Search Results (352)

Sub-sag 21 in the eastern Yangjiang Sag, Pearl River Mouth Basin, South China, contains a thick lacustrine source-rock interval within the lower Wenchang Formation and is a major exploration target on the northern margin of the South China Sea. However, the timing of deposition during the early to middle Eocene remains poorly constrained, and the applicability of quantitative palaeoclimate reconstruction methods in low-latitude lacustrine basins requires further evaluation. In this study, we analyzed mudstones from the lower Wenchang Formation in Well E1. Using cyclostratigraphic constraints, we applied AstroGeoFit to construct an astronomically tuned age model, and combined palynological coexistence analysis with geochemical weathering proxies and linear–regression calibration to quantitatively reconstruct and cross-validate mean annual temperature and mean annual precipitation. Within this time-calibrated framework, we further quantified organic-carbon burial to evaluate the relationship between palaeoclimate evolution and organic-matter enrichment. The AstroGeoFit results indicate that the top of the lower Wenchang Formation in Well E1 is constrained to 44.563 Ma, and that the studied succession spans 50.249–44.563 Ma. Palynological coexistence analysis identifies three palaeoclimate phases within this interval. Method evaluation shows that the temperature reconstruction based on major-element geochemistry agrees well with the pollen-based temperature record, whereas one precipitation reconstruction based on weathering proxies shows the most robust agreement and stability relative to the pollen-based precipitation record. Reconstructed mean annual temperature ranges from 10.77 to 22.20 °C, and reconstructed mean annual precipitation ranges from 1188.27 to 1871.89 mm. Correlation analyses on the tuned timescale show that precipitation is more strongly associated than temperature with organic-matter accumulation parameters, including total organic carbon and organic carbon accumulation rate, indicating that organic carbon burial in the eastern Yangjiang Sag lake basin was mainly controlled by hydrological forcing. During the Early Eocene Climatic Optimum, carbon burial in low-latitude lakes was, therefore, not a simple response to elevated temperature, but instead reflected the integrated effects of precipitation, runoff, stratification, material supply, transport, and preservation. The evolutionary sequence further suggests that early high productivity was diluted by rapid sedimentation, reducing total organic carbon; subsequent cooling, lake deepening, and strengthened stratification enhanced organic matter preservation; and finally, tectonic subsidence together with regional humidification promoted the development and long-term preservation of high-quality lacustrine source rocks. Full article

Soldier beetle larvae are characterised by numerous very small setae on their body surface, giving them a velvety appearance and hydrophobic properties, and paired gland openings on the segments of the thorax and abdomen for defensive purposes. Only recently, such a larva has been recognised in Cretaceous amber. Previously, only two specimens from Baltic amber were known from the fossil record. This provides the impression that such larvae are rare. We report 45 new larval specimens from Eocene Baltic amber and Cretaceous Kachin amber (Myanmar), demonstrating that these fossils are, in fact, more common, but simply not reported. We use the expanded dataset (with fossil and extant larvae and adults, more than 300 specimens) to explore the ontogeny of soldier beetles by quantitatively comparing morphological aspects over time. It appears that there is no major loss in the morphology of adults and larvae. On the contrary, certain larvae known in the modern fauna, so-called pre-larvae, seem absent in the fossil record. Due to the pre-larvae, some modern soldier beetles have certain characteristics of hypermetamorphosis. This type of developmental pattern is also characterised by a distinct change in the direction of the developmental trajectory. However, such a change could not be identified in soldier beetles. Full article

During warm intervals such as the Early Eocene, megathermal vegetation belts expanded toward higher latitudes, displacing mesothermal and microthermal biota. Here, we examine the diversity and paleoclimate of the Early Eocene Ligorio Márquez Formation (LMF) in the context of other Paleogene Patagonian palynofloras, and we model the potential distribution of Nothofagus using Early Eocene climate simulations. From 35 processed samples, 20 yielded palynomorphs and 85 morphospecies were distinguished. We hypothesize that species richness in the LMF is comparable to other Eocene microfloras, and that climate models will confirm mesothermal conditions for this formation while identifying western Gondwana as the primary region of climatic suitability for Nothofagus. Our results indicate that the LMF hosted a diverse flora under mesothermal, humid-temperate conditions (Köppen–Geiger climate Cfa, within the broader Cf no-dry-season regime). Ecological niche modeling further indicates that western Gondwana (South America, the Antarctic Peninsula, New Zealand, and Australia) provided broadly suitable climatic conditions for Nothofagus. In Experiment 1 (modern-to-Eocene transfer), Maxnet models showed high discriminatory power (AUC_test = 0.86–0.88) with low omission at P10 (OR_P10 = 0.099–0.128). In Experiment 2 (Eocene-to-Eocene calibration), performance was consistently high across GCMs (AUC_test = 0.87–0.98; OR_P10 = 0.091–0.182). However, conditions across Antarctica were likely challenging, limiting its effectiveness as a dispersal corridor during the Eocene. Finally, our results suggest that the ancient South Pacific High influenced the northern distributional limit of Nothofagus in South America. Full article

