Search Results (210)

The present work reconsiders our current knowledge of the presence of brachiopod genera in the Chattian and Aquitanian stages (late Oligocene and Early Miocene, respectively). Two of the most important sources of paleontological information were used. The uncertain presence of taxa in the particular stages was recorded. The results indicated that the total number of brachiopod genera in the Chattian and the Aquitanian was generally the same, irrespective of the chosen dataset. If so, the short-term paleoenvironmental perturbations did not affect the generic diversity of brachiopods. These findings contribute to a better understanding of the presently available, traditional estimates of the generic diversity of brachiopods. However, further critical consideration and improvement of the data and application of some advanced analytical tools is needed. Full article

To elucidate the development control factors, diagenetic evolution, and pore evolution of oil and gas reservoirs of the Huagang Formation in the East China Sea Shelf Basin Central Anticlinal Belt, this study involved geological analyses, including thin-section petrography, scanning electron microscopy (SEM), mineral analysis via TESCAN Integrated Mineral Analyzer (TIMA), X-ray diffraction (XRD), and petrophysical measurements. We investigated the reservoir characteristics and primary diagenetic processes of the Huagang Formation reservoirs using logging and nuclear magnetic resonance (NMR) data, identified provenance differences between the north-central (FN) and south-central (FS) areas, divided diagenetic environments, established distinct diagenetic sequences, and uncovered high-quality reservoir pore evolution patterns. The results showed that the provenance in the FN area of the Central Anticlinal Belt is primarily acidic igneous rocks, which exhibits low resistance to compaction but is susceptible to dissolution modification, and the “high-dissolution zone” developed at burial depths of 3600–3900 m constitutes the primary high-quality reservoir; the provenance in the FS area is a mixture of medium- and high-grade metamorphic rocks and acidic igneous rocks, which exhibits stronger resistance to compaction, but dissolution zones are poorly developed. The Huagang Formation has experienced multiple diagenetic processes, such as compaction, cementation, and dissolution. During destructive diagenesis, the average reduction in pore volume due to compaction accounts for 76% (FN area) and 81% (FS area), while cementation accounts for 18% (FN area) and 12% (FS area). Vertically, 3900 m and 4000 m are the boundaries between the acidic zone and acid-alkaline transition zone of the Huagang Formation in the FN and FS areas, respectively, and the whole Huagang Formation is considered within the meso-diagenetic A2 stage. The pore evolution is closely related to diagenesis. The porosity of the sandstones in the Upper Member of the Huagang Formation in the FN area changes from 37.5% to 10.62%, and the porosity of the sand-stones in the Lower Member of the Huagang Formation in the FS area changes from 36.5% to 8.90%. The results of this study provide a reference for the study of differential diagenetic evolution of sandstones in the Xihu Sag and the exploration of deep high-quality reservoirs. Full article

The Tuzla area, located in the Ayvacık district of Çanakkale (Biga Peninsula, northwestern Türkiye), hosts a Oligocene-Miocene volcanic system comprising andesitic, dacitic, rhyolitic lavas, trachyandesite, pyroclastics, and ignimbrites, and the Kestanbol Pluton. Petrographic and X-ray diffraction (XRD) analyses indicate that the altered volcanic units are dominated by porphyritic dacitic/rhyodacitic and trachyandesitic rocks, with silicification, iron oxide formation, and opacification. XRD results reveal smectite, smectite–illite/mica, illite–mica, kaolinite, cristobalite–opal, K-feldspar, plagioclase, dolomite, hematite, and quartz as the principal mineral phases. Geochemical data, including rare earth elements (REEs), suggest that fractional crystallization of primary mineral phases played a major role in controlling magmatic evolution. Chondrite-normalized REE patterns display enrichment in light REEs relative to heavy REEs, indicating derivation from a common magma source. K₂O–Na₂O and (Na₂O + K₂O)–FeOᵗ–MgO (AFM) diagrams show high-K calc-alkaline, calc-alkaline, and tholeiitic affinities, with most rhyodacite/dacite and all trachyandesite samples plotting in the tholeiitic field. Tectonic discrimination diagrams indicate formation in both volcanic arc and intraplate tectonic settings. Moderate enrichments in Ba and Sr reflect magmatic evolution and source characteristics, whereas the highest concentrations are attributed to post-magmatic fluid–rock interaction. Overall, the Tuzla volcanic rocks originated from a collision-related enriched lithospheric mantle source and subsequently evolved through fractional crystallization and assimilation processes, accompanied by crustal contamination and variable hydrothermal overprint. Full article

