The Lower Pleistocene Karnezeika locality, lies in the Peloponnese, southern Greece, and its fauna corresponds to the Middle Villafranchian biochronological unit (MN17). The recovered mammal assemblage includes, among others, a few remains of a large Cercopithecid. Herein, we describe this material, including an upper second molar, a partially preserved proximal radius and, possibly, an upper first incisor. The teeth show advanced stages of wear but retain their typical papionin characters, such as a strong lingual cleft and four bilophodont cusps in the molar. The general morphology and wear pattern of the teeth rules out the possibility that the remains belong to the genus Theropithecus, while the general size of the corresponding material excludes the possibility of a Macaca representative as well. On the contrary, the studied material better fits the size range of Paradolichopithecus. Even though this genus is likely represented in the Villafranchian of Europe by a single species, Par. arvernensis, the scarcity of the studied material imposes reservations and thus the Karnezeika papionin is referred at the moment to cf. Paradolichopithecus sp. As in the rest of Europe, the Paradolichopithecus record is rare in Greece, having been found in only two localities, Vatera and Dafnero. Despite its scarcity, the new material from Karnezeika indicates a wide distribution of this important taxon in the Greek peninsula.

This contribution provides insights into ocean-floor hydrothermal metamorphism of the fast-evolving Dinaridic Neotethys. Mineralogical, geochemical and Sr isotope data collected from altered ophiolites and non-ophiolite basalts/andesites and tuffs of the active continental margin are consistent with hydrothermal alteration trajectories that reflect the host-rock composition. This suggests that hydrothermal fluxes were restricted within a simple closed seawater-fed system. Based on the initial isotopic ratios of Sr, two fluid–rock interaction trends are established: (a) low-to-medium degrees of metasomatism in pre-Middle Jurassic anorogenic ophiolites that progressively abated, and (b) increased intensities of metasomatism in post-Middle Jurassic orogenic ophiolites. This agrees with chlorite thermometry and Ca-Al-(Fe)-silicate phase chemistry. The metamorphic assemblages belong to the zeolite, prehnite-pumpellyite, prehnite-actinolite and greenschist facies. The facies is reliant on the temperature of hydrothermal systems and their fluid chemistry. Rare earth element (REE) phase geochemistry shows (a) variable fluid–rock ratios in chlorite and pumpellyite dependent on fluid temperatures, (b) prominent Eu and Ce anomalies that reflect the fluid oxidation state, (c) light REE/heavy REE mobilization attributed to prevalent ligand complexation, and (d) multi-phase fluid percolation across reaction zones of heterogeneous permeability. This study proposes initiation of simple hydrothermal system(s) at or near a spreading centre(s) in the infancy of the Dinaridic Neotethys. Such a system became more complex during Middle Jurassic and Early Cretaceous time with reactive hydrothermal fluids passing the recharge area and reaching the hot reaction zone. An abrupt obliteration of the established high-temperature regime ensued, following the final closure of the Neotethys.

Organic carbon and nitrogen fixed in illite (I) clays were identified in a hydrothermal breccia structure from the Harghita Bãi area of the Neogene volcanism of the East Carpathians. The potassium-illite (K-I) alteration related to an early magmatic-hydrothermal event (9.5 ± 0.5 Ma) was later replaced by ammonium-illite (NH4-I) (6.2 ± 0.6 Ma) owing to circulation of an organic-rich fluid. Several textural evolutions of breccia structures were recognized, such as ‘shingle’, ‘jigsaw’, ‘crackle’ and hydraulic in situ fractures. The high-field-strength element behaviours of the K-I and NH4-I argillic altered andesite are close to chondritic ratios, indicating no contribution of hydrothermal fluid, especially on NH4-I andesite alteration and the CHArge-and-RAdius-Controlled (CHARAC) behaviour within silicate melts. The rare earth element normalized patterns show two distinct trends, one with a Eu* anomaly (K-I) and the other with a Nd* anomaly (NH4-I), indicating a boundary exchange with the organic-rich fluid. The strongly depleted δ13C (V-PDB) measured for the NH4-I clays reflects values (−24.39 to −26.67 ‰) close to CH4 thermogenic oxidation, whereas the δ15N (‰) from 4.8 to 14.8 (± 0.6) confirmed that the N2 originated from post-mature sedimentary organic matter. The last volcanism (6.3 to 3.9 ± 0.6 Ma) and simultaneous volcano-induced tectonics in the proximity of the eastern Transylvanian basin basement increased the heat flow, generating lateral salt extrusion, diapirism and increased pressure in the gas reservoir. New pathways were opened that provided new circulation routes for basinal fluids to new and old permeable zones and expelled seeps from the biogenic petroleum system.