The reconstruction of detrital flux, paleoclimate, paleosalinity, paleo-primary productivity, paleohydrodynamic conditions, and paleo-water depth enhances understanding of sedimentary processes and their drivers during deep-time greenhouse-icehouse transitions, such as the Eocene–Oligocene transition. This study uses detailed geochemical analyses of major oxides and trace elements in sediment samples collected from the Beni Suef Formation (Bartonian–Priabonian) and the Maadi Formation (Priabonian) in the southern Tethys shelf (Egypt, northeastern Desert). Detrital proxies, including Si/Al, Ti/Al, and Zr/Al, indicate an enhanced influx of terrigenous sediments in the middle portion of the Qurn Member of the Beni Suef Formation, as further supported by noticeable facies variations, particularly the transition from shale to coarser silt- and sand-sized fractions. Paleoclimate indicators (Sr/Ba, Rb/Sr, K₂O/Al₂O₃, and Sr/Cu) point to a climatic shift from humid to arid conditions, consistent with the regional Late Eocene aridification across the Tethyan realm. Paleosalinity proxies (Sr/Ba, Ca/Al, and Mg/Al×100) suggest episodic intensification of open-marine influence and a reduction in freshwater input, with an upsection increase in Sr/Ba ratios, reflecting phases of enhanced marine water settings or decreased terrestrial runoff. Primary productivity was evaluated using multiple geochemical proxies, including P, Ni/Al, Cu/Al, P/Al, P/Ti, and Babio ratios. These collectively indicate generally low primary productivity interrupted by intervals of enhanced paleoproductivity or increased organic matter export to the sediments. This interpretation is further supported by the low total organic carbon (TOC) values. These results highlight the sensitivity of the southern Tethys shelf to Middle–Late Eocene climatic variability and the key role of prevailing paleoenvironmental conditions in controlling sediment supply, water chemistry, and biological productivity. Full article

The Eocene Pinghu Formation in the Xihu Depression, East China Sea Shelf Basin, is a key coal-bearing unit for offshore China’s petroleum exploration. However, the mechanisms of coal accumulation controlled by astronomical cycles and the stacking patterns of coal seams remain underexplored. Recent studies using wavelet analysis have highlighted the need for further investigation into the role of Milankovitch cycles in coal formation. This study uses natural gamma-ray logging data from Well K and applies cyclic stratigraphy to investigate how astronomical orbital cycles control coal seam development, identifying the link between cyclic stratigraphy and coal accumulation, and the distribution patterns of coal seams across different cycle levels. The top of the Pinghu Formation was used as the astronomical anchor, and tuning was conducted from top to base following a “cycle identification–anchor tying–astronomical tuning” workflow. The resulting astronomical timescale indicates a depositional duration of 8.17 Ma. COCO/eCOCO analyses with 5000 Monte Carlo simulations (sedimentation-rate range: 7–11 cm/kyr; step: 0.1 cm/kyr) yield a mean sedimentation rate of 9 cm/kyr. Coal accumulation is influenced by Milankovitch cycles. High eccentricity periods correspond to warmer climates that promote coal development, while low eccentricity phases synchronize with optimal climatic conditions for coal formation. Based on these findings, this study proposes a coal seam development model for the Pinghu Formation in Area A of the Xihu Depression, offering insights for cyclic stratigraphy and coal accumulation research in similar basins and supporting sustainable development of coal-bearing strata in the East China Sea Basin. Full article

