Cameros Basin Research Articles

Subsidence and thermal history of an inverted Late Jurassic‐Early Cretaceous extensional basin (Cameros, North‐central Spain) affected by very low‐ to low‐grade metamorphism

AbstractThe Cameros Basin (North Spain) is a Late Jurassic‐Early Cretaceous extensional basin, which was inverted during the Cenozoic. It underwent a remarkable thermal evolution, as indicated by the record of anomalous high temperatures in its deposits. In this study, the subsidence and thermal history of the basin is reconstructed, using subsidence analysis and 2D thermal modelling. Tectonic subsidence curves provide evidence of the occurrence of two rapid subsidence phases during the syn‐extensional stage. In the first phase (Tithonian‐Early Berriasian), the largest accommodation space was formed in the central sector of the basin, whereas in the second (Early Barremian‐Early Albian), it was formed in the northern sector. These rapid subsidence phases could correspond to relevant tectonic events affecting the Iberian Plate at that time. By distinguishing between the initial and thermal subsidence and defining their relative magnitudes, Royden's (1986) method was used to estimate the heat flow at the end of the extensional stage. A maximum heat flow of 60–65 mW/m2 is estimated, implying only a minor thermal disturbance associated with extension. In contrast with these data, very high vitrinite reflectance, anomalously distributed in some case with respect to the typical depth‐vitrinite reflectance relation, was measured in the central‐northern sector of the basin. Burial and thermal data are used to construct a 2D thermal basin model, to elucidate the role of the processes involved in sediment heating. Calibration of the thermal model with the vitrinite reflectance (%Ro) and fluid inclusion (FI) data indicates that in the central and northern sectors of the basin, an extra heat source, other than a typical rift, is required to explain the observed thermal anomalies. The distribution of the %Ro and FI values in these sectors suggests that the high temperatures and their distribution are related to the circulation of hot fluids. Hot fluids were attributed to the hydrothermal metamorphic events affecting the area during the early post‐extensional and inversion stages of the basin.

Early Syn-Rift Evolution In the West Cameros Basin (Upper Jurassic, NW Iberian Range), Spain

Abstract Alluvial systems are sensitive sedimentary systems that can preserve useful information about tectonics, drainage area (lithology and size), and climate. However, research on this subject over the last three decades has made it evident that the interaction of these three factors and their control over the alluvial architecture and facies are complex. The stratigraphic and sedimentological analysis of the earliest syn-rift sedimentary record (Tithonian) in the West Cameros Basin has confirmed that sedimentation during the beginning of extension in this area took place in a series of halfgraben basins in which three different types of fan-shaped alluvial systems were deposited: two relatively large systems, specifically, a “highly channelized alluvial fan system” and a “distributive fluvial fan system changing downstream to an axial tributary fluvial system,” were the exception; and small “poorly channelized alluvial fan systems” were the norm. A semiarid climate is inferred during this earliest syn-rift sedimentary record from the steady and extensive calcrete development. This semiarid climate should play an important role both in how coarser sediment discharges to the rift halfgraben basins occurred and in the dominant transverse organization of the alluvial depositional systems. However, the climate and source-area lithology can be considered steady factors, so the main factors considered as the cause of these sedimentary and architectural heterogeneities are the tectonics and drainage-area sizes, and specifically, the different behavior of each extensional structure in terms of the rate of tectonic uplift and subsidence. This indicates how fault activity and drainage-area sizes during the earliest stages of a rift system can generate high degrees of heterogeneity in the architecture of alluvial basins and how this heterogeneity is recorded by the alluvial systems in the form of differences in their facies association and architecture. Therefore, this work concludes that both tectonics and catchment sizes exerted primary control on the sedimentary characteristics of associated alluvial systems in basins generated from this type of extensional setting, and care must be taken when making climatic and tectonic interpretations using the sedimentary record of these alluvial systems because many changes that traditionally have been attributed to climate variability can be explained solely by the differential behavior of each extensional structure and/or changes in its associated drainage area.

