Search Results (60)

Pre-Cenomanian Nubia sandstone is recognized one of the most prolific reservoirs in the Gulf of Suez, Egypt. Accurately determining its reservoir rock type (RRT) is crucial for reservoir characterization and modeling, especially when the reservoir is extremely heterogeneous. This study addresses the critical challenge of characterization in extremely heterogeneous reservoirs by introducing a novel integrated workflow that bridges the gap between traditional sedimentological geology, traditional x-y approaches, and advanced machine learning methods. To achieve this, this study utilizes sedimentological core description, routine core analysis, and conventional well log data from two wells (well A and well B) located in the southern Gulf of Suez, Egypt. The results demonstrate that the complete Nubia interval in the southern Gulf of Suez can be separated into seven distinct lithofacies (LF1–LF7). The first six lithofacies comprise various types of sandstone, while the seventh is composed of shale. The traditional techniques used to predict the RRTs show that the normalized reservoir quality index (NRQI) was the most effective method for predicting the Nubia rock types. The machine learning K–means clustering and self-organizing map (SOM) techniques utilizing raw log data and principal component analysis (PCA) can properly predict the Nubia reservoir rock types. The reservoir quality ranges from poor to very good; well A is dominated by moderate reservoir quality, while well B exhibits predominantly very good reservoir quality. This discernible difference in reservoir quality between the two wells is probably attributed to post-depositional diagenetic processes and variations in sandstone texture. Full article

Mesozoic tree ferns related to the extant Loxsomopsis, a relict and taxonomically isolated genus endemic to tropical South America, are exceedingly rare, making it difficult to trace its origin and evolution. Here, we describe a mid-Cretaceous fossil attributable to Loxsomopsis, Loxsomopsis minor sp. nov., based on two fertile pinnules preserved in Myanmar amber. The new species is assigned to the extant genus based on a suite of diagnostic features, including pinnate fertile segments with short lobes, marginal paraphysate sori, narrowly cyathiform to urceolate indusia, columnar and exserted receptacles, oblique sporangial annuli, and trilete spores. This discovery extends the fossil record of Loxsomopsis back to the Albian–Cenomanian and provides new evidence that the lineage—now restricted to tropical South America—was once more widespread. The occurrence of Loxsomopsis in the Myanmar amber biota is consistent with a Gondwanan affinity for this mid-Cretaceous forest ecosystem and suggests that the genus may have likely originated prior to the breakup of Pangaea. Full article

Four new genera with four new species and one new combination of Mantispidae are described from the Upper Cretaceous (Cenomanian) amber of northern Myanmar: Tholomantispa quinata gen. et sp. nov., Tholomantispa zhangzhiqiae comb. nov., Heteromantispa polytricha gen. et sp. nov., Trimantispa poseidoni gen. et sp. nov., and Tribelomantispa yangjiani gen. et sp. nov. These species exhibit unique morphological characteristics, such as scale-like setae on forewings, unique male genitalia structure, and specialized raptorial foreleg, which provide valuable information for the study of character transformation and adaptive evolution within Mantispidae. The scale-like setae on the forewings suggests potential secondary loss in extant taxa. Similarly, the documentation of processes on the forefemur across multiple genera introduces a novel morphological trait within Mantispidae, enriching our knowledge of their structural diversity. Full article

This study re-evaluates the hydrogeological framework of the Bohemian Cretaceous Basin (Czech Republic), where preliminary surveys unexpectedly identified old groundwater in several springs and abstraction wells. Traditional distinction into a Cenomanian (A) and a single Turonian (C) aquifer failed to explain the observed hydraulic head discrepancies and the occurrence of old groundwater. By integrating the spatial correlations of hundreds of well logs with hydraulic head data, environmental tracers (chemistry, ²H, ³H, ¹³C, ¹⁴C, ¹⁸O, ³⁹Ar, ⁸⁵Kr, CFCs, SF₆, and noble gases), and field measurements, we objectively delineated the hydrostratigraphic architecture of the basin. The results demonstrate three distinct aquifers (A, Ca, and Cb), challenging long-standing interpretations. Several flow systems were identified, with mean residence times of the old water exceeding 300 years. The hydrogeochemical and isotopic evidence confirmed mixing of Holocene groundwater between Ca and Cb aquifers while excluding Last Glacial Period fossil groundwater that is typical of the A aquifer. These findings highlight the necessity of a multi-proxy approach to validate conceptual models in seemingly “well-understood” regions. The newly characterized subdivision of Turonian aquifers is critical for protecting old groundwater resources, optimizing the design of geothermal and water supply wells to prevent hydraulic short-circuiting, and identifying previously unrecognized groundwater resources currently discharging to the Jizera River. Full article

