Post-Archean Australian Shale Research Articles

Geochemistry and clay mineralogy of shales in the Sulu Orogenic Belt, East China: suggestion for continental weathering during an Early Cretaceous hyperthermal interval

ABSTRACT Understanding past weathering–climate feedback mechanisms under greenhouse conditions has significance for guiding the development of climate mitigation strategies. The continental paleoweathering state of Early Cretaceous shales in the Sulu Orogenic Belt of East China during a hyperthermal interval related to oceanic anoxic event 1a (OAE1a) was investigated via geochemical and clay mineralogical analyses of shale samples. The resulting diagrams of ternary 15Al2O3–Zr–300TiO2 discrimination, Th/Sc and Zr/Sc show that the geochemical composition was mainly controlled by source composition. This is supported by observations of low Zr contents, high indexes of compositional variability (ICV; > 1), and micropetrological characteristics. All samples showed narrow SiO2/Al2O3 and (Fe2O3 + MgO)/Al2O3 ranges that were within the predicted weathering trends of the ternary A-CN-K diagram, indicating that the shale geochemistry was not influenced by silicification and K-metasomatism. The chondrite-normalized rare-earth-element pattern suggests that all samples had the same felsic igneous parent rock. The geochemistry of whole rocks and their silicate fractions indicates that the shale had low chemical indexes of alteration (CIA) but high ICV values compared to post-Archean Australian Shale, indicating low sediment maturity and extremely weak chemical weathering in the source terrane and/or sedimentary basin under hot-dry conditions. Moreover, the clay minerals in the shale were mainly illite, suggesting low mineral weathering. Thus, during the OAE1a-related hyperthermal interval, chemical weathering was relatively weak in some mid-latitude arid inland areas. This may be mainly due to aridification decreasing water–rock reactions. Chemostratigraphic analysis suggests that the CIA, Ga/Rb, and Rb/Sr values of shales from the upper strata of the Yangjiazhuang and Shuinan formations were greater than those from lower strata. Moreover, the opposite trend in K2O/Al2O3 ratios was found. These indices suggest gradual increases in chemical weathering as the climate changed from hot-dry to warm-humid. In contrast, proxy indices of shale from the Zhifengzhuang Formation showed the opposite trend, suggesting a gradual decrease in chemical weathering as the climate changed from warm-humid to hot-dry. Considering the composition of the clay minerals, it is speculated that continental weathering was dependent on atmospheric humidity rather than temperature under the extreme greenhouse conditions, resulting in ineffective climate regulation by chemical weathering. This comprehensive study advances our understanding of the weathering–climate feedback mechanism under greenhouse regimes.

Geochemistry of cherts from the northern Jiangxi region, South China: Implication for paleoenvironment

The extensive bedded cherts deposited during the Ediacaran–Cambrian (E–C) transition period play a crucial role in understanding the geological evolution of this period, yet the origin of these cherts remains disputed. Here, we present new geochemical data for cherts of the Piyuancun (PYC) Formation deposited during the Late Ediacaran and the Hetang (HT) Formation deposited during the Early Cambrian in northern Jiangxi region, Lower Yangtze region, South China. The PYC cherts contain a small amount of monaxons sponge spicules and radiolarian fragments, while the HT cherts lack siliceous organism evidence. Major and trace element analysis, coupled with discriminant diagrams, indicate a possible shift in redox conditions of seawater during the E–C transition in the northern Jiangxi region. The shift suggests a change from weakly–moderately restricted euxinic conditions to strongly restricted euxinic conditions. Furthermore, the location of both cherts are distant from the source area of siliceous organisms. Fossil evidence, as well as the values of Fe/Ti and Fe/(Mn+Ti), Eu anomalies, Post-Archean Australian Shale (PAAS) normalized REE+Y patterns, and various discriminant diagrams, support the conclusion that the PYC and HT cherts originated primarily from direct seawater precipitation, with the PYC cherts exhibiting weak hydrothermal evidence. Upwelling contributes to the formation of HT cherts and organic matter (OM) accumulation. Ocean acidification, triggered by OM degradation and biodegradation processes during the E–C transition period, leads to the extensive silica precipitation and preservation. These results enhance our understanding of the geological processes during the E–C transition.

MINERALOGIA, GEOQUÍMICA, FERTILIDADE E ORIGEM DOS SEDIMENTOS DE PRAIA (BARRA EM PONTAL) DAS BACIAS DOS RIOS PURUS E JURUÁ NOS TERRENOS DO ESTADO DO ACRE