The SE Baltic area, the former Eastern Prussia, is renowned for complex natural history. Over the past millions of years, the area experienced major geological events and geomorphic landscape transformations, resulting in the present relief configuration. Past climates and environments gave rise to the specific life-forms that proliferated in the Paleozoic and Mesozoic–Early Cenozoic shallow sea/lacustrine basins, and the Late Cenozoic riverine and continental settings. During the Paleogene, forested sub-tropical lands and deltaic settings of coastal sea lagoons gave rise to the famed amber formations (Blue Ground) hosting inclusions of resin-sealed insect and other small invertebrates that offer an unprecedented look into the 35–34 million-year habitats. Ferruginous sandstones, formed in shallow waters incorporating remains of thermophilous fauna—bivalves and gastropods, bryozoans, and sea urchins, among others—lie above the amber-bearing deposits. Oligocene–Miocene continental (riverine, lacustrine, and palustrine) conditions relate to the “Brown Coal Formation”, embedding a variety of fossil plants. Finally, the Quaternary Period brought dramatic geo-environmental shifts, with cyclic interstadial sea transgressions and massive glacial erosion events delivering fossiliferous erratics with an array of primitive Paleozoic and later Mesozoic life-forms. Overall, the extraordinary paleontology of the SE Baltic area adds, within its geological context, to the European geoheritage and the world natural heritage. Full article

The Colombian Orinoquia was shaped within a tectonic and sedimentary framework linked to the uplift of the Andean cordilleras during the Oligocene–Miocene. This orogenic event generated two tectonic fronts and facilitated extensive fluvial sedimentation across a broad alluvial geosyncline. The present geomorphological configuration reflects the cumulative interaction of tectonic and erosional processes with Quaternary climatic dynamics, which together produced complex landscape assemblages characterized by plains with distinctive drainage patterns. To delineate and characterize geomorphological units, we employed multidimensional imagery and Machine Learning techniques within the Google Earth Engine platform. The classification model integrated dual polarizations of synthetic aperture radar (L-band) with key topographic variables including elevation, slope, aspect, convexity, and roughness. The analysis identified three major physiographic units: (i) the Foothills and the Floodplain, both dominated by fluvial environments; (ii) the High plains and Serranía de La Macarena (Macarena Mountain Range), where denudational processes predominate; and (iii) localized aeolian environments embedded within the Floodplain. These contrasting dynamics have generated a broad spectrum of landforms, ranging from terraces and alluvial fans in the Foothills to hills and other erosional features in La Macarena. The Floodplain, developed over a sedimentary depression, illustrates the combined action of fluvial and aeolian processes, whereas the High plains is characterized by rolling plains and peneplains formed through the uplift and erosion of Tertiary sediments. Such geomorphic heterogeneity underscores the interplay between tectonic activity, climatic forcing, and surface processes in shaping the Orinoquia landscape. The geomorphological classification using Random Forest demonstrated high effectiveness in discriminating units at a regional scale, with accuracy levels supported by confusion matrices and associated Kappa indices. Nevertheless, some degree of classificatory overlap was observed in fluvial environments, likely reflecting their transitional nature and complex sedimentary dynamics. Overall, this methodological approach enhances the objectivity of geomorphological analysis and establishes a replicable framework for assessing landform distribution in tropical sedimentary basins. Full article