Las huellas de tortuga del Grupo Oncala (Berriasiense, Cuenca de Cameros, España)

Although the dinosaur footprints are very frequent in the Oncala Group (Cameros Basin), it does not happen with the tracks of other reptiles, especially in the case of crocodiles and turtles. Up to now, only one ichnogenus freshwater turtle track morphotype (Emydhipus) is known in this group, and it is possible the existence of other terrestrial tortoises tracks. The finding of new tracks and the general review of the known material, suggest that the turtle tracks are more variable and widespread than we previously thought, which corresponds with the existence of a large representation of a recently recognized turtle genus from the Lower Cretaceous of Cameros Basin and also from the whole the Iberian Peninsula.

A new dinosaur tracksite with small footprints in the Urbión Group (Cameros Basin, Lower Cretaceous, La Rioja, Spain)

A new dinosaur tracksite (La Rueda) with ten small tridactyl footprints (the length ranges between 9 and 15 cm) from the Urbión Group (Cameros Basin, Lower Cretaceous, La Rioja, Spain) is described. The footprints are approximately as long as wide and have high divarication angles between digits II-IV (~80º), some pad impressions on each digit, claw marks, a medial notch and a circular heel pad impression. They are here classified as indeterminate ornithopod footprints and contribute to the increase in the dinosaur ichnodiversity of the Urbión Group. Small dinosaur footprints are scarce in the worldwide fossil record. In the Urbión Group, large dinosaur tracks are much more frequent than small ones. This scarcity could be explained as ecological biases (dearth of small individuals in an area). Nevertheless, the number of small footprints in the Urbión Group is instead the product of by preservation biases (coarse grain sediments and fluvial erosive bases) and the weathering and erosion processes (brittle nature of the rock) that affect especially to small tracks than large ones identified in this Group.

Unusual sauropod tracks in the Jurassic-Cretaceous transition. Cameros Basin (Burgos, Spain)

The Las Sereas site includes at least 14 ichnological outcrops along 5.6 km, in the Lara area, southwest Burgos Province. 67 ichnites of dinosaurs are documented at Las Sereas 7, identified as theropod and sauropod trackways occurring in shallow carbonates of lacustrine environment. Sauropod trackways have intermediate-gauge and low heteropody, and show different anatomical features to other tracks found in the ichnological record, especially in the disposition and orientation of pes digits. They are similar to Polyonyx from the Middle Jurassic of Portugal. However, since they do not preserve reliable manus data they are classified as aff. Polyonyx. The three sauropod trackways are related to the same kind of trackmaker. They differ from each other only in size, and gregarious behavior has not been detected. Analysis of these trackways reveals changes in travel direction even when there are few tracks in each sequence. At the Las Sereas 7 tracksite, the pace length (PL), width of the angulation pattern (WAP) and the WAP/PL ratio and depth analysis via photogrammetry show a direction change in two sauropod trackways. This tracksite and that at La Pedraja are unique in the Tithonian-Berriasian interval of the Iberian Peninsula that occur in a lacustrine environment, and could be indicate of the relationship between the diversity of Iberian, Tithonian-Berriasian sauropod tracks and sedimentary environments.

Sedimentology of Ancient Coastal Wetlands: Insights From A Cretaceous Multifaceted Depositional System

