The Jurassic Period

Astronomical Calibration of the Tithonian - Berriasian in the Neuquén Basin, Argentina: A Contribution From the Southern Hemisphere to the Geologic Time Scale

Chapter

Sep 2018

Detailed cyclostratigraphical analyses have been made from five TithonianeBerriasian sections of the Vaca Muerta Formation, exposed in the Neuquén Basin, Argentina. The Vaca Muerta Formation is characterized by decimetre-scale rhythmic alternations of marlstones and limestones, showing a well-ordered hierarchy of cycles, where elementary cycles, bundles of cycles and superbundles have been recognized. According to biostratigraphic data, elementary cycles have a periodicity of 21 ky, which correlates with the precession cycle of Earth’s axis. Spectral analysis based on time series of elementary cycle thicknesses allows us to identify frequencies of w400 ky and w90e120 ky, which we interpret as the modulation of the precessional cycle by the Earth’s orbital eccentricity. Correlation between studied sections allowed us to estimate a minimum duration for each Andean ammonite zone. Moreover, cyclostratigraphic data allowed us to build the first continuous floating astronomical time scale for the Tithonian e Berriasian, which is anchored to the geological time scale through magnetostratigraphy. We estimated a minimum duration of 5.67 myr for the Tithonian and 5.27 myr for the Berriasian. The resulted durations of some polarity chrones are also different with respect to the GTS2016, however such differences could be due to condensation or discontinuities not detected in the studied sections.

Magnetostratigraphy of the Jurassic Through Lower Cretaceous in the Neuquén Basin

Chapter

Mar 2020

The first magnetostratigraphic scales for the Jurassic through Early Cretaceous from the Southern Hemisphere have been constructed over the last decades from marine sections in the Neuquén Basin. Paleomagnetic sites were tied to ammonite zones in order to achieve well-refined ages of studied sections. Diverse field tests for the paleomagnetic stability proved the primary origin of isolated magnetizations. In the case of Upper Jurassic–Lower Cretaceous studies, magnetostratigraphic and biostratigraphic data were combined with cyclostratigraphy. Finally, polarities were tied to Andean ammonite zones and from their correlation with the standard zones, calibrated to the GTS2016 (Geomagnetic Polarity Time Scale 2016). For the Early Jurassic, a composite magnetostratigraphic scale was derived out of five sections spanning the Hettangian–Toarcian. The magnetostratigraphic scale portrays 16 reverse (Jr1–Jr16) and 16 normal (Jn1–Jn16) polarity zones that encompass at least 19 ammonite zones. A major difference between both scales rises in the Hettangian encompassing Jr1–Jr3 polarity zones. For the Middle Jurassic, the resultant magnetostratigraphy obtained in the Lajas Formation is a pattern of dominantly reverse polarity. According to the correlation with the GTS2016, the studied section is assigned to the Lower-uppermost Middle Bathonian (Chrons M41 through M39). For the Late Jurassic–Early Cretaceous, the magnetostratigraphic scale obtained in the Vaca Muerta Formation comprises Subchrons M22r.2r through M15r, spanning the V. andesensis (Lower Tithonian)–S. damesi Zones (Upper Berriasian). The use of diverse chronostratigraphic tools such as biostratigraphy, magnetostratigraphy and cyclostratigraphy, enabled to determine with unprecedented precision the position of the Jurassic–Cretaceous boundary, as well as to assess durations of ammonite zones.

Magnetostratigraphy of the Upper Jurassic–Lower Cretaceous from Argentina: Implications for the J-K boundary in the Neuquén Basin

Article

Feb 2017

A systematic sedimentologic and paleomagnetic study was carried out in the Vaca Muerta Formation, cropping out in the northern Neuquén Basin, west-central Argentina. The studied section is c.280 m-thick and represents a carbonate ramp system bearing ammonites that indicate Late Jurassic–Early Cretaceous ages. The Vaca Muerta Formation is one of the most important unconventional hydrocarbon reservoirs in the world and its thorough study has become a relevant target in Argentina. The J-K boundary is comprised within this unit, and although it is well-dated through biostratigraphy -mainly ammonites-, the position of particularly the boundary is yet a matter of hot debate. Therefore, the systematic paleomagnetic and cyclostratigraphic study in the Vaca Muerta Formation was considered relevant in order to obtain the first Upper Jurassic–Lower Cretaceous magnetostratigraphy of the southern hemisphere on the first place and to precise the position of the J-K boundary in the Neuquén Basin, on the other. Biostratigraphy is well studied in the area, so that paleomagnetic sampling horizons were reliably tied, particularly through ammonites. Almost 450 standard specimens have been processed for this study distributed along 56 paleomagnetic sampling horizons that were dated using ammonites. Paleomagnetic behaviours showed to be very stable, and their quality and primary origin have been proved through several paleomagnetic field tests The resultant magnetostratigraphic scale is made up of 11 reverse and 10 normal polarity zones, spanning the Andean Virgatosphinctes mendozanus (lower Tithonian) to Spiticeras damesi Zones (upper Berriasian). These polarity zones were correlated with those of the International Geomagnetic Polarity Time Scale 2012 and 2016 through the correlation between Andean and Tethyan ammonite zones. Cyclostratigraphy on the other hand, proved to be quite consistent with the magnetostratigraphy. Through the correlation of the resultant paleomagnetic and cyclostratigraphic data, it was possible to date the section with unprecedented precision, and therefore, to establish the position of the Jurassic-Cretaceous boundary. The paleomagnetic pole calculated from the primary magnetization is located at: Lon= 191.6°E, Lat= 76.2°S, A95= 3.5°, indicating a c. 24° clockwise rotation for the studied section, which is consistent with structural data of the region.

Toward a multidisciplinary chronostratigraphic calibration of the Jurassic-Cretaceous transition in the Neuquén Basin

Article

Full-text available

Jan 2018

Detailed systematic studies have been carried out in the Vaca Muerta Formation in order to achieve an integrated multidisciplinary calibration of the Jurassic/Cretaceous transition in the Neuquén Basin. Although this unit has a very well-established ammonite biostratigraphy, the temporal distribution of biozones is yet a matter of hot debate. In this contribution we present the results of a well constrained integrated data from the Arroyo Loncoche section (southern Mendoza), where comprehensive cyclostratigraphic, paleomagnetic and biostratigraphic sampling/data allowed us to elaborate a very strong chronostratigraphic scheme for the Titho-nian-Berriasian interval. The proposed stratigraphic calibration of the Tithonian-Berriasian Andean succession brings foward two key points: 1) The base of the Vaca Muerta Formation shows a polarities pattern which would only be compatible to the uppermost part of Hybonotum Zone (lowermost Lower Tithonian). 2) The position of the Jurassic-Cretaceous boundary is located within the lower third of the S. koeneni Zone. RESUMEN Calibración estratigráfica multidisciplinaria de la transición Jurásico-Cretácico en la Cuenca Neuquina Se realizaron estudios sistemáticos de detalle en la Formación Vaca Muerta con el fin de lograr una calibración multidisciplinaria integrada de la transición jurásico/cretácica en la Cuenca Neuquina. Aunque esta unidad se caracteriza por presentar una bioestra-tigrafía basada en amonites, la distribución temporal de las biozonas es todavía un tema de importante debate. En esta contribución se presentan los resultados integrados de la sección Arroyo Loncoche (sur de Mendoza), en donde exhaustivos estudios cicloestra-tigráficos, paleomagnéticos y bioestratigráficos han permitido elaborar un robusto esquema de correlación cronoestratigráfico para el intervalo Tithoniano-Berriasiano. La calibración estratigráfica propuesta para la sucesión tithoniano-berriasiana andina presenta dos puntos clave: 1) La base de la Formación Vaca Muerta muestra un patrón de polaridades que solo sería compatible con la parte superior de la Zona de Hybonotum (Tithoniano Inferior bajo). 2) La posición del límite Jurásico-Cretáceo está ubicada dentro del tercio inferior de la Zona de S. koeneni.

Toward a multidisciplinary chronostratigraphic calibration of the Jurassic-Cretaceous transition in the Neuquén Basin

Article

Jun 2018

Detailed systematic studies have been carried out in the Vaca Muerta Formation in order to achieve an integrated multidisciplinary calibration of the Jurassic/Cretaceous transition in the Neuquén Basin. Although this unit has a very well-established ammonite biostratigraphy, the temporal distribution of biozones is yet a matter of hot debate. In this contribution we present the results of a well constrained integrated data from the Arroyo Loncoche section (southern Mendoza), where comprehensive cyclostratigraphic, paleomagnetic and biostratigraphic sampling/data allowed us to elaborate a very strong chronostratigraphic scheme for the Titho-nian-Berriasian interval. The proposed stratigraphic calibration of the Tithonian-Berriasian Andean succession brings foward two key points: 1) The base of the Vaca Muerta Formation shows a polarities pattern which would only be compatible to the uppermost part of Hybonotum Zone (lowermost Lower Tithonian). 2) The position of the Jurassic-Cretaceous boundary is located within the lower third of the S. koeneni Zone.

