Several new localities bearing megalooithid eggs were discovered along of the Sierra de Loarre (Huesca, northeastern Iberian Peninsula), forming a sequence of paleontological sites bearing well-preserved fossil eggs. At the Santa Marina 1 site, the egg clutches occur at the top of extensively developed and vertically-stacked paleosols, while numerous isolated eggshells appear grouped in three roughly levels across the 1.5 m-thick of an alluvial profile subspherical to slightly ellipsoidal eggs with thick discretispherulithic eggshells and compatituberculated outer surface ornamentation are here assigned to Megaloolithus siruguei, in coherence with other Late Cretaceous localities of the Iberia and Europe. Many biological and taphonomic features based on the facies analysis, eggshell preservation and geochemical composition suggest reconsidering some aspects of the dinosaur nesting behavior, indicating that Santa Marina 1 could have been a recurrent nesting area, although in the last nesting horizon the number of unsuccessful eggs and anomalous eggshells are very common. The multidisciplinary study allows us to discriminate between biologic-induced against environmental-forced in the location of the sauropod egg accumulations, reconsidering some aspects about the origin of the paleontological sites and of the M. siruguei preservation.

This study investigates a karst bauxite deposit from NE Spain with a dual objective incorporating the novel aspect of directly linking genetic processes to industrial ceramic performance. First, the bauxite is mineralogically and texturally characterized using X-ray diffraction and field emission scanning electron microscopy. Second, the mineralogical and textural transformations of the bauxite during firing at 1000, 1200 and 1300 degrees C are analyzed, together with their effects on the physical properties of the fired products. The Lower Cretaceous bauxite is autochthonous, shows a pisolithic structure, and formed in situ under tropical monsoon conditions through intense chemical weathering involving dissolution-crystallization processes. For ceramic testing, the bauxite was mixed with illitic-kaolinitic clays in a 90/10 proportion. During firing, kaolinite and illite destabilize and transform into mullite, initially by solid-state reactions at 1000 degrees C and subsequently by crystallization from a vitreous phase at higher temperatures, producing larger crystals and composition closer to the empirical mullite formula. The formation of vitreous phase and mullite leads to reduced porosity and increased density and linear shrinkage, particularly between 1000 and 1200 degrees C. Specimens fired at 1300 degrees C show higher mechanical strength, related to higher mullite content and a larger size of its crystals. The results demonstrate the potential interest of these bauxites for ceramic manufacturing.

Bauxitic deposits serve as valuable sedimentary archives, offering insights into paleoclimatic, paleogeographic, and geodynamic processes over time. A multidisciplinary analysis of bauxitic deposits in the Cuenca Domain (Iberian Ranges, central Spain) aims to reconstruct their genesis in the framework of the geological evolution of this region during the Late Jurassic-Early Cretaceous rift episode. The bauxitic deposits preserve paleosol profiles that show multi-episodic processes of sedimentation, reworking, erosion, pedogenesis, and bauxitization, reflecting a landscape's dynamics that was strongly influenced by episodic tectonic activity. The presence of book-type kaolinite aggregates, ferruginous pisoids and ooids, and soil horizons provide evidence of in situ bauxitization. On the other hand, the presence of fractured pisoids and ooids, brecciated textures, and bauxitic C horizons also points to some degree of reworking. Authigenic boehmite suggests optimal conditions for bauxitization, whereas ferruginous crusts and peds at the top of the deposits point to a later ferruginization phase. A subsequent kaolinitization episode, probably driven by the infiltration of silica-rich fluids, is also recorded. By integrating stratigraphic, sedimentological, and mineralogical data, a succession of genetic stages in bauxite development has been identified, shaped by the tectonic evolution of the area. The proposed stratigraphic and pedogenetic model enhances the regional significance of the findings and enables a refined chronology of its tectonic evolution. The results highlight the potential of bauxitic materials, not only as paleoclimatic indicators but also as robust tools for reconstructing paleogeographic and tectonic conditions in complex settings where the sedimentary record is apparently homogeneous and extremely incomplete.