Coastal wetlands are prominent modern environments widely studied in geomorphology and ecology, but the term ‘‘coastal wetland’’ is still barely used for the sedimentological classification of ancient deposits. The depositional system studied here (Leza Formation, Cameros Basin, Early Cretaceous, N Spain) includes diverse carbonate and clastic facies deposited at the sea–land transition, and is an illustrative example of the wide array of sedimentary environments that may occur in coastal wetlands systems. The studied system was composed mainly of carbonate water bodies whose salinity ranged from fresh to brackish and near-marine, and which had variable input of clastic material due to their lateral connection with alluvial fans. In addition, the system also included carbonate water bodies with stronger marine influence, tide-influenced oolitic areas, and relatively restricted evaporative settings. The deposits of all these environments occur alternating with each other throughout a unit 30–280 m thick, and they range from continental to marine conditions in a relatively small area (approximately 10 km 3 30 km). Thus, this sedimentological study of the Leza Fm provides an ideal opportunity to investigate challenging ancient deposits with both continental and marine features. Comparison with other modern and ancient coastal settings allows the conclusion that ‘‘coastal wetland’’ may be the most accurate sedimentological classification for the Leza Fm, since it was not part of a major coastal system (e.g., delta or estuary). A series of general sedimentological characteristics of coastal wetland deposits are gathered from the Cretaceous case study and from the modern and ancient examples examined. These characteristics include: predominance of shallow-water facies; common subaerial exposure and edaphic features; great variety of interrelated continental, transitional, and marine environments with contrasting hydrodynamic and hydrochemical conditions; and low-diversity biotic communities, including both continental and marine fossils, as well as fossils of ambiguous affinities.

From carbonate–sulphate interbeds to carbonate breccias: The role of tectonic deformation and diagenetic processes (Cameros Basin, Lower Cretaceous, N Spain)

Interpreting the origin of carbonate breccias requires a detailed analysis because they may be the result of a wide variety of processes that produce similar features. This is the case of the Lower Cretaceous carbonate breccias of the Cameros Basin (previously interpreted as slump or collapse breccias), whose origin is interpreted after performing a detailed sedimentary, petrographic and tectonic study.The studied carbonate breccias consist of angular carbonate mudstone fragments floating in a matrix of calcite and quartz crystals. The breccias are interbedded with, and laterally associated to, alternating layers of carbonate mudstone and calcite and quartz pseudomorphs after gypsum, which show strong similirities to the breccia fragments and matrix, respectively, suggesting that the brecciated beds were originally composed of identical alternating carbonate mudstone and gypsum layers as the unbrecciated layers. The breccias are associated with frequently polyharmonic deformation structures, which are similarly oriented as the regional tectonic structures, indicating that they are related with the alpine contractional deformation of this area of the Cameros Basin. All these features suggest that the carbonate breccias were formed by tectonic deformation of alternating layers of carbonate mudstone and calcium sulphate, which have very different rheological behaviours. As a result, during tectonic deformation, sulphate flowed and carbonate layers were broken and displaced, producing a breccia of carbonate fragments within a sulphate groundmass. Afterwards, the sulphate groundmass was replaced by quartz and calcite, and the breccia acquired its final composition.

Understanding the Mesozoic kinematic evolution in the Cameros basin (Iberian Range, NE Spain) from magnetic subfabrics and mesostructures

Analysis of anisotropy of magnetic susceptibility (AMS) and brittle mesostructures (hydroplastic synsedimentary faults and tension gashes) is applied in this study in order to characterize the Mesozoic tectonic events in the Cameros basin (NW Iberian Range), formed between Tithonian and Albian times. Low-field AMS at room and low temperature (LF-AMS at RT and LF-AMS at LT, respectively) together with high-field AMS (HF-AMS) measurements allow separating ferro- and paramagnetic fabrics. The combination of LF-AMS at LT and HF-AMS torque measurements confirms the reliability of both procedures in terms of isolating the paramagnetic contribution to the AMS. Magnetic fabric results combined with the analyses of synsedimentary faults indicate a NW–SE extension direction during Aptian (and probably Barremian) times. This extension direction is perpendicular to the main extension direction (NE–SW) prevailing during early and late stages of basin evolution. It is also consistent with extension direction deduced from large-scale bending folds and tension gashes, developed after partial lithification. Cleavage development during Albian enhanced the orientation of the magnetic fabric in lithologies where the previous extensional magnetic lineation is coaxial with the expected one for compression.