Toarcian ammonitico rosso facies from the South Iberian Paleomargin (Betic Cordillera, southern Spain): paleoenvironmental reconstruction

Article

Oct 2015

The Toarcian ammonitico rosso facies were widespread in the Mediterranean Tethys (between 15 and 30°N latitude) in the North Gondwana Paleomargin (Apulian promontory and North African Margin) and southern Iberian Paleomargin (Betic Cordillera). These facies were associated with epi-oceanic slopes of a sedimentary swell-trough system related to the extensional phase of continental rifting. In the Median Subbetic (southern Iberian Paleomargin), ammonitico rosso facies show a progressive change through the Toarcian on the hemipelagic swells after the fragmentation of a carbonate platform. During the latest Pliensbachian to the Bifrons Zone (middle Toarcian), sedimentation was dominated by epi-oceanic limestone and marl with a high influence of neighboring shallow-water environments represented by common turbidite–tempestite beds (with foraminifera and ooids). Microfossils and trace fossils provide no evidence of oxygen-restricted conditions. In the Gradata Zone (middle Toarcian), the ammonitico rosso facies appear (red nodular limestone and marly-limestone rich in the trace fossils Phycodes, Planolites, Thalassinoides, and Chondrites). Progressively more pelagic conditions and a restricted influence of emergent lands and carbonate platforms are reflected by the reduced input of turbidite–tempestite beds and increase of ammonitellas and radiolaria. A sea-level fall affected the hemipelagic swell during the middle–late Toarcian and favored sediment-winnowing by currents, with subsequent nodulation. The combined action of burrowing, compaction, and dissolution controlled nodulation, which ranges from diffuse nodules to sharp-edged nodules. The sedimentation rate conditioned the time available for nodule growth, the migration of the Ca2+ and HCO3− precipitation horizon, and the degree of nodulation (from horizons with diffuse-edged nodules to semi-continuous to continuous layers formed by the coalescence of sharp-edged nodules).

Filling the gap: New precise Early Cretaceous radioisotopic ages from the Andes

Article

Full-text available

May 2015

Two tuffs in the Lower Cretaceous Agrio Formation, Neuquén Basin, provided U–Pb zircon radioisotopic ages of 129.09±0.16 Ma and 127.42±0.15 Ma. Both horizons are well constrained biostratigraphically by ammonites and nannofossils and can be correlated with the ‘standard’ sequence of the Mediterranean Province. The lower horizon is very close to the base of the Upper Hauterivian and the upper horizon to the Hauterivian/Barremian boundary, indicating that the former lies at c . 129.5 Ma and the latter at c . 127 Ma. These new radioisotopic ages fill a gap of over 8 million years in the numerical calibration of the current global Early Cretaceous geological time scale.

U–Pb detrital zircon ages of Upper Jurassic continental successions: implications for the provenance and absolute age of the Jurassic–Cretaceous boundary in the Neuquen Basin

Article

Full-text available

Mar 2014

New U–Pb detrital zircon ages are presented for the Tordillo Formation. The ages indicate that the most important source region of sediment supply was the Jurassic Andean arc (peaks at c. 144, 153 and 178 Ma), although two secondary sources were defined at c. 218 and 275 Ma. Temporal variation in the provenance indicates that at the beginning of the sedimentation, Carboniferous to Lower Jurassic magmatic rocks and Lower Palaeozoic metamorphic rocks were the most important sources. Towards the top, the data suggest that the Andean arc becomes the main source region. The comparison between provenance patterns of the Tordillo Formation and of the Avilé Member (Agrio Formation) showed some differences. In the former, the arc region played a considerable role as a source region, but this is not identified in the latter. The results permit a statistically robust estimation of the maximum deposition age for the Tordillo Formation at c. 144 Ma. This younger age represents a discrepancy of at least 7 Ma from the absolute age of the Kimmeridgian and Tithonian boundary (from the chronostratigraphic timescale accepted by the International Commission of Stratigraphy, IUGS), and has strong implications for the absolute age of the Jurassic–Cretaceous boundary. Supplementary material Sample coordinates, values of the sandstone compositional framework and U–Pb (LAM-MC-ICP-MS) age measurements of zircons grains are available at http://www.geolsoc.org.uk/SUP18718

Astronomical calibration of the Toarcian Stage: Implications for sequence stratigraphy and duration of the early Toarcian OAE

Article

Full-text available

Jan 2014
EARTH PLANET SC LETT

The Toarcian Oceanic Anoxic Event (T-OAE) of the early Jurassic period involves one of the largest perturbations of the carbon cycle in the past 250 Ma, recorded by a pronounced negative carbon-isotope excursion (CIE). Numerous studies have focused on potential causes of the T-OAE and CIE, but are hampered by an uncertain timescale. Here we present high-resolution (∼2 kyr∼2 kyr) magnetic susceptibility (MS) measurements from the marine marls of the Sancerre-Couy drill-core, southern Paris Basin, spanning the entire Toarcian Stage. The MS variations document a rich series of sub-Milankovitch to Milankovitch frequencies (precession, obliquity and eccentricity) with the periodic g2–g5 (405 kyr) and quasi-periodic g4–g3 (∼2.4 Myr∼2.4 Myr Cenozoic mean periodicity) eccentricity terms being the most prominent. The MS-related g4–g3 variation reflects third-order eustatic sequences, and constrains the sequence stratigraphic framework of the Toarcian Stage. In addition, MS variations reveal a modulation of g2–g5 by g4–g3 eccentricity related cycles, suggesting that sea-level change was the main control on the deposition of the Toarcian Sancerre marls, in tune with the astro-climatic frequencies. The stable 405 kyr cyclicity constrains a minimum duration of the Toarcian Stage to ∼8.3 Myr∼8.3 Myr, and the well documented CIE, associated with the T-OAE, to ∼300 to 500 kyr. The 405 kyr MS timescale calibrates the periodicity of the prominent high-frequency δC13 cycles that occur in the decreasing part of the CIE to 30 to 34 kyr, consistent with the Toarcian obliquity period predicted for an Earth experiencing sustained tidal dissipation.

Biotic and environmental dynamics through the Late Jurassic–Early Cretaceous transition: evidence for protracted faunal and ecological turnover

Preprint

Jun 2018

The Late Jurassic to Early Cretaceous interval represents a time of environmental upheaval and cataclysmic events, combined with disruptions to terrestrial and marine ecosystems. Historically, the Jurassic/Cretaceous (J/K) boundary was classified as one of eight mass extinctions. However, more recent research has largely overturned this view, revealing a much more complex pattern of biotic and abiotic dynamics than has previously been appreciated. Here, we present a synthesis of our current knowledge of Late Jurassic–Early Cretaceous events, focusing particularly on events closest to the J/K boundary. We find evidence for a combination of short-term catastrophic events, large-scale tectonic processes and environmental perturbations, and major clade interactions that led to a seemingly dramatic faunal and ecological turnover in both the marine and terrestrial realms. This is coupled with a great reduction in global biodiversity which might in part be explained by poor sampling. Very few groups appear to have been entirely resilient to this J/K boundary ‘event’, which hints at a ‘cascade model’ of ecosystem changes driving faunal dynamics. Within terrestrial ecosystems, larger, more-specialised organisms, such as saurischian dinosaurs, appear to have suffered the most. Medium-sized tetanuran theropods declined, and were replaced by larger-bodied groups, and basal eusauropods were replaced by neosauropod faunas. The ascent of paravian theropods is emphasised by escalated competition with contemporary pterosaur groups, culminating in the explosive radiation of birds, although the timing of this is obfuscated by biases in sampling. Smaller, more ecologically diverse terrestrial non-archosaurs, such as lissamphibians and mammaliaforms, were comparatively resilient to extinctions, instead documenting the origination of many extant groups around the J/K boundary. In the marine realm, extinctions were focused on low-latitude, shallow marine shelf-dwelling faunas, corresponding to a significant eustatic sea-level fall in the latest Jurassic. More mobile and ecologically plastic marine groups, such as ichthyosaurs, survived the boundary relatively unscathed. High rates of extinction and turnover in other macropredaceous marine groups, including plesiosaurs, are accompanied by the origin of most major lineages of extant sharks. Groups which occupied both marine and terrestrial ecosystems, including crocodylomorphs, document a selective extinction in shallow marine forms, whereas turtles appear to have diversified. These patterns suggest that different extinction selectivity and ecological processes were operating between marine and terrestrial ecosystems, which were ultimately important in determining the fates of many key groups, as well as the origins of many major extant lineages. We identify a series of potential abiotic candidates for driving these patterns, including multiple bolide impacts, several episodes of flood basalt eruptions, dramatic climate change, and major disruptions to oceanic systems. The J/K transition therefore, although not a mass extinction, represents an important transitional period in the co-evolutionary history of life on Earth.

