Geothermal energy is one of the most viable sources of renewable heat. However, the potential risk of induced seismicity associated with geothermal operations may slow down the growth of the geothermal sector. Previous research has led to significant progress in understanding fluid-injection-induced seismicity in geothermal reservoirs. However, an in-depth assessment of thermal effects on the seismic risk was generally considered to be of secondary importance. This study aims to investigate the relative influence of temperature and key geological and operational parameters on the slip tendency of pre-existing faults. This is done through coupled thermo-hydro-mechanical simulations of the injection and production processes in synthetic geothermal reservoir models of the most utilized and potentially exploitable Dutch geothermal reservoir formations: Slochteren sandstone, Delft sandstone and Dinantian limestone.

In our study, changes in the slip tendency of a fault can largely be attributed to thermo-elastic effects, which confirms the findings of recent studies linking thermal stresses to induced seismicity. While the direct pore pressure effect on slip tendency tends to dominate over the early phase of the operations, once pore pressure equilibrium is established in a doublet system, it is the additional stress change associated with the growing cold-water front around the injection well that has the greatest influence. Therefore, the most significant increase in the slip tendency was observed when this low-temperature front reached the fault zone. The distance between an injection well and a pre-existing fault thus plays a pivotal role in determining the mechanical stability of a fault. A careful selection of a suitable target formation together with an appropriate planning of the operational parameters is also crucial to mitigate the risk of induced seismicity. Besides the well-known relevance of the in situ stress field and local fault geometry, rock-mechanical properties and operation conditions exert a major influence on induced stress changes and therefore on the fault (re)activation potential during geothermal operations.

The historically important mosasaur fossil (known as ‘le grand animal fossile des carrières de Maestricht’) has been known as Mosasaurus hoffmanni for almost two centuries now. Recently, it has been proposed to amend the spelling of the species name, by adding a second ‘i’ to the species epithet. We present historical evidence to the contrary, and recommend, following article 33.2.3.1 of the ICZN, to retain the specific epithet hoffmanni.

Brachiopods from the lower upper Maastrichtian (Upper Cretaceous) white chalk succession exposed at Chełm (eastern Poland) comprise Lingula cretacea, Isocrania costata, Cryptoporella antiqua, Cretirhynchia sp., Neoliothyrina sp., Carneithyris sp., Terebratulina chrysalis, T. faujasi, T. longicollis, Terebratulina spp., Gisilina sp., Bronnothyris bronni, Magas chitoniformis, Leptothyrellopsis polonicus and ?Aemula sp. This assemblage is relatively poor in terms of taxonomic diversity and specimen abundance and is dominated by stratigraphically long-ranging species. It is best comparable to that from the micromorphic brachiopod Rugia tenuicostata–Meonia semiglobularis Zone as distinguished in the white chalk successions of Denmark and northern Germany, although this zone is usually placed in the upper lower Maastrichtian. The Chełm succession represents a relatively deep-water and ‘benthos-poor’ variety of white chalk deposited in the Boreal Chalk Sea of Europe. The brachiopod assemblage studied is typical of such a habitat, having been controlled largely by the low availability of minute skeletal substrates suitable for brachiopod settlement.

The late Pleistocene to Holocene subaerial pyroclastic deposits of the Quill stratovolcano on the Caribbean island of St Eustatius form seven stratigraphic divisions. New radiocarbon ages of charcoal are presented for the second, third and seventh divisions in order to better constrain the Quill’s eruption history. Three samples from the same layer of Division 2 at two localities on the northeast coast yield ages of 18,020 ± 40 (1σ), 18,310 ± 45 and 18,490 ± 45 14C yr BP (∼19,800–20,600 yr cal BC). These are considerably younger (∼4400 yr) than a previously published result for this division. A single sample of Division 3 gave an age of 8090 14C yr BP (∼7100 yr cal BC) and overlaps with previously published 14C ages for this division. A charred root in the pyroclastic unit deposited by the last eruption of the Quill (Division 7) gave an age of 919 14C yr BP (∼1100–1200 yr cal AD). This result is ∼600 years younger than a previously published age, and its origin is attributed to human activity. The timing of the last eruption of the Quill therefore remains poorly constrained but is older than 600 AD. Terrestrial gastropods found in paleosols and organic material found in small streams that developed in Division 3 indicate that Division 4 must be younger than 6100 ± 500 yr cal BC. The oxygen and carbon isotope composition of the terrestrial gastropods derived from Division 3 paleosols indicates that the C4 and CAM-type vegetation was dominant and that the climate subsequently changed to wetter conditions. The minimum eruption frequency for the Quill volcano is one eruption every ∼1400 years during the past 22,000 years. This eruption frequency of the Quill volcano is of the same order of magnitude as other recent northern Lesser Antilles volcanoes, Soufrière Hills (Montserrat, ∼5000 years) and Mt Liamuiga (St. Kitts, ∼2500 years).

