Protracted post-eruptive basaltic weathering of the Emeishan large igneous province constrained by U-Pb CA-ID-TIMS geochronology

The post eruptive basaltic weathering of the Emeishan large igneous province is proposed to cause early Wuchiapingian cooling globally. However, the endpoint of this cooling event has not been evaluated yet, preventing the further understanding of long-term interaction between climate and weathering. In this study, abundant thick and highly weathered basaltic paleosols at the Emeishan volcanic landscapes have been identified, providing direct evidence for intense post-eruptive basaltic weathering. By using CA-TIMS zircon U-Pb dating on paleosols and adjacent tuffs, the onset and the termination of the intense weathering are constrained to similar to 259.6 Ma and similar to 253.4 Ma, respectively. The onset of intense weathering is coincident with the early Wuchiapingian cooling, supporting the CO2-forced cooling model triggered by the post-eruptive basaltic weathering of the Emeishan large igneous province. Moreover, the temporal correlation between the long-term weathering and the paleoclimate and carbon isotope records indicate that this cooling is possible persisting until at similar to 253.4 Ma

Coupled effects of iron (hydr)oxides and clay minerals on the heterogeneous oxidation of aqueous Mn(II) and crystallization of manganese (hydr)oxides

The formation of nanominerals and mineral nanoparticles (NMMNs) has drawn broad attention due to their high reactivity and omnipresence in the environment. While the heterogeneous formation of NMMNs on surfaces of various minerals has been extensively studied, there is limited understanding of how mineral heteroaggregates influence this process. In this study, we investigated how heteroaggregates of iron (hydr)oxides and clay minerals affect the heterogeneous oxidation of aqueous Mn(II) and crystallization of manganese (hydr)oxides (MnOx). Our results revealed that iron (hydr)oxides (ferrihydrite) and clay minerals (kaolinite or montmorillonite) in heteroaggregates exerted coupled effects on these processes, dictating the distribution of Mn and the morphology of MnOx. Specifically, ferrihydrite catalyzed gradual oxidative removal of Mn(II) and triggered MnOx nucleation; in contrast, kaolinite/montmorillonite rapidly adsorbed Mn(II) but hardly catalyzed its oxidation. These reactions collectively resulted in fast adsorption and gradual oxidation of Mn(II) on the heteroaggregates. Further, MnOx nanoparticles formed on ferrihydrite surfaces migrated to kaolinite/montmorillonite surfaces, leading to interactions between MnOx and various component minerals within the heteroaggregates. This significantly altered the subsequent growth pathways and the eventual morphology of MnOx. Consequently, while MnOx nanoparticles in the ferrihydrite-only system aggregated freely and formed well-extended nanowires, those in the ferrihydrite-kaolinite system predominantly became short nanorods due to the immobilization by kaolinite surfaces; in the ferrihydrite-montmorillonite system, considerable MnOx nanoparticles attached to montmorillonite surfaces due to strong electrostatic attraction, and subsequently grew into blocky particles via particle attachment. These findings illustrate that surface reactivities of heteroaggregated ferrihydrite and kaolinite/ montmorillonite are coupled when they interact with aqueous Mn(II) or MnOx. Our work exemplifies, for the first time, the cooperation between surfaces of various minerals during the heterogeneous formation of NMMNs. Findings from this study also enhance our understanding of MnOx formation on surfaces with diverse atomic structures, and contribute to the knowledge of Mn cycling in the environment

Sedimentary responses to climatic variations and Kuroshio intrusion into the northern South China Sea since the last deglaciation