Tectono-stratigraphic evolution of an inverted extensional basin: the Cameros Basin (north of Spain)

The Cameros Basin is a part of the Mesozoic Iberian Rift. It is an extensional basin formed during the late Jurassic and early Cretaceous, in the Mesozoic Iberian Rift context, and it was inverted in the Cenozoic as a result of the Alpine contraction. This work aims to reconstruct the tectono-stratigraphic evolution of the basin during the Mesozoic, using new and revised field, geophysical and subsurface data. The construction of a basin-wide balanced section with partial restorations herein offers new insights into the geometry of the syn-rift deposits. Field data, seismic lines and oil well data were used to identify the main structures of the basin and the basin-forming mechanisms. Mapping and cross-sectional data indicate the marked thickness variation of the depositional sequences across the basin, suggesting that the extension of the depositional area varied during the syn-rift stage and that the depocentres migrated towards the north. From field observation and seismic line interpretation, an onlap of the depositional sequences to the north, over the marine Jurassic substratum, can be deduced. In the last few decades, the structure and geometry of the basin have been strongly debated. The structure and geometry of the basin infill reconstructed herein strongly support the interpretation of the Cameros Basin as an extensional-ramp synclinal basin formed on a blind south-dipping extensional ramp. The gradual hanging-wall displacement to the south shifted the depocentres to the north over time, thus increasing the basin in size northwards, with onlap geometry on the pre-rift substratum. The basin was inverted by means of a main thrust located in a detachment located in the Upper Triassic beds (Keuper), which branched in depth with the Mesozoic extensional fault flat. The reconstruction of the tectono-stratigraphic evolution of the Cameros Basin proposed herein represents a synthesis and an integration of previous studies of the structure and geometry of the basin. This study can be used as the basis for future basin-scale research and for modelling the ancient petroleum system of the basin.

Palaeoecological inferences about dinosaur gregarious behaviour based on the study of tracksites from La Rioja area in the Cameros Basin (Lower Cretaceous, Spain)

In La Rioja the widespread ichnological record of dinosaurs ranges from the Berriasian to the Aptian age (Early Cretaceous). There, due to the high palaeodiversity, several evidences of gregarious behaviour can be observed in different types of footprints (sauropods, theropods and ornithopods). Moreover, due to the huge dimensions of some sites, different types of dinosaur tracks representing gregarious behaviour can be found very close in space and time. All these evidences have been compiled and analysed, obtaining an overview of this type of behaviour in relation to the type of trackmaker. Twenty-eight evidences of gregariousness have been found, of which nine are of sauropod footprints, twelve of theropod, seven of ornithopod, and one of unknown bipedal dinosaurs. These data have been further divided into accumulations and sets of parallel trackways. In sauropod footprints the main evidence is represented by the accumulations of tracks made by herds of individuals of the same size. In ornithopod footprints there are accumulations and parallel trackways of large size individuals and even family groups. In theropod footprints, sets of parallel trackways of few individuals of the same size (from small to medium) are the most common evidence and there are no data about gregariousness in large theropod footprints. Thus, data were obtained on different sizes of herds, size of individuals and structure of the groups depending on different ichnotypes, providing information about important palaeoecological aspects of their trackmakers, such as population structure.

Intra-Trackway Morphological Variations Due to Substrate Consistency: The El Frontal Dinosaur Tracksite (Lower Cretaceous, Spain)

An ichnological and sedimentological study of the El Frontal dinosaur tracksite (Early Cretaceous, Cameros basin, Soria, Spain) highlights the pronounced intra-trackway variation found in track morphologies of four theropod trackways. Photogrammetric 3D digital models revealed various and distinct intra-trackway morphotypes, which reflect changes in footprint parameters such as the pace length, the track length, depth, and height of displacement rims. Sedimentological analyses suggest that the original substrate was non-homogenous due to lateral changes in adjoining microfacies. Multidata analyses indicate that morphological differences in these deep and shallow tracks represent a part of a continuum of track morphologies and geometries produced by a gradient of substrate consistencies across the site. This implies that the large range of track morphologies at this site resulted from similar trackmakers crossing variable facies. The trackways at the El Frontal site present an exemplary case of how track morphology, and consequently potential ichnotaxa, can vary, even when produced by a single trackmaker.