The Acre state is in the southwestern part of the Brazilian Amazon region with an area of 164.123.738 km2 and a low population density (5.52 inhabitants/km2 for 2021). The geological context is mainly related to recent units that outcrop at the Acre basin and associated with the Solimões Formation, besides old alluvial terraces that follow main drainages. The Solimões Formation comprises fossil-bearing clayey siltstones intercalated to fine sandstones. The old alluvial terraces are composed by sand, silt, clay, and occasionally fossil fragments. The area of the Acre state is crossed by two main hydrographic basins: The Purus and Juruá rivers in the eastern and western part, respectively. Both rivers are the so-called “white-water rivers”. They exhibit a typical dendritic drainage pattern and are extremely meandering what give rise to lakes formed after abandoned meanders. During dry season, several beaches (point bars) are exposed on river‘s meanders, frequently used for swimming but also playing a very important role in the small-scale agriculture. These beaches are also used for planting corn (Zea-Mays) and beans (Vigna unguiculata (L) Walp). The main purpose of this work is to investigate the mineralogical and geochemical aspects of those beach sediments to understand their high fertility and to identify their primary source. Fourteen stations were selected for sampling purposes throughout the river valley close to BR-364 highway. Laboratory analyses were carried out as follow: grain sizes, x-ray diffraction, scanning electron microscopy and optical microscopy of heavy minerals concentrates; sediment whole chemistry (major and traces elements analyses including rare-earth elements) by means of ICP-MS; macronutrients (P, Mg, Ca, and K) besides available Na and Al and organic matter. The river sediments are mainly fine-grained, angular sub-angular and selected moderately. Mineralogical assemblage is represented by quartz, clay minerals (smectite, illite and kaolinite) and feldspars (K-feldspars and albite). The heavy minerals contents ranged from 0.5 to 4.6% and are mainly represented by zircon, epidote, kyanite, tourmaline, garnet, rutile, apatite, staurolite, ilmenite and hematite. Chemical results shown that the sediments are mainly composed by SiO2, besides minor amounts of Al2O3, Fe2O3, K2O, CaO and MgO, what is compatible with mineralogical composition. High SiO2 contents are mainly related to quartz and Al2O3 contents reflects the presence of clay minerals. Contents for alkaline and alkali-earths are relatively high for such beach environment related to feldspars and smectites. P2O5 is related to apatite and can also be adsorbed on smectite. Fe2O3 contents are mainly associated to smectite and a minor amount to ilmenite and hematite, the most common opaque minerals found in the beach sediments. Strong correlation coefficients were observed between Al2O3 and most major and trace elements, except for Zr, Hf, Ni and As. On the other hand, strong negative correlation was obtained between SiO2 and major and trace elements what points to the importance of smectites as scavenger of trace elements in such environment. The chemical results were compared with the mean of the Upper Crust and post-Archean Australian Shales (PAAS) and show that they are impoverished in MgO, CaO, Na2O and K2O in comparison with the former and MgO, in comparison with the latter. Such impoverishment is higher in samples enriched on sand fraction. The same comparison was carried out with the Chinese Changliang and Huanghe river sediments, showing impoverishment in CaO and MgO in comparison with the Changjiang River and MgO, CaO, Na2O and Sr, in comparison with the Huanghe River. The small value obtained for the Chemical Index of Alteration (CIA) shows that these sediments have experienced small degree of chemical weathering and consequently, physical weathering has prevailed in the source area. The beach sediments also exhibit high immature index as evidenced by the following very low rations: SiO2 / Al2O3 (11,64) and K2O/ Na2O (2,08). Rare-earth elements were normalized to the Upper Crust and to the PAAS patterns. They show similar patterns of LREE depletion and HREE enrichment. On the other hand, normalized to the chondrites present enrichment in LREE and horizontalization of the HREE, with similar standards of distribution between each other, presenting typical Eu negative anomalies of granitic and intermediary nature rocks. Analytical results for macronutrients exhibited high concentrations for P, Mg, Ca and K, and low contents of available Na and Al. Organic matter contents in below 1%. The sediments show high cation exchange capacity, base saturation over 70% and low Na and Al saturation. Accordingly, those sediments can be interpreted as representing a redistribution of the recent Miocene sediments (Solimões Formation) and the own sediments that were deposited in old alluviums. Chemical and mineralogical characteristics with a silty granulometry indicate that beach sediments are like the eutrophic cambisols.

Rare earth elements and yttrium along eastern Atlantic estuaries

Rare earth elements (REE) are widely used as tracers of geochemical and anthropogenic processes across diverse environments. We investigated the abundances, sources, and fractionation of REE and Y in 12 estuaries along the Southwest Atlantic Coast. Additionally, we assessed the concentrations of Al, Fe, Mn, and organic carbon (OC) to elucidate the influence of diagenetic remobilization and facilitate comparison between estuaries. The ƩREEY varied widely, ranging from 6 mg kg-1 (Santa Cruz Channel; > 90% sand) to 337 mg kg-1 (Piraquê-Açú; 30% silt+clay). Normalized REE abundances relative to post-Archean Australian shale (PAAS) revealed enrichment of light REE (LREE) over heavy REE (HREE). Moreover, the northern estuaries of the Todos os Santos Bay (São Paulo, Mataripe, Subaé), Vitória Bay, and the Doce River exhibited enrichment of medium REE (MREE) over HREE. Positive correlation between ƩREEY and Al, Fe, and Mn were observed in 5 of the studied estuaries. LREE showed a positive correlation with Al (r2 > 0.7) and Fe (r2 > 0.8) across most of the areas studied. Additionally, REE were significantly correlated with Mn (r2 > 0.8) in only 5 out of the 12 estuaries, while a positive correlation with OC (r2 > 0.8) was observed in 8 estuaries. The concentration of REEY, Al, Mn, Fe, and OC depends on the bottom types and position along the estuarine zones. The observed REEY abundances contribute to the characterization of estuaries along the east coast of Brazil and can serve as a baseline reference for the region.