The Cretaceous dinosaur record from Normandy, in NW France, is reviewed. It includes several enigmatic specimens that were briefly mentioned in short notes published during the 19th and 20th centuries that have since then been destroyed in World War II or lost. Since they were neither described in detail nor illustrated, their identification must remain uncertain, but some may have been ankylosaur remains, while another specimen may have belonged to a bird or a non-avian theropod. Specimens that were properly described and are kept in museums in Normandy come from Albian and Cenomanian horizons in the coastal cliffs of Seine-Maritime. The Albian record, from Cape La Hève (Le Havre) includes an incomplete titanosaurian sauropod skeleton, described as Normanniasaurus genceyi, and an isolated caudal vertebra from the same provenance, probably belonging to that taxon. The Cenomanian record is limited to a group of bones and a tooth of the furileusaurian abelisaurid theropod Caletodraco cottardi from the glauconitic Chalk at Saint-Jouin-Bruneval. All these specimens come from marine sediments and are in all likelihood derived from floating carcasses that drifted over a fairly long distance from an emergent land area corresponding to the Armorican massif in the west. Although scanty, the record from Normandy sheds some light on the poorly known dinosaurs that inhabited north-western Europe during the middle part of the Cretaceous, some of which apparently had Gondwanan affinities. Full article

A new species of pectinid bivalve, Syncyclonema goyi sp. nov., is described in honour of Professor Antonio Goy, one of the leading stratigraphers who shaped Mesozoic studies in Iberia over the past half century. It represents one of the smaller fossil scallops currently known from the Upper Cretaceous of Europe, alongside a few boreal species previously assigned to the family Entoliidae. The type specimens have orbicular valves, almost smooth, with unequal auricles. The right valve is more convex and bears a well-marked paleal sinus. The sculpture of the shell is weak, exhibiting concentric growth lines and lamellae. However, nearly 90 very small, uniform radial striae are discernible beneath the outer shell layer. This species is frequent in open marine, fine-grained, inner shelf facies of the Tethyan West Portuguese Carbonate Platform, near the main localities of Coimbra, Tentúgal, and Condeixa-a-Nova, in the Baixo Mondego region of West Portugal. It mostly occurs in the upper Cenomanian beds of the Trouxemil Formation, with Euomphaloceras septemseriatum and Vascoceratidae ammonites. Full article

The middle–late Cenomanian paleontological area of Algora represents the main concentration of vertebrate remains from the basal Late Cretaceous for southwestern Europe. An unpublished macro-plant assemblage is studied here, being recognized as composed of ferns, conifers, and various other types of gymnosperms and angiosperms, constituting the first well-defined reference of a Cenomanian macro-flora in Spain. Comparison of this assemblage with other coeval ones from the western Tethys region suggests a possible influence of both Central European Laurasian plant elements and those from northern Gondwana (originating in North Africa and the Middle East) in this area of the Iberian Plate, a key region for understanding the dispersal of fauna and flora during the early Late Cretaceous. Full article

Vertebrate remains from the Upper Cretaceous of Portugal have been studied for more than 140 years, beginning with the pioneering work of the Geological Commissions and early vertebrate specialists. The Cenomanian of Portugal occupies a key position in understanding vertebrate assemblages from the south-western European Late Cretaceous archipelago. Recent discoveries in the Cenomanian of the onshore northern sector of the Portuguese West Iberian Margin have revealed two new genera of Squamata and Crocodylomorpha, as well as extended biogeographical ranges for groups such as Obaichthyidae. Although Campanian–Maastrichtian fossils are limited to the northern sector, they provide valuable insights into the composition and evolution of western Iberian vertebrate faunas, including significant remains of small dinosaurs and mammals, and the westernmost European occurrences of Pycnodontiformes, Holostei, Elopiformes, Amphibia, Testudines, Squamata, and Crocodylomorpha. The Upper Cretaceous of the Portuguese onshore northern sector of the West Iberian Margin has yielded six vertebrate holotypes, four lectotypes, and syntypes though much material remains undescribed or in need of revision. Identifying additional fossil sites is essential to further expand the dataset. This contribution integrates historical and current knowledge and highlights key priorities for future research. Full article

