Science China Earth Sciences最新文献

The current and potential impacts of global warming have generated widespread concerns about food security among all sectors of society. Central Asian countries located deep in the interior of Asia with fragile ecological environments and lower agricultural technology are particularly more prone to severe threats from climate change. Based on panel data acquired in five Central Asian countries from 1990 to 2019, a C-D-C model was developed to study how climate change affects food security in the region and to predict future trends The study found that the level of food security has generally increased for these five Central Asian countries over the past 30 years, with Kazakhstan and Tajikistan having the highest and lowest food security levels, respectively. The average annual temperature and precipitation exhibit an inverted U-shaped relationship with the region’s food security, with the most positive effect on the food security of Kazakhstan. Extremely high and low temperatures have significantly affected food security in the studied region, with Turkmenistan experiencing the most significant negative impacts. The number of frost days had no significant effect on food security. An analysis of future climate showed that the temperature and precipitation in Central Asia will continue to increase from 2030 to 2090, which will negatively impact the food security of these countries. It is recommended that the Central Asian countries enhance their understanding of climate risks, strengthen scientific climate research, and develop multiple adaptation strategies in advance. Simultaneously, they are encouraged to consolidate international cooperation, reducing greenhouse gas emissions effectively and maintaining the ability to ensure food security.

Quantitative characterization of tight sandstone oil migration and accumulation is an emerging research frontier in the field of oil and gas exploration. In this study, a conceptual model containing multiple basic geological elements is developed, and a nonlinear seepage numerical model for tight sandstone oil migration and accumulation is established. The effects of the slip effect, overpressure driving force, buoyancy, and capillary force on the migration and accumulation of tight oil are examined. The results showed that (1) the differences in oil migration and accumulation between tight and conventional reservoirs are reflected in the growth mode of oil saturation, distribution characteristics of oil and water, and extent of the effect of the formation dip angle; (2) the slip effect has a significant impact when the average pore throat radius is less than 150 nm and the overpressure driving force and capillary force are the main mechanical mechanisms controlling oil migration and accumulation in tight sandstone, while the coupling effect of buoyancy, capillary force, and overpressure driving force controls the upper and lower limits of oil saturation. Finally, a dimensional and dimensionless identification chart for rapidly predicting the oil saturation of tight sandstone is proposed and verified using the measured data. This study provides a basis for analyzing the migration and accumulation mechanisms of tight sandstone oil and a new approach for predicting oil saturation. Additionally, we developed digital and visual analysis methods for the migration results, enriching the expression of the dynamics of hydrocarbon accumulation.

Lake-level changes can significantly affect paleoenvironmental evolution, resource occurrence, terrestrial carbon budget, and biodiversity in continental basins. Climate is one of the most critical factors controlling lake-level changes. Paleoclimate of the Early Jurassic has been evidenced by oscillating icehouses to (super) greenhouses with interrupted intermittent extreme climatic events (hyperthermal and cooling), e.g., the Toarcian oceanic anoxic event (~183 Ma) and the late Pliensbachian cooling event (~185 Ma). Lake-level evolution and hydrologic cycling on Earth’s surface during the Early Jurassic icehouses-to-(super)greenhouses are thus far poorly understood due to a lack of continuous high-resolution nonmarine evidence. Here we present a super-long nonmarine lake level record for this pivotal interval from the early Pliensbachian to Toarcian by sedimentary noise modeling, and construct a 16.7-Myr-long astronomical time scale (174.2 Ma to 190.9 Ma) based on cyclostratigraphy analysis of rock color datasets (CIE b*) of the Qaidam Basin. Our results document lake-level oscillations on a 5-to 10-million-year (Myr) scale which shows a pronounced correlation with long-term climate variation and extreme climatic events, and 1- to 2.5-Myr-scale lake-level changes that are prominently paced by the 2.4-Myr long-eccentricity forcing and the 1.2-Myr obliquity forcing. At the Pliensbachian Stage, the 1.2-Myr-scale lake-level changes are in phase with the coeval sea-level variations. Orbitally forced growth and decay of the ephemeral or permanent ice sheets in polar regions are interpreted to control the synchronous ups-and-downs of continental lake level and global sea level. However, during the Toarcian ice-free greenhouses to (super)greenhouses, the 1.2-Myr-scale lake-level variations show an anti-phase relationship with global sea level, indicating a ‘seesaw’ interaction between continental reservoirs (lakes and groundwater) and global oceans. The 2.4-Myr long-eccentricity cycles mainly regulate variations of lake level and sea level by controlling the growth and decay of small-scale continental ice sheets, which is especially notable during the Pliensbachian Stage. These findings indicate a remarkable transition of hydrological cycling pattern during the Pliensbachian-Toarcian icehouses to (super)greenhouses, which provides new perspectives and evidence for investigating the hypothesis of global sea-level changes (e.g., glacio-eustasy and aquifer-eustasy) and long-period astronomical forcing in nonmarine stratigraphy.

