Earth-Science Reviews最新文献

The global distribution of clay minerals is intricately linked with climatic conditions and bedrock composition, which interact to control the weathering intensity of silicate and other minerals. However, the quantitative relationship between clay minerals and climate is not well understood, partly due to the lack of quantitative assessments of the role of the various factors responsible for clay mineral formation. Here we examine the quantitative relationship between soil clay minerals and climatic factors on the global scale, by extrapolating clay mineral abundances to a large scale. We found that mean annual precipitation (MAP) is the first order control on the global clay mineral distribution, while mean annual temperature (MAT), elevation, slope, lithology, upland hillslope soil thickness (UHST), and upland hillslope regolith thickness (UHRT) have secondary roles or localized impacts on clay mineral distributions. We found that precipitation thresholds exist in weathering intensity and clay mineral formation: (1) Illite decreases monotonically and kaolinite increases monotonically with increasing MAP below the threshold of 1800–2000 mm, whereas gibbsite increases monotonically with increasing MAP below the threshold of 2200–2400 mm. (2) Smectite and Fe oxides increase with increasing MAP below the threshold of 600–800 mm, and then decrease with increasing MAP between 600 and 800 mm and 1800–2000 mm. (3) All clay minerals are insensitive to extremely high MAP, above 1800–2000 mm. We suggest that paleoprecipitation can be semi-quantitatively reconstructed based on variations in the relative contents of clay minerals, which can be used as a proxy indicator of wet and dry variations for paleoclimate studies.

Identification of geological features from seismic data such as faults, salt bodies, and channels, is essential for studies of the shallow Earth, natural disaster forecasting and evaluation, carbon capture and storage, hydrogen storage, geothermal energy development, and traditional resource exploration. However, manual seismic interpretation is distinctly subjective and labor-intensive. With the advent and rise of 3D surveys, the size of seismic data has increased dramatically, making purely manual interpretation impractical. Since 1989, a large number of machine learning-based methods for identifying geological features have been proposed to address these challenges. To date, these methods have not been reasonably synthesized. Motivated by a progressive increase in applications, this review presents an overview of advances in the utilization of machine learning to identify geological features from seismic data. First, we classify these methods from five different perspectives. Second, we provide a comprehensive overview of 241 publications related to seismic geological feature identification and offer a detailed analysis of the development of these methods categorized by geological feature type. Third, 20 field and 12 synthetic seismic datasets, which are publicly available and relevant to the identification of faults, salt bodies, channels, caves, and horizons, are cataloged. Fourth, we discuss the issue of false positive identification caused by the limited geological features in the training dataset. To address the problems of false positives and insufficient labeled training datasets, we propose a simulation framework for generating 3D synthetic seismic data and corresponding geological labels that include a rich variety of geological features. To the best of our knowledge, this is the synthetic seismic dataset that contains the richest geological features. Finally, we discuss in depth the current challenges and future opportunities to inspire further relevant research.

Big Data-driven research is thriving in the geosciences, with initiatives such as The Deep-Time Digital Earth (DDE) program (https://deep-time.org/), which is a “big science program” by the International Union of Geological Sciences (IUGS). Northern and northwestern Chinese environments produced a significant number of typically inertinite-rich coals during the Jurassic, which have been extensively researched and represent a high-quality subject for Big Data-driven studies. Inertinite in coals are widely accepted and applied as direct evidence of palaeowildfire with important palaeoclimatic significance, but the enrichment mechanism of inertinite in Jurassic coals have not yet been comprehensively understood. In this research, Big Data methodology and thinking were used to collect 1298 sources of information with inertinite content, and to reconstruct the palaeogeographic distributions of that inertinite. In addition, >300 datasets on polycyclic aromatic hydrocarbons (PAHs) and inertinite reflectance were collected. Based on these data and in combination with palaeoclimatic databases, two enrichment mechanisms for the high levels of inertinite are proposed. The results show that Jurassic coals in China are significantly enriched in inertinite compared to coals in the rest of the world, with an average inertinite content of 18.9% in the Early Jurassic and up to 36.8% in the Middle Jurassic. Combustion-sourced PAHs are widespread in Jurassic coal seams in different basins and are dominated by 4-ring and 5-ring PAHs. Both coal petrology and PAHs characteristics are indicative of a wildfire origin for inertinite, and the inertinite reflectances suggest that the palaeowildfire types were mainly low-temperature fires. It is proposed that the abundant inertinites in Jurassic coals were formed as the result of the multi-factorial coupling of palaeoflora, palaeoclimates, and palaeoenvironmental evolution. The enrichment models for the inertinite in the Early-Middle Jurassic coals indicate that these inertinites were mainly formed during periods of more obvious seasonal contrasts. Based on analysis from a Big Data review of inertinite concentrations in coals, a quantitative classification criterion is proposed to define those with >30% inertinite as “inertinite-rich coal”, and those with >50% inertinite as “inertinite coal”.