A pair of connected flowers preserved in a mid-Cretaceous (early Cenomanian) Myanmar amber is described and named Antiquigemina pilosa Wang and Li gen. et sp. nov. Antiquigemina pilosa has bisexual flowers with a calyx of at least 3 sepals, a corolla of 5 petals, a whorl of at least 4 stamens and a tricarpellate pistil with a semi-inferior ovary. The differences in style divergence and calyx presence between paired flowers indicate different developmental stages. Considering that differentiated calyx and corolla and pentamery of corolla are features frequently observed in core eudicots, we propose treating Antiquigemina pilosa, which has a pentamerous perianth and differentiated sepals and petals, as an earlier representative of core eudicots. Antiquigemina pilosa provides first-hand evidence for the early diversification of core eudicots. Full article

The Cenomanian Bahariya Formation exposed at Gebel El Dist in the Western Desert of Egypt provides valuable surface analogues for evaluating the reservoir quality of subsurface Bahariya sandstones. The formation was analyzed using 27 oriented samples and 91 core plugs from quartz arenite (QA) and quartz wacke (QW) facies. Analyses included XRD, petrography, SEM, helium porosity–permeability, and capillary tests, as well as measurements of pore-throat radii (R) at 35% and 36% mercury saturation. X-ray diffraction analyses reveal a heterogeneous mineral composition dominated by quartz, feldspars, dolomite, pyrite, siderite, goethite, hematite, clay minerals, glauconite, and gypsum. QA displays higher porosity and permeability than QW, along with larger pore radii, and lower specific surface area per unit pore volume (Spv) and per unit grain volume (Sgv). Multivariate regression equations, specific to each facies, were developed to convert standardized XRD mineral percentages directly into pore-system and flow attributes (ϕ, k, r, Spv, Sgv, R35, R36), quantifying capillary-based recovery contrasts between facies. Across both facies, regressions linking mineralogy to ϕ, k, r, Spv, Sgv, R35, and R36 are strong (R² = 0.78–1.00). The established predictive equations provide a low-cost method to estimate reservoir quality from mineralogy alone, enabling rapid screening of Cenomanian Bahariya analogues and similar clastic reservoirs where core data are limited. Full article

In the context of the current global transition toward low-carbon energy, the issue of $C{O}_2$ utilization has become increasingly important. One of the most promising natural targets for $C{O}_2$ sequestration is the terrigenous sedimentary formations found in oil, gas, and coal basins. It is generally assumed that $C{O}_2$ injected into such formations can be stored indefinitely in a stable form. However, the dissolution of $C{O}_2$ into subsurface water leads to a reduction in pH, which may cause partial dissolution of the host formation, altering the structure of the subsurface in the injection zone. This process is relatively slow, potentially unfolding over decades or even centuries, and its long-term consequences require careful investigation through mathematical modeling. The geological formation is treated as a partially soluble porous medium, where the dissolution rate is governed by surface chemical reactions occurring at the pore boundaries. In this study, we present an applied mathematical model that captures the coupled processes of mass transport, surface chemical reactions, and the resulting microscopic changes in the pore structure of the formation. To ensure the model remains grounded in realistic geological conditions, we based it on exploration data characterizing the composition and microstructure of the pore space typical of the Cenomanian suite in northern Western Siberia. The model incorporates the dominant geochemical reactions involving calcium carbonate (calcite, $CaC{O}_3$), characteristic of Cenomanian reservoir rocks. It describes the dissolution of $C{O}_2$ in the pore fluid and the associated evolution of ion concentrations, specifically $H^{+}$, $C{a}^{2+}$, and $HC{O}_3^{-}$. The input parameters are derived from experimental data. While the model focuses on calcite-based formations, the algorithm can be adapted to other mineralogies with appropriate modifications to the reaction terms. The simulation domain is defined as a cubic region with a side length of 1 $\mathsf{\mu }$m, representing a fragment of the geological formation with a porosity of 0.33. The pore space is initially filled with a mixture of liquid $C{O}_2$ and water at known saturation levels. The mathematical framework consists of a system of diffusion–reaction equations describing the dissolution of $C{O}_2$ in water and the subsequent mineral dissolution, coupled with a model for surface evolution of the solid phase. This model enables calculation of surface reaction rates within the porous medium and estimates the timescales over which significant changes in pore structure may occur, depending on the relative saturations of water and liquid $C{O}_2$. Full article