The origin of sedimentary dolomite has become a long-standing problem in the Earth Sciences. Some carbonate minerals like ankerite have the same crystal structure as dolomite, hence their genesis may provide clues to help solving the dolomite problem. The purpose of this study was to probe whether microbial activity can be involved in the formation of ankerite. Bio-carbonation experiments associated with microbial iron reduction were performed in batch systems with various concentrations of Ca²⁺(0–20 mmol/L), with a marine iron-reducing bacterium Shewanella piezotolerans WP3 as the reaction mediator, and with lactate and ferrihydrite as the respective electron donor and acceptor. Our biomineralization data showed that Ca-amendments expedited microbially-mediated ferrihydrite reduction by enhancing the adhesion between WP3 cells and ferrihydrite particles. After bioreduction, siderite occurred as the principal secondary mineral in the Ca-free systems. Instead, Ca-Fe carbonates were formed when Ca²⁺ ions were present. The CaCO₃ content of microbially-induced Ca-Fe carbonates was positively correlated with the initial Ca²⁺ concentration. The Ca-Fe carbonate phase produced in the 20 mmol/L Ca-amended biosystems had a chemical formula of Ca_0.8Fe_1.2(CO₃)₂, which is close to the theoretical composition of ankerite. This ankerite-like phase was nanometric in size and spherical, Ca-Fe disordered, and structurally defective. Our simulated diagenesis experiments further demonstrated that the resulting ankerite-like phase could be converted into ordered ankerite under hydrothermal conditions. We introduced the term “proto-ankerite” to define the Ca-Fe phases that possess near-ankerite stoichiometry but disordered cation arrangement. On the basis of the present study, we proposed herein that microbial activity is an important contributor to the genesis of sedimentary ankerite by providing the metastable Ca-Fe carbonate precursors.

The Late Triassic witnessed significant collisional orogenic events in the Qinling orogenic belt, accompanied by magma underplating and tectonic deformation. These processes potentially resulted in substantial crustal thickening and uplift of the Qinling orogen. However, due to the absence of igneous rock records from this period in the eastern section of the Qinling orogen, the changes in crustal thickness during this orogenic process have not been thoroughly investigated. A series of foreland basins emerged during the Early Mesozoic to the south of the East Qinling orogenic belt. These basins have preserved clastic sedimentary rocks derived from the uplift and erosion of the orogenic belt. These sedimentary records serve as crucial records to reconstruct the evolutionary history of the Qinling orogen. To further clarify the collisional orogenic process of the Qinling orogenic belt, this study conducted in situ volcanic lithic fragment geochemistry, detrital zircon U-Pb chronology and trace element composition analysis on the sandstones of the Lower Jurassic Tongzhuyuan Formation in the Zigui Basin. The results suggest that the sandstones, which exhibit a significant abundance of volcanic lithic fragments, has a characteristic detrital zircon age group of 250–200 Ma, indicating a major provenance from the Triassic volcanic rocks. Combined with regional correlation and paleocurrent analysis, the detrital zircon U-Pb age data show that the source area of volcanic rocks should be in the Qinling orogenic belt to the north of the basin. This interpretation is further supported by the Triassic granitic rocks exposed in the western part of the orogenic belt, representing the magmatism during the Triassic collisional orogenesis in the Qinling orogen. Based on the co-varying relationships between present-day crust thickness with the chemical compositions of granite rocks and zircons, the La/Yb ratio of volcanic lithic fragments in the Tongzhuyuan Formation and the Eu/Eu ratio of detrital zircons with Triassic ages indicate that the Qinling orogen experienced crustal thickening during the Late Triassic, reaching its maximum thickness of 60–70 km at ca. 220–210 Ma. This crustal thickening in the eastern Qinling orogen is temporally consistent with that in the western orogen as recorded by the Triassic granitic rocks and may be related to large-scale crustal shortening and magmatism during the collisional orogeny.

