Jurassic Early Cretaceous Research Articles

Quantifying the temporal pattern of shape change in trigoniids through the Middle Jurassic–Early Cretaceous of Kutch: A geometric morphometric approach

Quantifying the temporal pattern of shape change in trigoniids through the Middle Jurassic–Early Cretaceous of Kutch: A geometric morphometric approach

Hydrologically sensitive carbonates: Tectonic and groundwater controls on synrift sedimentation in the Late Jurassic–Early Cretaceous of the western Cameros Basin, Northern Spain

AbstractBasin hydrology and subcrop are key controls on carbonate sedimentation in continental basins. Hydrologically sensitive carbonates can record groundwater fluctuations within an aquifer in deep time. Late Jurassic extension, footwall uplift, erosion and karstification of marine Jurassic carbonates in the western Cameros Basin (Spain) saw deposition of ?Upper Kimmeridgian‐Tithonian syntectonic alluvial fan deposits (Señora de Brezales Formation). Biogenic laminar calcretes and phreatophytic rhizocretions record roots exploiting capillary fringe groundwater. Progressive infill of rift topography and footwall erosion lowered sedimentary gradients and clastic supply during deposition of the ?Tithonian–Berriasian Rupelo Formation. Distal alluvial marls (Las Viñas Member) contain charophytes, with 2 m thick carbonate lenses at the top reflecting intermittent rise of groundwater in ponds on the basin floor. Stacked palustrine limestones with rare charophytes and laminar calcretes (Ladera Member) record overstep of seasonal carbonate wetlands onto basin margins and footwall highs with intense pedogenetic modification during lengthy seasonal exposure. Overlying Berriasian charophyte‐ostracod wackestones, displaying microkarst cavities and interbedded intraclastic conglomerates, with vivianite sauropod bones, footprints and polygonal desiccation cracks at the top (Mambrillas de Lara Member) record open lacustrine conditions with limited subaerial exposure and high water tables. Desiccation‐cracked limestones and marls with correlatable evaporite horizons (Rio Cabrera Member) contain marginal marine foraminifera and dasycladaceae at the top. Lagoonal conditions reflected transgression to seaward and intermittent marine connection via the Basco‐Cantabrian Basin. The distribution and thicknesses of hydrologically sensitive carbonates reflected onlap onto a faulted and karstified marine Jurassic carbonate pediment and the subtle influence on hydroperiod of fault (and potentially localised Triassic salt) controlled differential subsidence and transgressive groundwater rise. Hydrological facies evolution reflects progressive basin infilling and eustasy beyond. Transitions in this continental succession from clastic to carbonate facies and from closed to open hydrology record hydrological change over time rather than contemporaneous deposition under Walther's Law.

Enhanced flight performance and adaptive evolution of Mesozoic giant cicadas.

Insects have evolved diverse ecological flight behaviors and adaptations that played a key role in their large-scale evolutionary patterns. However, the evolution of their flight performance is poorly understood because reconstructing flight abilities of extinct insects is highly challenging. Here, we propose an integrated approach to reveal the evolution of flight performance of Palaeontinidae (giant cicadas), a Mesozoic arboreal insect clade with large bodies and wings. Our analyses unveil a faunal turnover from early to late Palaeontinidae during the latest Jurassic-earliest Cretaceous, accompanied by a morphological adaptive shift and remarkable improvement in flight abilities including increased flight speed and enhanced maneuverability. The adaptive aerodynamic evolution of Palaeontinidae may have been stimulated by the rise of early birds, supporting the hypothesis of an aerial evolutionary arms race (Air Race) between Palaeontinidae and birds. Our results provide a potential example of predator-induced morphological and behavioral macroevolution and contribute to our understanding of how powered flight has shaped animal evolution.

Age and provenance relationships between the basal Great Valley Group and its underlying basement: implications for initiation of the Great Valley forearc basin, California, U.S.A.