Conodonts are an important biostratigraphic tool for many Phanerozoic stages. Along with graptolites, they define all global Ordovician Stage boundaries. Within the Upper Ordovician interval, a known species of Amorphognathus tvaerensis (Bergström) is present in both Sandbian and Katian stratotype sections. Study of changes in the succession of A. tvaerensis revealed that elements in the upper part of its range differ morphologically quite distinctly from those in its lower part. Here, they are described as a new conodont species, A. viirae sp. nov. This new species is recognized in several Estonian and Swedish sections, with apparent occurrence also in Mójcza Quarry, Holy Cross Mountains, Poland and Black Knob Ridge, Oklahoma, USA. Detailed analysis of early Amorphognathus elements from Estonian and Swedish sections revealed the absence of A. inaequalis (Rhodes) in both regions, although a conodont subzone based on this species was identified earlier by some authors. Both the absence of A. inaequalis (Rhodes) and recognition of the new species A. viirae sp. nov. resulted in the revision of the conodont zonation, and a new version of it is proposed for the Sandbian Stage in the Atlantic Realm. The new zonation includes (from below) Pygodus anserinus, Baltoniodus variabilis, A. tvaerensis, B. gerdae, A. viirae and B. alobatus Conodont zones.

Brittle reactivation of plastic shear zones is frequently observed in geologically old terranes. To better understand such deformation zones, we have studied the >700 Ma long structural history of the Himdalen–Ørje Deformation Zone (HØDZ) in SE Norway by K–Ar and 40Ar–39Ar geochronology, and structural characterization. Several generations of mylonites make up the ductile part of HØDZ, the Ørje Shear Zone. A 40Ar–39Ar white mica plateau age of 908.6 ± 7.0 Ma constrains the timing of extensional reactivation of the Ørje mylonite. The mylonite is extensively reworked during brittle deformation events by the Himdalen Fault. 40Ar–39Ar plateau ages of 375.0 ± 22.7 Ma and 351.7 ± 4.4 Ma from pseudotachylite veins and K–Ar ages of authigenic illite in fault gouge at c. 380 Ma are interpreted to date initial brittle deformation, possibly associated with the Variscan orogeny. Major brittle deformation during the Early–Mid Permian Oslo Rift is documented by a 40Ar–39Ar pseudotachylite plateau age of 294.6 ± 5.2 Ma and a K–Ar fault gouge age of c. 270 Ma. The last datable faulting event is constrained by the finest size fraction in three separate gouges at c. 200 Ma. The study demonstrates that multiple geologically significant K–Ar ages can be constrained from fault gouges within the same fault core by combining careful field sampling, structural characterization, detailed mineralogy and illite crystallinity analysis. We suggest that initial localization of brittle strain along plastic shear zones is controlled by mechanical anisotropy of parallel-oriented, throughgoing phyllosilicate-rich foliation planes within the mylonitic fabric.

