Science China Earth Sciences最新文献

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.

Despite a specific data assimilation method, data assimilation (DA) in general can be decomposed into components of the prior information, observation forward operator that is given by the observation type, observation error covariances, and background error covariances. In a classic Lorenz model, the influences of the DA components on the initial conditions (ICs) and subsequent forecasts are systematically investigated, which could provide a theoretical basis for the design of DA for different scales of interests. The forecast errors undergo three typical stages: a slow growth stage from 0 h to 5 d, a fast growth stage from 5 d to around 15 d with significantly different error growth rates for ensemble and deterministic forecasts, and a saturation stage after 15 d. Assimilation strategies that provide more accurate ICs can improve the predictability. Cycling assimilation is superior to offline assimilation, and a flow-dependent background error covariance matrix (P^f) provides better analyses than a static background error covariance matrix (B) for instantaneous observations and frequent time-averaged observations; but the opposite is true for infrequent time-averaged observations, since cycling simulation cannot construct informative priors when the model lacks predictive skills and the flow-dependent P^f cannot effectively extract information from low-informative observations as the static B. Instantaneous observations contain more information than time-averaged observations, thus the former is preferred, especially for infrequent observing systems. Moreover, ensemble forecasts have advantages over deterministic forecasts, and the advantages are enlarged with less informative observations and lower predictive-skill model priors.

A geologic time scale is a chronological system that separates the geological strata of a planetary body into different units in temporal sequence and shows its progressive evolution. The time scale of the Moon was established a half-century ago during the telescopic-early Apollo exploration era, using data with limited spatial coverage and resolution. The past decades have seen a wide array of studies, which have significantly extended our understanding of global lunar geologic evolution. Based on a comprehensive review of lunar evolution with respect to the dynamical changes, we propose two major updates to the current lunar time scale paradigm to include the evolution of both endogenic and exogenic dynamic forces now known to have influenced early lunar history. Firstly, based on the temporal interplay of exogenic and endogenic processes in altering the Moon, we defined three Eon/Eonothem-level units to represent three dynamical evolutionary phases. Secondly, the pre-Nectarian System is redefined and divided as the magma ocean-era Magma-oceanian System and the following Aitkenian System beginning with the South Pole-Aitken basin. The ejecta of this basin, Das Formation, was deposited on the primordial lunar crust as the oldest stratum produced from exogenic processes. The updated lunar time scale, facilitated by the post-Apollo exploration and research advances, provides an integrated framework to depict the evolution of the Moon and has important implications for the geologic study of other terrestrial planets.

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.

Abstract

Rheology of rocks controls the deformation of the Earth at various space-time scales, which is crucial to understand the tectonic evolution of continental lithosphere. Researches of rock rheology are mainly conducted via high-pressure and high-temperature rheological experiments and multi-scale observations and measurements of naturally deformed rocks. At present, a large amount of data from such kinds of studies have been accumulated. This paper first provides an up-to-date comprehensive review of the rheological mechanisms, fabric types and seismic properties of the main rock-forming minerals at different depths of continental lithosphere, including olivine, orthopyroxene, clinopyroxene, amphibole, plagioclase, quartz and mica. Then, progress in high-pressure and high-temperature experiments and natural deformation observations is introduced, mainly regarding the rheological strength and behavior, seismic velocity and anisotropy of lithospheric mantle peridotite, eclogite, mafic granulite, amphibolite and felsic rocks. Finally, by taking the Tibetan Plateau as an example, the application of rock rheology for quantitative interpretation of seismic anisotropy data is discussed. The combination of mineral deformation fabrics and seismic anisotropy is expected to make an important breakthrough in understanding the rheological properties and structure of continental lithosphere.