah-Makkah region, Saudi Arabia: Implications for provenance, tectonic setting, paleoweathering, paleoclimate and paleogeography

This study aims to evaluate the provenance of sandstones of the Ash Shumaysi Formation (Early Eocene to Oligo-Miocene) exposed in the Jeddah-Makkah region (an intra-continental cratonic region in the west of the central part of the Arabian Shield), in addition to re-establish the tectonic setting, paleoclimate and paleo-weathering of their source rocks. This aim has been achieved by petrographic investigation and geochemical (major, trace and rare earth elements) analysis of the sandstones. Integration of both petrographic and geochemical data reflects a derivation of the sandstones from intensively-weathered and multi-recycled felsic igneous (granites) rocks, with a minor contribution of intermediate (granodiorite), mafic igneous (andesite), metamorphic (mainly gneisses) and recycled sedimentary rocks, which correspond to the Precambrian rock units of the west of the central part of the Arabian Shield. The latter was developed under semi-humid climatic conditions in the source area. Tectonically, the source rocks are of a cratonic interior in a passive continental margin of the Upper Continental Crust. This passive continental margin was later affected by rifting as revealed from the discrimination function diagrams of high-silica samples of sandstones. In general, the Ash Shumaysi sandstones may represent erosional products of the nearby high-topographic crystalline rocks of the Western Arabian Shield that were located in a tectonically stable passive margin subjected to a subsequent continental rift. Results of this study could add to the knowledge about paleoweathering, paleoclimate and tectonic setting in the Arabian Shield which is a part of the southern margin of the broad stable continental shelf of the northern margin of the Gondwana supercontinent.