Acta Geochimica最新文献

This study investigates the distribution, geochemical behavior, and potential anthropogenic influences of rare earth elements (REEs) in the surface sediments of Qinghai Lake, the largest saline lake in China. A total of 36 surface sediment samples were analyzed for REE concentrations with a combination of self-organizing maps (SOM) and positive matrix factorization (PMF). Results indicate distinct enrichment patterns, with light REEs (LREEs) exhibiting higher concentrations than heavy REEs (HREEs), reflecting natural abundances and geochemical behaviors. The minimum value was found in Lu as low as 0.091 mg/kg, and the maximum concentration was exhibited in Ce at 78.877 mg/kg. Geoaccumulation index (I_geo) analysis reveals minor to moderate enrichment of specific REEs of Sm and Nd, suggesting possible localized anthropogenic inputs, particularly near river mouths. Spatial analysis using inverse distance weighting (IDW) and self-organizing maps (SOM) highlights significant correlations between REE distributions and riverine inputs, underscoring fluvial transport's role in sedimentary REE dynamics. PMF identifies mixed natural and anthropogenic sources, with agricultural and industrial activities contributing to elevated REE levels in sediment. These findings provide critical insights into the geochemical behavior of REEs in saline lake systems and offer a foundation for pollution control and sustainable resource management in sensitive environments like Qinghai Lake.

Pollution of transboundary rivers can result from anthropogenic activities in their watersheds. In this study, sediment traps were deployed to determine the fluxes, concentrations, and health risks associated with arsenic, cadmium, mercury, lead, and iron in the estuaries of three transboundary rivers (Comoé, Bia, and Tanoé) in West Africa. Thus, the analysis of metal-associated sedimentation particle samples collected in rainy, flood, and dry seasons was required. Sediment traps were used to calculate the metal fluxes associated with sedimentation particles towards the Atlantic Ocean. Finally, the carcinogenic and non-carcinogenic risks of ingestion and dermal contact associated with sedimentation particles were assessed. The results showed that the total concentrations of trace metals in particulate matter were higher than in the UCC (Upper Crust Continental), with the exception of lead. The highest fluxes of lead, mercury, iron and arsenic associated with sedimented particles were observed during flood periods in the estuary of the Comoé, Bia and Tanoé rivers. Cadmium fluxes associated with sedimentation particles were highest in the rainy season in the Bia and Comoé estuaries and in the flood season in the Tanoé estuary. Pearson’s correlation analysis and the enrichment factor showed that the trace metals were derived from anthropogenic activities such as mining and farming. In addition, contamination indices showed that sediment particles in the estuaries of the three rivers were severely contaminated with mercury. However, the results of potential human health risks associated with trace metals show that there is no probability of exposure of the community to harmful and carcinogenic effects through ingestion and dermal absorption of sediment particles. It is essential to integrate the information from this study into policy- and decision-making processes for better management of transboundary river water resources in coastal countries, particularly the Côte d’Ivoire.

This geo-historical case study analyses Vistelius’ ingenious idea of conceptual stochastic models and their application as Markov chain analysis in the geosciences. Vistelius (1915–1995) is regarded as one of the founders of mathematical geology. He was the first to define mathematical geology as “a scientific discipline concerned with the construction, analysis and use of conceptual mathematical models of geological events to solve concrete problems” (Vistelius in Principles of mathematical geology, Nauka, Leningrad, 1980; Principles of mathematical geology, Kluwer Academic Publishers, Dordrecht, 1992). Mathematical models in this context should be primarily probabilistic because of the large number of influencing natural factors. They must be conceptual to avoid fundamental errors in application. Vistelius devoted his seminal book to geological random sequences and their description and analysis using Markov models as stochastic tools. He applied this approach to grain sequences in granitic intrusive rocks and to sedimentary rock layers. Among other things, Vistelius has used Markov chain analysis in mineral resource exploration to distinguish between “ideal” granites, which are not subsequently mineralized, and mainly hydrothermally mineralized, sometimes ore-bearing granites which contain at least two generations of main minerals. The application of this special conceptual stochastic model is demonstrated on Lusatian granite (Saxony, Germany).

An enhanced understanding of the history of the western Qinling-Dabie orogen is pivotal in reconstructing geological processes of the east Asian mainland. However, less attention has been paid to its early-stage uplift-erosion history after closure of surrounding oceanic basins at the mid-Paleozoic. In this study, we undertook a comprehensive study including paleocurrent reconstruction, sandstone petrology, and detrital zircon U–Pb dating on Late Carboniferous to Early Permian successions in the southern Ordos neighboring the northern Qinling-Dabie. New provenance data reveal a significant provenance shift at the Carboniferous-Permian transition. The older Benxi Formation was sourced southerly from the North Qinling Terrane that provided detritus mostly of Neoproterozoic and Early Paleozoic ages. In contrast, Early Permian samples yield age relation dominated by Neoarchean, Paleoproterozoic, Early Paleozoic, and Late Paleozoic age populations, with a significant gap of ca. 1600–550 Ma, implying a sediment derivation from the Inner Mongolia Continental Arc. This shift is further verified by paleocurrent transition from south to north then. We suggest that the North Qinling Terrane experienced a significant uplift history from ca. 500 Ma and remained as a highland until end-Carboniferous. From Early Permian, the North Qinling Terrane was submerged, covered by widespread deltaic sedimentation there. Northerly source from the Inner Mongolia Continental Arc began to be accumulated in the northern flank of the North Qinling Terrane, before termination approximately along the southern North Qinling Terrane, where shallow-water carbonate shelf sedimentation sustained from Devonian to Triassic. This new finding indicates that uplift of the North Qinling Terrane lasted about 150 Ma after the Proto-Tethys Ocean closure.