The terrigenous sediment source-to-sink processes in marginal seas are governed by intricate interactions among climate, sea level, and ocean currents. The continental slope of the northern South China Sea (SCS) provides an excellent setting to examine these processes due to its substantial terrigenous influx and continuous sedimentation. In this study, we present a high-resolution sedimentary record from the northern SCS continental slope covering the last deglaciation. Analyses of Rare Earth Elements (REEs) and Sr-Nd isotopic compositions in the NH07 core indicate that the predominant source of terrigenous sediment was Taiwan. Grain size-standard deviation analysis identified two sensitive grain size components, with the sensitive component 2 used as a marker of the Kuroshio intrusion into the northern SCS through Luzon Strait. The intensity of the Kuroshio intrusion into the northern SCS was found to be inversely related to that of the open Pacific. The Asian monsoon and El Nino- Southern Oscillation (ENSO) significantly influenced the variability of the Kuroshio Current throughout the deglaciation period. During the interval 16, 000-11, 700 cal yr BP, variations in terrigenous influx were collectively driven by sea level changes and the intensity of the Kuroshio intrusion, while chemical weathering intensity was affected by the reworking of previously exposed shelf sediments due to sea level fluctuations. During the Holocene, however, the East Asian summer monsoon intensity became the primary factor influencing variations in terrigenous influx and chemical weathering

<i>Using δD of methyl aromatics and oils to trace the reservoir charging characteristics of complex petroleum systems in Tarim Basin, northwestern China</i>

Aromatization occurs steadily during the petroleum evolution stage of light oil/condensate (LOC) formation, for which the composition and delta D of aromatics are of considerable geochemical significance. This paper presents a study on the composition and delta D of monomethyl aromatic compounds (toluene, methylnaphthalene, methylphenanthrene, and methyldibenzothiophene) and related hydrocarbon compounds in LOCs from the Tazhong uplift area of the Tarim Basin in China. Thermal maturity, the source rock of the LOCs, and the effect of gas washing on the oils are discussed. The calculated reflectance of the oils using methyldibenzothiophene and dimethylnaphthalene parameters is approximately 1.15%-1.5%. The thermal maturity of the oils in the Tazhong I fault-slope zone is slightly higher than that of the oils in the Tazhong 10 structural belt due to the more intense gas washing of the oils in the former. The varying degrees of gas washing also caused enrichment of low-carbon-number aromatic hydrocarbons and their H-2 isotopes in the oils of the Tazhong I fault-slope zone relative to those of the Tazhong 10 structural belt. In addition to the contributions from lower Cambrian and Middle-Upper Ordovician source rocks, these crude oils may have received contributions from upper Cambrian Furongian source rocks deposited within locally shielded environments. Crude oils such as TZ62(Silurian) and ZG432(Ordovician) contain heavy delta C-13 but light delta D isotopic compositions and may represent end member oils derived from Furongian source rocks

Metamorphic evidence of the Kuunga orogeny in South China: Highpressure pelitic granulites and gneisses from the Gaozhou Complex

The role of the South China Block in the Kuunga orogeny, a pivotal event marking the assembly of the Gondwana supercontinent, remains a subject of debate. This study investigates high-pressure (high-P) granulitefacies metamorphism in the Yunkai orogen of eastern South China to shed light on this controversy. Recently,highP pelitic granulites with a mineral assemblage of garnet, K-feldspar, and sillimanite pseudomorph replacing earlier kyanite were identified in the Gaozhou Complex. Petrographic observations, phase equilibria modeling, geothermobarometry, and laser ablation-inductively coupled plasma-mass spectrometry (LAICP-MS) zircon U-Pb dating have revealed a four-stage metamorphic evolution. The peak P stage (M1) is characterized by highP conditions of 10-11.8 kbar/760-830 degrees C in the kyanite and rutile stability fields. This is followed by the peak temperature (T) metamorphism (M2) at slightly lower pressures and higher temperatures of 7.8-9.5 kbar/840-870 degrees C, which suggests a subsequent period of thermal relaxation. Subsequent decompression and cooling (M3) led to the formation of cordierite + spinel coronae, which reflects a change in P-T conditions to 4.5-5.3 kbar/730-790 degrees C. The final retrogression (M4) occurred under lower-grade conditions of 3.7-4.4 kbar/600-640 degrees C. Consequently,highP pelitic granulites in this region have undergone a clockwise P-T path, which indicates a continental collision setting. Zircon U-Pb dating from thehighP granulites and gneisses yielded multistage metamorphic ages of ca. 520 Ma, ca. 440 Ma, and ca. 240 Ma, which correspond to the Pan-African, Caledonian, and Indosinian tectono-thermal events, respectively. These metamorphic ages, coupled with the clockwise P-T path, reveal a history of polymetamorphism associated with a longlived subduction-continental collision event during the assembly of Gondwana and the subsequent Indosinian overprinting. These multiple orogenic processes provide significant insights into the tectonic evolution of the South China Block. Our findings contribute to the evidence of the Kuunga orogeny in South China during the assembly of Gondwana and offer a robust framework for interpreting the complex metamorphic histories of orogenic belts