A set of samples from the Monte Castelo kaolin deposits (Burela, NW Spain), corresponding to igneous acidic rocks affected by chemical weathering with variable intensity have been investigated in order to establish the mineralogical and chemical changes with weathering, and the micro- and nano-scale textures developed. For the study, XRD, FESEM, HRTEM and chemical analyses have been used. The more intense the weathering, the more the dissolution of aluminosilicates (albite, K feldspars and K micas) and the crystallization of kaolinite is favored. Kaolinite grows, forming booklets and generating a fine-grained matrix and, along the cleavages of muscovite, forming mica–kaolinite intergrowths. Bidimensional crystallographic continuity between mica and kaolinite has been observed and no intermediate phases have been identified as a consequence of the high W/R ratio. Kaolin mainly contains kaolinite with high crystallinity; however, when there are quartz impurities, they interfere with the ‘optimal’ reflections for the calculation of the Hinckley index. In this case, the use of the AGFI index almost eliminates the effect that the relative intensities of the quartz and feldspar impurities may have on those of kaolinite. With weathering, there is a progressive decrease in the contents of most chemical elements, except Al, TiO2, HREEs, Ta, Hf, Th, U, V, Cr, S, Zr, Mo and Sn.

The intense chemical weathering processes that lead to the formation of laterites and bauxites result in the enrichment of critical metals (Sc, V, Co, Ga, Ge, Nb, In, Hf, Ta, W, and REEs), which are of great economic interest and are directly involved in the manufacture of various devices essential for the technology transition. This work focuses on combined geochemical and scanning transmission electron microscopy (STEM) studies of lateritic palaeosols developed in continental profiles (Lower Cretaceous, NE Iberia) in order to evaluate the distribution and concentration of critical metals and their possible relationship with weathering processes. In this study, we show that during the process of laterization the highest weathering produces the highest critical metal concentrations (reaching concentrations of 1914.80 ppm in the lateritic palaeosols and 926.30 ppm in the ferruginous macropisoids). Concentrations normalized to the upper continental crust (Taylor and McLennan, 1985) indicate that both the lateritic palaeosols and the macropisoids are enriched in LREEs (256.81 and 223.01 ppm, respectively) and HREEs (107.11and 110.53, respectively). In the lateritic palaeosols, the (La/Sm)c values are higher than those of (Gd/Yb)c, indicating that the LREEs exhibit higher fractionation with weathering, whereas the opposite occurs for the macropisoids, in which the HREEs have higher fractionation. These data indicate that the HREEs are less mobile than the LREEs during laterization. The critical metals present a good positive correlation with Fe, Ti, and Al, but a good negative correlation with K. STEM images and EDS analyses allowed us to identify REE-phases (including monazite, xenotime, and La, Ce and Nd oxides) and nanoparticles of gold adsorbed on the surface of kaolinite crystals. This shows not only that during the laterization process Fe and Ti oxides act as scavengers for the critical metals, but also that kaolinite controls their distribution.

Karst bauxite deposits in the North Dalmatian piggyback basin (NDPGB) are a part of the Mediterranean bauxite belt, which is the largest European bauxite deposit zone; however, there is a general lack of information regarding the genesis, age, and precursor of the bauxite deposits in this region. In this study, we combined detrital zircon U–Pb geochronology with compositional, mineralogical, and morphological data from four bauxite locations in the NDPGB to provide a new palaeogeographical and palaeoenvironmental evolution model for the Lutetian–Rupelian timeframe of the NDPGB. The Eocene climatic conditions began with the Palaeocene–Eocene Thermal Maximum event (∼56 Ma), followed by the Early Eocene Climatic Optimum (∼49 Ma) and Middle Eocene Climatic Optimum (∼40 Ma), and were completed as a cooling trend culminating around the Eocene/Oligocene boundary (∼34 Ma), with a shift towards an icehouse climate. These events were coeval with the continuous drift of the African continent towards Eurasia and the subsequent closure of the western part of the former Neo-Tethys Ocean associated with massive volcanic activity. Based on the bauxite deposits of the NDPGB, Early Eocene limestones formed in the last phase of the long-lasting Adriatic Carbonate Platform. The Middle Eocene orogenic activity resulted in an elevation in this area. High average temperatures, accelerated hydrological cycles and precipitation, and intensive continental weathering with increased volcanic carbon input resulted in favourable conditions for the development of karst bauxites at this time. Further Upper Eocene tectonic deformation of the NDPGB area resulted in the development of bauxite traps and enabled redeposition of the initial bauxite material. Subsequently, the bauxite deposits were covered with clastic carbonate molasse derived from the intensive erosion of the young Dinaric orogeny. The implications of this study are as follows. First, it provides new information on the timing of bauxitisation in the area by providing the first radiometric zircon geochronology, which refined and restricted the time window for bauxite formation in this region. Additionally, our results provide a new perspective on the possibility of aeolian precursors in karst bauxite formation and provide new constraints on the first tectonic marks of the initial Dinaric orogeny.