ABSTRACT The Great Valley forearc (GVf) basin, California, records deposition along the western margin of North America during active oceanic subduction from Jurassic through Paleogene time. Along the western GVf, its underlying basement, the Coast Range Ophiolite (CRO), is exposed as a narrow outcrop belt. CRO segments are overlain by the Great Valley Group (GVG), and locally, an ophiolitic breccia separates the CRO from basal GVG strata. New stratigraphic, petrographic, and geochronologic data (3865 detrital and 68 igneous zircon U-Pb ages) from the upper CRO, ophiolitic breccia, and basal GVG strata clarify temporal relationships among the three units, constrain maximum depositional ages (MDAs), and identify provenance signatures of the ophiolitic breccia and basal GVG strata. Gabbroic rocks from the upper CRO yield zircon U-Pb ages of 168.0 ± 1.3 Ma and 165.1 ± 1.2 Ma. Prominent detrital-zircon age populations of the ophiolitic breccia and GVG strata comprise Jurassic and Jurassic–Early Cretaceous ages, respectively, with pre-Mesozoic ages in both that are consistent with sources of North America affinity. Combined with petrographic modal analyses that show abundant volcanic grains (> 50%), we interpret the breccia to be mainly derived from the underlying CRO, with limited input from the hinterland of North America, and the basal GVG to be derived from Mesozoic igneous and volcanic rocks of the Sierra Nevada–Klamath magmatic arc and hinterland. Analysis of detrital-zircon grains from the lower and upper ophiolitic breccia yields MDAs of ∼ 166 Ma and ∼ 151 Ma, respectively. Along-strike variation in Jurassic and Cretaceous MDAs from basal GVG strata range from ∼ 148 to 141 Ma, which are interpreted to reflect diachronous deposition in segmented depocenters during early development of the forearc. The ophiolitic breccia was deposited in a forearc position proximal to North America < 4 Myr before the onset of GVG deposition. A new tectonic model for early development of the GVf highlights the role of forearc extension coeval with magmatic arc compression during the earliest stages of basin development.

Late Triassic to present-day tectono-thermal history of the coastal part of the Asturian basin: Implications for hydrocarbon exploration and for the North-Iberian margin evolution

The Asturian Basin, situated on the North Iberian margin, is a Permian-Mesozoic extensional basin developed over a Variscan Palaeozoic basement, subsequently inverted during the Cenozoic Alpine orogeny. The compilation of cartographic, structural, biostratigraphic and vitrinite reflectance data collected in a Late Triassic-Jurassic succession, excellently exposed along the Cantabrian Sea coast, has allowed us to gain insight into the Mesozoic and Cenozoic tectono-thermal history of this basin. The oldest recorded event occurred in Middle-Late Jurassic times and consisted of uplift, development of a large syncline, and normal faulting accompanied by circulation of hydrothermal fluids along the faults. The basin emersion caused an angular unconformity, together with a change in the sedimentary environment that passed from marine to continental. A second event, whose age was probably Late Jurassic-Early Cretaceous, was responsible for extensional reactivation of previous normal faults accompanied by a weaker fault-related hydrothermal episode. In Cenozoic (Eocene-Miocene) times, as a consequence of the Alpine orogeny some of the previous faults were reactivated as reverse and/or strike-slip faults, and folds developed. Here we analyse which structures were active during each event, their relationship with the hydrothermal fluids, the control they exerted on the hydrocarbon generation, and how the large-scale models proposed for this portion of the North Iberian margin fit the onshore field observations, in particular regarding the structural position of the Asturian Basin within the Iberian Plate Mesozoic rifts and the role of the Ventaniella Fault.