Anthropogenic gadolinium in the Tone River (Japan): an update showing a 7.7-fold increase from 1996 to 2020

BackgroundAnthropogenic gadolinium (Gd), originating from Gd-based contrast agents (GBCAs) used in magnetic resonance imaging (MRI), is widely identified in the aquatic environment with concerns about toxicity and accumulation. We aimed to present new data on anthropogenic Gd in the Tone River, which has the largest drainage area in Japan, and then to compare the current data with those obtained in 1996.MethodsThe water samples were collected on August 9−10, 2020, at 15 different locations of the Tone River in Japan. The concentrations of the rare earth elements (REEs) were measured by inductively coupled plasma-mass spectrometry and normalized to Post-Archean Australian Shale to construct shale-normalized REE patterns. The degree of Gd-anomaly was defined as the percentage of anthropogenic Gd to the geogenic background and used to compare the water samples from different locations. Pearson’s correlation coefficients were calculated.ResultsAll the samples displayed positive Gd anomalies. The Gd-anomaly ranged from 121 to 6,545% and displayed a repeating decrease-and-increase trend. The Gd-anomaly showed strong positive correlations to the number of hospitals (r = 0.88; p < 0.001) and their MRI units (r = 0.89; p < 0.001).ConclusionsOur study revealed notable anomalies of Gd concentrations in river water in Japan, with strong positive correlations to the number of major hospitals and their MRI units. Compared with the previous report in 2000, the Gd-anomaly in Tone River increased from 851% (sampled in 1996) to 6,545%, i.e., 7.7 times, reflecting the increased use of GBCAs in hospitals.Relevance statementNotable Gd concentration anomalies in river water in Japan were observed. This result underlines the importance of more extensive research on anthropogenic gadolinium, and investigations of risks to human health as well as the development of effective removal technologies may be necessary.Key points• All water samples from Tone River displayed positive Gd anomalies.• The Gd anomalies increased to 7.7 times higher over the past 24 years.• Correlations between Gd values and the number of hospitals and MRI units were observed.Graphical

A Cretaceous siliceous sinter in NE China: Sedimentological and geochemical constraints on its genesis

Phanerozoic sinter deposits have been reported globally, with their identification mainly based on sedimentological, petrological, and mineralogical studies. In this study, a detailed geochemical investigation, combined with sedimentological characterization, was conducted on the Wugonglilu siliceous deposit, a Cretaceous (106 Ma) sinter in NE China, to examine its genesis. The deposit is inferred as a siliceous hot spring deposit (sinter) owing to its geological setting in an epithermal gold-mining district, its morphologically variable microbial textures typical of subaerial sinters, and nearly pure silica composition. Three lithofacies were recognized in this study, including laminated to thinly bedded sinter, silica-cemented breccia, and epithermal vein, which represent deposits from three contrasting hydrothermal environments. The 87Sr/86Sr ratios of the sinter are similar to the bedrock through which the geothermal fluids passed, namely the Upper Triassic Dajiahe Formation (T3dj), a marine siliceous rock unit, and the Lower Cretaceous Datashanlinchang Formation (K1d), a rhyolite unit. Results indicate that both underlying units are possible Sr sources of the silica in the Wugonglilu sinter. The REE + Y (rare-earth elements and yttrium) patterns of the sinter exhibit significant variability, primarily due to terrestrial detrital contamination. Differential REE + Y contamination by terrestrial detritus was striking in the white and dark laminae/beds of the laminated to thinly bedded sinter. The white laminae/beds, generally less contaminated, were probably formed during the dry season, whereas the dark laminae/beds exhibiting greater detrital contamination were likely formed during the wet season. When excluding the samples strongly contaminated by detritus, the sinter exhibits Y anomalies comparable to Post-Archean Australian Shale (PAAS), and to the adjacent underlying K1d rhyolite and T3dj siliceous rock samples, indicating that these anomalies were not inherited from rocks dominating the reservoirs. Furthermore, the sinter shows a (Ce/Ce*)N range close to that of the underlying marine siliceous rock and rhyolite samples, reflecting that the (Ce/Ce*)N of the sinter is largely inherited from the reservoir rock(s). The overall REE + Y patterns of the sinter range from nearly flat to LREE-depleted, similar to some samples of the K1d rhyolite and T3dj siliceous rock units. However, most samples of the K1d rhyolite and T3dj siliceous rock display (Pr/Tb)N and (Pr/Yb)N higher than many studied sinter samples. This is likely because of the formation of strong HREE–carbonate complexes during groundwater migration. Based on these results, a generalized formation model of the studied sinter system was constructed. This study suggests that integrated sedimentological and geochemical investigations can aid in interpreting the genesis of sinter deposits, in particular the link between sinter deposits and corresponding reservoir rocks.