A new semionotiform actinopterygian fish from the Mesozoic of Spain and its phylogenetic implications

Camerichthys lunae gen. et sp. nov. is a semionotiform actinopterygian fish described from the newly reported locality of San Andrés de San Pedro (province of Soria, Spain). The material, an articulated, partial three-dimensional specimen, was unearthed from the Tithonian–Berriasian beds of the Matute Formation (Tera Group) in the continental Cameros Basin. The new taxon, Camerichthys lunae gen. et sp. nov., differs from other ginglymodians in presenting a unique combination of characters plus: presence of a suprapreopercular bone; antorbital intermediate in depth in relation to the other anterior infraorbitals; and infraorbital placed in the anterior border of the orbit subdivided into two portions (three uniquely derived characters). The results of the cladistic analysis show that the new genus from Soria cannot be assigned to any of the three semionotiform families, Callipurbeckiidae, Macrosemiidae or Semionotidae. It is considered Semionotiformes incertae sedis. In the more resolutive analysis, with ordered characters, Camerichthys lunae gen. et sp. nov. appears as the sister group of the clade formed by the families Callipurbeckiidae plus Macrosemiidae. The effects of the new genus on the phylogeny of these two families and Dapedium, Semionotus and Paralepidotus, are discussed. Camerichthys gen. nov. is the first ginglymodian genus endemic to the Iberian Peninsula.http://zoobank.org/urn:lsid:zoobank.org:pub:BBD15A41-5BFC-4BFF-AD40-ECD1891953F1

New insights on stratigraphy and sedimentology of the Oncala Group (eastern Cameros Basin): implications for the paleogeographic reconstruction of Iberia at Berriasian times

The Berriasian Oncala Group of the eastern Cameros Basin is a key element for the paleogeographic reconstruction of NE Iberia during this period of time, due to its intermediate position between the Basque-Cantabrian, southern Iberian, and Pyrenean Basins. The Oncala Group, which comprises up to 2500 m of sediments, consists of siliciclastic deposits in western areas of the basin, which pass gradually eastwards and upwards to carbonate-evaporitic deposits. The siliciclastic deposits consist of an alternation of laterally extensive laminae of siliciclastic mudstone and sandstone, and meander loop bodies. The carbonate deposits are made up of an alternation of laminae of carbonate mudstone and pseudomorphs after gypsum, interbedded with shales and carbonate breccias. These deposits had been traditionally interpreted as formed in fluvial and alluvial systems, and laterally related lakes, but recent and new sedimentological data discussed in this paper suggest that they were deposited in broad, siliciclastic tidal flats, laterally associated with a fluvial system to the west, and with shallow, coastal, carbonate-sulphate water bodies to the east. The development of these coastal environments in the Oncala Group indicates that a wide, shallow, coastal embayment was developed in the eastern Cameros Basin during the Berriasian. This new paleoenvironmental interpretation makes necessary a revision of the paleogeographic reconstruction of this area of Iberia during the Berriasian because it implies that the connection of the Cameros Basin with marine areas was much more important than previously considered. The presence of very similar facies associations in the Basque-Cantabrian Basin, which include siliciclastic tidal and lagoonal deposits in the western areas, and evaporites and carbonates of restricted marine environments in the eastern areas, the similar sulphur isotope compositions of the sulphates of the Basque-Cantabrian and Cameros Basins, and the similar vertical evolution of the Berriasian deposits of both basins, suggest that the Cameros Basin was connected with marine and transitional areas of the Basque-Cantabrian Basin during Berriasian times. Nevertheless, a connection with the southern Iberian Basins, which also contain siliciclastic and carbonate tidal deposits, cannot be excluded.