Oxygen and hydrogen isotope composition of neoformed clay minerals is commonly used as a palaeoclimatic proxy. Usually, sediments and rocks (including palaeosols) contain not only neoformed clay minerals, but also detrital and/or diagenetic ones. Together with the usually small size (micro- or nanometric) of the clay minerals in these materials, this can generate difficulties during isotopic analyses by conventional spectrometry. To avoid this problem, we used nanoscale secondary ion mass spectrometry (NanoSIMS) to analyse neoformed clay minerals included in palaeosol levels in early Barremian continental profiles located in NE Spain. The bottom levels of the profiles are rich in kaolinite, whereas the top levels contain smectite (beidellite-type). The isotopic compositions of pure powder standards of kaolinite and beidellite were measured in bulk by conventional mass spectrometry to obtain reference values for calibrating the instrumental mass fractionation. Two common preparation techniques for geological samples were tested (thin sections and thick polished sections), revealing that thin sections are more suitable for NanoSIMS analysis due to their lower resin content. The high spatial resolution of the instrument allowed the elemental mapping of the samples, permitting the localization of the minerals of interest and the measurement of isotopic ratios at selected points (1 x 1 μm2) within the samples. The preliminary isotopic results allowed to distinguish a decrease in the average 18O/16O and D/H ratios from the kaolinite in the bottom levels to the smectite in the top levels, reflecting a change in the climatic conditions. The average δ18O and δD values obtained for kaolinite (δ18OSMOW=18±15‰; δDSMOW=-82±36‰ and δ18OSMOW=14±4‰; δDSMOW=-97±37‰) and smectite (δ18OSMOW=13±14‰; δDSMOW=-167±87‰ and δ18OSMOW=11±6‰; δDSMOW=-180±40‰;), respectively, are consistent with the crystallization of the clays in weathering conditions. Despite the uncertainties of these preliminary isotopic measures, the results obtained allowed to estimate an average temperature for kaolinite formation of 21-22°C, and of 16-17°C for smectite. Given suitable calibration using pure isotopic standards and adequate sample preparation, NanoSIMS can thus have a great applicability in palaeoclimatic studies involving the oxygen and hydrogen isotopic composition of nanometre-sized clay minerals from palaeosols samples.

Textural features are widespread in many soils, provide pedogenetic evidence, and are fundamental in soil classification systems. The presence of these features and their conservation over time require certain processes and soil forming factors. This study investigates the genesis of textural pedofeatures, especially clay coatings, and the stressful conditions that can eventually lead to their disappearance. To achieve this goal, four profiles with clay-enriched horizons have been studied (macro-and micromorphology, physical, chemical and mineralogical properties and classification) along a transect in the siliceous Iberian Chain (NE-Spain).The profiles, which have unmistakable illuvial accumulations in various horizons (Bhs, Bt, Btk), are classified (ST/WRB) as: a Spodosol/Podzol in the headslope, two Alfisol/Luvisols in the backslope and an Alfisol/Calcisol in the footslope. For the latter soil, the apparently strong difference in their classification to the first hierarchical level is due to the weight that the WRB places on the presence of an argic recarbonated horizon on a calcic horizon.Clay illuviation was identified in all the soils, with coatings and infillings of microlaminated clay. These clayey pedofeatures are mostly mechanically fragmented or deformed, which is micromorphologically evidenced by an undulating, wavy extinction that does not run completely parallel to the surfaces they cover. Different destructive processes are identified along the soil transect; so, cryoturbation is the dominant process in the Podzol located at the highest elevation (Moncayo Massif). Instead, the clay coatings in the Btk horizon of the footslope (Calcisol) are covered and deformed by the growth of secondary calcite. The textural pedofeatures in this soil, which is very clayey, can also undergo argilloturbation processes, like in the backslope soils (Luvisols). In conclusion, several ongoing stress processes, that sometimes require different environmental conditions (polygenetic), affect most textural pedofeatures and lead to their progressive alteration and disappearance.