Geology, geochemistry, mineralization and fluid inclusion characteristics of the SW of Hormuz Island banded iron formations, southern Iran

The Hormuz Island banded iron formations (HIBIFs) are situated at the Zagros Folded Zone in southern Iran. The BIFs occur intercalated with the Neoproterozoic Hormuz series, an evaporite and siliciclastic succession with pyroclastic rocks, and were deposited on the continental rift margin of the Arabian plate. The HIBIFs are banded rocks consisting of the alternation of dark Fe-rich and reddish-brown Si-rich layers, and belong to oxide facies iron formations. The post-Archean Australian shale normalized rare earth elements and yttrium patterns of HIBIFs have the characteristics of both hydrothermal solutions and seawater. The sharp positive Eu anomaly (2.10–6.90) may be inherited from high-temperature hydrothermal solutions, while slightly negative Ce anomalies (0.57–0.82) are inherited from seawater. The homogenization temperature and salinity of primary fluid inclusions range from 180.7 to 474.3°C and from 2.24 to 12.85 wt% NaCl, respectively, which suggests that intermediate- to high-temperature hydrothermal fluids and seawater contributed to the formation of the HIBIFs. The Eu/Sm and Sm/Yb ratios in BIFs are between the values of hydrothermal fluids and seawater. In summary, all geological and geochemical data suggest that the HIBIFs are a post-great oxidation event iron formation pulse at the end of the Ediacaran period. However, this is actually not similar to Neoproterozoic syn-glacial iron formations. Instead, this is a new occurrence of iron formation in an overlooked/understudied time period when either global or local conditions were conducive to iron deposition. The iron deposition on Hormuz Island does not appear to be triggered by fluctuating atmospheric oxygen or sea-level variations, but instead may be related to syn-basinal volcanism in the active continental rift margin environment in anoxic submarine condition. Thematic collection: This article is part of the Geochemical processes related to mined, milled, or natural metal deposits collection available at: https://www.lyellcollection.org/topic/collections/geochemical-processes-related-to-mined-milled-or-natural-metal-deposits

Impact of volcanism on the formation and hydrocarbon generation of organic-rich shale in the Jiyang Depression, Bohai Bay Basin, China

Globally, most organic-rich shales are deposited with volcanic ash layers. Volcanic ash, a source for many sedimentary basins, can affect the sedimentary water environment, alter the primary productivity, and preserve the organic matter (OM) through physical, chemical, and biological reactions. With an increasing number of breakthroughs in shale oil exploration in the Bohai Bay Basin in recent years, less attention has been paid to the crucial role of volcanic impact especially its influence on the OM enrichment and hydrocarbon formation. Here, we studied the petrology, mineralogy, and geochemical characteristics of the organic-rich shale in the upper submember of the fourth member (Es41) and the lower submember of the third member (Es33) of the Shahejie Formation, aiming to better understand the volcanic impact on organic-rich shale formation. Our results show that total organic carbon is higher in the upper shale intervals rich in volcanic ash with enriched light rare earth elements and moderate Eu anomalies. This indicates that volcanism promoted OM formation before or after the eruption. The positive correlation between Eu/Eu∗ and Post-Archean Australian Shale indicates hydrothermal activity before the volcanic eruption. The plane graph of the hydrocarbon-generating intensity (S1+S2) suggests that the heat released by volcanism promoted hydrocarbon generation. Meanwhile, the nutrients carried by volcanic ash promoted biological blooms during Es41 and Es33 deposition, yielding a high primary productivity. Biological blooms consume large amounts of oxygen and form anoxic environments conducive to the burial and preservation of OM. Therefore, this study helps to further understand the organic-inorganic interactions caused by typical geological events and provides a guide for the next step of shale oil exploration and development in other lacustrine basins in China.

Variability of rare earth and heavy metal elements in a representative alluvial depositional system.

Heavy metals (Ni, Cr, W, Cd, and Pb) and rare earth elements (REE) were investigated in the flood plain sediments of an island of the lower Yangtze River near Nanjing to determine how the vertical distribution of heavy metals could be affected by natural sedimentation processes and anthropogenic contamination. Stratigraphic analyses of magnetic susceptibility and the mean grain size distribution of the deposits enabled us to identify layers associated with a relatively high influx of suspended sediments that resulted in sudden changes in the concentrations of heavy metals. The results show that layers associated with high sediment influx (0.8m depth) displayed low concentrations of Cr, Ni, W, and Cd that were mainly lithogenic in origin. The Post Archean Australian Shale (PAAS) normalized REE patterns in the flood plain cores were enrichment in Ce and Eu relative to PAAS, indicating that the sediments were most likely derived from a mixture of sediments and not from an anthropogenic source. Sharp increases in Y/Ho ratios, as well as heavy metal (Cd, Cr, Ni, and W) and Y concentrations were observed in the uppermost layer that could have been deposited from the rapid transport of sediment-laden, contaminated waters. The temporal (vertical) trends in Pb concentrations may be strongly influenced by coal burning. Elevated Pb concentrations (350ppm and 1000ppm) correlate with high magnetic susceptibility (> 200 m3 × kg-1) and the history of thermal power plant (1910-2002) activity. The anthropogenic inputs of Pb were, however, not diluted by high suspended sediment loads, which supports the argument that Pb was derived from fly ash.