Biotic and environmental dynamics through the Late Jurassic-Early Cretaceous transition: Evidence for protracted faunal and ecological turnover

Article

Full-text available

Feb 2016
BIOL REV

The Late Jurassic to Early Cretaceous interval represents a time of environmental upheaval and cataclysmic events,combined with disruptions to terrestrial and marine ecosystems. Historically, the Jurassic/Cretaceous (J/K) boundary was classified as one of eight mass extinctions. However, more recent research has largely overturned this view, revealing a much more complex pattern of biotic and abiotic dynamics than has previously been appreciated. Here, we present a synthesis of our current knowledge of Late Jurassic – Early Cretaceous events, focusing particularly on events closest to the J/K boundary. We find evidence for a combination of short-term catastrophic events, large-scale tectonic processesand environmental perturbations, and major clade interactions that led to a seemingly dramatic faunal and ecologicalturnover in both the marine and terrestrial realms. This is coupled with a great reduction in global biodiversity whichmight in part be explained by poor sampling. Very few groups appear to have been entirely resilient to this J/K boundary‘event’, which hints at a ‘cascade model’ of ecosystem changes driving faunal dynamics. Within terrestrial ecosystems,larger, more-specialised organisms, such as saurischian dinosaurs, appear to have suffered the most. Medium-sized tetanuran theropods declined, and were replaced by larger-bodied groups, and basal eusauropods were replaced by neosauropod faunas. The ascent of paravian theropods is emphasised by escalated competition with contemporary pterosaur groups, culminating in the explosive radiation of birds, although the timing of this is obfuscated by biases in sampling. Smaller, more ecologically diverse terrestrial non-archosaurs, such as lissamphibians and mammaliaforms,were comparatively resilient to extinctions, instead documenting the origination of many extant groups around theJ/K boundary. In the marine realm, extinctions were focused on low-latitude, shallow marine shelf-dwelling faunas,corresponding to a significant eustatic sea-level fall in the latest Jurassic. More mobile and ecologically plastic marinegroups, such as ichthyosaurs, survived the boundary relatively unscathed. High rates of extinction and turnover in other macropredaceous marine groups, including plesiosaurs, are accompanied by the origin of most major lineages ofextant sharks. Groups which occupied both marine and terrestrial ecosystems, including crocodylomorphs, document a selective extinction in shallow marine forms, whereas turtles appear to have diversified. These patterns suggest thatdifferent extinction selectivity and ecological processes were operating between marine and terrestrial ecosystems, which were ultimately important in determining the fates of many key groups, as well as the origins of many major extantlineages. We identify a series of potential abiotic candidates for driving these patterns, including multiple bolide impacts,several episodes of flood basalt eruptions, dramatic climate change, and major disruptions to oceanic systems. The J/K transition therefore, although not a mass extinction, represents an important transitional period in the co-evolutionary history of life on Earth.

Climate-controlled organic matter accumulation as recorded in the Upper Jurassic Argiles de Châtillon Formation, a shallow-marine counterpart of the Kimmeridge Clay Formation

Article

Full-text available

Dec 2022

Mudstones from the Argiles de Châtillon Formation exposed in the Boulonnais region of Northern France represent a proximal lateral equivalent of the organic-rich Kimmeridge Clay Formation. The Argiles de Châtillon Formation is composed of two subunits that straddle the Kimmeridgian–Tithonian boundary. Each subunit contains an organic-rich interval. The two conspicuous organic-rich intervals have been linked to either periods of high sea level or greenhouse warming. Here, we use palynology to further understand climate and environmental mechanisms that drove organic matter enrichment. We use bulk organic carbon isotope records (δ ¹³ C org ) to correlate the Boulonnais sections with those of the Kimmeridge Clay Formation. The palynological results suggest that the stratigraphically lower organic-rich interval (Kimmeridgian) was deposited under suboxic to anoxic stratified conditions. A large-scale climate shift from cooler/humid to warmer/arid conditions marked the Kimmeridgian–Tithonian boundary, influencing organic matter enrichment in the stratigraphically higher organic-rich interval (Tithonian). In contrast with the lower organic-rich interval, there are no indications of stratified conditions for the higher organic-rich interval. Within this thicker organic-rich interval, cyclic variations in amorphous organic matter distribution, total organic carbon and δ ¹³ C org trends on a 2 m scale are observed. They co-occur with fluctuations of the palynological assemblages, indicative of more humid versus arid climate conditions, likely alternating on a ∼100 kyr eccentricity timescale. Our results show that under the most humid phases of these overall arid climate conditions, sulfurization of carbohydrates was the dominant control on organic matter preservation. This climate-controlled process that drives organic matter enrichment in the Tithonian can be recognized on a basin-wide scale.

Calcispheres from the vaca muerta formation (Tithonian) in the Arroyo Covunco section, Neuquén Province

Article

Full-text available

Jan 2018

A parataxonomic, taphonomic, and biostratigraphic study of the calcispheres from the Vaca Muerta Formation (Tithonian) was carried out at the Arroyo Covunco section (Zapala, Neuquén province). We considered 215 specimens from 20 fertile samples collected every 3-10 m along 150 m of outcrop. The identified association includes 5 genera and 8 species (with 2 subspecies) already known for the Tethyan realm and the Neuquén Basin. In order to assess the existence of taphonomic biases, the effects of dissolution and neomorphism on the calcispheres walls were analysed. Vertical variations were observed in preservation, which were related primary to lithofacial differences. This allowed defining, for the first time, 5 categories of taphonomic modification to characterize the associations. Four bioevents of global importance were identified (FOs of C. pulla, P. malmica, C. tenuis and C. fortis), allowing to recognize the typical Tithonian Committosphaera tithonica?, Parastomiosphaera malmica, Colomisphaera tenuis and Colomisphaera fortis calcisphere biozones. The results of this study have allowed to adjust the position of the events with respect to previous works in the Neuquén Basin.

Reply to the Comment on "Astronomical constraints on the duration of the Early Jurassic Pliensbachian Stage and global climatic fluctuations" [Earth Planet. Sci. Lett. 455 (2016) 149-165]

Article

Jan 2018
EARTH PLANET SC LETT

Marine and terrestrial sedimentation across the T–J transition in the North German Basin

Article

Oct 2017
PALAEOGEOGR PALAEOCL

The global Mesozoic sea-level rise contributed to the stepwise flooding of the Central European Basin (CEB) across the T-J transition and transformed the CEB from a late Triassic inland playa to an early Jurassic semi-enclosed inland sea. The calibration of sections from North Germany and Thuringia using high-resolution palynomorph and ammonite biostratigraphy contributes to the improved temporal and spatial resolution of this decisive period. The herein proposed Deltoidospora-Concavisporites (DC) Zone, placed between the Rhaetian Ricciisporites-Polypodiisporites (RP) Zone and the Hettangian Pinuspollenites-Trachysporites Zone, marks the transitional zone of overlapping Rhaetian and Hettangian palynomorphs in brackish-marine, brackish and terrestrial environments of the North German Basin (NGB). Thus, the DC Zone enables the identification of the T-J transition in the NGB. Following a short-term ingression in the late Norian Corollina-Porcellispora Subzone, the first Rhaetian transgression contributed to substantial marine-terrestrial facies shifts. The diachronous transgressive onlap of brackish-marine strata culminated in a first Rhaetian maximum flooding in the upper Corollina-Enzonalasporites Zone to lower Rhaetipollis-Limbosporites (RL) Zone. After a regressive maximum in the middle RL Zone, the next transgression culminated in a second Rhaetian maximum flooding in the upper RL Zone. Following the end-Triassic regression, herein assigned to the upper RP Zone, the diachronous transgressive onlap of marine shales marks the change to marine Jurassic environments. The herein proposed Deltoidospora-Concavisporites (DC) Zone, placed between the Rhaetian Ricciisporites-Polypodiisporites (RP) Zone and the Hettangian Pinuspollenites-Trachysporites Zone, marks the transitional zone of overlapping Rhaetian and Hettangian palynomorphs in brackish-marine, brackish and terrestrial environments of the North German Basin (NGB). Thus, the DC Zone enables the identification of the T-J transition in the NGB. At the western gate of the CEB, the onset of marine Hettangian strata with ammonites, dated as the P. erugatum Biohorizon at St. Audrie's Bay, postdates the base Hettangian GSSP by ~. 250. kyr. From there to Thuringia, the diachronous onlap of marine Hettangian strata with ammonites, herein dated as the P. plicatulum Biohorizon, took place over ~. 100. kyr. The first Jurassic maximum flooding is dated as the interval of the P. psilonotum to P. plicatulum Biohorizons (lower Planorbis Zone). Rhaetian-Hettangian 3rd-order sequences of the CEB correlate with contemporaneous sequences described from Tethyan and peri-Tethyan basins pointing to circum-Tethyan eustatic cycles. The 4th-order sequences are evident in the Rhaetian-Hettangian, but only a set of Rhaetian 4th-order sequences can be correlated in the NGB so far.