Ball clay deposits in the SE of the Iberian Range (NE Iberian Peninsula) consist of Albian clays and siltstones with greyish and blackish colors, interbedded with subbituminous coals. The ball clays are nowadays mined for the manufacture of white color ceramics. The mineralogy of these deposits consists mainly of kaolinite, illitic phases, and quartz. The euhedral to sub-euhedral morphology of the kaolinites suggests their in-situ origin. The anhedral morphology of the illites and the presence of frayed illites suggest a detrital origin. At the micro-scale, authigenic kaolinite booklets are observed filling pores and forming mica/kaolinite intergrowths, in which the kaolinite grows between the cleavage sheets of pre-existing detrital mica. At nanometer scale, illite/smectite (IS) phases are detected forming interlayers with mica and kaolinite, and evidence of the replacement of mica by kaolinite is observed. The matrix consists of defective illite and kaolinite, and random mixed layers of kaolinite-I/S (Kln-IS), illite-I/S (Ilt-IS), and I/S-smectite (IS-S). The textures of illite and the presence of different types of mixed layers suggest that the expandable phases and kaolinite are products of mica alteration. The effectivity of the alteration was probably a consequence of the low pH that occurred in the environment due to the presence of abundant organic- and acidic- rich fluids.

The Miocene Climatic Optimum (MCO) represents a global warm period (approximately 17–14.7 Ma) interrupting a long-term period of Cenozoic cooling. To elucidate if bauxitization took place in southeastern European mid-latitude areas during the MCO, we studied a section of undated massive karst bauxite (Crveni Klanac, CK) in central Dalmatia, Croatia, hosted in Upper Cretaceous limestones and overlain by Miocene Sinj Basin lacustrine deposits. Integrated mineralogical, morphological and geochemical analyses indicate the predominant mineral phases of the homogenous bauxite matrix are authigenic, subhedral to euhedral kaolinite and gibbsite. The in-situ mineralization was a consequence of pedogenic processes, indicating the CK bauxites formed autochthonously. In situ U–Pb zircon ages of the lower, middle and upper parts of the CK bauxite are very similar, dominated by Miocene and Oligocene ages, indicating that they all share similar protolith(s). Subsequent high-precision chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) analyses indicate a maximum depositional age (MDA) for the pre-bauxitic material of 16.9576 ± 0.021 Ma (2 σ uncertainty, incorporating decay constant uncertainty). This MDA, a maximum age of autochthonous bauxitization, coincides with the onset of the MCO. Based on currently available geochronological constraints, the maximum timeframe for CK bauxitization was less than ~ 700 ka, which matches the records of the MCO in paleo-mid-latitude Europe. The potential imprint of pre-17 Ma bauxitization and contribution of older (i.e., Upper Paleogene) bauxite deposits resedimented to the CK profile, as well as degree of potential parautochthonous origin of the CK bauxites, is yet to be investigated. More than simply aligning with regional and local reconstructions of continental climatic conditions during the onset and the early stages of the MCO, the high degree of autochthony of the CK bauxites provide a precise climatic constraint. For in-situ bauxitization to occur in the southeastern parts of mid-latitude continental Europe, paleoclimatic and paleoenvironmental conditions must have had mean annual temperature greater than 17–22 °C and mean annual precipitation of more than 1100–1200 mm.