REE distribution and enrichment of drainage point sediments from Makran and Lasbela, Pakistan

Rare Earth Elements (REEs) are mobile during weathering and their distribution is susceptible to both natural and anthropogenic influences. Four major drainage points in the Makran and Lasbela areas were selected for sampling to examine their REE geochemistry. The mean values of ∑REE are highest in Dasht River (DR: 109.4) and lowest in Shadi River (SR: 84.4). The mean values of Eu/Eu* are highest in Rakhshan River (RR:0.95) and lowest in DR (0.70); these values are higher as compared to the Upper Continental Crust (UCC: 0.23) and Post-Archean Australian shale (PAAS: 0.21) in all drainage points. The mean values of (Gd/Yb)N are highest in RR (2.66) and lowest in DR (2.03), while the mean values of Ce/Ce*, (La/Sm)N, (La/Yb)N, and (La/Lu)N are highest in DR (1.01, 3.01, 9.86 and 9.66, respectively) and lowest in RR (0.93, 1.49, 5.75 and 5.93). DR and HR, covering the longest distances from headwater to mouth, pass through a variety of lithologies and convey a more diverse range of sediment compared to RR and SR. Noticeably depleted elemental concentrations relative to UCC (elemental ratios <1) are observed in the majority of sediments, implying the influence of weathered source rocks. Normalized chondrite distributions of the REEs exhibit consistent trends marked by an enrichment of LREEs and a depletion of HREEs, a characteristic pattern was found in upper crust materials exposed to weathering and erosion. The presence of a positive Eu anomaly in UCC and PAAS normalized patterns suggests the contribution of plagioclase minerals. However, leaching is insignificant for the studied sediments due to low average annual precipitation.

Multiproxy provenance analyses in the Devonian Villavicencio Formation of the Mendoza Precordillera, Argentina: correlation and geotectonic implications for the SW Gondwana margin

Abstract This work focuses on the sedimentary provenance of the Villavicencio Formation of the Mendoza Precordillera and integrates the information obtained with previous work on other coeval units of the Precordillera Central of San Juan province (Gualilán Group: Talacasto and Punta Negra formations) in western Argentina. Multiproxy provenance analyses are carried out from different applied methodologies (petrography, geochemistry, morphological, and cathodoluminescence studies of detrital zircon grains, and analysis of U-Pb and Lu-Hf isotopes). The Villavicencio Formation is mostly composed of pelites and very fine-grained psammites. The major components are quartz, both monocrystalline and polycrystalline, and metamorphic lithics that associate this unit with a recycled orogen. Regarding geochemistry, the Chemical Index of Alteration (CIA) values are similar to the Post-Archean Australian Shales (PAAS), indicating a null to incipient degree of weathering. The ratios between different trace elements and rare earth elements (REEs) suggest the felsic composition of the source area. Th/U ratios differ, but a secondary uranium enrichment is inferred. The morphological analysis of the zircon grains reveals their mainly plutonic origin. The integration of U-Pb data with Lu-Hf data shows a juvenile-mantle origin in which the populations are dominantly Mesoproterozoic and ɛHf of positive values (up to 12), indicating poor differentiation. The Villavicencio Formation would be the product of deltaic deposits in which its components are dominantly from the Western Pampean Sierras associated with the Grenville orogen, assuming exhumation and erosion of the Mesoproterozoic basement. The data support the hypothesis of equivalence and correlation with the Punta Negra Formation in the Devonian depocenters of the south-central region of the San Juan Precordillera.

REE + Y signatures of the Navay phosphate deposit, SW Venezuela: Seawater paleoredox conditions and diagenetic implications

Phosphate rock occurrences in western Venezuela are well-known in Cretaceous sedimentary sequences, which are associated to the Caribbean-Tethyan passive margin, along an SW-trend belt of the Venezuelan Andes chain. In this study, the geochemical characteristics of the Navay phosphate deposit were investigated to discuss the ocean paleo-oceanographic conditions and diagenetic controls that prevailed during the deposit formation. The rare earth elements plus yttrium (REY) concentrations were determined and normalized with the Post-Archean Australian Shale (PAAS) values to generate the REY patterns. Our results reveal a typical seawater signature, except for the absence of a marked negative Ce* anomaly (Ce/Ce* = 0.76–1.00). The determined seawater REY patterns, along to the calculated ratios for (La/Sm)N = 0.78–1.00, and (La/Yb)N = 0.34–0.66, are similar to the modern oceanic water ratios. These data point to a lack of diagenetic alteration on the primary REY signatures, which corresponds with a terrigenous-free marine sediment source for the REY content present in the deposit. In brief: i) the slightly negative anomalies displayed by the Ce* and Eu*, accompanied by the Mn depletion, ii) a relative enrichment of some transition metal elements (V, Cr, and Cu), and iii) the low Mo/U ratios, are all of them considered as geochemical indicators of suboxic to anoxic conditions, which were predominated during the phosphogenetic processes of the deposit. Furthermore, our data reveals an economic potential of the phosphorites as a raw material to produce phosphoric acid (H3PO4) as well as a source of supply for rare earth elements, by means of: i) relative high grades of P2O5 (15.46–30.09 wt %), ii) low CaO/P2O5 ratios (1.22–1.28), iii) a lack of organic matter, chert or chalcedony, iv) a low content of Mg (0.07–0.22%), v) REE concentrations varying from 141.82 to 256.53 μg/g, with an average value of 208.14 μg/g; and vi) concentrations for toxic elements (i.e., V, Cr, Co, Ni, Cu, Zn, As, Sr, Pb, and U) below or at the acceptable levels, in comparison to commercial phosphorites worldwide.