The Eastern Carpathians are thrust to the east and north over their Eastern European foreland, tectonically covering it over an area several hundred kilometers across. Information about the nature of the underthrust part of the Carpathian foreland can be obtained from the rock fragments preserved in the sedimentary successions of the Carpathian fold and thrust belt, specifically in the Outer Dacides and the Moldavides. Fragments of felsic rocks occurring within the sedimentary units of the Upper Cretaceous successions of the Moldavides have long been attributed to the Cuman Cordillera—an intrabasinal ridge in the Eastern Outer Carpathians. This work is the first complex geochemical and geochronological study on the exotic igneous clasts of the Cuman Cordillera. Igneous clasts from the southern part of the Moldavides (Variegated clay nappe/formation) are investigated here. They include mainly granites and rhyolites. Phaneritic rocks are composed of cumulus plagioclase, albite, amphibole and biotite, and intercumulus quartz and potassium feldspar, with apatite, magnetite, sphene, and zircon as main accessories, while the porphyritic rocks have a mineral assemblage similar to that mentioned above, displayed in a porphyritic texture with a usually crystallized groundmass. SHRIMP U-Pb zircon dating indicated the 583–597 Ma age interval for magma crystallization. Based on calcareous nannofossils, the depositional age of the investigated igneous clasts is Cenomanian to Maastrichtian, implying that the Cuman Cordillera was an emerged piece of land, herein an active source of sediments in the flysch basin for at least 40 Ma, from the Early Cretaceous (Aptian) to the Late Cretaceous (Maastrichtian). The intrusive and subvolcanic rocks show similar trends for trace and major elements, evincing their comagmatic nature. The enrichment in LILE and LREE relative to HFSE and HREE, as well as the element anomalies (e.g., negative Nb, Ta, and Eu and positive Rb, Ba, K, and Pb) suggest a convergent continental plate margin tectonic setting. Mineral chemistry suggests magma crystallization in relatively oxic conditions (magnetite series), during ascent within a depth of 15 km to 5 km. The igneous rocks attributed to the Cuman ridge display compositional and geochronological features similar to Brno and Thaya batholiths in the Brunovistulian terrane, which could be a piece of the Carpathian foreland not covered by the Tertiary thrusts. Our data confirm the non-Carpathian origin of the igneous clasts, revealing a Neoproterozoic history of the Carpathian foreland units, which include a Cadomian/Pan-African continental arc, exposed mainly during the Late Cretaceous as an intrabasinal island of the Alpine Tethys, traditionally known as the Cuman Cordillera. Full article