A re-evaluation of the basal age in the DSDP hole at Site 534, Central Atlantic

Article

Sep 2017

Leonidas Brikiatis

For 30 years, the initial sedimentation following the opening of the western Central Atlantic has been considered to be of Middle Callovian age (approximately 164.5 Ma) based on the biochronostratigraphical estimation for the basal sedimentary unit of the borehole from Site 534A of the Deep Sea Drilling Program (DSDP). That age has been used in kinematic models of the opening of the Central Atlantic. A reconsideration of the available biochronostratigraphical data and correlation of the δ¹³Ccarb record from Site 534A with those from the Tethyan and North Atlantic records suggest that the initial sedimentation at Site 534A is, in fact, of Middle Oxfordian age (approximately 160.6 Ma). The high biostratigraphic similarity among the basal sedimentary units of the boreholes at DSDP Site 534A and Ocean Drilling Program Site 801C in the Western Pacific suggest the same age for both sites. The Middle Oxfordian δ¹³Ccarb records from the different sites covary, marking the same palaeoenvironmental changes, although such an agreement was not previously acknowledged. A combination with additional data proposes that Middle Oxfordian age corresponds to the precise date of the opening of the Hispanic Corridor between the Atlantic and Pacific oceans.

Revised Middle–Upper Jurassic strontium isotope stratigraphy

Article

Jun 2017
CHEM GEOL

A study is conducted to supplement the uppermost Lower Jurassic–lowermost Cretaceous marine strontium isotope dataset and to present new statistical fits of the Middle–Late Jurassic seawater strontium isotope curve based on a numerical time scale and a detailed biostratigraphical zonal scheme. The use of the stratigraphical scheme allows reduction of dating errors related to uncertainty of numerical age determinations. The presented correlation tables enable direct calibration between strontium isotope stratigraphy and regional biostratigraphical frameworks. New strontium isotope data have been obtained from well-preserved Lower Bajocian, uppermost Callovian, Oxfordian, Kimmeridgian, and Upper Volgian belemnite rostra.

Geophysical evidence for the crustal variation and distribution of magmatism along the central coast of Mozambique

Article

Jun 2017
TECTONOPHYSICS

For our understanding of the timing and geometry of the initial Gondwana break-up, still a consistent image of the crustal composition of the conjugated margins of central Mozambique and Antarctica and the location of their continent-ocean boundaries is missing. In this regard, a main objective is the explanation for the source of the different magnetic signature of the conjugate margins. Based on a revised investigation of wide-angle seismic data along two profiles across the Mozambican margin by means of an amplitude modelling, this study presents the crustal composition across and along the continental margin of central Mozambique. Supported by 2D magnetic modelling, the results are compared to the conjugate margin in Antarctica and allow new conclusions about their joined tectonic evolution. An observed crustal diversity between the north-eastern and south-western parts of the central Mozambican margin, testifies to the complex break-up history of this area. Conspicuous is the equal spatial extent of the HVLCB along the margin of 190–215 km. The onset of oceanic crust at the central Mozambican margin is refined to chron M38n.2n (164.1 Ma). Magnetic modelling supports the presence of reversed polarized SDRs in the continent-ocean transition that were mainly emplaced between 168.5 and 166.8 Ma (M42–M40). Inferred SDRs in the Riiser-Larsen Sea might be emplaced sometime between 166.8 and 164.1 Ma (M39–M38), but got overprinted by normal polarized intrusions of a late stage of rift volcanism, causing the opposite magnetic signature of the conjugate margins. The distribution of the magmatic material along the central coast of Mozambique clearly indicates the eastern extension of the north-eastern branch of the Karoo triple rift along the entire margin. The main magmatic phase affecting this area lasted for at least 12 Myr between 169 and 157 Ma, followed by the cease of the magmatism, perhaps due to the relative southwards motion of the magmatic centre.

Provenance of Upper Devonian clastic (meta)sediments of the Böllstein Odenwald (Mid-German-Crystalline-Zone, Variscides)

Article

Full-text available

Mar 2017

Detrital zircons separated from paragneisses of the northern Böllstein Odenwald (Mid-German Crystalline Zone, Variscides) yielded Cambrian to Upper Devonian U–Pb ages. The age of the youngest detrital zircon population (371 ± 3 Ma) and the Lower Carboniferous metamorphic overprint indicate an Upper Devonian depositional age of the paragneiss protolith. The age spectra of detrital zircons suggest the latter to be derived from (1) Ordovician igneous rocks of the Saxothuringian Zone, (2) a late Cadomian magmatic arc (Teplá-Barrandian Unit) and (3) a Silurian-Devonian magmatic arc. Cadomian igneous activity is also documented by Cambrian zircon cores in Lower to Middle Devonian detrital zircons. Meso- and Paleoproterozoic detrital zircons, which are typical for the Old Red Continent and the Rhenohercynian Zone, are entirely lacking. The restricted Palaeozoic detrital zircon age spectrum is attributed to a Silurian-Devonian intra arc or trench setting. Both the lack of Mesoproterozoic detrital zircons and the striking similarity of the U–Pb ages of the detrital zircon obtained from the Böllstein Odenwald with U–Pb ages from crystalline rocks of the Saxothuringian basement, rules out that the Böllstein Odenwald is forming a tectonic window (Rhenohercynian lower plate) inside the Mid-German Crystalline Zone (Saxothuringian upper plate).

Magneto- and carbon-isotope stratigraphy of the Lower–Middle Bathonian in the Sokur section (Saratov, Central Russia): implications for global correlation

Article

Feb 2017
RUSS GEOL GEOPHYS+

The discovery of Tethyan and Boreal fossils in Bathonian deposits of the Sokur section in the vicinity of Saratov (Central Russia) reopened the possibility of direct correlation of the Bathonian sections in different paleobiogeographic provinces, which require further integrated studies involving both paleontological (based on different groups of fauna) and physicochemical (paleomagnetic and isotope-geochemical) methods. Stable carbon isotope data for belemnite (Cylindroteuthididae) rostra from the Sokur section show that the Subboreal Oraniceras besnosovi Zone and Boreal Arcticoceras harlandi Subzone are correlated with the Zigzag Zone of the standard scale, whereas the Boreal A. ishmae Subzone can be correlated completely or, even partly, with the Tenuiplicatus Zone. We identified equivalents of chrons of the geomagnetic polarity time scale (GPTS): e-Bath N, m-Bath R, and lt-Bath N, corresponding to the Lower–Middle Bathonian and, possibly, lowermost Upper Bathonian. Article link, which provides free access to the article and is valid until April 05, 2017 https://authors.elsevier.com/a/1UZ1n3p12uWtra

3D stratigraphic forward numerical modelling approach for prediction of organic-rich deposits and their heterogeneities

Article

Jan 2017
MAR PETROL GEOL

The source rock characteristics (e.g. thickness, lateral extension, richness) are known to be highly variable in both time and space. The Lower Jurassic formations of north-western Europe contain source rocks with organic-rich intervals showing different characteristics from one region to another: the Paris Basin differs from the South-East Basin of France, but organic content and hydrogen index also vary within a single basin. During the Early Jurassic, the overall depositional environment of north-western Europe corresponded to an epicontinental domain at the western extremity of the Tethys Ocean. The early transgressive phase of the Jurassic induced flooding of this European realm. Because of the evolution of the connections and threshold of the European basins and their associated sedimentary settings, this domain occupied a key position for the deposition of organic-rich layers. Using a forward modelling approach, we aim to predict the heterogeneous characteristics of such sediments. It is widely accepted that primary productivity and preservation are key factors favouring the accumulation of organic-rich layers. However, the roles of these factors remain to be assessed and the processes leading to accumulation and preservation need to be quantified.

Jurassic carbonate microfacies and relative sea-level changes in the Tethys Himalaya (southern Tibet)

Article

May 2016
PALAEOGEOGR PALAEOCL

Detailed microfacies analysis of carbonate rocks from the Tingri and Nyalam areas of southern Tibet allowed us to reconstruct the evolution of sedimentary environments and relative sea-level changes during the Early to Middle Jurassic. Based on texture, sedimentary structure, grain composition and fossil content of ~ 500 thin sections, 17 microfacies overall were identified, and three evolutionary stages of sedimentary environments were defined. Stage 1 (Rhaetian?-lower Sinemurian Zhamure Formation) is characterized by siliciclastic and mixed siliciclastic-carbonate sedimentation on a barrier-island environment. Stage 2 (upper Sinemurian-Pliensbachian Pupuga Formation) is characterized by high-energy grainstones with rich benthic faunas thriving on a carbonate platform, documenting transgressions in the early and late Pliensbachian. Stage 3 (Toarcian-lower Bajocian Nieniexiongla Formation) is characterized by low-energy mudstones intercalated with frequent storm layers on a carbonate ramp, documenting the climax of the early Toarcian transgression in the beginning of the unit. The transition from Stage 1 to Stage 2 points to a paleogeographic and paleoclimatic change, as the Tibetan Tethys Himalaya moved towards tropical latitudes characterized by highly suitable climatic and ecological conditions for carbonate sedimentation. The abrupt change from Stage 2 to Stage 3 is interpreted as a consequence of the early Toarcian Oceanic Anoxic Event, accompanied by short-term warming and sea-level rise. The failed recovery from the carbonate crisis in the early Bajocian, with continuing deposition on a low-energy carbonate ramp, may reflect tectonic migration towards higher southern latitudes and/or a reduction of the effect of warm tropical currents reaching the southern Tethys.