Geological characteristics and seismic identification of reservoirs in the Colorado Basin off the Atlantic coast of Argentina

Abstract The Colorado Basin is a hot exploration frontier basin conjugated with the southwest coast of Africa which has undergone four evolutionary stages: Carboniferous-Jurassic pre-rift, Jurassic-Early Cretaceous rift, Late Cretaceous transition and passive marginal drift since Paleocene. Major oil and gas discoveries have been made in the conjugated Orange Basin in recent years, including the Graff field and Venus field discovered in 2022 with recoverable reserves of 550 Mboe and 2.3 Bboe, respectively. This indicates that the basin has good oil and gas exploration potential. Based on the analysis of drilling data and seismic data, it is concluded that the basin has a mature oil-gas generation system and better reservoir conditions. The pre-rift and syn-rift source rocks are confirmed by 5 Wells with oil and gas shows in the shallow water shelf, and all have entered the hydrocarbon generation threshold. Reservoir distribution and trap-sealing conditions have become key factors in oil and gas exploration. this paper describes the reservoir characteristics in the drilling data, and extrapolates the seismic reflection characteristics of the same strata, and predicts the reservoir distribution in the unexplored area of the basin. The reservoir lithology and sedimentary facies are analyzed based on the gamma logging curves. Reservoir identification and reasonable prediction on seismic profile are mainly determined by seismic reflection amplitude and horizon calibration. The basin has three sets of reservoirs, namely, pre-rift Permian underwater fan sandstone, Lower Cretaceous alluvial fan sandstone of syn-rift period and Upper Cretaceous Colorado Formation shallow marine sandstone of transitional period. Among them, Colorado Formation sandstone reservoir has the best physical property conditions, with a maximum porosity of 32% and a thickness of 1000m. The Cretaceous and Paleogene turbidite sandstone of slope fan facies are potential reservoir in the deep waters, which mainly form litho-stratigraphic traps in the continental slope.

Sedimentology of Late Jurassic–Early Cretaceous Chia Gara Formation in Rawanduz area, Kurdistan region-Iraq

Sedimentology of Late Jurassic–Early Cretaceous Chia Gara Formation in Rawanduz area, Kurdistan region-Iraq

Significance of the Paleocene olistostrome–turbidite belt (Abant Formation) along the Intra-Pontide Suture, northern Turkey

A belt of Paleocene turbidites with olistostromes, the Abant Formation, crops out for 350 km along the Intra-Pontide Suture in northern Turkey. The suture constitutes the contact between two major Pontide tectonic units, the Istanbul and Sakarya zones, and the Abant Formation was used as evidence for the Paleocene–early Eocene closure of the Intra-Pontide ocean. We mapped and studied the Abant Formation along the Intra-Pontide Suture. The Abant Formation consists of deformed Paleocene siliciclastic turbidites with mass flows. The blocks in the olistostromes are mainly Late Cretaceous pelagic limestones; there are also Late Jurassic–Early Cretaceous, Late Cretaceous and Paleocene shallow-marine limestone blocks. Other rare block types include late Neoproterozoic and Permian granites, basalt, chert and serpentinite. The ophiolitic blocks make up less than 5% of the Abant Formation. Most of the blocks were derived from the south, from the Sakarya Zone; detrital zircon ages from the turbidite sandstones also indicate a predominantly southern source. The Abant Formation was deposited in a foreland basin, which was formed during the Paleocene collision between the Pontides and the Anatolide–Tauride Block. The basin was preferentially located on the Intra-Pontide Suture because the suture constituted an old crustal lineament.

Mesozoic tectonic evolution and dynamic mechanisms of the northern Bozhong depression of the Bohai Bay Basin, eastern China

The northern Bozhong depression of the Bohai Bay Basin in eastern China is an important area for oil and gas exploration in buried hills, which has complex structural styles and evolutionary processes. Based on 3D seismic and drilling data, the features of the Mesozoic structural deformation of the northern Bozhong depression are analyzed, and the tectonic evolution and dynamic mechanisms are also discussed. The complex Mesozoic structural styles of the northern Bozhong depression are composed of compression, strike-slip, and extension structures, which mainly trend in the near E-W, NW, NE, and NNE directions. Triggered by the collision and subduction between the North China, South China and Izanagi plates and associated stress fields of different periods, natures and directions, the northern Bozhong depression has experienced five stages of deformation at the end of the Middle Triassic, the Late Triassic, the Early-Middle Jurassic, the Late Jurassic-Early Cretaceous and the Late Cretaceous. Cyclical tectonic evolution has controlled the development of structural styles of different strikes and natures and the spatial distribution of strata in the northern Bozhong depression, providing an important foundation for hydrocarbon accumulation in buried hills.