Eustatic versus tectonic control in an intraplate rift basin (Leza Fm, Cameros Basin). Chronostratigraphic and paleogeographic implications for the Aptian of Iberia

The Leza Formation is a carbonate unit of the northern Cameros Basin (N Spain) with controversial age, stratigraphic position, and sedimentological interpretation. It was deposited in a series of fault-bounded tectonic depressions along the northern margin of the basin. The Leza Fm overlies and changes laterally to the siliciclastic Jubera Fm, and the thickness of both units is also controlled by faults. Although the Leza Fm has been traditionally interpreted as lacustrine with sporadic marine incursions, detailed sedimentological analysis reveals new and very abundant evidences of marine influence: sedimentary structures of tidal origin, common marine fossils (dasycladales and foraminifers), and homogeneous populations of porocharacean charophytes, indicative of brackish conditions. Thus, this unit is interpreted as deposited in a system of coastal-wetlands with both fresh-water and sea-water influence, laterally related with the alluvial deposits of the Jubera Fm and the fluvio-lacustrine deposits of the Enciso Gr towards the centre of the basin. Using the chronostratigraphic ranges of the marine fossils and the lateral relationship with adjacent units, the Leza Fm is confirmed as part of a depositional sequence late Barremian - early Aptian in age. Furthermore, a transgressive trend is defined in the Leza Fm, which is compared with the eustatic evolution of the neighbouring Basque-Cantabrian, Iberian and Pyrenean marine basins, allowing correlation of the upper part of this unit with the widespread eustatic maximum of the middle-upper part of the early Aptian. This eustatic influence provided additional accommodation space to that created by tectonics. These data from the Cameros Basin are contrasted with a thorough compilation of paleogeographic data, showing that, during the early Aptian transgression, marine influence was likely to reach the northern Cameros Basin, not only coming from the SE Iberian Basin, as previously interpreted, but also from the NW Basque-Cantabrian Basin. This resulted in a probable link between Boreal and Tethyan marine realms [RESUMEN] La Formacion Leza es una unidad carbonatica del norte de la Cuenca de Cameros (N Espana), cuya edad, posicion estratigrafica e interpretacion sedimentologica son controvertidas. Se deposito en una serie de cubetas tectonicas limitadas por fallas a lo largo del borde norte de la cuenca. La Fm Leza yace sobre y pasa lateralmente a los depositos siliciclasticos de la Fm Jubera, estando el espesor de ambas unidades tambien controlado por fallas. Pese a que la Fm Leza ha sido tradicionalmente interpretada como lacustre con incursiones marinas esporadicas, el analisis sedimentologico detallado revela nuevas evidencias muy abundantes de influencia marina: estructuras sedimentarias de origen mareal, y habituales fosiles marinos (dasycladales y foraminiferos), asi como poblaciones homogeneas de carofitas porocaraceas, que indican medios salobres. Esta unidad se interpreta como formada en un sistema de humedales costeros con influencia tanto de agua dulce como de agua marina, relacionado lateralmente con los depositos aluviales de la Fm Jubera y con los depositos fluvio-lacustres del Gr Enciso hacia el centro de la cuenca. Usando los rangos cronoestratigraficos de los fosiles marinos y las relaciones laterales con unidades adyacentes, se confirma la pertenencia de la Fm Leza a la secuencia deposicional de edad Barremiense superior - Aptiense inferior. Ademas, se define una tendencia transgresiva en la Fm Leza, que al ser comparada con la evolucion eustatica de las cuencas marinas coetaneas, Vasco-Cantabrica, Iberica y Pirenaica, permite la correlacion de la parte superior de esta unidad con el maximo eustatico generalizado de la parte media-superior del Aptiense inferior. Esta influencia eustatica produjo un espacio de acomodacion adicional al producido por la tectonica. Estos datos de la Cuenca de Cameros son contrastados con una recopilacion exhaustiva de datos paleogeograficos, mostrando que durante la transgresion del Aptiense inferior, la influencia marina probablemente alcanzo el norte de la Cuenca de Cameros no solo desde la Cuenca Iberica al SE, como ha sido interpretado previamente, sino tambien desde la Cuenca Vasco-Cantabrica al NO. Esto produciria la probable union entre los ambitos del Oceano Boreal y del Tetis.