Carbon cycle history through the Jurassic–Cretaceous boundary: A new global δ13C stack

Article

Mar 2016
PALAEOGEOGR PALAEOCL

Foraminifera from late Jurassic - Early Cretaceous hydrocarbon seep carbonates, central Spitsbergen, Svalbard - Preliminary results

Article

Full-text available

Jan 2012
NORW J GEOL

Mixed calcareous-agglutinated benthic foraminiferal assemblages have been obtained from five hydrocarbon seep carbonate structures in the upper Slottsmøya Member (Agardhfjellet Formation) in central Spitsbergen, Svalbard. The composition of the agglutinated component is comparable to faunas previously described from the surrounding dark shales of the Slottsmøya Member, as well as from deposits of Arctic Russia and other areas of the Boreal Realm. Calcareous foraminifera are observed only in thin-sections. The foraminifera date the hydrocarbon seep bodies as Late Volgian - Late Ryazanian; an age determination in part slightly divergent from ammonite datings previously recorded from these carbonates. This is the first systematic report of foraminifera from seep structures developed at the Jurassic-Cretaceous transition.

Ages of the Tuchengzi Formation in northern China and the terrestrial Jurassic-Cretaceous boundary in China

Article

Full-text available

Jan 2014

We here briefly introduce the distribution, sedimentary characteristics and filling sequence of the Tuchengzi Formation in northern North China. On the basis of the uncertainty of the age of the Tuchengzi Formation, we analyzed all the isotopic dating data and constrained the age of Tuchengzi Formation to be 154-137 Ma. Previous biostratigraphy research is consistent with the age of Tuchengzi Formation. The International Commission on Stratigraphy (ICS) proposed 145 Ma to be the age of Jurassic-Cretaceous boundary in 2013, which is supported by recent studies in the Tethys-Himalaya and Andes, although more high-precision geochronology is still needed for the final establishment. This boundary age suggests that the Tuchengzi Formation is the Late Jurassic-Early Cretaceous in age, and the terrestrial Jurassic-Cretaceous boundary in China exists in the Tuchengzi Formation. The international stratigraphic boundary, especially for the J/K boundary, should be established by the marine biostratigraphy. The establishment of the J/K boundary in China should give priority to obey the symbol and achievement derived from the marine biostratigraphy and organic evolution.

Unconformity surfaces in pelagic carbonate environments: A case from the Middle Bathonian of the Betic Cordillera, SE Spain

Article

Full-text available

Jan 2014
ANN SOC GEOL POL

Integrative studies of sedimentary and palaeontological topics for unconformity surfaces are useful in basin analysis. A middle Bathonian unconformity surface in the Ammonitico Rosso facies cropping out in the La Mola Unit (Subbetic Domain, Betic External Zone) was studied by integrating ichnological, palaeotectonic, and sedimentological analyses to decipher sea-level, tectonic, and palaeogeographic conditions during its development. The trace-fossil assemblage mainly consists of the Glossifungites (Thalassinoides, Arenicolites, and Gastrochaenolites) and Trypanites ichnofacies elements. Probable Ophiomorpha represents previous softground stages, Thalassinoides and Arenicolites were formed in firmground, Gastrochaenolites reflects an evolved firmground or early hardground, and Trypanites can be attributed to an incipient hardground. The degree of firmness, relative sea-level position, and continuity of deposition were related. The softground stage corresponds to a fall in relative sea level and continued deposition. The firmground (semi-consolidated substrate) probably reflects an extremely low sea level characterized by non-deposition, whereas the incipient hardground stage indicates an initial phase of relative sea-level rise, with an increase in marine current energy. The presence of two neptunian dyke systems reflects significant tectonic activity related to the transtensional deformation that affected the South Iberian Palaeomargin. Lateral variations in sedimentological and ichnological features recorded at similar discontinuity surfaces in nearby areas were considered and related to differences in bottom topography, with associated changes in sedimentation, and to the variable duration of the hiatus.

Two new ophthalmosaurids (Reptilia: Ichthyosauria) from the Agardhfjellet Formation (Upper Jurassic: Volgian/Tithonian), Svalbard, Norway

Article

Full-text available

Jan 2012
NORW J GEOL

Ichthyosaur diversity near the Jurassic-Cretaceous boundary, particularly from high paleolatitudes, is poorly known. Two recently collected specimens of medium- to large-bodied ichthyosaurs from the Slottsmøya Member of the Agardhfjellet, Svalbard, Norway represent two new taxa of ophthalmosaurids. The holotype specimen of Cryopterygius kristiansenae gen et sp. nov., PMO 214.578, is a nearly complete and largely articulated skeleton. The specimen consists of a nearly complete skull, the entire presacral and preflexural vertebral series, numerous dorsal ribs and gastralia, an articulated pectoral girdle and nearly complete forelimb, and an articulated left pelvic girdle and hindlimb. The new taxon is diagnosed on a unique suite of features, including a robust and moderately elongate rostrum, a reduced supranarial process, an elongate maxilla that bears a high number of teeth, the absence of a lacrimal-external naris contact, and an anteroposteriorly broad postorbital bar possessing an unidentified element (supratemporal?) that lies posterior to the quadratojugal. Cryopterygius has 52 presacral vertebrae, a distinctive forelimb, including a humerus that bears only two facets at its distal end, and an articulated left pelvic girdle and hindlimb, which facilitates the unequivocal orientation of the ophthalmosaurid femur. The holotype specimen of Palvennia hoybergeti, SVB 1451, includes a nearly complete skull and fragmented postcranial remains. It is diagnosed on its relatively short rostrum, greatly enlarged orbit, narrow postorbital bar, very large pineal foramen, basioccipital with broad extracondylar area laterally, and a gracile stapedial shaft. The Slottsmøya Lagerstätte is established as one of the most productive horizons for Upper Jurassic ichthyosaurs and considerably expands our knowledge of ophthalmosaurid diversity and distribution in the latest Jurassic.

Correlation of the Bajocian and Bathonian zones in light of new paleontological data

Article

Nov 2014

S.V. Meledina

The revision of the geochronological ranges of the Boreal genera Arctocephalites and Arcticoceras found in the Middle Volga region (Middle Povolzhye) together with Peri-Tethyan ammonites resulted in the revision of the stratigraphic position of several zones in the Middle Jurassic ammonite scale of Siberia. It is shown that the Arctic genus Arcticoceras appeared in the early Bathonian, rather than in the middle Bathonian, as is cited in the current Siberian zonal scale. The geochronology of zones preceding the zones with Arcticoceras also needs revision. The lower jugatus Subzone in the arcticus Zone (equivalent to the upper Bajocian niortense Zone in the northwestern European zonal standard) can be used as a correlation marker level. The upper arcticus Subzone is correlated to the two upper Bajocian zones, greenlandicus and harlandi zones, whereas the ishmae Zone correlates with the lower Bathonian zigzag Zone. The gracilis and borealis zones, considered as equivalents of the humphriesianum Zone, should be transferred to the lower Bajocian. No ammonites were found in the middle Bathonian.