Weathering-induced organic matter enrichment in marine-continental transitional shale: A case study on the early Permian Taiyuan Formation in the Ordos Basin, China

A comparative analysis of the factors controlling organic matter (OM) enrichment between marine-continental transitional (transitional hereafter) and marine or lacustrine shales is lacking. The early Permian Taiyuan Formation in the Ordos Basin, deposited during a shift from marine to continental settings in northern China, provides a unique opportunity to unravel the differences in OM enrichment mechanisms among these shales. The Taiyuan Formation is characterized by high TOC content (average 4.50%) and kerogen type II2-III. Most samples are thermally mature with a few high to post-mature samples relating to the Late Jurassic–Early Cretaceous Yanshanian magmatism. Rare earth elements and yttrium (REY) are dominated by light- and medium-types enrichments, with distinctly positive Gd anomaly, likely due to seawater incursion. A warm and humid climate prevailed during deposition of the Taiyuan Formation, consistent with the tropical-subtropical location of the North China Plate in the early Permian. The climatic conditions promoted intense continental weathering as reflected by high Th/Sc ratios, chemical index of alteration values, and feldspar alteration to scaly kaolinite. The V/(V + Ni) ratio is inconsistent with the other redox proxies, presumably due to variations in the redox buffer supply in the transitional facies (e.g., OM and pyrite), varying burial rates and dissimilar redox potential of different elements. Hence, this proxy should be interpreted with caution in such settings. Most redox proxies indicate oxic bottom water during deposition of the Taiyuan Formation transitional shale, in contrast to typical OM enriched marine and lacustrine shales where redox stratification or euxinic conditions are common. Instead, the dominant factor for OM enrichment in transitional shales appears to have been a high influx of terrestrial weathering products, including abundant higher-plants OM, associated with preservation of OM due to rapid burial. This process minimizes the detrimental effects of oxic conditions on OM accumulation in the transitional shale facies. This mechanism may hold relevance for analogous basins elsewhere.

Characteristics and Mechanism of the Ore-Forming Fluids in the Shimensi Tungsten Polymetallic Deposit in Southeastern China

The Shimensi super-large tungsten polymetallic deposit is located in the Late Jurassic–Early Cretaceous Porphyry–Skarn tungsten ore belt in the south Yangtze metallogenic belt. There are three types of mineralization: veinlet-disseminated type, thick quartz vein type and hydrothermal cryptoexplosive breccia type. Based on geological studies, this paper presents new petrographic, microthermometric, laser Raman spectroscopic and hydrogen and oxygen isotope research on the fluid inclusions from the deposit. The results show that there are five different types of fluid inclusions: liquid-rich inclusions, vapor-rich inclusions, pure liquid inclusions, pure vapor inclusions, and fluid inclusions containing a solid crystal. The homogenization temperatures of the fluid inclusion range from 140 °C to 270 °C, the salinities are 3 wt.%–5 wt.% NaCleq and the densities of ore-forming fluid range from 0.64 g/cm3 to 0.99 g/cm3. For the analyses of laser Raman spectroscopy, the ore-forming fluids can be approximated by a Ca2+-Na+-SO42−-Cl− fluid system with small amounts of CO2, CH4 and N2. Otherwise, the data of the pressure, pH and Eh show a fluid metallogenic environment of low pressure, weak acid and weak reduction. The values of the homogenization temperature in the three types of orebodies suggest that the mineralization is characterized by a decrease in temperature under the conditions of fluid immiscibility. The H-O isotope values are interpreted to indicate that the ore-forming fluids are mainly composed of magmatic water, and meteoric water is added with the process of magma rising.

