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Abstract

Dinosaurs dominated the land surface. Ammonites are the main fossils for correlating marine deposits. Pangea supercontinent began to break up, and at the end of the Middle Jurassic the Central Atlantic was born. Organic-rich sediments in several locations eventually became the source rocks helping to fuel modern civilization. HISTORY AND SUBDIVISIONS Overview of the Jurassic The term “Jura Kalkstein” was applied by Alexander von Humboldt (1799) to a series of carbonate shelf deposits exposed in the mountainous Jura region of northernmost Switzerland, and he first recognized that these strata were distinct from the German Muschelkalk (middle Triassic), although he erroneously considered his unit to be older. Alexander Brongniart (1829) coined the term “Terrains Jurassiques” when correlating the “Jura Kalkstein” to the Lower Oolite Series (now assigned to Middle Jurassic) of the British succession.

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... The uncertainties in the inter-regional biostratigraphic correlation constitute a major classic problem for this time interval across the world, and absolute data are still scarce and conflicting with each other (e.g., Remane, 1991;Wimbledon, 2008;Wimbledon et al., 2011Wimbledon et al., , 2013P alfy et al., 2000;P alfy, 2008;Vennari et al., 2014;Wimbledon, 2017). Cyclostratigraphy has become an important tool in measuring Jurassic -Cretaceous geologic time and establishing floating astronomical time scales (Ogg and Hinnov, 2012a;. Almost the entire Jurassic and Cretaceous have been calibrated using astronomical cycles, especially the long-term and short-term excentricity cycle. ...
... Almost the entire Jurassic and Cretaceous have been calibrated using astronomical cycles, especially the long-term and short-term excentricity cycle. However, the Tithonian (uppermost Upper Jurassic) remains still somewhat uncertain, and should be even carefully reviewed and compared with magnetostratigraphy and absolute dating (e.g., P alfy et al., 2000;P alfy, 2008;Huang et al., 2010;Ogg and Hinnov, 2012a). ...
... Our cyclostratigraphic data suggest a time span of 5.67 myr for the Tithonian and 5.27 myr for the Berriasian. However, if we take into consideration that the Tithonian most likely spans 7.1 myr (Ogg and Hinnov, 2012a), it would imply that c. four low-frequency eccentricity cycles An accurate astromomical time scale (ATS) for the TithonianeBerriasian is possible from the comparison and combination of available studies (Fig. 9). The lowermost Lower Tithonian was studied by Weedon et al. (1999Weedon et al. ( , 2004 using magnetic-susceptibility measures made on exposures, core material and down boreholes from the Kimmeridge Clay Formation (Kimmeridgiane Tithonian). ...
Chapter
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.
... The definition of Jurassic-Cretaceous boundary represents a drawback at a global scale, since the Cretaceous is the only system/period of the Phanerozoic that so far, has not been defined by a basal boundary stratotype. This is mainly due to the lack of significant evolutionary or physical/chemical event on either at regional or global scale within the commonly used boundary interval, coupled with the difficulty of correlating any biostratigraphic datum due to the pronounced provincialism of marine fauna (Ogg and Hinnov 2012;Ogg et al. 2016). After long years of debate, the Berriasian Working Group has concluded the boundary is marked by the explosion of Calpionella alpina, which is placed in the middle of Subchron M19n.2n. ...
... It enables correlation of rock strata of diverse depositional and faunal realms as well as the assignment of geologic ages to anomalies of marine magnetic intensities. For Middle Jurassic to present, magnetic anomalies of the ocean floor with their calibrations to biostratigraphy serve as a template against which magnetic polarities isolated, either on-land or in deep-sea sections, can be determined (Ogg and Hinnov 2012). Accordingly, magnetostratigraphy affords the employment of the reference Geomagnetic Polarity Time Scale (GTS) to the highresolution correlation of marine magnetic anomalies, and the use of the calibrated reference pattern of polarity changes to correlate polarity zones among sections (Ogg and Hinnov 2012). ...