Martian Smectites Formation Regulated by Environmental CO₂ and Si

Despite the anticipated abundant carbonates due to historical atmospheric CO2 levels, Mars presents a geological puzzle with MgFe-smectites dominating the Noachian and early Hesperian terrains, contrasted by sparse carbonate deposits. To address this point, we explored the impact of CO2 on MgFe-smectite formation, emphasizing the role of variable Si concentrations within the simulated Martian environment. Hydrothermal experiments, conducted under a constant CO2 concentration (C0.5) and varying Si concentrations (Si0.5 to Si4), reveal a transformation from pyroaurite to MgFe-smectite via lizardite as an intermediary phase. This transformation underscores the crucial role of Si in this mineral sequence. Notably, experiments demonstrate that the interlayer CO32- in pyroaurite is released into aqueous environments during the mineral conversion, potentially impacting the Martian CO2 budget. These findings could explain isolated carbonate outcrops and the possibility of hydrotalcite-group minerals on Mars today. Further Mars exploration should consider identifying hydrotalcite-group minerals for their implications on the planet's climate and habitability

Monsoon-regulated marine carbon reservoir effect in the northern South China Sea

The ubiquitous marine radiocarbon reservoir effect (MRE) constrains the construction of reliable chronologies for marine sediments and the further comparison of paleoclimate records. Different reference values were suggested from various archives. However, it remains unclear how climate and MREs interact. Here we studied two pre-bomb corals from the Hainan Island and Xisha Island in the northern South China Sea (SCS), to examine the relationship between MRE and regional climate change. We find that the MRE from east of Hainan Island is mainly modulated by the Southern Asian Summer Monsoon-induced precipitation (with 11.4% contributed to seawater), rather than wind induced upwelling. In contrast, in the relatively open seawater of Xisha Island, the MRE is dominated by the East Asian Winter Monsoon, with relatively more negative (lower) Delta R values associated with high wind speeds, implying horizontal transport of seawater. The average SCS Delta R value relative to the Marine20 curve is -161 +/- 39 14C years. Our finding highlights the essential role of monsoon in regulating the MRE in the northern SCS, in particularly the tight bond between east Asian winter monsoon and regional MRE

On-line hydropyrolysis gas chromatography-mass spectrometry (HyPy-GC-MS) for kerogen-bound biomarkers

Flash pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) is seldom used to release bound biomarkers, because its hydrogen-poor pyrolysis conditions usually result in a low yield of bound biomarkers and high concentrations of olefins. In this study, by using a Py-GC-MS system and immature kerogen/coal samples, we investigated the effects of heating rate (flash versus 30 degrees C/min), carrier/reaction gas (He versus H-2), hydrogen pressure, and catalyst [(NH4)(2)MoO2S2] on the yields and distributions of bound biomarkers. Also, the bound biomarkers obtained by different pyrolysis conditions were compared with those from catalytic offline hydropyrolysis (HyPy) and free biomarkers from extracted organic matter (EOM). We propose a new technology of hydropyrolysis-gas chromatography-mass spectrometry (HyPy-GC-MS) to be used to release bound biomarkers. HyPy-GC-MS using low-pressure H-2 at slow heating rate can increase the yield of bound biomarkers by 3-9 times, minimize the cracking of the hopanes side chain, better preserve the original sterane and terpane distributions, and have characteristics of lower maturity, compared with conventional flash Py-GC-MS without H-2. Additionally, the steroidal and terpenoid yields by HyPy-GC-MS using low-pressure H-2 at slow heating rate from immature kerogens were 3-6 times that by HyPy. Compared with EOM, biomarker maturity parameter derived from HyPy-GC-MS may not fully represent the actual maturity of samples. Higher hydrogen pressure can significantly facilitate the hydrogenation of unsaturated hydrocarbons into saturated hydrocarbons, but it can also decrease the yields of pyrolysates with higher carbon numbers (i.e., >C-25), leading to a change in the biomarker ratios related to carbon numbers (e.g., the proportion of C-27-C-28-C-29 alpha alpha alpha 20R steranes and TT23/H-30 ratio)