Pore pressure prediction gives drillers an early warning of potential oil and gas kicks, enabling them to adjust mud weight pre-emptively. A kick causes a delay in drilling practices, blowouts, and jeopardization of the wells. Changes in pore pressure affect the type of fluid contact in the reservoir. This study predicted the pore pressure and determined fluid contacts within the Lower Cretaceous and early Upper Cretaceous (Barremian to early Cenomanian) sandstone reservoirs of the Bredasdorp Basin using well logs and repeat formation test (RFT) data from three wells: E-BK1, E-AJ1, and E-CB1. Eaton’s method of developing a depth-dependent Normal Compact Trend (NCT), using resistivity and sonic wireline logs, as well as other methods including the Mathews and Kelly, Baker and Wood, and Modified Eaton and Bowers methods, were employed for pore pressure prediction. Eaton’s method provided reliable pore pressure results in all the wells when compared to alternative methods in this study. Overburden gradient and predicted pore pressures ranged from 1.84 gm/cc to 2.07 gm/cc and from 3563.74 psi to 4310.06 psi, respectively. Eaton’s resistivity and density/neutron log method results indicated normal pressure in E-BK1 and E-AJ1, as well as overpressured zones in E-AJ1. However, in E-CB1, the results showed only overpressured zones. The E-AJ1 significant overpressures were from 2685 m to 2716 m and from 2716 m to 2735 m in the pores exceeding 7991.54 psi. Gas–water contact (GOC) was encountered at 2967.5 m in E-BK1, while oil–gas contact (OGC) was at 2523 m in E-CB1, and gas–oil and oil–water contacts (GOC and OWC) were at 2699 m and 2723 m, respectively, in E-AJ1. In E-CB1, oil–water contact (OWC) was at 2528.5 m. Fluid contacts observed from the well logs and RFT data were in close agreement in E-AJ1, whereas there was no agreement in E-CB1 because the well log observations showed a shallower depth compared to RFT data with a difference of 5.5 m. This study illustrated the significance of an integrated approach to predicting fluid contacts and pore pressure within the reservoirs by showing that fluid contacts associated with overpressures were gas–water and oil–water contacts. In contrast, gas–oil contact was associated with normal pressure and under pressure. Full article

Carbonate sedimentation was spread widely on the southern margin of the Neo-Tethys Ocean in the mid-Cretaceous. New information from four exploration wells sheds light on the peculiarities of the Sarvak Formation (late Albian–Cenomanian) at the narrow transition between the Dezful Embayment and Coastal Fars in the southern Zagros. The solution of this task was necessary to understand whether the fragmentation of the Zagros Basin into domains affected the carbonate platform development. The methods included the analyses of carbonate microfacies, paleoecological patterns of foraminifera, and depositional environments. The results of this study show the existence of ten carbonate microfacies. Prevailing wackestones and packstones with a muddy matrix and absent carbonate buildups imply the development of a large carbonate ramp. Paleoecological interpretations based chiefly on foraminifers prove this model. For instance, the presence of oligosteginids signifies shallower parts of the platform, and the cooccurrence of planktonic foraminifera and oligosteginids suggests a deeper environment. The stratigraphical distribution of the established microfacies in the wells indicates three cycles in the evolution of this platform. The third of these cycles marked an abrupt deepening episode because it includes microfacies suggesting the relatively deeper environments. Three maximum flooding surfaces established in the study area are common to the Arabian plate. The discussion of the results suggests that the influence of the Kazerun fault on the carbonate ramp in the Cenomanian is uncertain. Neither eustatic nor tectonic factors of the carbonate platform development can be excluded. Conclusively, it appears that the studied Cenomanian carbonate ramp was integral at the transition between the Dezful Embayment and Coastal Fars. Full article

Groundwater resources are becoming increasingly scarce, especially in arid regions of western Kazakhstan. By 2070, the domestic and drinking water demands will increase from 640 to 901 thousand m³/day. This deficiency may be overcome by utilizing the Zhem Artesian Basin’s Cretaceous Albian–Cenomanian aquifer complex. The hydrodynamic interactions between the 123 known aquifer segments and recharge zones of these promising, exploitable, high-quality groundwater sources are unclear. While MODFLOW is a nominal platform for groundwater flow assessment, which is usually used for the simulation of simple hydrological scenarios, in this study, integrating several different scales and functional modules over a GIS platform enabled delineation and the forecast of this multi-layer aquifer complex. The MODFLOW simulation assessed exploitable groundwater resources and reservoir interactions, enabling the establishment of a simultaneous operation to the Zhem aquifer complex and its neighboring reservoirs. The model suggests that the total exploitable groundwater resources may grow to 629.4 thousand m³/day during the next 50 years. The simultaneous drawdown model suggests a water level decrease of up to 80 m at the end of this period, which will cause a river flow reduction of approximately 6% of the average long-term river flow. Thus, the assessed exploitable groundwater resources will cover more than 70% of the future regional water demand. The mathematical model developed may be used for monitoring and forecasting groundwater head and water balance changes and may be applied to attain a more detailed groundwater resource transfer scheme with economic criteria. Full article