End-Triassic nonmarine biotic events

Article

Full-text available

Oct 2015

The Late Triassic was a prolonged interval of elevated extinction rates and low origination rates that manifested themselves in a series of extinctions during Carnian, Norian and Rhaetian time. Most of these extinctions took place in the marine realm, particularly affecting radiolarians, conodonts, bivalves, ammonoids and reef-building organisms. On land, the case for a Late Triassic mass extinction is much more tenuous and has largely focused on tetrapod vertebrates (amphibians and reptiles), though some workers advocate a sudden end-Triassic (TJB) extinction of land plants. Nevertheless, an extensive literature does not identify a major extinction of land plants at the TJB, and a comprehensive review of palynological records concluded that TJB vegetation changes were non-uniform (different changes in different places), not synchronous and not indicative of a mass extinction of land plants. Claims of a substantial perturbation of plant ecology and diversity at the TJB in East Greenland are indicative of a local change in the paleoflora largely driven by lithofacies changes resulting in changing taphonomic filters. Plant extinctions at the TJB were palaeogeographically localized events, not global in extent. With new and more detailed stratigraphic data, the perceived TJB tetrapod extinction is mostly an artifact of coarse temporal resolution, the compiled correlation effect. The amphibian, archosaur and synapsid extinctions of the Late Triassic are not concentrated at the TJB, but instead occur stepwise, beginning in the Norian and extending into the Hettangian. There was a disruption of the terrestrial ecosystem across the TJB, but it was more modest than generally claimed. The ecological severity of the end-Triassic nonmarine biotic events are relatively low on the global scale. Biotic turnover at the end of the Triassic was likely driven by the CAMP (Central Atlantic Magmatic Province) eruptions, which caused significant environmental perturbations (cooling, warming, acidification) through outgassing, but the effects on the nonmarine biota appear to have been localized, transient and not catastrophic. Long-term changes in the terrestrial biota across the TJB are complex, dia-chronous and likely climate driven evolutionary changes in the context of fluctuating background extinction rates, not a single, sudden or mass extinction. ScienceDirect j ou rna l h ome pag e: http://www.journals.elsevier.com/journal-of-pal ae og eog raph y/ j o u r n a l o f p a l a e o g e o g r a p h y 4 (2 0 1 5) 3 3 1 e3 4 8

Palaeomagnetic study of the Jurassic from Argentina: Magnetostratigraphy and palaeogeography of South America

Article

Jan 2012

Maria Paula Iglesia Llanos

A palaeomagnetic study has been carried out in five Lower Jurassic sections from the Neuquén basin, made up mainly of ammonitebearing sedimentary and, subordinately, volcanic rocks. Sampled sections are located to the north of the basin, along the Atuel river (Hettangian to Toarcian) and to the centre (Pliensbachian to Toarcian) of the basin. The palaeomagnetic study shows two magnetic components carried by titanomagnetites, one soft with a direction in coincidence with the local dipolar field, and another harder that is interpreted as the original Jurassic based on the field tests for palaeomagnetic stability. From the polarity successions obtained in each locality, a composite magnetostratigraphic scale for the Southern Hemisphere has been constructed. The resultant scale bears 11 zones of dominant reverse polarity (JR 1 to JR 11), and 12 zones of dominant normal polarity (JN 1 to JN 12), which have been tied to 19 ammonite zones of the Andean Region. The regional scale has, in turn, been correlated to the international geomagnetic time scale. A good fit between the two scales is observed, allowing to date intervals with no diagnostic fossils. On the other hand, two palaeomagnetic poles have been calculated, one for the Hettangian-Sinemurian interval (223°E, 51°S, A 95= 6°, N = 25) and the other for the Pliensbachian- Toarcian (67°E, 74°S, A 95= 5°, N = 52). Such poles were combined with others from the literature to obtain the apparent polar wander (APW) path for South America, which turns out to be remarkably dissimilar from the classical ones that show the continent in a stationary position throughout the Mesozoic. From the new APW path, it has been interpreted that South America may have rotated clockwise while it moved to the north. Eurasia's path is also presented in this study, revealing the same shape and chronology of tracks. These latitudinal changes that we observed from the palaeomagnetic data are supported by palaeoecological data.

The Upper Jurassic of the Laptev Sea: interregional correlations and paleoenvironments

Article

Full-text available

Aug 2015
RUSS GEOL GEOPHYS+

The Late Jurassic evolution of Boreal and Arctic basins is reflected in the widespread deposition of organic-rich black shales (source rocks). In this connection, the priority should be placed on the development and refinement of zonal schemes for the Upper Jurassic of the Laptev Sea coast based on ammonites, foraminifers, ostracods, dinocysts, and spores and pollen from reference sections as the basis for stratigraphic, paleogeographic, and facies studies. The Upper Jurassic and Lower Cretaceous reference section of interest is located on the left side of the Anabar Bay of the Laptev Sea (Nordvik Peninsula, Urdyuk-Khaya Cape). An uninterrupted and continuous section from Upper Oxfordian to Lower Valanginian is exposed in coastal cliffs and consists mainly of silty clay deposits with abundant macro- and microfossils. A reliable biostratigraphic subdivision of the Upper Jurassic interval of this section was taken as the basis for the assessment of the correlation potential of different fossil groups and subsequent interregional correlations, facies analysis, and detailed paleogeographic reconstructions of the study area. The analysis of variations in the composition of macrobenthic communities and microphytoplankton and terrestrial palynomorph assemblages and the biofacies analysis allowed the reconstruction of the evolution of marine paleoenvironmental settings in the western part of the Anabar-Lena sea and in the terrestrial settings in the adjacent land area of Siberia.

Palaeoclimatic oscillations in the Pliensbachian (Lower Jurassic) of the Asturian Basin (Northern Spain)

Article

Full-text available

Aug 2015
CPD

One of the main controversial items in palaeoclimatology is to elucidate if climate during the Jurassic was warmer than present day, with no ice caps, or if ice caps were present in some specific intervals. The Pliensbachian Cooling event (Lower Jurassic) has been pointed out as one of the main candidates to have developed ice caps on the poles. To constrain the timing of this cooling event, including the palaeoclimatic evolution before and after cooling, as well as the calculation of the seawater palaeotemperatures are of primary importance to find arguments on this subject. For this purpose, the Rodiles section of the Asturian Basin (Northern Spain), a well exposed succession of the uppermost Sinemurian, Pliensbachian and Lower Toarcian deposits, has been studied. A total of 562 beds were measured and sampled for ammonites, for biostratigraphical purposes and for belemnites, to determine the palaeoclimatic evolution through stable isotope studies. Comparison of the recorded uppermost Sinemurian, Pliensbachian and Lower Toarcian changes in seawater palaeotemperature with other European sections allows characterization of several climatic changes of probable global extent. A warming interval which partly coincides with a negative δ13Cbel excursion was recorded at the Upper Sinemurian. After a "normal" temperature interval, a new warming interval that contains a short lived positive δ13Cbel peak, was developed at the Lower-Upper Pliensbachian transition. The Upper Pliensbachian represents an outstanding cooling interval containing a positive δ13Cbel excursion interrupted by a small negative δ13Cbel peak. Finally, the Lower Toarcian represented an exceptional warming period pointed as the main responsible for the prominent Lower Toarcian mass extinction.

Late Jurassic–Early Cretaceous hydrocarbon seep boulders from Novaya Zemlya and their faunas

Article

Oct 2015
PALAEOGEOGR PALAEOCL

The paper describes Late Jurassic–Early Cretaceous seep carbonate boulders from the Russian Arctic island of Novaya Zemlya, collected in 1875 by A.E. Nordenskiöld during his expedition to Siberia. The carbonates are significantly depleted in heavy carbon isotopes (δ13C values as low as ca. − 40‰) and show textures typical for carbonates formed under the influence of hydrocarbons, such as fibrous carbonate cements and corrosion cavities. The rocks contain index fossils of Late Oxfordian–Early Kimmeridgian, Late Tithonian (Jurassic) and latest Berriasian–Early Valanginian (Cretaceous) age. The fossil fauna is species rich and dominated by molluscs, with subordinate brachiopods, echinoderms, foraminifera, serpulids and ostracods. Most of the species, including two chemosymbiotic bivalve species, likely belong to the ‘background’ fauna. Only a species of a hokkaidoconchid gastropod, and a possible abyssochrysoid gastropod, can be interpreted as restricted to the seep environment. Other seep faunas with similar taxonomic structure are suggestive of rather shallow water settings, but in case of Novaya Zemlya seep faunas such structure might result also from high northern latitude.

BIOSTRATIGRAPHY AND GEOCHRONOLOGY OF THE PLIENSBACHIAN-TOARCIAN BOUNDARY IN ARGENTINA

Conference Paper

Full-text available

Jun 2014

Tithonian–Berriasian ammonites from the Baños del Flaco Formation, central Chile

Article

Full-text available

Apr 2015

The Baños del Flaco Formation in central Chile contains abundant and well-preserved Tithonian (Late Jurassic) and scarce Berriasian (Early Cretaceous) ammonites. At Rio Maitenes in Curicó Province an assemblage referred to 10 genera and 12 species is here described. Windhauseniceras internispinosum, Corongoceras alternans and Substeueroceras koeneni were mentioned previously, but not described and discussed. Aulacosphinctes proximus, Micracanthoceras spinulosum and Corongoceras evolutum are new records for the Baños del Flaco Formation. Pseudolissoceras cf. zitteli, Lithacoceras malarguense, Choicensisphinctes windhauseni, Catutosphinctes cf. americanensis, Virgatosphinctes scythicus and Micracanthoceras microcanthum are documented in Chile for the first time. Micracanthoceras spinulosum shows strong ontogenetic changes. Virgatosphinctes scythicus is a morphologically variable species and is synonymous with the South American species Virgatosphinctes andesensis, V. mendozanus, V. mexicanus and V. leñaensis. Windhauseniceras internispinosum is relatively abundant at Rio Maitenes but rare elsewhere; its morphology varies considerably during ontogeny. Virgatosphinctes aff. pseudolictor and V. cf. raja, both recorded from Argentina, and V. guadalupensis, are synonymous with L. malarguense; V. tenuilineatus is synonymous with C. windhauseni and Aulacosphinctes chilensis with A. proximus. Micracanthoceras lamberti and M. tapiai are junior synonymies of M. microcanthum. Windhauseniceras internispinosum and Corongoceras alternans are Tithonian index fossils for Chile and Argentina, whereas Virgatosphinctes scythicus and Micracanthoceras microcanthum are Tithonian index fossils for the Russian platform and Tethys, respectively. Their co-occurrence at Río Maitenes confirms that most of the Baños del Flaco Formation is Tithonian (Upper Jurassic). However, the presence of Substeueroceras koeneni demonstrates that the uppermost strata of the Baños del Flaco Formation should be referred to the Lower Cretaceous (Berriasian).