Problemy ophiolitów Zagros i ciał bazaltowych, przykłady z Regionu Kurdystanu, północny Irak

In the Iraqi Zagros, there are ten ophiolites and basaltic bodies, the famous ones are Penjween, Mawat, Bulfat and Peshashan Ophiolite complexes in addition to basaltic bodies such as Kata Rash, Avroman, Gercus, Chalki, and Hamrin basaltic bodies. The present study describes more than 12 significant problems concerning the previous assigning of the bodies as igneous rocks. These problems are observable in the field, laboratory, and in most previous works of literature that oppose the magmatic origin of these bodies. Our study explicated all aspects of each problem and clarified how the problems contradict magmatic crystallization and aid the sedimentary origin of these claimed igneous bodies. Finally, the interpretations of all the problems were collected as conjugate pieces of evidence for appraisal of the new origin of all igneous bodies in the Iraqi and Iranian Zagros belt. The outcomes consider the ophiolitic and basaltic rocks metamorphosed volcaniclastic sandstones (greywackes or mafic sandstone). These sandstones belong to fresh or metamorphosed greywackes of stratigraphic units of the Paleocene-Eocene Walash Formation (as distal facies) and Kata Rash Conglomerate (as proximal facies) which were previously considered volcanic rocks. These sediments are sourced originally from Urumeiah-Dokhtur Magmatic Arc (ADMA) and deposited inside Neo-Tethys, present Sanandaji-Sirjan Zone (SSZ), during the Jurassic-Early Cretaceous. Later, the sediments were metamorphosed and uplifted during the Paleocene and deposited inside the Iraqi Zagros belt by turbidity currents inside the Zagros Foreland basin. These ideas are shown in detail by tectonic and paleogeographic models.

Filling the gap in the evolution of the genus Echinochara Peck (Clavatoraceae, Charophyta)

Echinochara is a poorly known charophyte genus of the extinct family Clavatoraceae that thrived in the Middle Jurassic–Early Cretaceous of North America, Europe, and North Africa. It represents the most ancient and plesiomorphic genus of this family. However, the fossil record of Echinochara is discontinuous, showing several gaps, one of them especially significant in evolutionary terms between the Kimmeridgian and the early Barremian. The new species Echinochara pontis sp. nov., described here from the late Berriasian of the Maestrat Basin (NE Spain), bridges, in part, this gap, shedding light on the evolution of the genus during the earliest Cretaceous. The fructification (utricle) has bilateral symmetry, formed by two superimposed series of bract cells that abaxially cover the gyrogonite. The inner series has three long cells that are born by a short basal cell and reach the oospore apex. The outer series shows a central fan of bract cells, composed of a small basal cell, triangular in shape, that bears three long cells growing upwards, which are in turn flanked by two long bract cells on each side. The central basal cell and these two lateral cells are directly attached to the base of the utricle. The thallus is corticated with cells twisting at an angle of 30°. The utricle of Echinochara pontis displays a combination of features present in Echinochara peckii (Bathonian?–Kimmeridgian) and Echinochara lazarii (Barremian–early Aptian). For instance, the bilateral symmetry of the utricle and the morphology of the inner bract-cell series allow comparison with E. lazarii, whilst the morphology of the outer bract-cell series is closer to E. peckii. Moreover, the thallus of the new species shows cortical cells with a twisting angle intermediate between that of Echinochara peckii (40°–45°) and Echinochara lazarii (not twisted). The unique combination of morphological characters in the utricle of Echinochara pontis fits well with its intermediate chronostratigraphic position between the two former species. Echinochara pontis formed monospecific meadows in brackish settings. A preference for brackish settings is also observed for Echinochara peckii and in the older populations of Echinochara lazarii, suggesting that this habitat is probably a basal character in the evolution of the genus Echinochara.