Interpretation of gravimetric and magnetic anomalies in the Cameros Basin (North Spain): combination of deep and shallow sources

Outstanding potential field anomalies (gravimetric and magnetic) in the Cameros Basin (N Spain) follow a WNW-ESE trend, parallel to the geological structures resulting from Mesozoic extension and Tertiary basin inversion. The positive Bouguer gravity anomaly (15 mGal) is interpreted as the result of a strong contrast between the density of Tertiary rocks of the foreland basin and the Paleozoic and Mesozoic rocks, combined with crustal thickening in the Iberian Chain with respect to the Ebro Basin. The dipolar magnetic anomaly, slightly shifted to the south with respect to the relative maximum of the Bouguer anomaly, can be interpreted as related to volcanic rocks within the basement, which are linked to Triassic rifting as witnessed by outcrops of basalts along the basin margins. An exhaustive analysis of rock properties (density, magnetic susceptibility and remanence) and basin geometry from other sources (seismic reflection profiles) allow to constrain variations in crustal thickness and the location of large-scale basement faults.

Depositional Depth of Laminated Carbonate Deposits: Insights From the Lower Cretaceous Valdeprado Formation (Cameros Basin, Northern Spain)

The Lower Cretaceous (Berriasian) Valdeprado Formation (Cameros Basin, northern Spain) contains more than 900 m of laminated carbonates and pseudomorphs after sulfates. Traditionally, many sedimentary packages of different ages and lithologies have been interpreted as deep-water deposits based essentially on the abundance of laminations and the absence of subaerial exposure features. In contrast, the Valdeprado Formation provides an example of a shallow-water deposit dominated by laminations with scarce evidence of subaerial exposure, and gives criteria to solve the challenge of distinguishing shallow-water and deep-water, ancient laminated deposits. The two most abundant facies all along the Valdeprado Formation are: a) parallel-laminated limestone, formed by alternating carbonate mudstone and calcite and quartz pseudomorphs after displacive gypsum, and b) graded-laminated limestone, consisting of quartz, mica, ostracodes, and pseudomorphs after detrital gypsum grains at the base, which changes gradually upwards to carbonate mudstone. Parallel-laminated limestone and graded-laminated limestone could have been deposited in either deep or shallow environments as a result of salinity fluctuations driven by alternation of flooding and evaporation and by sediment resuspension processes, respectively. Subaerial exposure features, such as desiccation mudcracks, are scarce in most of the succession, except in a few meter-scale stratigraphic intervals where they are very abundant. Interestingly, in these intervals desiccation cracks are present at the tops of several successive laminae (up to 25 mudcracked laminae per meter of deposit), indicating that, at least during those periods of time, deposition occurred in shallow water bodies that were desiccated frequently. In the upper part of the stratigraphic section, parallel-laminated and graded-laminated limestones are associated with current-ripple and wave-ripple cross-laminated arenites, and ostracode mudstone to wackestone with centimeter-size pseudomorphs after lenticular gypsum, and abundant desiccation mudcracks and tepees, which also suggest sedimentation in shallow-water environments. Moreover, the laminated carbonates display continuous, parallel layering, and the same facies along the 40-km-long outcropping area. These deposits are directly interbedded with, and pass laterally to, siliciclastic sandy–muddy flat deposits in the western area of the basin, without clinoforms, slump structures, or slide masses in between. All of these features suggest deposition in shallow, perennial carbonate–sulfate water bodies and their peripheral mudflats, developed in a flat-bottomed basin with no marked gradients.