Industrial-scale sustainable rare earth mining enabled by electrokinetics

Owing to their irreplaceable role in several essential technologies, rare earth elements (REEs) are critical raw materials for the global economy. However, the supply of REEs raises serious sustainability concerns due to the large environmental footprint of conventional mining processes. We previously proposed an electrokinetic mining (EKM) technique that could enable green and selective extraction of REEs from ores. Here we further develop this technique to industrial scale by addressing challenges related to electrode reliability and flow leakage and evaluate its mining efficiency, environmental footprint and economic performance. Moreover, a voltage gradient barrier strategy based on electroosmosis is developed to facilitate electrokinetic REEs mining. As a result, we successfully achieved a high REE recovery efficiency of 95% on a 5,000-ton REEs ore. A rigorous environmental risk assessment revealed a 95% reduction of ammonia emissions, indicating a notably reduced environmental footprint. A comparative technoeconomic analysis between the conventional and the EKM techniques demonstrates the economic viability of the EKM technique. This work validates a new sustainable path for REEs mining, paving the way to a greener resources supply

Dual-pressure pyrolysis apparatus unravelling how fluid and lithostatic pressure matter in hydrocarbon expulsion

Improvement in thermal simulation technology will increases the accuracy of predictive geochemistry. A dual- pressure pyrolysis apparatus was developed, to precisely control the fluid pressure and lithostatic pressure during simulated source rock maturation. Two series of pyrolysis experiments were carried out, simulating the same generation process but different expulsion fluid pressure condition. Episodic hydrocarbon expulsion from source rocks under controlled lithostatic pressure and fluid pressure was for the first time observed through thermal simulation experiments. The results were applied to (1) hydrocarbon expulsion efficiency (HEE) analysis, and (2) compositional analysis of oil and gas expelled under different pressures. Results show that HEE is strongly influenced by both fluid and lithostatic pressures. If the oil discharged during depressurization and normal pressure is taken into account, the calculated HEE was 2-31 times the HEE that only considers the high fluid pressure expelled oil. Compared with previous experimental results, HEE under controlled dual pressure is also lower. Therefore, before applying the results of thermal simulation experiments to unconventional and deep oil/gas evaluation, sufficient attention should be paid to the pressure conditions of the experiments. Within the oil window, when the temperature and hydrostatic pressure of source rocks are dropped due to tectonic events such as uplift, they can discharge more oil and gas than before uplift, as a consequence of adjustment of overpressured fluid to re-equilibrate to the adjacent hydrostatic conditions. In addition, during pressure and temperature reduction, the expelled fluids have a higher gas to oil ratio. This helps to indicate that sedimentary basins that experienced tectonic events still have great exploration potential. The temperature program, pressure setup, expulsion conditions in the two-series experiments is a tentative work tested on a representative source rock from the Triassic Yanchang Formation (Ordos Basin), indicating that control of fluid and lithostatic pressure are essential for improving the accuracy of thermal simulation predictions. The dual-pressure pyrolysis apparatus has high exploration relevance, particularly when quantitative results are integrated with the depositional, tectonic and thermal histories of specific source rocks