The recurrent extreme El Niño events are commonly linked to reduced vegetation growth and the land carbon sink over many but discrete regions of the Northern Hemisphere (NH). However, we reported here a pervasive and continuous vegetation greening and no weakened land carbon sink in the maturation phase of the 2015/2016 El Niño event over the NH (mainly in the extra-tropics), based on multiple evidences from remote sensing observations, global ecosystem model simulations and atmospheric CO₂ inversions. We discovered a significant compensation effect of the enhanced vegetation growth in spring on subsequent summer/autumn vegetation growth that sustained vegetation greening and led to a slight increase in the land carbon sink over the spring and summer of 2015 (average increases of 23.34% and 0.63% in net ecosystem exchange from two independent datasets relative to a 5-years average before the El Niño event, respectively) and spring of 2016 (6.82%), especially in the extra-tropics of the NH, where the water supply during the pre-growing-season (November of the previous year to March of the current year) had a positive anomaly. This seasonal compensation effect was much stronger than that in 1997 and 1998 and significantly alleviated the adverse impacts of the 2015/2016 El Niño event on vegetation growth during its maturation phase. The legacy effect of water supply during the pre-growing-season on subsequent vegetation growth lasted up to approximately six months. Our findings highlight the role of seasonal compensation effects on mediating the land carbon sink in response to episodic extreme El Niño events.

The Tibetan Plateau is one of the most complicated geographical units worldwide in terms of its tectonic and environmental background. Although a hotspot for continental weathering and carbon cycling studies, accurate determination of the weathering carbon budget is challenging in this area, especially sink and source flux quantification and the controlling mechanisms. Compared with other major rivers on the plateau, the Nujiang River is characterized by less human disturbance and maintains a relatively pristine state. This study investigates the high spatiotemporal resolution hydrochemistry and dual-carbon isotope composition (δ¹³C_DIC and Δ¹⁴C_DIC) of river water in the Nujiang River Basin. The results revealed that the solutes and dissolved inorganic carbon in the river water are predominantly derived from rock weathering by carbonic and sulfuric acids, mainly due to the carbonate weathering process, and significantly enhanced by deep carbon sourcing from hot springs in the fault zone. The average contributions of geological and modern carbon in the main stream of the Nujiang River are 35.2% and 64.8%, respectively, and sulfide oxidation contributes >90% of sulfate ions in the river water. After considering the involvement of sulfuric acid generated by sulfide oxidation during rock weathering, the calculated consumption fluxes of atmospheric CO₂ by silicate and carbonate weathering in the watershed were decreased by approximately 52.0% and 37.4%, respectively, compared with those calculated ignoring this process. Rock weathering of the Nujiang River Basin is a “CO₂ sink” on a short time scale, while the participation of sulfuric acid makes it a “CO₂ source” on a geological time scale. The high-frequency observations of ion concentrations, elemental ratios, and calculated contributions of different rock weathering materials indicate that carbonate rock weathering is more sensitive to temperature and runoff variations than silicate rock weathering, with the solute contribution from carbonate weathering increasing significantly during monsoon period. The material input from different rock types is dominated by the hydrological pathways and water-rock reaction times in the basin. This study reveals the river solute origins and weathering CO₂ sequestration effect in response to a monsoonal climate in one of the most representative pristine plateau watersheds in the world, which is of great importance for elucidating the weathering control mechanisms and CO₂ net source-sink effect in plateau watersheds.