The Late Cretaceous was a time of blossoming teleost diversification that came to a sudden restriction and partial termination during the extinction event at the Cretaceous–Paleogene (K/Pg) boundary. Among the dominant and diverse Late Cretaceous teleost groups prior to the K/Pg boundary event were certain pelagic Aulopiformes (e.g., Ichthyotringoidei and Enchodontoidei) and a large variety of basal Acanthomorpha whose relationships are difficult to determine. The skeletal record diminishes during the late Campanian and is low in the Maastrichtian and Paleocene, constituting the so-called ‘Patterson’s Gap’. Recent studies of fossil otoliths, however, have significantly increased the number of taxa recognised for this time inerval, but most of the putative extinct forms lack adequate calibration with otoliths found in situ in articulated skeletons. However, the otolith assemblages do confirm the presence of great morphological diversity among Aulopiformes and Acanthomorpha incertae sedis that became extinct at the K/Pg boundary. In the present review, we elucidate the effect of the K/Pg boundary from an otolith perspective and categorise extinct lineages and survivors. It is interesting to recognise that several of the surviving lineages are represented by groups that probably originated during the Late Cretaceous but were not particularly common up to the K/Pg boundary and began to expand rapidly and diversify during the early Paleogene. Such lineages probably took advantage to populate void ecospace that may have opened following the extirpation of previously dominant lineages. During the early Paleogene, the otolith record shows that the Ophidiiformes and perciforms s. lat. were the ones that diversified the most rapidly and became the most abundant, and in certain areas associated with the Gadiformes.

The lower Maastrichtian (Upper Cretaceous) section at Nahoryany, south of Lviv (western Ukraine), has been known as a rich source of fossils since 1843. However, the section is not available since a long time ago and fossils collected from it can only be studied in museum collections. In the present paper, ammonites of the scaphitid genus Hoploscaphites are studied based on Nahoryany material, comprising Hoploscaphites pumilus, H. constrictus and H. sp. Specimens from Nahoryany in museum collections lack data on their provenance level within the section so it cannot be determined whether or not they occurred together or formed a succession; data on inoceramid bivalves indicate the presence of two successive zones at Nahoryany. Some specimens from Nahoryany here referred to as H. pumilus are similar to the controversial H. constrictus anterior from the lower Maastrichtian of Poland. This morphology suggests an ancestor–descendant relationship between H. pumilus and H. constrictus, a common species once considered as an informal index for the Boreal Maastrichtian in Europe. The inferred evolutionary transition from H. pumilus to H. constrictus was towards a less robust, recoiled shell, which would have enhanced the horizontal swimming ability and manoeuvrability of these cephalopods. Recoiling trends occurred in several lineages of Late Cretaceous scaphitids.

The comprehensive overview of Neogene lithostratigraphy in the eastern Netherlands dates back to the mid-1970s. In the present study, continuous gamma-ray logs and in situ sediment core samples from six boreholes in the area allowed palynological and mollusc analyses and wireline log-based correlation. These investigations were aimed at updating and revising the existing Neogene lithostratigraphy within the Stratigraphic Nomenclature of the Netherlands by integrating litho-, bio-, and sequence-stratigraphic approaches. The analytical results yielded the establishment of new holo- and lectostratotype sections, together with cross-border interregional correlation. The lithostratigraphic revision resulted in the modified definition of the Aalten, Eibergen and Delden members and the definition of two new proposed members: the Dale and Doetinchem members. The Ticheloven bed, removed in earlier studies, is proposed to be reinstated, and the Stemerdink Bed is upgraded in its hierarchical status to the Stemerdink member. All lithostratigraphic units are included in the present Miocene subdivision of the Groote Heide and Diessen formations, which include three recognisable unconformities: the Early-Miocene Unconformity (EMU), Mid-Miocene Unconformity (MMU) and Late-Miocene Unconformity (LMU). The new, revised, reintroduced and existing local lithostratigraphic units and sequences are discussed with their counterparts in the south and southeast of the Netherlands, in Germany and Belgium, and from this a regionally consistent framework has emerged of the regional Neogene lithostratigraphy.