Lamprophyre dikes and quartz veins in the Sizhuang gold deposit are used to date and unravel the Early Cretaceous stress regime in the Jiaodong Peninsula, North China Craton. The lamprophyre dikes are grouped into two major sets, trending NNW–SSE and NNE–SSW, respectively, and a subsidiary one, trending WNW–ESE, whereas the quartz veins trend mainly NNE–SSW. The age of lamprophyre dikes’ intrusion was robustly calculated at c. 119 Ma by phlogopite 40Ar–39Ar dating. The fuzzy clustering technique defined four stress states, which were grouped into three stress regimes in Sizhuang. Furthermore, these stress regimes were interrelated with two regional far-field stress regimes, ST1 and ST2, defined by the available published fault-slip data near Sizhuang by applying the separation and stress inversion TR method (TRM). The palaeostress reconstruction indicates that extension and strike-slip tectonics (i.e. transtension) affect the emplacement of the lamprophyre dikes and quartz veins. More precisely, the dike emplacement occurred under unstable stress conditions related to the shift from E–W pure extension–transtension to WNW–ESE transtension, whereas the quartz veins formed under relatively stable WNW–ESE transtension with the variant and increasing fluid pressure ( ${P_{\rm{f}}})$ giving rise to the strike-slip against dip-slip kinematics along the faults. The change from the ST1 to ST2 stress regimes reflects the significant clockwise rotation in the palaeo-Pacific plate subduction direction and defines the switching time at c. 119 Ma as precisely obtained by the lamprophyre dating.

Brachiopod taxonomy is based on descriptions of shell morphology and key characters, but diagenesis generally modifies or erases some of them, hindering brachiopod identification. Brachiopods that are taxonomically related usually present shells with similar appearance but can differ in size (i.e., Rhynchonellata). Some aspects of morphology – for example the angular measurement of the curvature of the shell or details of shell microstructure – could aid taxonomic identification. Gigantoproductids, which lack a robust taxonomy, have the largest shells among brachiopods and are ideal for this kind of study because of their gigantic size and morphological variability. Furthermore, they have a great abundance and worldwide distribution during the mid-Carboniferous. More than 700 samples have been collected from Sierra Morena (Spain), Montagne Noire (France) and Adarouch (Morocco) identifying up to six gigantoproductid genera: Globosoproductus, Semiplanus, Kansuella?, Latiproductus, Gigantoproductus and Datangia. Microstructural features from 170 thin sections belonging to gigantoproductid ventral valves have been studied, and six crystal morphologies have been distinguished within the tertiary layer: subhorizontal, imbricated, crenulated, acicular, short and long columnar morphologies. Moreover, 23 complete shells from all genera have been selected to investigate shell size and curvature. Results from this study emphasise that shell size, curvature and crystal shape are taxa-related. Finally, a remarkable morphological change in the gigantoproductid populations from the western Palaeo-Tethys occurred during the Viséan–Serpukhovian, from thin-shelled genera with subhorizontal morphology (Viséan) to thick-shelled genera with a tertiary layer consisting of long columnar crystals (Serpukhovian). This study proves that microstructure, maximum thickness and shell spiral characterisation are robust characters when applied to gigantoproductid taxonomy, but also have great potential in other brachiopod groups.

The recovery of a new partial cranium of Decennatherium rex Ríos et al. 2017 bearing two anterior and two posterior ossicones from the Late Miocene deposits of the site Batallones-10 (MN-10, Cerro de los Batallones, Madrid Basin) sheds light on the complex variability of the cranial appendages of these extinct giraffids. The special features of the anterior ossicones of BAT10’18-C6-40, each formed by two bosses and separated by a septum increase the range of morphological variability found in the anterior ossicones of giraffids. Posterior ossicone variability has already been described in several sivatherine taxa as Sivatherium maurusium (Harris, 1974) but anterior ossicone variability has never been discussed for four-ossicone taxa. This new specimen accounts for the third morphotype found in D. rex anterior ossicones. BAT10’18-C6-40 is identified as an adult D. rex male on the basis of the development of the posterior ossicones. These are large and already show the first large bump which in this taxon is always located on the middle of the dorsal surface at a similar height on the right and left ossicones which agrees with Solounias (1988) who stated that these small irregular protuberances have a somewhat fixed position, suggesting a genetic basis. This new specimen represents a new example of cranial variability in D. rex, and makes it the extinct giraffid with the largest anterior ossicone variability found so far.