Elemental concentrations of the siliciclastic sediments from a sedimentary basin provide clues on paleo-weathering, paleoclimate, provenance, and tectonic setting of the basin. Records for Permo–Triassic mass extinction and climatic fluctuations are commonly traced from the sediments in the Gondwana basins. Nevertheless, our understanding on sedimentation, provenance, and regional tectonics of the Raniganj Basin, a Gondwana basin in the eastern India is poor. Minerals including clay particles and major and trace element concentrations of the siliciclastic sediments from different formations of the Raniganj Basin have been studied to establish the paleo-weathering, paleoclimate, provenance, and tectonic settings of the basin. This study suggests that the Talchir Formation experienced cold and dry climatic conditions at the sediment source area, while the Barakar, Raniganj, and Panchet formations had prevailing semiarid climates. The sources of the siliciclastic sediments are from the felsic rocks of the Chotanagpur Granite Gneissic Complex (CGGC). Further, the geochemical results suggest a rift-like (passive) tectonic setting for the Raniganj Basin, while few samples represent the collision tectonic setting of the basement CGGC, formed due to collision of major Indian blocks during the Paleo-Neoproterozoic time.

The majority (up to 90%) of riverine materials is transported from the continent to the ocean mainly in flood events. It is thus crucial to characterize the geochemistry of elements and their flux in river system in order to better constrain their global biogeochemical cycling and impact on the oceanic ecosystem. However, the geochemical behavior including the distribution, migration and partitioning of typical metal elements amongst different phases, during hydrodynamic flood event remains still to be well explored. Here, we investigated the geochemical behaviors of typical metal elements in dissolved phase and suspended particulate matter collected from a single flood event in the natural Chishui River, Southwest China. The results showed clearly that the geochemistry of metal elements was largely controlled by the hydrodynamic effect, of which the different flowrates introduce a natural sorting of different mineral particles transported at different flood stages, depending on their shape, size and density. The maximum concentrations of alkaline and alkaline earth metals (Li, Mg, K, Rb and Sr) in SPM appeared before the flood peak, which was largely controlled by aluminosilicate minerals. However, transition metals (Cr, Mn, Fe, Ni and Cu) showed their abundance peaks lagging behind the flowrate summit, as a result of the late arrival of coarse particles or heavy minerals, evidenced by the mineralogical phase analysis. In addition, the distribution coefficient (K_d) between particulate and dissolved loads were lower and stable for soluble alkali/alkaline earth metals which could be affected by pH, while higher and fluctuant for transition metals that were largely influenced by SPM content. Overall, the present study reveals clear effects of hydrodynamic sorting on the geochemistry of metal elements during the flood event of the natural Chishui River, which should be taken into account when characterizing the riverine flux and their impact on marine ecosystem.

NWA 16080 is a representative reduced CV carbonaceous chondrite (CV_red), consisting mainly of chondrules (47 vol%) and matrix (42 vol%), along with minor quantities of calcium- and aluminum-rich inclusions (CAI) and amoeboid olivine aggregates (AOA) (CAI + AOA, 6 vol%) and opaque minerals (5 vol%). The chondrules exhibit well-preserved outlines and can be categorized into Type I (Fa < 10) and Type II (Fa > 10). They primarily consist of magnesium-rich olivine, along with both low-Ca and high-Ca pyroxenes, and contain minor amounts of secondary plagioclase. Olivines present in chondrules display compositional zoning characterized whereas the matrix is composed of fine-grained olivine. Nickel-rich metal and nickel-poor sulfides are also present, along with trace amounts of magnetite. In contrast to standard oxidized CV chondrites (CV_ox), the presence of high metal, Ni-poor sulfides, and reduced magnetite in NWA 16080 indicates a more reduced parent-body environment. Shock metamorphism is classified as mild (S1), while terrestrial weathering is characterized as low (W2). Raman spectroscopy indicates a diverse spectrum of organic matter (OM) maturity: certain areas exhibit characteristics akin to other CV_red chondrites, whereas others reach maturity levels comparable to those observed in CV_ox chondrites. The Raman parameters indicate that this meteorite is classified as approximately type 3.4 to 3.5. The overlapping OM maturity with certain CV_ox chondrites provides a contradiction to the anticipated depth-thermal layering outlined in the onion-shell model. This suggests that the CV parent body probably experienced more intricate processes, including impacts and fluid-rock interactions, rather than merely depth-dependent heating.