The first isolated and well-preserved phalanx (autopodial element) of a generically and specifically indeterminate (probably xenopsarian) plesiosaur from the Maastrichtian type area (south-east Netherlands) is described and illustrated. Morphological features of this bone, such as the articular subchondral surfaces, allow it to be distinguished from phalanges of co-occurring mosasaurs (Mosasauridae, Squamata) and could imply rapid growth in plesiosaurs, similar to that observed in extant leatherback turtles. The large size of the phalanx indicates that it originates either from a large juvenile or from a paedomorphic individual. The paucity of plesiosaur remains in biocalcarenites of late Maastrichtian age in the Maastrichtian type area could be explained by the shallow settings, in which these strata were deposited, which may not have offered suitable ecological resources conducive to abundant plesiosaur inhabitation. Presumably, the lack of steep continental slopes in the type Maastrichtian, at which oceanic upwelling of cold, nutrient-rich water supported a higher prey density for pelagic predators such as plesiosaurs, may have inhibited plesiosaur occupation. Rather, decomposing floating carcasses may have been the source of dissociated elements of plesiosaurs in this area, such as isolated teeth, vertebrae and the autopodial element described here.

A fragmentary nerineoid gastropod collected from the Maasvlakte 2 beach may be identified as Ptygmatis cf. bruntrutana (Thurmann, 1832). Probably originating from Upper Jurassic strata in north-eastern France, it must have been transported here by a forerunner of the River Meuse (Maas).

Here we report a well-preserved isolated physeteroid tooth of Late Miocene age from Liessel, the Netherlands. The presence of several morphological features allows attribution to the macroraptorial physeteroids. Size and morphology are to some extent comparable to Zygophyseter and almost identical to the primarily tooth-based Tortonian taxon Scaldicetus caretti. However, the genus Scaldicetus was declared unutilizable, which is supported here with an overview of modern classifications of Scaldicetus species and specimens. Despite the restrictions, the type species S. caretti is still valid, although the name is to be restricted to the type material. Based on its morphological resemblance, the tooth is identified as Physeteroidea indet. cf. Scaldicetus caretti.

Wireline log correlation panels of palynologically analysed boreholes illustrate lateral facies transitions within Rupelian age strata of the Dutch Rupel Formation across the southeastern North Sea Basin. The middle to upper part of the Rupel Formation consists of clays and silts of the Boom Member and the overlying sandier Steensel Member. In the Mill and Goirle boreholes in the Dutch Province of North Brabant, the Boom Member is thickly developed and represents the middle to upper Rupelian (biozones NSO3 to NSO5a), while the Steensel Member is rather thinly developed and only comprises the uppermost Rupelian (biozone NSO5a). Borehole log correlations show that towards the south (or more proximal to the palaeo-continent) the Rupel Formation becomes sandier and the clayey Boom Member thins in favour of the sandy superjacent Steensel Member. Palynological analyses confirm that the Boom Member is restricted to the middle Rupelian (biozone NSO3) age here, and that the superjacent Steensel Member is of middle to upper Rupelian age (biozones NSO3 to NSO5a). Geological models constructed for northern Belgium propose that this facies transition occurs rather sharply, along a WSW-ENE oriented zone parallel to the presumed shoreline at that time. The results of this study support this interpretation and extend the trend towards the Netherlands.

The lower Maastrichtian chalk of the Isle of Rügen was deposited in a pelagic setting in the aphotic zone. Its rich fossil content has attracted research attention for centuries, whereas its ichnological characteristics remain poorly understood, even though horizons with intense bioturbation and occurrences of trace fossils in flint are common. The enhanced colour contrast of smooth chalk faces reveals repeated phases of benthic colonisation; larger burrows are commonly subject to silicification, while flint nodules also can preserve burrows in chalk. A total of 37 ichnogenera, including 47 ichnospecies of bioturbation and bioerosion trace fossils have been recognised; these are here briefly described, in addition to indeterminate material. Many ichnotaxa are recorded for the first time from the Rügen chalk. Bioerosion is restricted mainly to local hardgrounds in the form of biogenic components (such as shells and belemnite guards).

The Maastricht Formation is a mostly calcarenitic unit that belongs to the Chalk Group but is unlike the typical North Sea chalk in that it is much coarser and at times contains a significant terrigenous component. The formation was deposited between the late Maastrichtian and the early Danian in a proximal zone of the Chalk Sea immediately north of the Anglo-Brabant and Rhenish massifs. The formation crops out in South Limburg, the Netherlands, in the German state of North Rhine–Westphalia, near Aix-la-Chapelle (Aachen), and in the Belgian provinces of Liège and Limburg, and it is present in the subsurface in the Campine Basin and in the Roer Valley Graben, in Belgium and the Netherlands.