Phylogenetic analysis of molecular and morphological data highlights uncertainty in the relationships of fossil and living species of Elopomorpha (Actinopterygii: Teleostei)

Article

Apr 2015
MOL PHYLOGENET EVOL

Late Jurassic (Volgian) radiolarians from Central Spitsbergen - A preliminary study

Article

Full-text available

Sep 2012

Radiolarians were studied in silt and shale samples from the Upper Jurassic Volgian part of the Slottsmøya Member (Agardhfjellet Formation) of Central Spitsbergen, Svalbard. Identifications could only be made from thin-sections, which hinders precise species level identifications. Nevertheless the preservation is sufficient to reliably identify some taxa and to establish general attributes of the fauna. The overall composition of the fauna is characterised by an abundance of spongy spumellarians and a dominance of parvicingulids among the nassellarians. These attributes have also been noted in samples assignable to the bipolar Boreal and Austral Realms, and the Svalbard fauna shows all the characteristics of the Northern Boreal Province as would be expected from its high palaeolatitude in the Late Jurassic.

An Upper Jurassic Boreal echinoderm Lagerstätte from Janusfjellet, central Spitsbergen

Article

Full-text available

Sep 2012
NORW J GEOL

A well-preserved, low-diversity assemblage of fossil echinoderms from the early Middle Volgian in the Slottsmøya Member (Agardhfjellet Formation) has been discovered at Janusfjellet, Sassenfjorden area, central Spitsbergen. Five species are recognised: the isocrinid Chariocrinus sp., the pedinoid Hemipedina sp., the forcipulate asteroid Asteriidae sp., the ophiacanthid Ophiacanthidae sp. and the ophiurid Ophiurinae sp. A depositional environment model reconciling autecologic, taphonomic and sedimentary evidence is presented. The Janusfjellet Lagerstätte was formed by a single, rapid burial event during a storm, entombing together autochthonous asteroids and ophiurids, and allochthonous crinoids and echinoids on a dysoxic muddy sea-floor. Comparable echinoderm material from the Boreal Late Jurassic-Early Cretaceous is scarce, outdated and usually poorly described and illustrated. The scarcity of reported occurrences probably results from a collector bias for rare complete specimens and does not reflect the true echinoderm composition of Mesozoic high-latitude communities.

Organic carbon isotope chemostratigraphy and cyclostratigraphy in the Volgian of Svalbard

Article

Full-text available

Sep 2012
NORW J GEOL

We present δ13Corg curves for the Upper Jurassic to lowermost Cretaceous of central Spitsbergen. The three sections span the Slottsmøya Member (Agardhfjellet Formation) at Janusfjellet and Knorringfjellet in the Sassenfjorden area. The results indicate that bulk organic carbon isotope chemostratigraphy can be used as a tool for high-resolution, local chronostratigraphic correlation in central Spitsbergen, resolving problems of possible overthrusts, slumping and diachronous lithological boundaries. Moreover, the curves can be compared with published data from carbonates on the Russian Platform, recording a negative δ13C trend through the Lower Volgian followed by a positive trend from the lower part of the Middle Volgian and into the Upper Volgian. The minimum in the curve in the lower Middle Volgian is sharply defined, and this negative excursion may provide a useful chemostratigraphic marker for correlation between the Barents Sea and the Russian Platform, and possibly globally. The excursion is here called VOICE (Volgian Isotopic Carbon Excursion). There are indications of a c. 400 kyr periodicity, which can be interpreted as a result of orbital forcing (long eccentricity). In contrast, inorganic carbon and oxygen isotopes from carbonates in the Sassenfjorden area mainly reflect diagenetic processes.

Volcanism of the Central Atlantic magmatic province as the trigger of environmental and biotic changes around the Triassic-Jurassic boundary

Article

Full-text available

Sep 2014

In the last decade, major advances have been made in our understanding of the end-Triassic mass extinction, related environmental changes, and volcanism of the Central Atlantic magmatic province. Studies of various fossil groups and synoptic analyses of global diversity document the extinction and subsequent recovery. The concomitant environmental changes are manifested in a series of carbon isotope excursions (CIE), suggesting perturbations in the global carbon cycle. Besides the earlier-recognized initial and main negative anomalies, a more complex picture is emerging with other CIEs, both negative and positive, prior to and following the Triassic-Jurassic boundary. The source of isotopically light carbon remains debated (methane from hydrate dissociation vs. thermogenic methane), but either process is capable of amplifying an initial warming, resulting in runaway greenhouse conditions. Excess CO2 entering the ocean causes acidification, an effective killing mechanism for heavily calcified marine bio

Cyclostratigraphy of an orbitally-driven Tithonian–Valanginian carbonate ramp succession, Southern Mendoza, Argentina: Implications for the Jurassic–Cretaceous boundary in the Neuquén Basin

Article

Jan 2015
SEDIMENT GEOL

Detailed sedimentological, sequence stratigraphical and cyclostratigraphical analyses have been made from four lower Tithonian–lower Valanginian sections of the Vaca Muerta Formation, exposed in the southern Mendoza area of the Neuquén Basin, Argentina. The Vaca Muerta Formation is characterized by decimetre-scale rhythmic alternations of marls, shales and limestones, and consists of five facies associations, which reflect different paleoenvironmental conditions: basin to restricted outer ramp, outer ramp, and middle ramp. Vertical organization within the Vaca Muerta Formation shows a well-ordered hierarchy of cycles, where elementary cycles, bundles and superbundles with frequencies within the Milankovitch band have been recognized. According to biostratigraphic data, elementary cycles have a periodicity of ~ 20 ky, which correlates with the precession cycle of Earth's axis. Spectral analysis based on series of cycle thickness allows us to identify frequencies of about 400 ky and 90–120 ky, which we interpret as the modulation of the precessional cycle by the Earth's orbital eccentricity. Cycles are probably driven by variations in carbonate exportation, as fluctuations in shallow-water carbonate production involve modifications in carbonate basinward exportation. Cyclostratigraphic data allowed us to build a floating orbital scale for the Tithonian–lower Valanginian interval in the Neuquén Basin. Correlation between studied sections allowed us to recognize a discontinuity between the Substeueroceras koeneni and Argentiniceras noduliferum ammonite zones in the Malargüe Anticline area. Orbital calibration of these sections is consistent with Riccardi's biostratigraphic scheme, wich place the Jurassic-Cretaceous boundary within the Substeueroceras koeneni ammonite Zone. On the other hand, the base of the Vaca Muerta Formation (Virgatosphinctes mendozanus ammonite Zone) would be probably placed in the base of the middle Tithonian rather than the lower Tithonian, which is also consistent with our preliminary palaeomagnetic data.

A new species of Pliosaurus (Sauropterygia: Plesiosauria) from the Middle Volgian of central Spitsbergen, Norway

Article

Full-text available

Jan 2012
NORW J GEOL

Eight seasons of fieldwork in the Upper Jurassic black shales of the Slottsmøya Member of the Agardhfjellet Formation (Upper Jurassic; Middle Volgian) in the Arctic archipelago of Svalbard have yielded numerous skeletal remains of plesiosaurs and ichthyosaurs. Among the new discoveries from the Slottsmøya Member are two very large specimens of short-necked plesiosaurians. Dental and postcranial morphology suggest that they represent a new species of the genus Pliosaurus, a taxon known from several specimens of Kimmeridgian and Tithonian-aged strata in England, France and Russia. Skeletal dimensions of this new taxon suggest that it was one of the largest members of the Pliosauridae and that it possessed comparatively longer front limbs than other known pliosaurids. A morphometric analysis of pliosaurids indicates they had a wide range of interspecific variability in relative paddle lengths compared to body size.