... For Middle Jurassic to present, magnetic anomalies of the ocean floor with their calibrations to biostratigraphy serve as a template against which magnetic polarities isolated, either on-land or in deep-sea sections, can be determined (Ogg and Hinnov 2012). Accordingly, magnetostratigraphy affords the employment of the reference Geomagnetic Polarity Time Scale (GTS) to the highresolution correlation of marine magnetic anomalies, and the use of the calibrated reference pattern of polarity changes to correlate polarity zones among sections (Ogg and Hinnov 2012). From present to the Kimmeridgian (Chron M25r), polarities from the GTS are directly derived from sea-surface marine magnetic anomalies, whereas from the Kimmeridgian to the Bajocian (Chrons M27 to M44), polarities are modeled from deep-tow surveys. ...
Chapter
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.
... In contrast to most geological systems, the Jurassic/Cretaceous transition is characterized by the absence of a significant faunal turnover, as well as by the remarkable increase of faunal provinciality, especially in ammonites (e.g., Remane, 1991;Wimbledon, 2008;Michalík and Reh akov a, 2011;Wimbledon et al., 2011Wimbledon et al., , 2013Ogg and Hinnov, 2012, and references cited there). The uncertainties in the inter-regional correlation constitute a major classic problem for this time interval across the world. ...
... Since polarity reversals are recorded simultaneously in all type of rocks all over the world, they provide a distinctive pattern or finger-print for a certain time interval. Marine magnetic anomalies and their calibrations to biostratigraphy make up the reference against which magnetostratigraphic sequences, either on land or in deep-sea cores, are correlated (Ogg and Hinnov, 2012). Thus, one fundamental requisite to attempt a non-ambiguous paleomagnetic correlation between a section on-land and the GPTS is a good biostratigraphic definition (e.g. ...
... Thus, one fundamental requisite to attempt a non-ambiguous paleomagnetic correlation between a section on-land and the GPTS is a good biostratigraphic definition (e.g. Ogg and Hinnov, 2012). In the Jurassic, biostratigraphic, magnetostratigraphic, chemostratigraphic and other events are calibrated typically to the standard ammonite zones in Europe, although during the Oxfordian and Tithonian other paleogeographic realms take place such as the Boreal (Arctic and northernmost Europe), sub-Boreal (northern Europe), sub-Mediterranean (southern Europe) and Tethyan (southernmost Europe). ...
Article
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.
... Myr vs. 0.3 Myr in GTS2004), our cyclostratigraphic estimates could be used in the future generation of GTS. The recent GTS2012 used our estimate of ∼8.3 Myr from preliminary results (Huang et al., 2010a(Huang et al., , 2010b and added a 200 kyr duration assuming a condensation at the basal Tenuicostatum Zone in Sancerre, for a total duration of ∼8.6 Myr (Ogg and Hinnov, 2012, their Table 26.3). ...
... Also, a duration of 0.8 Myr for the Polymorphum Zone was inferred from the Peniche section, Portugal , although a problem in their cyclostratigraphic interpretation is likely (Kemp et al., 2011; see below, Section 5.1.2). In place of adding an arbitrary 200 kyr duration to the basal Toarcian Stage to compensate for a possible condensation (Ogg and Hinnov, 2012) we suggest future high-resolution cyclostratigraphic studies from thick Lower Toarcian sections (e.g., the Amellago section, Morocco) to constrain the chronology of the Tenuicostatum Zone. ...
Article
Full-text available
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.
... Particularly, the studies of calcareous nannofossils (Bown and Ellison 1995, Scasso and Concheyro 1999, Bown and Concheyro 2004, Lescano and Concheyro 2009, Vennari et al. 2014, as well as other Tethyan calcareous microfossils, such as calpionellids, saccocomid microcrinoids and calcareous dinoflagellate cysts (Fernández Carmona et al. 1996, Fernández Carmona and Riccardi 1998, Kietzmann and Palma 2009, Kietzmann et al. 2011a, Kietzmann 2017, Ivanova and Kietzmann 2017. The remarkable increase of faunal provinciality, as well as the uncertainties in the inter-regional correlation constitutes a major classic problem for the Tithonian-Berriasian across the world (e.g., Ogg and Hinnov 2012). The definition of the base of the Cretaceous System is still controversial. ...