The Tinjar–West Baram Fault in the southern South China Sea is a major NW-trending strike-slip fault that has remained tectonically active since the Oligocene. It forms a key structural boundary between the Zengmu, Beikang, and Nansha Trough basins. Multi-phase strike-slip movements have strongly controlled sediment provenance dispersal pathways, and reservoir development in the Zengmu Basin, yet the sedimentary response to these tectonic processes remains poorly understood. This study integrates 2D seismic profiles to analyze the fault geometry, kinematics, and impact on deep-water sedimentary systems. Results indicate that Oligocene right-lateral motion directed sediment supply from the southwest, mainly sourced from Kalimantan, forming fluvial–deltaic systems with depocenters in the southern basin. Since the Late Miocene, a transition to left-lateral motion reoriented sediment provenance toward the southeast, leading to delta-front complexes and northward migration of depocenters. Strike-slip activity deformation enhanced rock fragmentation and sediment supply, producing fan delta, fluvial, and shallow lacustrine facies near the fault. Associated uplift and subsidence induced relative sea-level fluctuations, resulting in alternating transgressive–regressive sequences. From the Late Eocene to Miocene, the basin evolved from a land–sea transitional system to a deltaic–carbonate complex controlled by the paleo-Sunda River. During the Pliocene–Quaternary, sedimentation was dominated by shallow-marine shelf and semi-deep-marine deposits. Fault-related fracturing significantly enhanced porosity and permeability, creating favorable conditions for hydrocarbon migration and entrapment in both sandstone and carbonate reservoirs. These findings demonstrate a strong coupling between strike-slip fault activity and sedimentary system evolution, providing important insights into sedimentary processes and hydrocarbon potential in strike-slip fault-bounded basins globally. Full article

This study investigates the rare-earth element (REE) geochemistry of twenty-nine clastic rock samples from the Paleogene Liushagang Formation in the Weixi’nan Sag. The primary objectives were to quantitatively evaluate the depositional paleoenvironment, determine the provenance lithology, and constrain the tectonic setting of the source area. Results reveal distinct chondrite-normalized REE distribution patterns characterized by light REE (LREE) enrichment, relatively flat heavy REE (HREE) segments, and pronounced negative Eu anomalies. The cerium anomaly index (Ce_anom, normalized to the North American Shale Composite) ranges from −0.06 to 0.00, implying broadly suboxic to anoxic-reducing conditions in the water column during deposition. The chondrite-normalized (La/Yb)_N ratio, utilized as a proxy for relative depositional residence time, decreases stratigraphically from member 3 to member 1, reflecting a transition to shorter residence times and higher relative sedimentation rates. Laterally, (La/Yb)_N increases toward the basin center, accurately recording progressively lower sedimentation rates basinward. Provenance analysis indicates that the sediments were predominantly derived from felsic igneous rocks of the upper continental crust. Spatially, the northern steep-slope belt reflects a uniform source, whereas the southern gentle-slope belt and the Weixi’nan low-uplift periphery record multisource mixed inputs. Finally, tectonic discrimination reveals an “active continental margin” affinity. This geochemical signature represents the inherited tectonic environment of the Mesozoic parent rocks in the surrounding source uplifts, rather than the Cenozoic extensional rift setting of the Weixi’nan Sag itself. Full article

The deep reservoir of the K gas field in the Xihu Depression of the East China Sea Basin has ample storage space and a vast reserve scale. However, these deep intervals remain poorly explored and developed, and their reservoir attributes and key controlling factors are not yet well constrained. Using integrated analyses of cores, cast thin sections, scanning electron microscopy, petrophysical statistics, grain-size data, high-pressure mercury intrusion, and nuclear magnetic resonance imaging, together with conventional well logs, we evaluate the roles of sedimentation, diagenesis, and overpressure in the development and distribution of high-quality reservoirs. Based on clastic grain texture and composition, authigenic minerals, diagenetic types and intensities, pore architecture, petrophysical properties, and gas saturation, two types of high-quality deep sandstone reservoirs are identified: rigid, moderately porous sandstones and strongly compacted, low-porosity sandstones. Compaction is the dominant diagenetic process controlling reservoir quality in the Eocene Pinghu Formation. Overpressure prolongs kaolinite stability and promotes precipitation within pore throats, enhancing fluid sealing and retention, yet does not significantly reduce porosity. Rigid moderately porous reservoirs mainly occur in subaqueous distributary channels, whereas strongly compacted low-porosity reservoirs are concentrated in mouth bars and sheet-sand microfacies. This distribution pattern provides guidance for exploring high-quality deep sandstone gas accumulations. Full article