Previous hydrocarbon explorations in the middle of the Tarim Basin indicate that strike-slip faults play an important role in the development of Ordovician carbonate reservoirs and hydrocarbon accumulation. The SB5 fault in the Tarim Basin was the target of this investigation. An evaluation of the stress in situ was carried out and provided boundary conditions to build a 3D geomechanical model. The distribution and application of present in situ stress in the strike-slip fault were studied. The results show good agreement between the absolute measured stress in situ and the modelled stresses, revealing a different stress regime along the strike-slip fault. The uplift segment belongs to a strike-slip stress state, and other areas belong to a normal fault stress state. The strike-slip fault has a significant influence on the present in situ stress distribution. The direction of the maximum horizontal stress deflects near the fault and tends to be parallel to the fault strike. This work introduces a comprehensive evaluation of the present in situ stress of the fractured carbonate reservoirs controlled by the strike-slip fault system. The present in situ stress direction can clarify the propagation direction of hydraulic fracturing and serve to evaluate the effectiveness of natural fractures.

The Niagara Escarpment is a fractured Palaeozoic sedimentary cuesta, subject to year-round weathering in a temperate climate. We examined the temperature of the rock surface and fractures at three in situ sites with varying aspect and lithology, as well as the surface and interior of three control blocks maintained in outdoor conditions between December 2020 and March 2021. The objectives were to examine the interplay between freeze–thaw and thermal weathering in the winter months and to identify potential factors influencing these processes. Both diurnal-scale and prolonged freeze–thaw cycles differing in spatial and temporal extent were identified, coincident with periods of high moisture. We frequently observed rapid temperature changes (>1 °C min−1) at sites with strong insolation, which implies that the temperature regime is suitable for thermal shock and fatigue to occur. Site-specific factors, such as the aspect of the escarpment face and lithology, impact the mechanism and extent of weathering. Southeast-facing sites with high insolation are dominated by diurnal-scale freeze–thaw; west- and east-facing sites with lower insolation experience a more prominent prolonged freeze–thaw cycle. Across all sites there is a gradient between surface and fracture temperature that follows diurnal trends in air temperature and insolation. Variability in the surface-fracture gradient may enhance weathering processes by shifting the orientation and magnitude of stress, and by changing the spatial distribution of freezing and thawing. Our research indicates that site-specific factors and pre-existing fractures moderate the influence of air temperature and insolation on thermal gradients, and ultimately the weathering regime.

Thrombolite reefs with archaeocyaths are common in the subtidal limestones of the lower Cambrian in the western Anti-Atlas of Morocco. The Igoudine Formation of the Tata Group recorded the first replacement of the microbial consortium (stromatolite-dominated) by thrombolite reefs with archaeocyaths and shelly metazoans. In order to better understand the role of the microbial community in the formation of thrombolite reefs with archaeocyaths across this critical transition, the macro-, micro- and ultra-fabric of thrombolites have been studied in detail. Three major components are identified within the first thrombolytic reef: archaeocyaths, calcimicrobes and micritic matrix. The studied thrombolites are typically dominated by the calcimicrobe Renalcis with subordinate Epiphyton and Girvanella. Scanning electron microscopy of the dark micrite of the Renalcis chambers showed amorphous translucent sheet-like structures interpreted as extracellular polymeric substances, closely associated with organominerals including nanoglobules and polyhedrons. Exceptionally well-preserved Renalcis chambers contain bacterial fossils similar to those described in modern microbialites, including microspherical coccoid fossils and filamentous bacteria that are either spaced or in close associations forming colonies. These organomineralization-related features suggest a bacterial origin for the Renalcis calcimicrobe. The matrices between the Renalcis chambers consist predominantly of clotted peloidal micrite. Mineralization of Renalcis microframes may involve two major biomineralization processes: (1) replacement of organic matter by organominerals resulting from anaerobic degradation of extracellular polymeric substances and bacterial sheaths and (2) encrustation of bacterial sheaths and extracellular polymeric substances due to increasing alkalinity of the microenvironment. These mechanisms played a crucial role in the early diagenetic cementation and preservation of the studied reefs.