Tetradactyl footprints and plant material from the Jurassic-Cretaceous boundary, Tarapaca Region, Northern Chile

We report new ichnites corresponding to a trackway composed of three tetradactyl pedal footprints and plant remains near Southeastern Guatacondo, Tarapacá Region, within the transition of Majala and Chacarilla Formations (Late Jurassic-Early Cretaceous). The fossils were found in the context of a Copper Mining road construction at the PK23 site, Quebrada Blanca Phase 2 project, by the Teck Mining Company Quebrada Blanca S.A.We performed stratigraphical, paleobotanical, and paleoichnological studies, along with the footprint characterization and comparisons by Principal Component Analysis, and Discriminant Analysis of I-II, II-III and III-IV interdigital angles, using a large tetradactyl footprint morphological database of potential producers (dinosaurs, crocodiles, lepidosaurs, and pterosaurs). Additionally, we performed 3D pedal computer modeling kinematic analysis of the Chilesaurus diegosuarezi's 3D tetradactyl foot under two different sedimentary conditions (i.e. hard soil with superficial impression, and soft sediment with a penetrative impression), to test it as a potential trackmaker.The stratigraphic section reveals an association of siliciclastic facies, formed by the intercalation of fine-grained sandstones and wackes, with ripple marks, cross and horizontal lamination, evidencing intermittent moderate to low sedimentation energy.Among the plant material, several organs of the family Cheirolepidiaceae were identified such as, leaves and leafy branches of Brachyphyllum type, Classostrobus pollen cone, ovuliferous scales, and wood fragments related to Cupressinoxylon. The monodominance of Cheirolepidiaceae among the preserved macroflora allows inferring the characteristics of the environment in which the plants lived, highlighting halophytic, and temporarily arid conditions. Evidence as a whole, permits to interpret the depositional environment as an arid deltaic-littoral plain, temporarily covered with an ephemeral water layer associated with a stunted woody vegetation, in which terrestrial vertebrates walked by.Despite the low predictive power of the multivariate analysis, due to the various sources of morphological variability inherent to footprint formation, the PK23 footprints seem to better correspond to Dinosauria or Avialae as the most likely producers, rather than to Lepidosauria or Crocodylia, discarding the dinosaur Chilesaurus due to very low interdigital mediolateral rotation capabilities.

Mitochondrial metagenomics reveal the independent colonization of the world’s coasts by intertidal oribatid mites (Acari, Oribatida, Ameronothroidea)

Oribatid mites are an ancient group that already roamed terrestrial ecosystems in the early and middle Devonian. The superfamily of Ameronothroidea, a supposedly monophyletic lineage, represents the only group of oribatid mites that has successfully invaded the marine coastal environment. By using mitogenome data and nucleic ribosomal RNA genes (18S, 5.8S, 28S), we show that Ameronothroidea are a paraphyletic assemblage and that the land-to-sea transition happened three times independently. Common ancestors of the tropical Fortuyniidae and Selenoribatidae were the first to colonize the coasts and molecular calibration of our phylogeny dates this event to a period in the Triassic and Jurassic era (225–146 mya), whereas present-day distribution indicates that this event might have happened early in this period during the Triassic, when the supercontinent Pangaea still existed. The cold temperate northern hemispheric Ameronothridae colonized the marine littoral later in the late Jurassic-Early Cretaceous and had an ancient distribution on Laurasian coasts. The third and final land-to-sea transition happened in the same geological period, but approx. 30 my later when ancestors of Podacaridae invaded coastal marine environments of the Gondwanan landmasses.

Testing alternative tectonic models for the Permian-Pleistocene tectonic development of the Kyrenia Range, N Cyprus: Implications for E Mediterranean Tethyan palaeogeography