Camerochelys vilanovai gen. et sp. nov., a new pan-cryptodiran turtle in the Early Cretaceous of the Iberian Range (Spain)

A new turtle taxon, Camerochelys vilanovai gen. et sp. nov., from Hauterivian–Barremian levels of the eastern Cameros Basin (La Rioja, Iberian Range, Spain), is proposed here. Elements of the shell corresponding to five individuals are assigned to it. Camerochelys vilanovai is a turtle with a low, oval and longer than wide shell. It is diagnosed by a combination of characters that includes, among others, the presence of an ornamentation pattern, restricted to the medial area of the vertebral scutes, and composed of thin, numerous and poorly developed radiating striations; shallow nuchal notch; short, and more than four times wider than long cervical scute; five vertebral scutes, all of them substantially wider than long, the second and third ones being more than two times wider than long, and the fourth one two times wider than long; sagittal contact of the last pair of costal plates; presence of inframarginal scutes; absence of mesoplastra. Camerochelys vilanovai is identified as a member of Pan-Cryptodira not assigned to Eurysternidae, to the clade including representatives of Paracyptodira and Plesiochelyidae, or to the crown group Cryptodira. This new taxon could be a representative of Xinjiangchelyidae, a clade belonging to the stem group of Cryptodira, and identified in the Asian and European record. The description of this new taxon further increases the known diversity of turtles in the Early Cretaceous of the Iberian Range, a region where members of several clades of the stem group of Testudines, Pan-Pleurodira and Pan-Cryptodira have been previously identified.

A new varanoid squamate from the Early Cretaceous (Barremian–Aptian) of Burgos, Spain

A new anguimorph lizard from the late Barremian–Aptian of the Salas de los Infantes area (Cameros Basin, Iberian Peninsula) is described here as Arcanosaurus ibericus gen. et sp. nov. It corresponds to the first squamate remains from the Burgos Province. The unique combination of morphological and microanatomical characters enables us to erect a new genus and species that we tentatively assign to Varanoidea despite the strange seemingly absence on the axis of a posterior hypapophysis. The combination of both microanatomical and geological data suggests an essentially terrestrial mode of life. This discovery reveals itself particularly interesting concerning the evolutionary history of varanoids as this new Spanish taxon might correspond to the oldest terrestrial varanoid known to date.

Evidence of predation in Early Cretaceous unionoid bivalves from freshwater sediments in the Cameros Basin, Spain

Here, we present evidence of possible vertebrate predation on freshwater bivalves from the Lower Cretaceous strata of the Cameros Basin (Spain). The described collection contains the largest number of vertebrate-inflicted shell injuries in freshwater bivalve shells yet reported in the Mesozoic continental record. Several types of shell damage on fossil shells of Protopleurobema numantina (Bivalvia: Unionoida) are described and their respective modes of formation interpreted in the context of morphological attributes of the shell injuries and the inferred tooth morphology of predators that could have inflicted such injuries. Detailed study of these bite marks shows similarities with the well-documented injuries in the shells of marine molluscs, namely ammonoids, that have likewise been attributed to reptilian predators. The most parsimonious interpretation suggests crocodiles as the vertebrates interacting with the bivalves in the Cameros Basin. □Barremian–Aptian; bite marks; freshwater bivalves; predation; reptile; Unionoida.

Ethological variations in gauge in sauropod trackways from the Berriasian of Spain

Castanera, D., Pascual, C., Canudo, J.I., Hernandez, N. & Barco, J., 2012: Ethological variations in gauge in sauropod trackways from the Berriasian of Spain. Lethaia, Vol. 45, pp. 476–489. Two sauropod trackways from the Early Cretaceous (Berriasian) of the Cameros Basin (Spain) show important variations in trackway gauge, along the same trackway. These variations seem to be associated with different behaviours; on the one hand with a significant variation in the direction of travel (turning phenomena) and on the other hand with a decrease in speed, probably associated with the properties of the substrate. These variations in sauropod trackways provide the trackway gauge debate with new data, supporting the hypothesis that the walking style and substrate properties may in some cases determine this sauropod character. The study of turning sauropod trackways improves our knowledge of sauropod locomotion. □Ethology, intermediate-gauge, sauropod trackways, substrate properties, wide-gauge.