... One interval at c. 30 m from the base bears no polarity, were a Cenozoic sill was intruded. Based on the correlation between ammonite zones from the Andean and Tethys Regions, these polarities were calibrated according to the last Geomagnetic Polarity Time Scale (GPTS) compiled by Ogg and Hinnov (2012). Results show a good correlation between both magnetostratigraphic scales. ...
Article
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.
... Applegate & Bergen (1988) used the FO of L. bollii as a marker for the base of CC4-A. The CC4-A and CC4-B boundary has been considered Early Hauterivian in the Tethyan Realm, and has been correlated with the Crioceratites loryi ammonite zone (Bergen, 1994) and with Polarity Chron CM9 (Ogg & Hinnov, 2012b). However, in several sections of the Neuquén Basin, the FO of L. bollii occurs at a higher level, near the base of the Upper Hauterivian (Aguirre-Urreta et al. 2005). ...
... The LO of L. bollii has been used as a reliable marker within the CC5 Zone. In the Tethyan region, it occurs within the Pseudothurmannia ohmi ammonite zone (Bergen, 1994), at the top of the Hauterivian (Aguado et al. 2014;Reboulet et al. 2014) and within the Polarity Chron CM5 (Ogg & Hinnov, 2012b). In the Neuquén Basin, this bioevent is recorded high in the Agua de la Mula Member, in beds included in the Paraspiticeras groeberi ammonite zone, which in turn is correlated with part of the Pseudothurmannia ohmi Zone (Fig. 4). ...
Article
Full-text available
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.
... Particularly, the studies of calcareous nannofossils (Bown and Ellison 1995, Scasso and Concheyro 1999, Bown and Concheyro 2004, Lescano and Concheyro 2009, Vennari et al. 2014, as well as other Tethyan calcareous microfossils, such as calpionellids, saccocomid microcrinoids and calcareous dinoflagellate cysts (Fernández Carmona et al. 1996, Fernández Carmona and Riccardi 1998, Kietzmann and Palma 2009, Kietzmann et al. 2011a, Kietzmann 2017, Ivanova and Kietzmann 2017. The remarkable increase of faunal provinciality, as well as the uncertainties in the inter-regional correlation constitutes a major classic problem for the Tithonian-Berriasian across the world (e.g., Ogg and Hinnov 2012). The definition of the base of the Cretaceous System is still controversial. ...
... One interval at c. 30 m from the base bears no polarity, were a Cenozoic sill was intruded. Based on the correlation between ammonite zones from the Andean and Tethys Regions, these polarities were calibrated according to the last Geomagnetic Polarity Time Scale (GPTS) compiled by Ogg and Hinnov (2012). Results show a good correlation between both magnetostratigraphic scales. ...
Article
Full-text available
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.
... According to the chronostratigraphic Mesozoic timescale of Ogg (2004), the boundaries of the Tithonian are, at the base, 150.8 + 4 Ma and, at the top, 145.5 + 4 Ma (Fig. 2), the latter being the present absolute age for the Jurassic -Cretaceous boundary accepted by the International Commission of Stratigraphy of the IUGS (Ogg 2004). Recent studies by Ogg & Hinnov (2012), moved the base of the Tithonian to an older age, and propose a limit at 152.1 Ma. However, in the Tordillo Formation, the U -Pb detrital zircon ages indicate a statistically robust measure of the maximum depositional age at c. 144 Ma. ...
... We used the youngest graphical age peak and this is defined by a prominent peak composed of 37 concordant zircon ages at c. 144 Ma. This younger age indicates a discrepancy of at least 7 Ma with the absolute ages for the Kimmeridgian and Tithonian boundaries from the chronostratigraphic timescale of Ogg & Hinnov (2012). This also raises questions about the true absolute age of the Jurassic -Cretaceous boundary. ...