The present work analyses a set of cylinders manufactured by pressing and fired from 1000 ?C to 1270 ?C, which are composed of pure Al-rich rocks (bauxite) and mixtures of bauxite with Al?K-rich clays. The aim of the study is to determine the mineral and textural transformations that take place in the mixtures with firing and their influence on the physical properties of the final products in order to evaluate their refractory potential by comparing them with various fired commercial bauxites. To this end, raw and fired samples were analysed by Xray diffraction, X-ray fluorescence, and optical and field emission scanning electron microscopy, and significant physical properties (e.g. density, linear shrinkage, porosity, colour, water absorption, thermal conductivity and point load resistance) were determined in the fired cylinders. The raw bauxite was mainly formed by boehmite, kaolinite and hematite whereas the illite- and kaolinite-rich clay was formed by quartz, illite and kaolinite. Kaolinite, illite and boehmite are not detected at 1000 ?C and, from this temperature upwards, mullite, corundum, ?-Al2O3, hercynite, ilmenite, cristobalite and vitreous phase are formed. Changes in physical properties with rising temperature are associated with the mineralogical changes. The increases in density and linear shrinkage are related to the formation of vitreous phase and the crystallization of mullite, and correlate with the decrease in porosity, water absorption and thermal conductivity. The changes in the colour of the samples are related to the hematite content at each temperature, whereas the point load resistance is greater with higher corundum content. Both the firing temperature and the clay content play an important role in the refractory potential of the mixtures, since samples mixed with illite- and kaolinite-rich clay present similar properties at lower temperatures to those of the fired commercial bauxites.

The Eocene continental sequence investigated in this study belongs to the Salta Group; it was deposited in an intracontinental rift, the Salta Basin (NW Argentina) that evolved from the Lower Cretaceous to middle Paleogene. The Salta Group contains the Maíz Gordo and Lumbrera Fms, spans the Paleocene-early Eocene, and shows excellent exposures in the region of the Valles Calchaquíes. This research is focused on the continental facies of the Lumbrera Fm, which correspond to the early Eocene. We studied the mineralogy of the fine-grained beds of the Lumbrera Fm in five locations (Valle Encantado, Tonco, Tin Tin, Luracatao, and Obelisco) by X-ray diffraction and scanning electron microscopy in order to examine the vertical variations in clay mineralogy and their relations with global paleoclimatic changes registered during the Eocene. The microtexture of the authigenic smectite-type clays (Sm to I/Sm R0) suggests that they mainly originated by crystallization from glassy volcanic materials. The high reactivity of the glass precludes the use of smectite-type-clay formation as an indicator of specific paleoclimatic conditions in the studied sediments. In contrast, the formation of kaolinite in sections with very low smectite proportions and a strong degree of weathering in crystalline silicates reflects intense weathering conditions and is a useful paleoclimatic proxy in terrestrial sediments. Significant variations in kaolinite/muscovite ratios at the base and in an intermediate bed in the Lumbrera Fm at Valle Encantado suggest the presence of cyclic hyperthermals through the Ypresian stage that may be tentatively correlated with the Eocene Thermal Maxima 2 and 3, which are the largest events that have been identified at a global scale in early Eocene marine sediments.

The facies and clay mineral study of clay/marl-rich levels from the Torrelapaja Formation (latest Hauterivian–early Barremian, NW Iberian Range, NE Spain) allowed to establish the palaeoclimatic and palaeoenvironmental conditions under they were generated. The muddy levels and pisoids contained therein of two logs were sampled and studied by X-ray diffraction and optical and electron microscopy. A similar mineralogical upwards trend is recorded in both logs, with a decrease in calcite coupled with an increase in quartz and orthoclase content and constant proportions in goethite, hematite, diaspore, anatase, rutile, ilmenite, and clay mineral content. The lower muddy levels have higher kaolinite content than the upper levels, where illitic phases are the dominant clay minerals. Smectite and intergrowths of illitic phases and kaolinite are also detected upwards. The kaolinite and smectite textures indicate an authigenic origin, whereas the illitic phases are former phases acting as a substrate for kaolinite crystallization. Pisoids mineralogy and texture show an in-situ origin, but some are fractured, indicating reworking processes. The mineral association found in the muddy levels is characteristic of oxisols formed under warm and humid conditions. The upward decrease in kaolinite content is coeval with an increase in the illitic phases and quartz content, related to siliciclastic input, but is also coeval with the presence of authigenic smectite. This indicates a decrease in chemical weathering, not fully registered due to the siliciclastic contribution, which was possibly associated with a change to colder, drier conditions during the latest Hauterivian–early Barremian in the studied area.