The structural characteristics of the Majiatan fault–fold system in the northwestern Ordos Basin are complex, and the detailed 3D distribution of faults and their evolutionary mechanisms remain insufficiently understood, which restricts effective petroleum exploration in this region. To address this, this study utilizes high-resolution 3D seismic data comprising 20 lines (total length 753.371 km, survey grid 3 × 3 km) and drilling and logging data from 13 wells (including synthetic seismograms) to establish a detailed 3D fault model. We aim to elucidate the fault styles and the formation mechanism of the fault–fold–thrust belt. Results indicate the presence of 47 Mesozoic faults, all of which are thrust faults classified into three types. Structural traps dominate the leading transition zone, whereas lithologic–structural traps are prevalent in the Tian-huan Syncline. Laterally, from south to north, the fault occurrence transitions from west-dipping east-thrust to east-dipping west-thrust, accompanied by a shift in tectonic style from thrusting nappe to late-stage reconstruction. The stress intensity generated during the Late Cretaceous increases northward, causing deformation to shift westward. Typical fault styles observed include “y-shaped”, “flower-shaped”, and “imbricated” structures. The middle-north zones of the Majiatan area and the Hengshanbu Thrust Belt share a unified formation mechanism: initiation in the Late Triassic, main development in the Late Jurassic, initial shaping in the Late Cretaceous, and final modification in the Eocene, driven by the rotation of the Ordos Basin and shear tectonic forces. The most favorable exploration zones are identified at the junctions between the leading zone, the fault–fold zone, and weakly transformed zones. The tectonic evolution model established in this study provides a valuable reference for understanding structural complexities and guiding hydrocarbon exploration in similar fold and thrust belts globally. Full article

We report new fossil larval specimens that have characters of the group Megaloptera, i.e., are either megalopteran or megalopteran-like larvae from the Triassic, Cretaceous, or Eocene. Fossils from the latter two times are preserved in amber. One of the new fossils reveals that some earlier reported presumed megalopteran-like fossils, that have been already suspected to be beetles, are indeed more likely beetles of the group Myxophaga. A quantitative morphological comparison supports that most fossil megalopteran (and megalopteran-like) larvae did not differ significantly from extant megalopteran larvae, indicating no major losses of morphology over time. However, two newly reported fossil specimens from Kachin amber indeed separate from the other larvae, representing an extinct morphotype. The morphotype is characterised by a prominent terminal filament, indicating that the specimen is a representative of Sialidae. However, unlike most of the known larvae of this group, it possesses a rather elongate prothorax and strongly curved mandibles. These two characters are more commonly known in larvae of Corydalidae. It seems most likely that the presence of these characters in the new morphotype does not represent a plesisomorphy, but is more likely the product of convergent evolution. Full article

In February 2024, the European Union published its Industrial Carbon Management Strategy, setting ambitious goals for carbon capture and storage (CCS), carbon capture and utilisation (CCU), and related technologies. Industrial decarbonisation will require a mix of solutions, CCUS, electrification, hydrogen and hydrogen-derived fuels, and energy efficiency, which are all dependent on affordable clean energy. Although carbon management technologies could contribute substantially to climate targets, their deployment has been slowed by technical barriers and public concerns. Sotacarbo has created a research centre dedicated to developing and testing carbon capture, utilisation, and storage technologies. Within this framework, the new Sotacarbo Fault Laboratory (SFL) was designed to investigate gas migration in faults and to test monitoring systems capable of detecting potential short- and long-term CO₂ leakages. This paper presents a preliminary study, including seismic full-waveform simulations for time-lapse surveys before and after CO₂ injection, and a suite of geophysical methods used to characterise the Matzaccara Fault within the Eocene Sulcis Basin. The results of the application of integrated geophysical methods support the selection of a safe and suitable injection-well location and demonstrate the value of these methods for detailed fault characterisation in CCUS applications. Full article

Investigating how climatic and hydrological conditions in ecological resource-enriched zones of marginal seas respond to external forcing, particularly during past greenhouse climates, holds considerable significance for understanding current environmental and resource challenges driven by global warming. In marginal seas, climatic hydrological states, including salinity, redox conditions, and productivity, are key environmental parameters controlling organic matter production, preservation, and ultimately the formation of high-quality shale. Herein, high-resolution cyclostratigraphic and multi-proxy geochemical analyses were conducted on a continuous core from the upper part of Member 4 of the Eocene Shahejie Formation (Es4cu) in Well NY1, Dongying Sag, Bohai Bay Basin. Based on these data, a refined astronomical timescale was accordingly established for the studied interval. By integrating sedimentological observations with multiple proxy indicators, including elemental geochemistry (e.g., Sr/Ba and Ca/Al ratios), organic geochemistry, and mineralogical data, the evolution of climate and paleo-water mass conditions during the study period was reconstructed. Spectral analyses revealed prominent astronomical periodicities in paleosalinity, productivity, and redox proxies, indicating that sedimentation was modulated by cyclic changes in eccentricity, obliquity, and precession. It was hereby proposed that orbital forcing governed periodic shifts in basin hydrology by regulating the intensity and seasonality of the East Asian monsoon. Intervals of enhanced summer monsoon associated with high eccentricity and obliquity were typically accompanied by increased sediment supply and intensified chemical weathering. Increased precipitation and runoff raised the lake level while promoting stronger connectivity with the ocean. In contrast, during weak seasonal monsoon intervals linked to eccentricity minima, basin conditions shifted from humid to arid, characterized by reduced precipitation, lower lake level, decreased sediment supply, and a concomitant decline in proxies for water salinity. The present results demonstrated orbital forcing as a primary external driver of cyclical changes in conditions favorable for resource formation in the Eocene lacustrine strata of the Bohai Bay Basin. Overall, this study yields critical paleoclimate evidence and a mechanistic framework for predicting the spatial-temporal distribution of high-quality shale under comparable astronomical-climate boundary conditions. Full article