Pincushion millipedes or bristly millipedes (Polyxenida) are common and widespread around the world, yet we still lack a proper understanding of the life of these elusive animals. This limit is even more expressed when looking at their extinct counterparts. Luckily, such fossils are usually preserved in amber, which has the potential to preserve unusual details. We investigated 44 new and 6 previously published fossils of Polyxenida, starting from the Cretaceous period (~100 mya) through the Eocene (~35 mya) and Oligocene/Miocene (~23 mya) to the present. As suggested by previous research, fossil bristly millipedes in the Cretaceous period shared the same lifestyle as their extant counterparts, including aggregation behaviour of both immatures and adults. In addition, we report newly observed behaviours for the fossils such as defecation, cohabitation between representatives of Polyxenidae and Synxenidae, and the possible role of frass and exuviae as defence. Altogether these findings improve our knowledge on the intricate life of bristly millipedes, revealing not only glimpses into their past but also clues and cues on their modern-day counterparts. Bristly millipedes are not just “simple” bark-dwellers; their communities and behaviours visibly testify to a rather complex lifestyle, which remained largely unchanged for 100 million years. Full article

A combination of fault and fracture analyses, paleostress reconstructions from calcite twins, and U-Pb dating of syn-kinematic calcite mineralization provides new insights into the Cretaceous–Tertiary tectonic evolution of the Provence fold-and-thrust belt. This approach helped unravel 90 million years of polyphase deformation in this belt, which represents the eastward continuation of the northern Pyrenees. Focusing on three main targets along an NNE-SSW transect oriented roughly parallel to the regional Pyrenean shortening (the southernmost Nerthe range, the Bimont Lake area, and the northern Rians syncline), we date a wide range of scales and natures of deformation structures such as stylolites, veins, mesoscale faults, and major thrust fault zones. The reconstructed long-lasting tectonic history includes (1) the Durancian uplift and related NNE-SSW extension (~110 to 90 Ma); (2) the ~N-S Pyrenean compression related to the convergence then collision between Eurasia and Iberia and the Corsica–Sardinia block (~80 to 34 Ma); the Oligocene E-W to WNW-ESE extension related to the West European Cenozoic Rift System (ECRIS) and the Oligo–Miocene NW-SE to NNW-SSE extension related to the Liguro-Provençal Rifting (LPR); and a middle-late (?) N-S to NW-SE Alpine compression. We show that the Pyrenean shortening in Provence occurred during two main phases, 81–69 Ma and 59–34 Ma, coeval with the inversion of the pre-Pyrenean rift and the main Pyrenean collision, separated by a tectonic quiescence as described in the Pyrenees. Together with the published literature, our U-Pb ages also support the overall northward (forelandward) in sequence propagation of Pyrenean shortening across Provence. Our U-Pb results further allow us to refine the interpretation of local and regional fracture sets and reveal unsuspected polyphase development of fractures sharing a common strike. Beyond regional implications, our study shows that sampling structures of various natures and scales for U-Pb geochronology is probably the most efficient strategy to encompass the entire time interval of deformation in fold-and-thrust belts. Full article

This study investigates the textural characteristics, mineral composition, and U–Pb ages of detrital zircon grains from the Playa Norte (PN) and Playa Tamiahua (PT) beach sediments along the Gulf of Mexico (GoM). The objective is to trace the sediment origin and to identify the possible environmental impacts in the coastal ecosystem. This work represents the first integrated provenance and geochemical analysis performed in these beaches, contributing to a broader regional sedimentological and geochronological database for the GoM. The results reveal distinct compositional and provenance signatures: PN sediments are rich in quartz (57.7% avg.), feldspars (15.7% avg.), and carbonate minerals (8.6% avg.), with zircon populations dominated by Proterozoic ages (~820–2200 Ma) and minor anthropogenic enrichment. In contrast, PT exhibits higher contents of quartz (78.6% avg.), andesine (9.6% avg.), and anorthite (8.5% avg.), with zircons mainly of Oligocene age (~32 Ma) and minimal contamination. Comparison with potential source regions indicates that PN sediments were derived primarily from the Sierra Madre Oriental, while PT sediments were originated from the Mesa Central and Eastern Mexican Alkaline Provinces. Overall, the findings demonstrate that, beyond littoral mixing and sediment recycling, the composition of GoM coastal sediments reflects the region’s complex tectono-sedimentary evolution and variable natural versus anthropogenic influences. PN is enriched in arsenic content, which is associated with agricultural activities and oil industries, while PT exhibits low values with no evidence of contamination. Meanwhile, Cr in PN suggests an anthropogenic input, which is linked to oil exploration activities in the GoM. Full article