This paper presents a study of a newly discovered pollucite-lepidolite-albite granite (PLAG) in the Himalayan leucogranite belt, which marks the first occurrence of pollucite, a major cesium silicate mineral, in the Himalayan orogenic belt (China). The rock appears at the northern part of the Gyirong pluton, coexisting with the tourmaline-bearing two-mica granite (TMG). Primary rare-metal minerals include lepidolite (Li), spodumene (Li), pollucite (Cs), cassiterite (Sn), and microlite (Ta). Micas, mainly lithian muscovite to lepidolite, contain 4.07 wt.% Li₂O and 0.76 wt.% Rb₂O on average. The average Li₂O content of the spodumene is 7.95 wt.%. Pollucite not only has an average Cs₂O content of 34 wt.%, but also has an elevated Rb₂O content of about 0.16 wt.%. Notably, this granite attains industrial grades for rare metals, specifically with Li₂O, Rb₂O, and Cs₂O contents of 0.49–1.19 wt.%, 0.12–0.24 wt.%, and 0.69–2.33 wt.%, respectively. Dating results of magmatic accessory cassiterite and monazite indicated that the PLAG was formed at 19–18 Ma, slightly later than the TMG (22–20 Ma) of the Gyirong pluton. Thus, these two types of granites may form within the same magmatic system considering their pulsating intrusive contact, formation ages, and whole-rock and mineral chemical compositions. Furthermore, the abundant presence of pollucite suggests that the PLAG experienced high degrees of magmatic fractionation. In comparison to the Pusila spodumene pegmatite in the Himalaya and the Yashan topaz-lepidolite granite in Jiangxi, South China, the Gyirong PLAG exhibits different whole-rock and mineral compositions, resulting from differences in source materials and fractionation processes. Notably, the difference in fluorine (F) content may determine the degree of rare-metal element enrichment. The discovery of Gyirong PLAG highlights multiple stages and types of rare-metal mineralization in the Himalayan leucogranite belt, which is controlled by the South Tibetan Detachment System. The Cs-bearing geyserite deposit exposed along the Yarlung-Zangbo River, together with Himalayan leucogranites, constitutes two systems of rare-metal elements migration and enrichment. These two systems reflect the interaction among Earth systems across time and space, emphasizing how the Himalayan orogeny controls mineralization. As a result, the Himalayan leucogranite belt has considerable prospecting potential for cesium and rubidium resources and may be a crucial area for future exploration and resource utilization.

The timing and mechanisms of the human occupation of the demanding high-altitude Tibetan Plateau environment are of great interest. Here, we report on our reinvestigations and dating of the Nwya Devu site, located nearly 4600 meters above sea level on the central Tibetan Plateau. A new microblade techno-complex was identified on a lower lake shore at this site, distinct from the previously reported blade tool assemblage. These two lithic assemblages were dated to 45.6±2.6 and 10.3±0.5 ka using optically stimulated luminescence and accelerator mass spectrometry ¹⁴C methods. They represent, respectively, the earliest known Paleolithic and microlithic sites on the interior Tibetan Plateau, indicating multiple occupation episodes of hunter-gatherers during the past 45 ka. Our studies reveal that relatively stable depositional conditions and a paleoenvironment characterized by a comparatively warm climate facilitated these multiple occupations at Nwya Devu. The contemporaneous occurrence of the Upper Paleolithic blade technology on the Tibetan Plateau and most of Eurasia between 50 and 40 ka indicates rapid, large-scale dispersals of humans that profoundly affected human demography on a large scale. Combining new archaeological evidence and previously reported genetic data, we conclude that the Tibetan Plateau provided a relatively stable habitat for Upper Paleolithic hunter-gatherers, which may have contributed to the complex and multiple-origin gene pool of present-day Tibetans.