Jurassic carbonate strata in the eastern Paris Basin exhibit several generations of faults, tension gashes and stylolites. Although their relative chronology can sometimes be determined according to cross-cutting relationships, the duration of major deformation phases and their influence on fluid flow and carbonate cementation are still uncertain. This contribution aims to clarify the timing of brittle deformation and associated calcite cementation. Tension gashes filled by calcite in Jurassic carbonates were sampled in outcrops and boreholes and dated through U–Pb geochronology. Almost all the sampled fractures were cemented during the Cenozoic period. Continuous deformation spread from c. 50 to 30 Ma. Tension gashes oriented N10° to N20° dated at 48–43 Ma show the main Pyrenean contractional stage. A second set of calcites were dated at c. 35–33 Ma and document a Late Eocene – Oligocene extension. A transition from the compressional to the extensional regime is expressed by tension gashes dated between 43 and 35 Ma. Finally, tension gashes oriented N150° to N175°, dated between 32 and 18 Ma, may result from the propagation of the horizontal stress generated by the Alpine orogen or by late Pyrenean deformation. Clumped isotope thermometry on five samples revealed both low crystallization temperatures (from 27 to 53 °C) and the meteoric origin of calcite-precipitating fluids. Our research therefore documents a continuous fracturing from Ypresian to Rupelian times, and less expressed brittle deformation during the Miocene period.

To study the ore mineralization at the outcrop scale we merge an advection–diffusion simulation with the geochemical software iphreeqc to model the mixing of two realistic fluids. We simulate the infiltration of a metal-rich fluid into a rock that is saturated with pore fluid. We test the feedback effects with a number of scenarios based on an outcrop-scale 5 × 5 m model consisting of two high-permeable vertical faults within a low-permeable host rock that lead into a permeable layer. The hot metal-rich fluid enters the model through the faults from below. We solve the advection–diffusion equation for 12 chemical species and temperature, and use iphreeqc to determine the resulting properties of local fluid domains as well as related saturation indices for minerals. The faults in the model act as pathways for the metal-rich fluid, with the infiltrating fluid displacing the pore fluid. Mixing in the model takes place as a function of advection along permeable faults coupled with diffusion of chemical species at the interface between two fluids, while heat diffusion is fast enough (103 times faster) to equilibrate temperature. Simulations show a high saturation index of mixing-derived minerals such as barite at the interface between the two fluids as a result of fluid mixing. Fast fluid pathways (i.e. faults) show travelling waves of high saturation indices of barite, while low-permeability zones such as fault walls and areas below less permeable layers experience stationary waves of high saturation indices. Our results show that, depending on the dominant transport process (advection or diffusion), mineralization will localize next to permeability contrasts in zones where local diffusion dominates.

Fractures that form when fluid pressure ruptures the rock are referred to as fluid-driven fractures or hydrofractures. These include most dykes, inclined sheets and sills, but also many mineral veins and joints, as well as human-made hydraulic fractures. While considerable field and theoretical work has focused on the geometry and arrest of hydrofractures, how they select their propagation paths, particularly in layered and faulted rocks, has received less attention. Here I propose that of all the possible paths that a given hydrofracture may follow, it selects the path of least (minimum) action as determined by Hamilton’s principle. This means that the selected path is that along which the energy transformed (released) multiplied by the time taken for the propagation is a minimum. Hydrofractures advance their tips/fronts in steps, with a time lag between the fracture front and the fluid front. In the present framework, each step is then controlled by Hamilton’s principle. The results suggest that when the hosting rock body is regarded as homogeneous, isotropic and non-fractured, hydrofracture paths are everywhere perpendicular to the trajectories of the minimum compressive (maximum tensile) principal stress σ3 and follow the trajectories of the maximum principal compressive stress σ1. When applied to layered and faulted rock body, the results indicate that hydrofracture paths may follow existing faults for a while, depending primarily on (1) the dip of the fault (steep faults are the most likely to be used by vertically propagating hydrofractures), and (2) the tensile strength across the fault compared with the tensile strength of the host rock along a path following the direction of σ 1. The results suggest that hydrofractures may use faults as parts of their paths primarily if the fault is steeply dipping and with close to zero tensile strength.