espanolEn este trabajo se presenta una secuencia didactica donde el alumnado analiza e interpreta datos con el objetivo de construir explicaciones cientificas en un contexto de gamificacion. Se utilizan las variaciones climaticas del pasado como eje central de la secuencia aprovechando la gran repercusion mediatica que tiene el problema del cambio climatico y, por tanto, el interes que suscita entre los estudiantes. Los resultados muestran que el alumnado utiliza los datos que aporta la Geologia en el conocimiento de los contextos climaticos en el pasado. EnglishIn this work, we propose a didactic sequence where the students analyze and interpret data with the aim of finding scientific explanations in a context of gamification. Past climate changes are used as a key point of the sequence, taking advantage of the great media interest aroused by the present climate change, and the related interest among the students. Results show that students use the data provided by Geology to broaden the knowledge of past climate changes.

A set of materials from Teruel (NE Spain), which includes a karst bauxite deposit overlain by an Albian (Lower Cretaceous) kaolin-rich clay succession, has been characterized from a mineralogical, textural and geochemical point of view. The materials under study were examined by X-ray diffraction, optical and electron microscopy and by inductively coupled plasma (ICP) optical emission spectroscopy (OES) and mass spectroscopy (MS). The bauxite is pisolitic and predominantly red and the overlying clay succession is mainly made up of grey claystones. Upper-section of the clay succession is a layer with carbonate nodules and scarce pisolith-like particles that can be distinguished. The studied materials are mainly composed of kaolinite, coupled with gibbsite and accessory boehmite in the bauxite. Gibbsite is also identified in the layer with carbonate nodules. Mineralogical data, kaolinite crystallinity and the Chemical Index of Alteration indicate that the layer with carbonate nodules has recorded a weathering event that was not as intense as the one that led to the in-situ formation of the bauxite deposit. The geochemical behaviour of the analysed elements, especially the REEs, also supports the existence of a weathering event recorded in the layer with carbonate nodules, given the similar trends observed in this layer and in the bauxite. The weathering led to REE + Y leaching, with the HREEs being less mobile than the LREEs, and thus the Albian clay succession, except the layer with carbonate nodules, shows a greater potential as source of these strategic elements. The research has revealed that redox fluctuation made a significant contribution to the distribution of Fe and Ce during bauxitization concerning the precipitation of Fe oxides and accessory minerals such as those of the goyazite-crandallite series.

The use of natural uranium and thorium long-lived isotopes was applied to study the evolution of kaolinitic materials. To do that, a radiochemical method for separation of Th and U in phyllosilicate samples was developed with the main aim of their analysis by ICP-MS/MS. Given the lack of certified phyllosilicate reference materials with certified isotope abundances, the method was tested using a stepwise approach. First, a preliminary setup was done using a sediment reference sample. Then, the extrapolation of this method to the samples of interest has been tested using a phyllosilicate sample certified for U and Th concentrations. The results showed that an extension of the plateau time of digestion in the used microwave system was peremptory as to get full digestion of the sample. The use of the isotope dilution technique allowed both the quantification of major isotopes (238U and 232Th) simultaneous to the determination of isotope ratios (234U/238U, 235U/238U for quality control and 230Th/232Th). The established method was applied to six kaolinitic samples from the Iberian Range (NE Spain), showing the potential of this isotope approach for the characterization of their time evolution.