Rare earth elements and yttrium (REY) composition of paleo-seawater and redox conditions of localized water masses during deposition are documented by the REY preserved in modern pristine chemical sedimentary phosphorites. However, contrary to modern phosphorites, some older ones (e.g., Cambrian and Proterozoic phosphorites) display anomalous REY patterns that deviate from modern seawater, and limit the use of their parameters (e.g., Ce anomalies) as a reliable proxy for redox conditions in this case. In this work, elements of bulk-rocks and apatite grains, SrNd isotopes, and phosphate oxygen isotopes (δ¹⁸O_P) from Jingxiang (JX), Yichang (YC), and Xingshen (XS) phosphorites of the Ediacaran Doushantuo Formation in South China were investigated to address this quandary. The REY indexes and patterns of bulk-rocks and apatite, as well as Nd isotopes of bulk-rocks, suggest that the phosphorites deposited in the lower, middle, and upper members of the Ediacaran Doushantuo Formation record the sources of REY as being of terrigenous, mixed, and seawater origins, respectively. During the deposition of the Ediacaran Doushantuo Formation, high δ¹⁸O_P values (18.61 ± 1.04) of all bulk-rocks, close to contemporary marine authigenic apatite, indicate that phosphorus has been involved in strong marine bio-cycling, assuming a final terrestrial source. However, REY composition of the seawater column recorded by authigenic apatite in the lower member of Doushantuo Formation exhibited a right-leaning REY pattern, representing a terrestrial REY end-member. The ⁸⁷Sr/⁸⁶Sr ratios of bulk-rocks (0.71031 ± 0.00719) and apatite grains (0.71098 ± 0.00099) also remained consistent throughout the Ediacaran Doushantuo Formation, except for the high ⁸⁷Sr/⁸⁶Sr values found in bulk-rocks (0.72200 ± 0.00085) and apatite (0.72271 ± 0.00064) in the lower member of JX, which are presumed to result from source rocks with high radioactive Sr. Combined with REY indexes (Ce anomalies, Y/Ho ratios, and the differentiation of REY) and constant ⁸⁷Sr/⁸⁶Sr values of apatite, varying REY patterns from the lower to upper members of the Doushantuo Formation indicate that the scavenging rate of terrestrial REY inputs to the ocean by suspended particles (e.g., FeMn oxyhydroxides) in the water column is controlled by the degree of seawater oxidation. Our study highlights that REY inputs to seawater could undergo seawater cycling (i.e., the removal of REY by particulates of seawater under oxygen-containing conditions), and only REY that undergo sufficient seawater cycling can reflect the true redox conditions of the water column. Therefore, the sources and cycling of REY in seawater should be carefully identified when applying Ce anomalies and Y/Ho ratios of phosphorites to trace the redox conditions of ancient seawater.

The complicated flow behaviors of multiphase fluids in shale reservoirs are significantly influenced by fluid-fluid and fluid-rock interactions due to the non-negligible intermolecular forces at the nanoscale, which is crucial for the effective development and efficient extraction of shale oil. The complexity of multiphase fluid distribution and flow behaviors in shale reservoirs is further increased by low porosity, low permeability, poor connectivity, high inhomogeneity, and multi-component minerals, making the development process more challenging. Molecular dynamics simulation is widely to precisely capture the intermolecular forces and effectively explain the complex distribution and flow behaviors of these fluids under fluid-fluid and fluid-rock interaction forces. In this review, the characteristics of mineral composition, pore structure, porosity, permeability, and fluid types are first elaborated to illustrate the particularity of shale reservoirs and fluids compared to conventional scale reservoirs. The results show that shale minerals are composed of inorganic and organic matter with extremely low porosity and permeability, and nanoscale pore size, in which the complicated oil-water-CO₂ multiphase fluid types are caused by the primary underground water, fracturing water and injected CO₂. The research progress of molecular simulation on the fluid-fluid and fluid-rock interaction mechanisms and on multiphase shale fluids flow behaviors are then reviewed in detail. The strong intermolecular interaction forces can result in the different occurrence states of fluids, the fluid-fluid interfacial slip, the fluid-rock boundary slip and heterogeneous fluid viscosity/density, significantly exacerbating the complexity of fluids flow. Meanwhile, the injected CO₂ in the formation becomes a supercritical state with high diffusivity and strong solubility, and causes oil expansion, density and viscosity reduction, interfacial tension reduction, wettability alteration and molecular diffusion, which effectively replaces adsorbed hydrocarbon components by competitive adsorption behaviors, and promotes oil flow. The challenges and outlook of molecular simulation research and upscaling applications are finally discussed. This review aims to provide a microscopic understanding of the distribution characteristics and flow behaviors of multiphase shale fluids in nanoconfined space for both unconventional oil and gas researchers and industry professionals.

Palaeontological and zooarchaeological deposits have been recovered from underwater caves across the globe, but studies on site formation processes in these environments are scattered and have never been systematically examined. Flooded caves in the phreatic zone of karst systems include sinkholes and fensters (windows) that form a connection between the sub-aerial and sub-terranean landscapes, and conduits and chambers that establish underground networks of tunnels. Burial environments in these spaces are variable, and sedimentary, cave morphologic, and hydrologic variability within a single site can have profound impacts on taphonomic processes. The key determinant on long term preservation in these spaces is, however, the presence of water which dictates the nature of any habitation and by which species, and the process of decay. Water tables can fluctuate with long- and short-term sea level changes, with concomitant shifts in burial environments between flooded ‘wet’ or exposed ‘dry’ settings in near-shore cave systems. Distinguishing wet and dry burial conditions is necessary to reconstruct site formation processes in caves exhibiting evidence of changing or cyclical phreatic and vadose conditions. Signatures of aquatic deposition have been identified in underwater sites under marine, lacustrine and fluvial settings, but similar investigations are lacking for submerged cave landscapes. Water influences the decay process, alters bone surfaces, and modifies internal physical and chemical properties of bones. By exploring the environmental properties of flooded caves alongside known aquatic modifications, this review aims to build a framework for taphonomy of underwater cave palaeontological and archaeological sites. We detail biostratinomic and diagenesis processes that can be explored by actualistic, experimental, and observational studies. Future consideration could be given to the effects of human actions on the spatial distribution and modifications of bones in these spaces and the combined effects of environmental and anthropic agents.