The often spectacular fossil content of the Maastricht Formation has been extensively studied but its sedimentological aspects remain understudied. Indeed, the lithostratigraphy of the formation is largely informal and based on the abundance and morphology of flint and on the quantification of fossil content. The paucity of facies studies and the lack of a lithostratigraphic framework based on modern facies studies hampers stratigraphic correlation between outcrops and, more importantly, boreholes. A facies characterisation and facies-based lithostratigraphic framework of the Maastricht Formation in South Limburg is particularly urgent because groundwater is abstracted from aquifers in the formation and geological models currently in place fail to predict facies heterogeneity and, consequently, aquifer properties.

We studied eight outcrops of the Maastricht Formation across South Limburg and carried out a (micro)facies analysis of the outcrops. We show that the Maastricht Formation can be subdivided into three lithofacies and five microfacies. The lithofacies reflect the traditional subdivision of the formation into Maastricht and Kunrade limestones. Our results suggest that the current subdivision of the Maastricht Formation into six members is untenable. The formation is best subdivided into lower and upper members. The Kunrade limestone should be afforded the status of formation.

We interpret the Maastricht Formation as having been deposited in an epeiric ramp, in which facies distribution was controlled by water temperature, nutrient levels and storminess. The (micro)facies of the Maastricht Formation can be organised into two depositional stages: stage 1, representing the lower part of the formation, is characterised by heterozoan carbonates deposited under cooler, mesotrophic conditions in a nutrient-rich, more proximal region of the epeiric sea; stage 2 is characterised by heterozoan-photozoan carbonates deposited in a warmer and stormier environment with slightly lower nutrient levels.

Maastrichtian scleractinian corals from 94 localities in 26 Maastrichtian regions world-wide with strata of that age are taxonomically and palaeobiogeographically evaluated. A total of 205 taxa, belonging to 116 genera and 37 families, are included in the present study. Most coral taxa have been recorded from non-reefal environments. A significant majority of these taxa (genera = 70.7%; species = 75.6%) appear to have been endemic during the Maastrichtian. The Maastrichtian coral fauna is dominated by solitary and cerioid-plocoid forms (both accounting for 41 genera = 70%), having mainly medium- and large-sized corallites. The most diverse coral assemblages are those that have been recorded from arid (Jamaica: 63 species, Mexico: 29 species), warm-temperate (the Netherlands-Belgium: 32 species) and tropical regions (Iran: 27 species). The occurrence of Cunnolites polymorphus (Goldfuss) is newly recorded for the Netherlands (southern Limburg). Compared to the microstructural composition of the coral fauna of the lowermost Cretaceous (Berriasian; 91% of the species and 83% of the genera belonged to previously established microstructural groups), in the Maastrichtian, corals belonging to previously established microstructural groups were of minor importance (genera = 26%; species = 29.3%). The majority of Maastrichtian scleractinian taxa (both solitary and colonial) from the type area of the Maastrichtian Stage in the southeast Netherlands and northeast Belgium are illustrated.

For centuries, fossils from the Maastrichtian type locality and adjacent quarries have provided key evidence of vertebrate diversity during the latest Cretaceous, yet until recently the Maastrichtian type area had revealed no important insights into the evolutionary history of birds, one of the world’s most conspicuous groups of extant tetrapods. With the benefit of high-resolution micro-CT scanning, two important avian fossils from the Maastrichtian type area have now been examined in detail, offering profound, complementary insights into the evolutionary history of birds. The holotype specimens of these new taxa, Janavis finalidens Benito, Kuo, Widrig, Jagt and Field, 2022, and Asteriornis maastrichtensis Field, Benito, Chen, Jagt and Ksepka, 2020, were originally collected in the late 1990s, but were only investigated in detail more than twenty years later. Collectively, Janavis and Asteriornis provide some of the best evidence worldwide regarding the factors that influenced stem bird extinction and crown bird survivorship through the Cretaceous-Palaeogene transition, as well as insights into the origins of key anatomical features of birds such as an extensively pneumatised postcranial skeleton, a kinetic palate, and a toothless beak. Asteriornis also provides scarce evidence of a Cretaceous-aged divergence time calibration within the avian crown group, while together, Janavis and Asteriornis constitute the only documented co-occurrence of crown birds and non-neornithine avialans. Here, we review key insights into avian evolutionary history provided by these discoveries from the Maastrichtian stratotype, document undescribed and newly discovered Maastrichtian fossils potentially attributable to Avialae and provide the first histological data for the holotype of Asteriornis, illustrating its skeletal maturity at the time of its death.