Three published alternative tectonic models of the Permian-Pleistocene development of the Kyrenia Range, N Cyprus are tested, supported by new field, geochemical and micropalaeontological evidence: 1. The Kyrenia Range represents the northern continental margin of the S Neotethys, close to its present relative position. The range initiated as a Permian-Cretaceous rift/passive margin, switching to a N-facing active margin during Late Cretaceous-Neogene; 2. The Range was located along the N African continental margin until the Neogene when northward subduction transferred it to the southern margin of the Eurasian plate; 3. The Range is a far-travelled allochthon that was emplaced to near its present position, probably during the Eocene.In the light of regional comparisons, especially with southern Turkey, the combined evidence mainly supports tectonic model 1. Sedimentary and palaeontological data show that the restored stratigraphy of the Kyrenia Range indicates Late Permian initial rifting and Early-Middle Triassic advanced rifting, followed by Jurassic-Early Cretaceous passive margin subsidence. Small exposures of ophiolite-related melange located between the Mesozoic carbonate platform and the overlying latest Cretaceous-Palaeogene deep-water volcanic-sedimentary succession include evidence of HP/LT metamorphism, pointing to Late Cretaceous subduction. MORB/boninites, diabase-gabbro and extensive harzburgitic serpentinite originated as a SSZ ophiolite, together with a possible high-grade metamorphic sole (garnet amphibolite) and an accretionary prism (E-MORB/OIB; metachert). Microfossil evidence indicates exhumation of the melange and the underlying platform prior to Late Maastrichtian. A mass-transport complex formed within a compression-related foredeep during the Middle Eocene. Associated southward thrusting and folding culminated in emergence and subaerial erosion, generating a major unconformity, that was followed by subaerial and then marine deltaic deposits (Late Eocene-Oligocene). Following major Late Miocene southward thrusting, uplift of the Kyrenia Range took place during the Pleistocene, related to collision of the leading edge of the North African plate (Eratosthenes Seamount) with the Eurasian (Anatolian) plate.

Uplift and denudation history of the Ellsworth Mountains: insights from low-temperature thermochronology

Abstract. While thermochronological studies have constrained the landscape evolution of several of the crustal blocks of West and East Antarctica, the tectono-thermal evolution of the Ellsworth Mountains remains relatively poorly constrained. These mountains are among the crustal blocks that comprise West Antarctica and exhibit an exceptionally well-preserved Palaeozoic sedimentary sequence. Despite the seminal contribution of Fitzgerald and Stump (1991), who suggested an Early Cretaceous uplift event for the Ellsworth Mountains, further thermochronological studies are required to improve the current understanding of the landscape evolution of this mountain chain. We present new zircon (U–Th) / He (ZHe) ages, which provide insights into the landscape evolution of the Ellsworth Mountains. The ZHe ages collected from near the base and the top of the sequence suggest that these rocks underwent burial reheating after deposition. A cooling event is recorded during the Jurassic–Early Cretaceous, which we interpret as representing exhumation in response to rock uplift of the Ellsworth Mountains. Moreover, our results show that while ZHe ages at the base of the sequence are fully reset, towards the top ZHe ages are partially reset. Uplift and exhumation of the Ellsworth Mountains during the Jurassic–Early Cretaceous was contemporaneous with the rotation and translation of this crustal block with respect to East Antarctica and possibly the Antarctic Peninsula. Furthermore, this period is characterized by widespread extension associated with the disassembly and breakup of Gondwana, with the Ellsworth Mountains playing a key role in the opening of the far southern Atlantic. Based on these results, we suggest that uplift of the Ellsworth Mountains during the disassembly of Gondwana provides additional evidence for major rearrangement of the crustal blocks between the South American, African, Australian and Antarctic plates. Finally, uplift of the Ellsworth Mountains commenced during the Jurassic, which predates the Early Cretaceous uplift of the Transantarctic Mountains. We suggest that the rift-related exhumation of the Ellsworth Mountains occurred throughout two events: (i) a Jurassic uplift associated with the disassembly of southwestern Gondwana and (ii) an Early Cretaceous uplift related with the separation between Antarctica and Australia, which is also recorded in the Transantarctic Mountains.