Subduction polarity reversal typically occurs in intra-oceanic arc settings; the existence of an ancient intra-oceanic arc and its associated back-arc system within the Neotethyan plate has been deliberated. In this study, we investigate the possible role of subduction initiation of polarity reversal in the formation of Nagaland-Manipur ophiolite (NMO), evaluate the petrological and geochronological data and compare it with the neighboring natural examples of subduction polarity reversal of the Andaman-Nicobar ophiolite (ANO). The ancient intra-oceanic arc, namely the Incertus-Woyla Arc, and its associated back-arc remnant have been correlated with the back-arc mafic of the ANO. We found that the geochemical signatures of mafic rocks of NMO and ANO are comparable, and the available geochronology data of ~ 145 Ma from the NMO basalt and chert fit well with the evolution and formation of the intra-oceanic arc, i.e., Incertus-Woyla Arc. The evolution and age of the Incertus-Woyla Arc are between 135 and 150 Ma. Although the oldest age of the ANO has been reported from metamorphic sole at about 106.4 and 105.3 Ma, the back-arc affinity of the amphibole has been credited to the back-arc spreading that occurred behind the Woyla Arc. Previous paleomagnetic and geochronological studies have suggested that the development of the back-arc basin behind the Incertus-Woyla Arc was a result of divergent double subduction. Therefore, we have inferred a similar scenario for the development of the back-arc affinity rocks of the NMO behind the Incertus-Woyla Arc and the reinterpretation for the evolution of the supra-subduction zone affinity rocks of NMO and ANO during subduction initiation after subduction polarity reversal.

Examining carbonate dissolution kinetics at mineral-water interface is crucial to understand numerous environmental and geochemical processes, including global carbon cycling, CO₂ sequestration in deep geological reservoirs, and trace elements release in terrestrial and aquatic environments. Here we explored the effect of circumneutral to alkaline pH solutions (pH 6–11) on dissolution kinetics of pure dolomite and Ca and Mg release stoichiometry in flow-through reactor experiments at 25 ± 1 °C. Results revealed that the dolomite dissolution rates obtained from effluent Ca and Mg concentrations (R_Ca and R_Mg in mol/cm²/s) were dependent on input solution pH and HCO₃⁻ log activity. The pH dependence of dissolution rates showed two distinct trends, i.e., at circumneutral pH ranging between 6 and 8, the dissolution rate decreased with increasing pH, with minimum rate at pH 8. While in the highly alkaline pH range (pH 9–11), the dolomite dissolution rate increased with an increasing pH. Irrespective of the input pH, the dolomite dissolution rates indicated a reverse relationship with HCO₃⁻ log activity, with the lowest dissolution rate (R_Ca = 3.80 × 10^–12 mol/cm²/s) at pH 8 where HCO₃⁻ log activity attained the highest value (− 3.957). The lower R_Ca and R_Mg obtained at pH 8 compared to all the other pH could possibly be attributed to an inhibition caused by high HCO₃⁻ log activity in solution at this pH. Dolomite dissolution rates were non-stoichiometric at all the experimental pH values, showing higher preferential Ca over Mg release (R_Ca > R_Mg) whereas an opposite trend was observed at pH 8, with R_Ca < R_Mg at the steady state. Saturation index values calculated using geochemical speciation modelling were positive for Mg-bearing minerals (brucite, dolomite, artinite) at alkaline pH of 10–11, indicating favourable conditions for their precipitation under studied conditions. This study provides insights on the significance of log ion activities of HCO₃⁻ and Me-OH⁺ under varying pH for elucidating the dissolution mechanism of dolomite in circumneutral to alkaline aqueous environments.

A comprehensive examination of detrital sandstone modes from the Sylhet Trough reveals a diverse range of sub-lithic to sub-feldspathic quartz arenites. Soil samples were gathered from Dupi Gaon (Jaintiapur) in Bangladesh, followed by a thorough analysis using field examination, X-ray diffraction (XRD), X-ray fluorescence (XRF), petrography, and heavy mineral concentration analyses. Field observations revealed the soil sample varying from white to yellowish to variegated, with thicknesses ranging from 15 cm to about 4 m, and exhibiting moderate softness. XRF analysis revealed significant SiO₂, Al₂O₃, and Fe₂O₃ levels in the samples, with zirconium (Zr) and copper (Cu) showing consistently high concentrations. XRD analysis identified quartz as predominant, along with muscovite, biotite, and accessory minerals like rutile and magnetite. Petrographic analysis highlighted quartz as dominant, with fractures suggesting tectonic influences, while heavy mineral separation techniques identified zircon, garnet, goethite, rutile, and magnetite. These findings provide insights into sediment provenance, depositional processes, and environmental conditions during the formation of the Dupi Tila Formation. The comprehensive geochemical data of the entire rock indicates that most of the sediments originated from felsic igneous sources, and also suggests a moderate to high level of weathering in the source region. Overall, the analyses suggested an in situ origin of the Dupi Tila Formation, with parent materials being predominantly detrital rather than authigenic, supported by the presence of detrital quartz and an assessment of the depositional environment, providing insights into the geological conditions of the era and potential modes of sediment transportation.