Geochemistry, U-Pb zircon geochronology, and Fe isotopes of the Shanzhuang banded iron formation in the North China Craton: Implications for genesis and depositional environment

The Shanzhuang banded iron formation (BIF) occurs in the Shancaoyu Formation, Taishan Group, in the western Shandong Province (WSP), eastern North China Craton (NCC). We constrained the Shanzhuang BIF depositional age of ∼2.50 Ga based on the zircon U-Pb dating of the leptynite interlayers and the cross-cutting metagranitoid. After deposition, the Shanzhuang BIF was subsequently metamorphosed into amphibolite facies at 2.50–2.45 Ga. According to different mineral assemblages, the Fe ores can be divided into three types: magnetite + quartz ± hornblende (type-1 ore), magnetite + quartz + hornblende + garnet ± hematite (type-2 ore), and quartz + hematite ± magnetite ± hornblende (type-3 ore). In the Post-Archean Australian Shale (PAAS)-normalized rare earth element and yttrium (REY) patterns, the three ore types show consistent flat REY curves. All ore types have moderate ƩREY concentrations (27.24–143 ppm), (La/Yb)N values of 0.29–2.31, significant positive Eu anomalies (1.05–3.47), slightly negative or positive Ce anomalies (0.87–1.26), slightly positive Y anomalies (1.16–1.48), and no apparent fractionation between light REEs (LREEs) and heavy REEs (HREEs), indicating mixing of hydrothermal fluid and seawater. The similar REY patterns and heavy Fe isotopes (0.47–1.02‰) of the three ore types suggest a certain amount of continental detritus was incorporated during the precipitation of the Fe phases in the Neoarchean-Paleoproterozoic oceans. The post-depositional metamorphism did not significantly affect the original REY geochemical signature of the BIF. The Shanzhuang BIF ores are not highly pure chemical sediments, but the type-1 ore is relatively pure and more representative of the original sedimentary composition. By contrast, the type-3 ore tends to have higher δ56Fe ratios (0.74–1.02‰) but lower δEu (1.27–1.97‰), implying substantial post-depositional hydrothermal alteration. The Shanzhuang Fe deposit is an Algoma-type BIF, and the surrounding rock consists of pyroclastic materials. Our model indicates that the Shanzhuang BIF was probably deposited in a redox stratified paleo-ocean environment.

Chronolgy and Geochemistry of the Sijiaying Iron Deposit in Eastern Hebei Province, North China Craton: Implications for the Genesis of High-Grade Iron Ores

The Sijiaying iron deposit is located in the Eastern Hebei area of the southern section of the northern margin of the North China Craton (NCC) and is the largest single iron deposit in China. The deposit contains many banded iron formations (BIFs) and was proven to have more than 3 million tons of high-grade iron ore resources. This study carried out geochemistry and zircon U–Pb analysis of normal-grade iron ore, high-grade iron ore, and wall rock (biotite–leptynite, chlorite–sericite schist) in the Sijiaying deposit and discussed the genesis and metallogenic age of high-grade iron ore. BIFs have low concentrations of Al2O3 and TiO2 and high field strength element (HFSE) depletion, indicating almost no contamination via terrestrial debris. The standardized post-Archean Australian shale (PAAS) rare earth element (REE) distribution pattern indicates that the iron formation exhibits positive Eu, Y, and heavy rare earth element (HREE) anomalies and lacks negative Ce anomalies, indicating that the Sijiaying BIF was enriched with iron sources via high-temperature hydrothermal fluids from the seabed and deposited in an anoxic ancient marine environment. In addition, geological field work identified two types of high-grade iron ore in the mining area: primitive sedimentary and hydrothermally altered high-grade iron ore. Further ore geochemical research showed that the primitive sedimentary-type iron ore is similar in geochemistry to the BIF. In addition to low Eu/Eu* values, the hydrothermally altered high-grade iron ore shows geochemical characteristics similar to those of the BIF, suggesting that they share the same iron source but did not form at the same time. The total large ion lithophile element (LILE) (Sr, Ba, Pb) contents in primitive sedimentary-type high-grade iron ore are higher than those in hydrothermally altered high-grade iron ore, indicating that LILEs are carried away via fluids during the hydrothermal alteration process in normal-grade iron ore. The geochemical characteristics of biotite–leptynite and chlorite–sericite schist include high contents of SiO2 and Al2O3, light rare earth elements (LREEs), LILE enrichment (Rb, Ba, Sr, Zr), and HFSE depletion (Nb, Ta, P, Ti), characteristics that are similar to island arc volcanic rocks. The reconstruction of the original rock indicates that the wall rock is a product of volcanic sedimentary cycles in an island arc setting. Zircon cathodoluminescence images and LA–ICP–MS zircon U–Pb dating can be divided into four age groups (3283 Ma, 2547 Ma, 2500 Ma, and 2407 Ma), which correspond to the earliest volcanic activity in eastern Hebei, the main mineralization age of the Sijiaying BIF (the mineralization age of primitive sedimentary high-grade iron ore), a regional tectonic–metamorphic event, and the occurrence of migmatization (the mineralization age of hydrothermally altered high-grade iron ore), respectively. Therefore, the Sijiaying BIF and primitive sedimentary high-grade iron ores were deposited and mineralized at 2547 Ma, and the iron orebody was later altered via the hydrothermal solution at 2407 Ma, forming large-scale high-grade iron ores.