A theropod tooth from the Missão Velha Formation (Late Jurassic-Early Cretaceous) of the Araripe Basin: oldest Brazilian Abelisaurid record

ABSTRACT The Missão Velha Formation (Late Jurassic-Early Cretaceous), often referred to as Brejo Santo Formation, is one of the stratigraphic units of the Araripe Basin, included within the Vale do Cariri Group. This locality, characterised by its fluvio-estuarine paleoenvironment, yielded a diverse paleoichthyofauna while its terrestrial vertebrate record is still poorly known, with a single isolated theropod lateral tooth being briefly cited until now. This study aims to revisit this specimen (UERJ-PMB R008) in order to identify it through the current quantitative and qualitative methods. The quantitative analyses were unable to properly classify the Missão Velha specimen to a single theropod group, indicating paravian, piatnitzkysaurid and abelisaurid affinities, while most of cladistic analyses assigned the UERJ-PMB R008 as an abelisaurid tooth. The specimen was finally assigned as an abelisaurid lateral tooth due to its almost straight distal margin, hooked denticles, similarly sized mesial and distal denticles, a lanceolate cross section and an irregular enamel texture. This assignment represents not only the first definitive theropod record for Missão Velha Formation as it is also the oldest abelisaurid record in the South America, filling part of the 30-million-year gap between Eoabelisaurus and Spectrovenator.

Provenance and the U–Pb age constraints on the tuff beds of the Late Jurassic–Early Cretaceous Bazhenovo Formation, West Siberian Basin

AbstractThin tuff beds of the Late Jurassic–Early Cretaceous Bazhenovo Formation are laterally widespread in the central part of the West Siberian Basin (ca 0.5 million km2). However, the source of the tuff beds remains unclear. The stratigraphy, geochemistry and geochronology of the tuff beds were investigated to reveal their magmatic origin and potential source region. Most of the tuff beds are recorded in member 4 and can be correlated through the Bazhenovo sequence. Thin‐section petrography and X‐ray diffraction indicate that the tuffs mostly comprise clay minerals and K‐feldspars. Less common minerals are plagioclase, quartz and pyrite. The geochemical composition of the Bazhenovo tuff beds suggests a parental magma origin of andesite/basalt, which came from volcanic arc‐related settings. Considering the results of geochemical studies along with LA‐ICP‐MS zircon U–Pb dating (141.3 ± 0.3/2.8 Ma), the palaeovolcanoes of the Caucasus region or south‐east Mongolia–North‐East China are one of the potential source regions of the tuffs. The record of these tuffs indicates the intensive volcanic eruption during the Volgian–Ryazanian, accompanied by a very low‐sedimentation rate and preservation in a reducing environment. The tuff beds have broad implications as an isochronous marker horizon and constraints for the numerical age of the Jurassic–Cretaceous boundary in the Boreal Realm.

On the Rhodopean protoliths and their Middle Jurassic to Early Cretaceous evolution. A review

The Rhodope Massif represents a large high-grade metamorphic complex situated in the Balkan Peninsula, straddling the border between Bulgaria and Greece. Geological studies carried out during the last thirty years clearly established that the complex is composed of three major lithotectonic units characterized by differing protolith ages and Alpine thermotectonic evolution. The Rhodope Massif consists of Upper and Lower terranes representing continental fragments composed mainly of pre-Mesozoic magmatic rocks and covered by Early Mesozoic sedimentary sequences. These two entities are separated by an Intermediate Terrane comprising a Jurassic magmatic arc and its host rocks tectonically intercalated with Jurassic ophiolitic fragments together with the Early Mesozoic sediments. Detailed analyses of the previously published geochronological data revealed that the three main tectonic terranes were juxtaposed in the Late Jurassic–Early Cretaceous during the continental collision and northward subduction of the Lower and Intermediate terranes. These rocks experienced Middle Jurassic to Early Cretaceous high-pressure metamorphism, followed by high-temperature one accompanied by anatexis. At that time, the Upper Terrane was metamorphosed and deformed only partially. Being part of the European margin, this terrane represented an upper continental plate during the subduction, and therefore is not considered as a part of the Alpine Rhodope metamorphic complex. It is important to note that, although most of the present-day fabric and major tectonic zones in the Rhodope metamorphic complex are younger than Early Cretaceous, and therefore they postdate the geological evolution discussed in this study, they often reactivate the old boundaries between the main terranes and units.