Tenthredinidae (Hymenoptera: Tenthredinoidea), the most species-rich sawfly family, features a controversial subfamily classification, particularly regarding Eriocampa Hartig, 1837, Conaspidia Konow, 1898, and their relatives. In this study, we sequenced and characterized 15 complete mitochondrial genomes from Eriocampa, Eriocampopsis Takeuchi, 1952, and Conaspidia, and reconstructed the phylogeny of Tenthredinidae using a mitogenomic dataset including 69 species from 16 subfamilies. The mitochondrial genomes of these genera exhibited genus-specific tRNA rearrangements within the IQM and ARNS1EF clusters. Phylogenetic analyses using both Maximum Likelihood and Bayesian Inference consistently recovered (Eriocampa + Eriocampopsis + Conaspidia) as a monophyletic lineage distinct from other subfamilies of Tenthredinidae. Divergence-time estimates indicate that the Eriocampa lineage diverged from other tenthredinids around the Late Cretaceous–Paleocene boundary (~70 Ma) and diversified during the Eocene. This timing coincides with the radiation of their host plants (Araliaceae, Betulaceae, and Juglandaceae). We also compared the morphology of Eriocampinae with that of other subfamilies of Tenthredinidae and summarized the diagnostic characters of Eriocampinae. Integrating morphological and mitogenomic evidence supports the recognition of Eriocampinae Rohwer, 1911 stat. nov. This study not only clarifies the phylogenetic position of these genera but also provides new insights into the coevolutionary history between sawflies and angiosperms. Full article

The validity of the youngest representative of Neochelys described to date, representing the last European freshwater member of Erymnochelyinae, has been considered doubtful. A revision of the previously documented specimens of this Spanish Bartonian or Priabonian (MP 16 or MP 17, middle or late Eocene) species is performed here, along with the analysis of additional unpublished remains from the same geological formation. The principal character originally used to diagnose the species (i.e., paired gular scutes) is refuted here, and interpreted instead as an anomalous variation that is also found in other representatives of the genus. However, Neochelys arribasi is supported as a valid species based on other morphological features. We recognize here an increase in size for the representatives of Neochelys from the Duero Basin over time, which are also the youngest known species of Neochelys. Full article

The Eocene fourth member of the Shahejie formation (Es4x) in the Bonan Depression, Bohai Bay Basin, records syn-rift sedimentation under alternating arid and humid climates. It provides insight into how orbital-scale climatic fluctuations influenced tectonics, facies patterns, and reservoir distribution. This study integrates 406 m of core data, 92 thin sections, 450 km² of 3D seismic data, and multiple geochemical proxies, leading to the recognition of five facies associations (LFA): (1) alluvial fans, (2) braided rivers, (3) floodplain mudstones, (4) fan deltas, and (5) saline lacustrine evaporites. Three major depositional cycles are defined within the Es4x. Seismic reflections, well-log patterns, and thickness trends suggest that these cycles represent fourth-order lake-level fluctuations (0.8–1.1 Myr) rather than short 21-kyr precession rhythms. This implies long-term climate and tectonic modulation, likely linked to eccentricity-scale monsoon variability. Hyperarid phases are marked by Sr/Ba > 4, δ¹⁸O > +4‰, and thick evaporite accumulations. In contrast, Sr/Ba < 1 and δ¹⁸O < −8‰ reflect humid conditions with larger lakes and enhanced fluvial input. During wet periods, rivers produced sand bodies nearly 40 times thicker than in dry intervals. Reservoir quality is highest in braided-river sandstones (LFA 2) with 12%–19% porosity, preserved by chlorite coatings that limit quartz cement. Fan-delta sands (LFA 4) have <8% porosity due to calcite cementation, though fractures (10–50 mm) improve permeability. Floodplain mudstones (LFA 3) and evaporites (LFA 5) act as seals. This work presents a predictive depositional and reservoir model for arid–humid rift systems and highlights braided-river targets as promising exploration zones in climate-sensitive basins worldwide. Full article