Rare earth elements in soil around coal mining and utilization: Contamination, characteristics, and effect of soil physicochemical properties

REEs are emerging contaminants, and soils nearby coal and coal ash with high REEs composition are vulnerable to REEs contamination. Besides, coal industry can alter surrounding soil characteristics. However, there is information paucity about REEs contamination and geochemical behaviors along with soil characteristics around coal industrial areas, which are essential for understanding their toxicity and mobilization. The study was conducted in soils surrounding Kriel coal-fired power plant (KCM) and Greenside coal mining in Witbank (GSCM), South Africa. Multivariate statistical analysis, pollution and fractionation indices, and BCR sequential extraction were applied. The ∑REEs in the soils were compared to ∑REEs abundance in the upper earth's crust (UEC), and slightly higher ∑REEs was found in KCM but slightly lower in GSCM. Generally, LREEs are abundant. The soil REEs were normalized using the Post-Archean Australian Shale (PAAS) and Eu and Gd in KCM and Gd in GSCM were >1. Contamination assessment revealed that the soils are slightly to moderately contaminated by REEs. ∑REEs in KCM was significantly correlated with soil particle sizes of 2.00–50.00 μm, Al2O3, Fe2O3, and MnO, while with 2.00–3.00 μm and Al2O3 in GSCM. Fractionation characteristics showed a positive Ce anomaly, with positive linear regressions with Fe2O3 and MnO. In contrast, a negative Eu anomaly was found with positive linear regressions with Al, Ca, and Mg-oxides. Oxidizable fractioned REEs accounted for 32.33% of the ∑REEs in GSCM and 35.85% in KCM, and their high EF suggests enrichment that could be due to coal mining and utilization. Most soil physicochemical properties appear to be negatively correlated with the exchangeable REEs. Overall, the soils are contaminated by REEs and the REEs characteristics are considerably influenced by major elements oxide, U, and Th contents. Therefore, more attention should be paid to REEs contamination and impacts around coal mining and utilization.

Early Cretaceous monsoonal upwelling along the northern margin of the Gondwana continent: Evidence from radiolarian cherts

Radiolarian-bearing cherts are widely exposed in the volcanic-sedimentary sequences associated with the Purang ophiolitic mélange in the western segment of the Yarlung Tsangpo suture zone. Highly diverse and well preserved Lower Cretaceous (Valanginian–Hauterivian) radiolarian assemblages that correlate to the Cecrops septemporatus Zone occur in bedded cherts in the Peiersanggangmu section of the southern Purang ophiolitic mélange. Fifty-five species belonging to 38 genera, including characteristic species: Archaeodictyomitra apiarium (Rüst), Cecrops septemporatus (Parona), Hemicryptocapsa capita Tan, Pseudodictyomitra carpatica (Lozyniak), and Svinitzium pseudopuga Dumitrica, have been recognized.Geochemistry of the cherts reveals high SiO2 contents (average: 92.23 wt%), Al/(Al + Fe + Mn) ratios, and low LaN/CeN ratios. Post Archean Australian Shale (PAAS) normalized rare earth element (REE) abundance patterns exhibit moderately positive Ce anomalies (mean Ce/Ce* =1.35) with relative enrichment in light rare earth elements (LREEs). These features are indicative of deposition in an oceanic basin close to a continental margin environment. Lithological characteristics and geochemical results suggest that the paleogeographical location for these radiolarian-bearing bedded cherts closely matches northern regions of the Indian continent, where existed enhanced upwelling activity and surface mixing resulting from monsoon activities.

Ferromanganese precipitates from the Jiawang Seamount, Bransfield Strait, Antarctica

The Jiawang Seamount is a young volcanic edifice in the central Bransfield Basin, Antarctica. Ferromanganese precipitates were collected from its top during the R/V “Xianghong 01” cruise during the austral summer season of 2017/2018. The mineralogical and chemical compositions of typical species were analyzed to decipher their origin. These ferromanganese fragments were very light in weight and characterized by channel/cavity structures. Their mineralogy was mainly amorphous Fe-Si oxyhydroxide, with minor amounts of pyrite, arsenopyrite and metal compounds. Geochemically, they were enriched in Fe and Si and depleted of Mn, with Mn/Fe ratios of approximately 0.009. Most trace elements were depleted in these species, but Mo and Ge were enriched relative to the elemental contents of the upper continental crust. Additionally, these samples were depleted in rare earth elements, with an average of 77.64 μg/g. The post-Archean Australian shale (PAAS)-normalized rare earth element (REE) patterns showed negative Eu anomalies but no Ce anomalies. Biomorphic-like structures were present in the samples, probably indicating that bacteria such as Leptothrix ochracea, Gallionella ferruginea and Mariprofundus ferrooxydans had, to some extent, affected sample formation. All of these facts also indicated that one mixing process (hydrothermal process and biological process) affected the ferromanganese deposits in the Bransfield Basin.