Caenocentron was previously hypothesized to have originated in Mesoamerica from Xiphocentronidae ancestors that dispersed from Asia to the Americas during Eocene hyperthermal events. Under this scenario, the genus underwent early diversification in Mesoamerica and reached South America only during the late Miocene, following the uplift and connection of Central America. However, the discovery of Caenocentron roosevelt sp. nov. in savanna areas of the Brazilian Amazon significantly revises this understanding. A morphology-based parsimony analysis of Caenocentron and related xiphocentronids (26 taxa, 46 characters) recovered C. roosevelt sp. nov. as the sister species to all other members of the genus. This placement implies that Caenocentron was in South America far earlier than previously inferred, likely by the late Oligocene. Caenocentron roosevelt sp. nov. is distinguished by the following combination of characters: the absence of a setose ventral projection on the coxopodite (present in all other congeners), the presence of apical lobes on tergum IX (reduced in other species), paired digitate lobes beneath the posterior margin of tergum IX (otherwise found only in one Nearctic species), and a distinct line of robust setae along the apical projection of the coxopodite (absent in other species). Additionally, a key to the males of all 10 currently recognized species of Caenocentron is provided. Full article

The Evevpenta gold–silver epithermal deposit, belonging to an adularia–sericite or low-sulfidation type, is in the northern part of the Kamchatka Peninsula within the Oligocene–Quaternary Central Kamchatka volcanic belt. Variously native gold, silver, and Au–Ag chalcogenides, including calaverite, petzite, hessite, acanthite, uytenbogaardtite-petrovskaite, and naumannite, constitute its Au–Ag mineralization. Extensive fluid inclusion studies, involving fluid inclusion petrography, Raman spectroscopy, and microthermometry, revealed that quartz from gold-bearing adularia–quartz veins crystallized from low-salinity fluids (T ice melting from −0.1 to −3.3 °C) at moderate to low temperatures (140 to 364 °C). The mineralizing fluids consisted of Na, K, and Mg sulfate and bicarbonate-bearing aqueous solutions and low-density CO₂. The gold-bearing mineral assemblages were formed within narrower temperature ranges. The gold–telluride–quartz assemblage was deposited between 325 and 175 °C, while the telluride–sulfide–quartz formed between 219 and 258 °C. Possible influx of meteoric waters led to progressive cooling and a decrease in salinity from the early to late fluid generations during mineral deposition. Overall data on ore and associated with metasomatic alteration mineralogy indicate that the ore formation occurred under relatively reduced or neutral conditions from weakly acidic to near-neutral aqueous solutions, possessing relatively high sulfur and tellurium fugacity. Full article

The shallow-water delta-front reservoir in Member II of the Oligocene Dongying Formation (Ed2), located in an oilfield within the Bohai Bay Basin, is a large-scale composite sedimentary system dominated by subaqueous distributary channels and mouth bars. Within this system, reservoir sand bodies exhibit significant thickness, complex internal architecture, poor injection–production correspondence during development, and an ambiguous understanding of remaining oil distribution. To enhance late-stage development efficiency, it is imperative to deepen the understanding of the genesis and evolution of the subaqueous distributary channel–mouth bar system, analyze the internal reservoir architecture, and clarify sand body connectivity relationships. Based on sedimentary physical modeling experiments, integrated with core, well logging, and seismic data, this study systematically reveals the architectural characteristics and spatial stacking patterns of the mouth bar reservoirs using Miall’s architectural element analysis method. The results indicate that the study area is dominated by sand-rich, shallow-water delta front deposits, which display a predominantly coarsening-upward character. The main reservoir units are mouth bar sand bodies (accounting for 30%), with a vertical stacking thickness ranging from 3 to 20 m, and they exhibit lobate distribution patterns in plan view. Sedimentary physical modeling reveals the formation mechanism and stacking patterns of these sand-rich, thick sand bodies. Upon entering the lake, the main distributary channel unloads its sediment, forming accretionary bodies. The main channel then bifurcates, and a new main channel forms in the subsequent unit, which transports sediment away and initiates a new phase of deposition. Multi-phase deposition ultimately builds large-scale lobate complexes composed of channel–mouth bar assemblages. These complexes exhibit internal architectural styles, including channel–channel splicing, channel–bar splicing, and bar–bar splicing. Reservoir architecture analysis demonstrates that an individual distributary channel governs the formation of an individual lobe, whereas multiple distributary channels control the development of composite lobes. These lobes are laterally spliced and vertically superimposed, exhibiting a multi-phase progradational stacking pattern. Dynamic production data analysis validates the reliability of this reservoir architecture classification. This research elucidates the genetic mechanisms of thick sand bodies in delta fronts and establishes a region-specific reservoir architecture model. This study clarifies the spatial distribution of mudstone interlayers and preferential flow pathways within the composite sand bodies. It provides a geological basis for optimizing injection–production strategies and targeting residual oil during the ultra-high water-cut stage. The findings offer critical guidance for the efficient development of shallow-water delta front reservoirs. Full article