Two new species of long-necked plesiosaurians (Reptilia: Sauropterygia) from the Upper Jurassic (Middle Volgian) Agardhfjellet Formation of central Spitsbergen

Article

Full-text available

Jan 2012
NORW J GEOL

At present, very little is known regarding the diversity and morphological disparity of long-necked plesiosaurs in Tithonian-aged (latest Jurassic) units globally. Here, we describe two species of a new, long-necked plesiosaur genus Spitrasaurus from the Upper Jurassic Slottsmoya Member of the Agardhfjellet Formation on Svalbard. The holotype species of the genus, S. wensaasi, is the most complete long-necked specimen found in this unit to date and is readily diagnosed on the basis of having at least 60 cervical vertebrae possessing a prominent lateral longitudinal ridge, as well as the presence of a column of well-developed preaxial accessory ossicles in the limbs. A second taxon, S. larseni, includes a partial skull that broadly resembles the Kimmeridgian taxon Kimmerosaurus, but differs in the morphology of its basioccipital, and in having a distinctive lower jaw with a greatly elongate and strongly dorsally inflected retroarticular process, among other characteristics. Each species of Spitrasaurus can be differentiated on the basis of cervical vertebral proportions and in the morphology of the cervical ribs, rib facets and neural arches, in addition to being stratigraphically separated. The high number of cervical vertebrae in Spitrasaurus significantly exceeds that for described Middle to Late Jurassic plesiosaurs, but is comparable to some Cretaceous elasmosaurids. The Middle Volgian age of this material helps to bridge the temporal and morphological gap between better known Middle and Late Jurassic plesiosaurians from Europe and Late Cretaceous taxa primarily known from North America.

Redescription and taxonomic clarification of ‘Tricleidus’ svalbardensis based on new material from the Agardhfjellet Formation (Middle Volgian)

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Jan 2012
NORW J GEOL

A partial postcranial plesiosaurian skeleton uncovered on Svalbard in the winter of 1930-31 was described and named Tricleidus svalbardensis Persson, 1962. However, the precise geographic location and stratigraphic unit in which the skeleton was found were not published. Recent fieldwork on Svalbard has uncovered two more plesiosaur skeletons that are demonstrated herein to be conspecific with the 1931 taxon. These new specimens, along with recently discovered historic documents produced by the excavation members of the 1930-31 expedition, reveal that the holotype specimen, PMO A 27745, was recovered from the Upper Jurassic Slottsmøya Member of the Agardhfjellet Formation, which is Middle Volgian in age. Collectively, the Svalbard material is neither morphologically nor stratigraphically consistent with the Callovian taxon Tricleidus Andrews, 1909 and is here referred to Colymbosaurus Seeley, 1874 from the Kimmeridge Clay Formation (Kimmeridgian to Tithonian) of the UK.

A new plesiosauroid (Reptilia: Sauropterygia) from the Agardhfjellet Formation (Middle Volgian) of central Spitsbergen, Norway

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Jan 2012
NORW J GEOL

At present, our knowledge of plesiosauroid diversity from the uppermost Jurassic (Tithonian/Volgian) is very limited. Newly discovered material from the Slottsmøya Member of the Agardhfjellet Formation of central Spitsbergen, Svalbard, contributes significant new information on this poorly known interval and helps bridge a temporal gap between better known plesiosaurians from the older Jurassic deposits of Europe, and Cretaceous of North America. The partially articulated skeleton of a juvenile long-necked plesiosaurian, PMO 216.839, is one of the most complete plesiosaur fossils known from Spitsbergen and represents a new taxon, Djupedalia engeri gen. et sp. nov. Whilst sharing some similarities with previously described taxa from the Oxford Clay (Muraenosaurus, Tricleidus, and Cryptoclidus) and the Kimmeridge Clay formations (Kimmerosaurus) of England, the new taxon can be diagnosed by features of the cervical vertebrae, including centrum proportions and morphology, a very pronounced posterior shift in the neural spines relative to the centrum, fused prezygapophyses and greatly elongated postzygapophyses, as well as extremely short dorsal neural spines and femora that are longer than the humeri. The new taxon can also be distinguished from other newly-described plesiosauroids from Svalbard, thus indicating that several plesiosaurian taxa existed at high paleolatitudes during the Late Jurassic.

Evaluating the temporal link between the Karoo LIP and climatic–biologic events of the Toarcian Stage with high-precision U–Pb geochronology

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Dec 2014
EARTH PLANET SC LETT

We present four new (CA-ID-TIMS) U–Pb ages from ammonite-bearing rocks in Peru.•We present new U–Pb zircon and baddeleyite data from the K-LIP in South Africa.•The age of the falciferum CIE is between and .•The falciferum CIE correlates with Karoo sill emplacement at .

Stratigraphic continuity and fragmentary sedimentation: The success of cyclostratigraphy as part of integrated stratigraphy

Article

Oct 2014

The Milankovitch theory of climate change is widely accepted, but the registration of the climate changes in the stratigraphic record and their use in building high-resolution astronomically tuned timescales has been disputed due to the complex and fragmentary nature of the stratigraphic record. However, results of time series analysis and consistency with independent magnetobiostratigraphic and/or radio-isotopic age models show that Milankovitch cycles are recorded not only in deep marine and lacustrine successions, but also in ice cores and speleothems, and in eolian and fluvial successions. Integrated stratigraphic studies further provide evidence for continuous sedimentation at Milankovitch time scales (104 years up to 106 years). This combined approach also shows that strict application of statistical confidence limits in spectral analysis to verify astronomical forcing in climate proxy records is not fully justified and may lead to false negatives. This is in contrast to recent claims that failure to apply strict statistical standards can lead to false positives in the search for periodic signals. Finally, and contrary to the argument that changes in insolation are too small to effect significant climate change, seasonal insolation variations resulting from orbital extremes can be significant (20% and more) and, as shown by climate modelling, generate large climate changes that can be expected to leave a marked imprint in the stratigraphic record. The tuning of long and continuous cyclic successions now underlies the standard geological time scale for much of the Cenozoic and also for extended intervals of the Mesozoic. Such successions have to be taken into account to fully comprehend the (cyclic) nature of the stratigraphic record.

A geochemical constraint on the formation process of a manganese carbonate nodule in the siliceous mudstone of the Jurassic accretionary complex in the Mino Belt, Japan

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Nov 2014
J ASIAN EARTH SCI

Manganese (Mn) carbonate nodules, which differ from seafloor Mn nodules mainly composed of MnO2, are occasionally embedded in the form of a lens shape in the Jurassic accretionary complexes, such as the Mino Belt in Japan. The interpretation of the formation process of Mn carbonate is still controversial, particularly concerning whether the Mn carbonate was formed primarily or secondarily. In this study, a fresh Mn carbonate nodule incorporated into the red siliceous mudstone was collected for geochemical and sedimentological analysis. The optical observation of thin sections indicates that the Mn carbonate nodules are composed of abraded grains of rhodochrosite spherule with radiolarians and are sedimentary embedded in siliceous mudstone. Microfossil radiolarians from the Mn carbonate nodules and the host red siliceous mudstone are dated as the Bajocian, but the radiolarians in the nodules are somewhat older than those in the host red siliceous mudstone.

Effects of Karoo–Ferrar Volcanism and Astronomical Cycles on the Toarcian Oceanic Anoxic Events (Early Jurassic)

Article

Jun 2014
PALAEOGEOGR PALAEOCL

One of the most profound environmental changes in the Mesozoic took place during Pliensbachian-Toarcian (Early Jurassic), including oceanic anoxia (Toarcian Oceanic Anoxic Event; T-OAE). The T-OAE is thought to have been caused by increased atmospheric CO2 triggered by Karoo–Ferrar volcanism. This idea, however, remains debated, primarily due to uncertainties in their age constraints of the relevant sedimentary sequences. To examine their temporal relationships, herein, we provide the astronomical time scale of the Lower Jurassic deep-sea bedded chert sequences from the pelagic Panthalassa superocean, which are exposed in the Inuyama area, central Japan. A 405-kyr tuned astrochronology, anchored to the end-Triassic extinction as 201.4 ± 0.2 Ma (Ikeda and Tada, 2013), allows us to constrain the ages of two black bedded cherts (T-OAE1 and T-OAE2). The ages of these T-OAEs overlap U–Pb ages of Karoo volcanic rocks. T-OAE in the European region is also synchronous with the Karoo–Ferrar volcanism, based on radiolarian and ammonite biostratigraphic correlation. These temporal relationships support the potential impact of Karoo–Ferrar volcanism on T-OAEs on a global scale. On the other hand, the onset of T-OAEs occur at the maxima of ~ 40 kyr, ~ 100 kyr, and 405 kyr cycles of chert thickness variation. The termination of T-OAEs and the recovery to oxic conditions in pelagic ocean coincide with the minima of ~ 40 kyr, ~ 100 kyr, and 405 kyr cycles of chert thickness. Moreove, the termination of final black chert and grey chert deposition coincide with the minima of ~ 1800 kyr cycles of chert thickness. These temporal relationships imply that orbital-scale productivity cycles were important in controlling the onset and termination of T-OAEs through the carbon cycle dynamics, which have been already amplified by Karoo–Ferrar volcanism.

A 70 million year astronomical time scale for the deep-sea bedded chert sequence (Inuyama, Japan): Implications for Triassic–Jurassic geochronology

Article

Aug 2014
EARTH PLANET SC LETT

Abstract

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