This study presents the cyclostratigraphic analysis of a detailed, 1,371 m-thick stratigraphic section logged in the Lower Cretaceous syn-rift lacustrine and alluvial deposits of the Enciso Group, in the eastern Cameros Basin. The spectral analysis of a time series based on lithology reveals periodic sedimentary cycles attributable to variations in the eccentricity of the Earth's orbit around the Sun (131.8 and 39.9 m-thick sedimentary cycles for the long and short orbital eccentricity cycle) and to changes in the obliquity (12.6 m-thick cycle) and the two precession modes (7.7-5.5 m-thick cycles) of the Earth's rotation axis. We have constructed a floating astrochronological time scale based on the spectral analysis allowing us to propose that the time interval registered in the studied series is ca. 5.4-5.7 Ma, and to estimate an average sedimentation rate of similar to 255-239 m/Ma. The presence of cycles representing a similar time span but having different thickness, reveals a higher influence of tectonic activity in the central and upper parts of the succession, and discriminate tectonic from climatic signal, the latter being significant throughout the succession. The sedimentary facies and paleontological content of the studied profile, deposited very close to the coastline, have allowed us to interpret a deepening-shallowing cycle that it is proposed to be eustasyrelated (transgressive-regressive cycle). The anchoring of this cycle with the sea level curve in combination with the scarce paleontological dates permit the Enciso Group to be located in the Hauterivian-Barremian, that was approximately deposited between 132.5-126.8 or 132.3-126.9 Ma, depending on whether the short or long eccentricity cycle is considered, respectively.

A combined fades and clay mineralogy analysis of the continental succession recorded in the lower part of the Blesa Formation (early Barremian, Oliete subbasin, NE Spain) allowed us to specify the palaeoclimatic and palaeoenvironmental conditions under which this sedimentary record originated. Six outcrops including clays, days/marls and dm-thick interbedded palustrine-lacustrine limestone levels were logged and sampled for X-ray diffraction and optical and electron microscopy analysis. The lower levels consist of red clays with abundant ferruginous pisoids (1-5 mm in size) and macropisoids (>5 mm), whereas the intermediate and upper levels are ochre and violet days/marls with few or no pisoids. The pisoids normally consist of a nucleus and a cortex made up of several layers. Some pisoids have a fragment of a previous pisoid acting as a nucleus, indicating local reworking processes. Both the nucleus and the cortex are formed by hematite, goethite, variable contents of kaolinite, and minor proportions of ilmenite. Their texture and mineralogy show an in-silo growth. Interbedded limestone beds within the clay- and clay/marl-dominated levels are formed by micrite, microsparite and sparite. These limestones are cemented by kaolinite and they also have pisoids, indicating the occurrence of edaphic processes. The red clays have the lowest calcite content and the highest hematite, anatase, diaspore, goethite and kaolinite content. By contrast, the ochre and violet clays/marls have higher illite content. Smectite is only detected in the ochre days/marls. This mineral association is characteristic of lateritic palaeosols, formed under warm and humid conditions. Kaolinite and smectite textures indicate that they are authigenic, whereas illite may be of detrital origin. The upward decrease in kaolinite, hematite, anatase, diaspore and goethite content, along with the increase in quartz content and the presence of smectite and illite, reflect a change from warm and humid conditions to drier and colder conditions during the early Barremian in the studied area. (C) 2020 Elsevier B.V. All rights reserved.

The aim of this study is to analyze natural clinkers (= calcined clays by coal combustion) from a lower Cretaceous coal outcrop in Ariño (Teruel, NE Spain) in order to describe mineral and textural transformations produced during the spontaneous combustion of coal. To achieve this aim, samples were analyzed using X-ray diffraction and optical and electron microscopy. Spontaneous combustion resulted in the melting of the surrounding clays, with the generation of an Al–Si-rich vitreous phase. Subsequently, high-temperature phases crystallized from this vitreous phase. These new minerals are interesting due to their similarity with those formed during ceramic processes, used in the manufacture of stoneware and ceramic tiles, as well as in refractory ceramics, and with natural events such as metamorphic and igneous processes. The studied natural clinkers are composed of vitreous phase mullite, hematite, hercynite, cristobalite, quartz, pyroxenes, cordierite, gypsum, pyrite, and calcium oxides. A trend from hematite to hercynite composition indicates compositional variations at sample scale, which evidence d-spacing differences in hercynite and may be related to the Al and Fe content in hercynite depending on its texture. The mullite shows higher Si/Al ratio (1.21) than the theoretical composition (0.35), indicating that this mullite is more Si-rich. Three pyroxene-type compositions (diopside-type, ferrosilite-type, and a Ca–Al-rich pyroxene) were found. Both the mullite and the pyroxenes are nonstoichiometric.