Bedding-parallel fractures represent a crucial flow-path network in shale oil reservoirs, yet their timing of opening and driving mechanisms remain subjects of long-standing debate. This study investigates the origin and opening mechanisms of bedding-parallel fractures within the Paleogene Funing shale oil reservoir of the Huazhuang area, Subei Basin, eastern China. A combination of petrography, fluid-inclusion analysis, PVTx paleo-pressure modeling, hydrocarbon generation history modeling, and reflectance measurements was employed. The results reveal the presence of abundant oil inclusions and bitumen within the bedding-parallel veins, indicating that the initiation of fracture was essentially synchronous with the oil emplacement. The studied Funing shale, with vitrinite reflectance values of 0.85% to 1.04%, is mature, identifying it as an effective oil-prone source rock. Thermal maturity of bitumen is comparable to that of the host shale, suggesting a local oil source. Homogenization temperatures (T_h) of coeval aqueous inclusions record fracture opening temperatures of approximately 100–150 °C, consistent with oil-window conditions. By integrating T_h data with burial history modeling, the timing of fracture formation and coeval oil injection is constrained to the peak period of local hydrocarbon generation, rather than the Oligocene Sanduo tectonic event. This indicates that fracture opening was primarily associated with hydrocarbon generation rather than tectonic compression. Petroleum-inclusion thermodynamic modeling demonstrates that the bedding-parallel fracture opening occurred under moderate to strong overpressure conditions, with calculated paleo-pressure coefficients of ~1.35–2.36. This finding provides direct paleo-pressure evidence supporting the mechanism of bedding-parallel fracture opening driven by fluid overpressure created during oil generation. These oil-bearing, overpressured fluids facilitated the initial opening and subsequent propagation of fractures along the bedding planes of shales. Concurrently, the precipitation of the calcite veins may have been triggered by pressure drop associated with the expulsion of some coexisting aqueous fluids. This study provides evidence addressing the debated mechanisms of bedding-parallel fracture opening in organic-rich shales, highlighting the critical role of oil generation-induced overpressure. Full article