Renewed interest in bryozoan assemblages from the various members of the Gulpen Formation (upper Campanian–upper Maastrichtian) in the Liège-Limburg area (southeast Netherlands and northeast Belgium) during recent years has resulted in the discovery of a number of species previously unrecorded from the area. Nineteen species are here recorded from the Zeven Wegen, Vijlen, Lixhe and Lanaye members (Gulpen Formation) in the study area, occurring in three distinct assemblages. The vast majority of the bryozoan taxa belong to the order Cheilostomata; only two taxa are assigned to the order Cyclostomata. The species recorded here are Clinopora aff. costulata, Disporella obvallata, ‘Vincularia’ (sensu lato) marssoniana, Herpetopora laxata, Heteroconopeum ovatum, Wilbertopora aff. oxyteichos, Biaviculigera sacerdotalis, Semiflustrella britannica, Aechmellina anglica, Escharifora papyracea, Onychocella cyclostoma, Onychocella cylindrica, Onychocella matrona, Rhebasia disparilis, Stichomicropora sicksi, Coscinopleura elegans, Coscinopleura lamourouxi, Pachydermopora pachyderma and Beisselina aviculifera. While not previously recorded from the Liège-Limburg area, the bryozoan taxa identified from the Gulpen Formation are well known from coeval Cretaceous strata elsewhere in Europe, North America and Russia, highlighting their broad palaeobiogeographical distribution.

The geographical and stratigraphical distribution of the heteromorph ammonite genus Diplomoceras within the North-West Pacific Province is briefly reviewed. Although Diplomoceras ranks amongst the more important, globally distributed taxa during the latest Cretaceous, its precise stratigraphical range still is uncertain. Moreover, the status of the various species assigned to this genus is a matter of debate; for instance, two commonly cited forms, Diplomoceras cylindraceum and D. notabile, are considered to be conspecific by some authors, but treated as discrete taxa by others. The majority of records of species of Diplomoceras are from Maastrichtian strata; however, several late Campanian finds bring some discrepancy into the discussion about their biostratigraphical significance. Here we record new specimens from the upper Maastrichtian Kokuy Unit, refer them to Diplomoceras cylindraceum and briefly consider the geographical, biostratigraphical and taxonomic issues surrounding the genus Diplomoceras.

The currently defined Global Stratotype Section and Point for the Campanian/Maastrichtian boundary at Tercis (France) lacks any belemnite record. However, the detailed correlation of Tercis with the Kronsmoor section in northern Germany has enabled recognising this boundary in terms of belemnite stratigraphy close to the first appearance datum (FAD) of Belemnella obtusa Schulz, 1979. Originally, the FAD of the genus Belemnella Nowak, 1913 (e.g. of Belemnella lanceolata (von Schlotheim, 1813)) has been widely used for defining the base of the traditionally understood Maastrichtian stage in the Boreal Realm. Belemnella appeared almost contemporaneously across a significant portion of epicontinental Europe in what is now considered topmost Campanian and dominated the lower Maastrichtian belemnite assemblages, co-occurring with Belemnitella d’Orbigny, 1840 and rare Fusiteuthis Kongiel, 1962. It disappeared in Western and Central Europe during the mid-Maastrichtian, and as a consequence, the FAD of Belemnitella junior Nowak, 1913 served as a biomarker defining the base of the upper Maastrichtian substage. It is only at the end of the Maastrichtian that the genus Neobelemnella Naidin, 1975 became abundant, replacing Belemnitella steadily from the east to the west as the dominating species. The factors underlying those remarkable shifts in belemnite assemblages remain uncertain, but various environmental elements, especially water depth and temperature, in addition ocean currents, and oceanic chemical composition are considered influential.

Over recent decades, the type area of the Maastrichtian Stage in southern Limburg (the Netherlands) and contiguous Belgian territory, and the former ENCI-HeidelbergCement Group quarry (Sint-Pietersberg, Maastricht) in particular, has yielded an exquisitely preserved ichnocoenosis of bioerosional trace fossils, mainly preserved as natural casts in scleractinian corals. More than 20 ichnospecies are here documented, the majority from the type Maastrichtian for the first time. These ichnotaxa constitute a good record of successive colonisation sequences; the present bioerosional ichnocoenosis is regarded to belong to the Entobia ichnofacies.