During the early Bajocian, a conspicuous coal-bearing siliciclastic succession was deposited in the northern Tabas Bock, which is important for understanding the regional geodynamics of the Central-East Iranian Microcontinent (CEIM) as well as for the Jurassic coal genesis in this part of Laurasia. Sedimentary facies analysis in a well-exposed section of the lower Bajocian Hojedk Formation (Kalshaneh area, northern Tabas Block) led to the recognition of ten characteristic sedimentary facies and three facies associations, representing channels with point bars and floodplains of a Bajocian meandering river system. Modal analysis indicates that the mature quartz arenites and quartzo-lithic sandstones of the Hojedk Formation originated from the erosion and recycling of older, supracrustal sedimentary rocks on the Yazd Block to the west. The coal petrography and maturity show an advanced maturation stage, whereas the great thickness of these continental strata points to a pronounced extension-related subsidence in the northern Tabas Block. The rapid rate of differential subsidence can be explained by accelerated normal block-faulting in the back-arc extensional basin of the CEIM, facing the Neotethys to the south. Compared to the thick Jurassic, the post-Jurassic strata are relatively thin and played a limited role in the thermal history of the coal in the northern Tabas Block. A relatively high geothermal gradient in the tectonically highly mobile area of the northern Tabas Block and/or heating by regionally widespread Palaeogene intrusions were most probably the key drivers of the thermal maturation of the Middle Jurassic coals.

Horseshoe crabs as a group are renowned for their morphological conservatism punctuated by marked shifts in morphology associated with the occupation of non-marine environments and have been suggested to exhibit a consistent developmental trajectory throughout their evolutionary history. Here, we report a new species of horseshoe crab from the Ordovician (Late Sandbian) of Kingston, Ontario, Canada, from juvenile and adult material. This new species provides critical insight into the ontogeny and morphology of the earliest horseshoe crabs, indicating that at least some Palaeozoic forms had freely articulating tergites anterior to the fused thoracetron and an opisthosoma comprising 13 segments.

Rounded to angular granoblastic textured mafic xenoliths, ranging from ∼1 to 6 cm in dimension, occur together with mantle peridotite xenoliths in a small Neogene/Quaternary alkali basalt cone in northeastern Iran. These crustal xenoliths consist of plagioclase feldspar, clinopyroxene, orthopyroxene and minor olivine, spinel, titanomagnetite and apatite. Their bulk compositions are similar to tholeiitic basalts and they are interpreted as meta-gabbroic rocks derived from mid- to lower crustal depths of 18 to 30 km. Rb–Sr dating suggests an age of c. 457 ± 95 Ma for these crustal xenoliths, and their geochemistry shows some similarities to Ordovician gabbros that crop out ∼20 km to the west. The data suggest that the gabbroic proto-lithologies of the xenoliths formed by intrusion of mafic magmas into the mid- to lower crust, possibly during extension and magmatism related to the opening of the Hercynian Palaeotethys ocean that separated central and eastern Iran from the Eurasian plate during the Late Palaeozoic.

Turbidity currents commonly bypass sediment in submarine channels on the continental slope, and deposit sediment lobes farther down-dip on the flat and unconfined abyssal plain. Seafloor and outcrop data have shown that the transition from bypass to deposition usually occurs over complex zones referred to as channel–lobe transition zones (CLTZs). Recognition of these zones in cores and outcrop remains challenging due to a lack of characteristic sedimentary facies and structures. This paper focuses on Unit E of the Permian Fort Brown Formation in the Karoo Basin, South Africa, in the Slagtersfontein outcrop complex, which has previously been interpreted as a CLTZ. This study integrates thin-section micrographs, sedimentary facies, bed-set and stratigraphic architecture, and palaeoflow directions to achieve a multiscale analysis of CLTZ features. A novel process-based facies scheme is developed to evaluate deposits in terms of the depositional or erosional tendencies of the flows that formed them. This scheme allows bypass to be distinguished from depositional zones by the spatial distribution of certain sediment facies. Areas of net sediment bypass were predominantly marked by erosive sediment facies and a larger variability in palaeoflow direction while depositional areas showed a lower variability in palaeoflow directions. Metre-scale structures in the bypass-dominated area reveal seafloor erosion and scour formation. Field relations suggest the presence of a ∼500 m long mega-scour in the CLTZ. The characteristic structures documented here are applicable for identifying CLTZs in sparse datasets such as outcrops with limited palaeogeographical context and sediment cores obtained from subsurface systems.