Synthesis of published and new data from the Govorov and Kocebu guyots provide geochemical and chronostratigraphic constraints on hydrogenetic cobalt-rich Fe-Mn crusts from the Western Pacific Magellan Seamount Trail (MST). The history of the crusts began about 65–60 Ma, when the relict layer R was deposited in the Campanian—Maastrichtian and Late Paleocene along the shores of guyots. The growth of the old-generation crusts continued in the Late Paleocene—Early Eocene (Layer I-1) and in the Middle—Late Eocene (Layer I-2) in a shallow-water shelf environment. The younger layers formed in the Late Oligocene—Early Miocene (Layer I-2b), Miocene (Layer II), and Pliocene—Pleistocene (Layer III) at depths about the present sea level. The precipitation of Fe and Mn oxyhydroxides from seawater was interrupted by several times, with the longest gap from 38 to 26.5 Ma between the old (R, I-1, and I-2) and young (I-2b, II, and III) layers. Fe and Mn oxyhydroxides in the crusts were affected by two global events of phosphogenesis in the Pacific: Late Eocene—Early Oligocene, from 43 to 39 Ma (Layers R, I-1, I-2) and Late Oligocene—Early Miocene, from 27 to 21 Ma (Layer I-2b). The trace element patterns in different layers of the Co-rich Fe-Mn crusts are grouped using factor analysis of principal components (varimax raw) into four factors: (1) +(all REEs except Ce and La); (2) +(Ce, La, Ba, Mo, Sr, Pb); (3) +(Zr, Hf, Nb, Rb, As)/-Pb; (4) +(U, Th, Co, As, Sb, W)/-Y. The factor score diagrams highlight fields which are especially contrasting for Layers I-1, I-2, and II + III according to factors 2 and 4. Consistent REE and Y variations in Layers I-2b → II → III of the crust from Pallada Guyot correlate with gradual ocean deepening between the Late Oligocene—Early Miocene and Present when the MST guyots were submerging. Large variations in the trace element contents across coeval layers may be due to the hydrodynamics of currents on the guyot surfaces. Furthermore, the geochemistry of the crusts bears effects from repeated episodes of Cenozoic volcanism in the MST region of the Pacific Plate. Higher contents of Nb, Zr, As, Sb, and W in the younger layers II and III may result from large-scale volcanism, including Miocene eruptions of petit-spot volcanoes. Full article

White-lipped tree frogs, Polypedates braueri, are currently included in the list of terrestrial wildlife with important ecological, scientific, and social value in China. Understanding the structure and characteristics of the mitochondrial genome provides essential information for resource conservation and phylogenetic analyses of P. braueri. While the complete mitochondrial genomes serve as important molecular markers for phylogenetic and genetic studies, the mitochondrial genome of P. braueri has received little attention. In this paper, we analyzed the characterization of the mitochondrial genome of P. braueri and investigated the phylogenetic relationships of Rhacophoridae. The complete mitochondrial genome of P. braueri was 20,254 bp in length, containing thirty-six genes (twelve protein-coding genes (PCGs), two ribosomal RNA genes (rRNAs), twenty-two transfer RNA genes (tRNAs)), three non-coding regions for the origin of light strand (O_L), and two control regions (CR). There were six overlapping regions and seventeen intergenic spacer regions in the mitogenome. The mitogenome also showed a bias towards A + T content (61.87%) and had negative AT-skew (−0.039) and GC-skew (−0.209). All the PCGs employed the ATG, ATA, or ATT as the start codon and TAA, TAG, AGG, or single T as the stop codon. Additionally, all of the tRNAs displayed a typical cloverleaf secondary structure, except trnS1, which lacked the D arm. The phylogenetic analysis, based on the maximum likelihood (ML) and Bayesian inference (BI) methods, revealed that Rhacophoridae could be classified into four monophyletic genera. The phylogenetic status of P. braueri was closely related to that of Polypedates megacephalus and Polypedates leucomystax. Additionally, selective pressure analysis suggested that COX1 and ND1 were highly efficient for discriminating closely related species in the genus Polypedates, while ND4L was the most appropriate marker for population-level genetic analyses. The diversification of the Polypedates commenced during the Late Oligocene and extended into the Miocene. The present study provides valuable genomic information on P. braueri and new insights into the phylogenetic relationships of Rhacophoridae. Full article

Warsaw’s Oligocene Groundwater Intakes (OGIs) represent a unique but overlooked component of the city’s Urban Water System (UWS), originally developed to supplement municipal supply. This study investigates whether the existing OGI network can still contribute to Urban Water Resilience (UWR) under contemporary conditions. A mixed-methods approach was applied, combining archival research, geospatial analysis of 89 public intakes, and on-site assessments of selected facilities in the Praga Północ and Praga Południe districts. The results show that while OGIs form a decentralized and technically functional system with high resilience potential, their spatial coverage is uneven, their public use has sharply declined, and management is fragmented across multiple entities. Despite this marginalization, OGIs retain strategic value as an emergency safeguard and could be revitalized as part of Warsaw’s resilience strategy. Full article