Geochemistry of Major and Trace Elements in Recent Balakian River Sediments, Northern Iraq: Evidence for Provenance and Source Rocks

The chemical characterization study of the river sediment contributes to understanding the weathering and transportation trend and their impacts on the nature of the source rocks in the catchment region. Accordingly, sixteen samples of recent stream sediment were collected from the Balakian River, northern Iraq. The significant correlation coefficients for the major oxids (CaO, MgO, K2O, Na2O) with the majority of the trace elements indicate that the abundance of carbonate and clay minerals significantly influenced the concentrations of these elements during the weathering and transport of BR sediments. The average values of the Chemical Index of Weathering (CIW = 57.77%) and Chemical Index of Alteration (CIA = 60.70%) reflect moderately intense weathering in the basin. The Upper Continental Crust and Post-Archean Australian Shale normalized ratios, as well as a comparison between the sediment chemistry and the composition of the source rocks, would suggest that these elements were lost from source rocks during weathering, with Na2O experiencing a significant degree of loss. Moreover, the Fe2O3, MgO, and CaO normalized ratios show that these elements were derived from the closest supplied outcrops of source rocks, which are represented by the Late Campanian carbonate and clastic rocks (Tanjero and Shiranish) formations and the Pliocene (Red Bed Series) in the catchment areas. Available Upper Continental Crust and Post-Archean Australian Shale normalized ratios for trace elements showed high enrichment values of most trace elements and slightly enriched values of Sr. This means that Sr is effectively more solubilized and more mobile than other metals. Thus, this demonstrates how distinct rock sources from different geological formations contributed to an enrichment in the concentration of certain elements in the river sediments.

Sedimentology and geochemistry of basinal lithofacies in the Mesoarchean (2.93 Ga) Red Lake carbonate platform, northwest Ontario, Canada

The > 200 m thick Red Lake carbonate platform of the 2.940-2.925 Ga Ball Assemblage (Red Lake Greenstone Belt, Superior Province, Canada) is the oldest known carbonate platform preserved on Earth. This study examined surface outcrops and multiple industry cored drill holes comprising a diverse assemblage of chemical and siliciclastic sedimentary rocks of the deeper water lithofacies associated with the shallow water carbonates. The offshore lithologies, underlying, interlayered with, and overlying the mainly stromatolitic carbonates, consist of alternating packages of sandstone, siltstone, carbonaceous slate, pyritic carbonaceous slate, chert, and oxide facies iron formation (OFIF). These interlayer with carbonate in transitional slope environments, which consist in places of carbonate with magnetite laminae above slumped carbonate debris in iron formation and/or carbonaceous slate. Chert and OFIF were deposited further offshore in a suboxic environment, with lithology dependent on concentrations of seawater Fe(II) and silicic acid. The iron sulfides were deposited in a reducing, anoxic, and organic-rich bottom water and muddy pore water environment not conducive to Fe hydroxide or chert precipitation. Carbonaceous mud was the background sediment, accumulating during intervals when the precipitation of chert, Fe hydroxides, or massive layers of Fe sulfides was inhibited. The interlayering of differing assemblages of chemical and siliciclastic sedimentary rocks indicates temporal and spatial fluctuations in the chemistry of local paleo-seawater and variable sedimentation rates on the margins of the Red Lake carbonate platform. Post-Archean Australian Shale (PAAS)- normalized rare earth element (REE) systematics of carbonate and OFIF show positive La and Gd anomalies, super-chondritic Y/Ho ratios, and depleted light rare earth elements (LREEs) relative to heavy rare earth elements (HREEs), similar to modern seawater, while the positive Eu anomalies in the carbonate and OFIF samples reflect hydrothermally influenced Archean seawater. The chemical sedimentary rocks exhibit enrichment of redox-sensitive elements (i.e., Cr, Mo, V, and U) compared to their siliciclastic associates. This, combined with concentrations of MnO up to 6.3 wt% and positive Ce anomalies in the iron formation directly below the carbonate platform, all indicate the likely presence of some O2 ca 2.93 Ga.

Trace and Rare Earth Element (REE) Geochemistry of Recently Formed Stromatolites at Lake Salda, SW Turkey

Stromatolites are the oldest recognized fossil recordings of life on Earth. Therefore, their study of them represents one of the most interesting topic that investigates the physio-chemical environmental conditions (formations and precipitations) at which the stromatolites formed. This work deals with the rare earth elements (REEs) geochemical characteristics and the redox-sensitive trace elements behavior of the stromatolites newly formed in Salda Lake, a closed system alkaline lake surrounded by serpentinite rocks in SW Turkey. The representative stromatolite samples collected from Salda Lake show higher contents of MgO (up to 41.5 wt.%), CO2+OH (up to 56.6 wt.%), and MgO/CaO ratio (up to 42.2 wt.%) referring to the stromatolites had been controlled by microorganisms and deposited in subtidal areas having hydro-magnesite and aragonite mineralogy. The average trace element contents of the stromatolites are 8.4 ppm V, 0.09 ppm Cr, 3.50 ppm Co, 95.6 ppm Ni, 0.73 ppm Cu, 1.55 ppm Rb, 37.6 ppm Sr, 0.59 ppm Y, 17.7 ppm Zr, 3.60 ppm Nb, 21 ppm Ba, 0.05 ppm Hf, 3.5 ppm As, 0.02 ppm Cd, 0.05 ppm U, 0.05 ppm Th, 2.85 ppm Pb, and 6.60 ppm Zn. The Post-Archean Australian Shale (PAAS)-normalized REE patterns of the stromatolites reveal that the heavy REEs (HREEs) are enriched relative to the light REEs (LREEs) with highly negative Y and Ce-anomalies and positive Eu-anomalies. This refers to the stromatolites formed in predominantly oxidizing environmental conditions at partially warm lake waters. In addition, the hydromagnesite composition of the Salda Lake stromatolites indicates that they were precipitated from the waters influenced by Mg-rich meteoric waters fed from the serpentinite rocks around the Lake.