Article
Full-text available
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
... Within the Iznalloz section, the Polymorphum Zone is much thinner than any other biozone of the section but this is affected by the hiatus located in the Pliensbachian-Toarcian boundary and in the Polymorphum-Serpentinum zone boundary also recorded in other sections of the Subbetic (e.g., Nieto et al. 2008;Reolid et al. 2014a). The Serpentinum Zone has a duration of 1.08 Ma from Ogg and Hinnov (2012), 1.5-1.62 Ma from Boulila et al. (2014) and 1.31 Ma from Ruebsam et al. (2014) and is 2.62 m thick, but it is not represented by ammonitico rosso facies (sedimentation rate ranging from 0.24 to 0.16 cm/kyr; Table 1). ...
... Ma from Boulila et al. (2014) and 1.31 Ma from Ruebsam et al. (2014) and is 2.62 m thick, but it is not represented by ammonitico rosso facies (sedimentation rate ranging from 0.24 to 0.16 cm/kyr; Table 1). The Aalensis Zone, represented by ammonitico rosso facies, is 3.00 m thick for a duration of 1 Ma from Gradstein et al. (2004), 0.13 Ma from Ogg and Hinnov (2012) and 0.44-0.51 Ma from Boulila et al. (2014), (2.31-0.59 ...
Article
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).
... In vertebrate groups, there is similar evidence for a faunal turnover in the marine (Steel, 1973; (1) Stratigraphic age of the J/K boundary Recently, there has been substantial progress in determining the age of the J/K stratigraphic boundary, along with attempts at a global correlation (Wimbledon et al., 2011). Mahoney et al. (2005) previously proposed an age of 145.5 ± 0.8Ma, a result that has since been widely accepted as the age of the J/K boundary (Ogg & Hinnov, 2012; although see below). Of particular note is the biostratigraphic use of calpionellids (calcareous microplankton), which have helped to refine the dating of the base of the Cretaceous (Blau & Grun, 1997;Hauser et al., 2007;Casellato, 2010;Pruner et al., 2010). ...
Article
Full-text available
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.
... In vertebrate groups, there is similar evidence for a faunal turnover in the marine (Steel, 1973; (1) Stratigraphic age of the J/K boundary Recently, there has been substantial progress in determining the age of the J/K stratigraphic boundary, along with attempts at a global correlation (Wimbledon et al., 2011). Mahoney et al. (2005) previously proposed an age of 145.5 ± 0.8Ma, a result that has since been widely accepted as the age of the J/K boundary (Ogg & Hinnov, 2012; although see below). Of particular note is the biostratigraphic use of calpionellids (calcareous microplankton), which have helped to refine the dating of the base of the Cretaceous (Blau & Grun, 1997;Hauser et al., 2007;Casellato, 2010;Pruner et al., 2010). ...
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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.
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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.
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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.
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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).
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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.
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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.
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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
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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.
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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 .
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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The Greater Caucasus (GC) forms a high Alpine fold-and-thrust belt on the southern margin of the East European Platform (EEP). The Triassic, and particularly, the Jurassic history of the Western Greater Caucasus region is important for our understanding of the palaeogeographic and tectonic evolution of the western Tethys area. In order to better constrain the nature and relevance of these events in the evolution of the region, which are classically described as the Late Triassic to Late Jurassic Cimmerian events, a field campaign in the Western Greater Caucasus was undertaken. Analysis of structural, sedimentological and petrological data from 41 sites in the Fore-Caucasus (Malaya Laba, Mount Tkhach-Belaya River), the Central Greater Caucasus (Georgievskoye, Otdaleni) and Southern Slope (Krasnaya Poliana) areas of the Western Greater Caucasus revealed that a broad asymmetric basin, with associated emergent volcanic islands, formed in the area in Jurassic times. Incipient back-arc rifting in Pliensbachian times was coeval with similar rifting episodes in the Pontides and South Caspian Sea areas. The synchroneity of these events may have been related to the renewal of the Tethys subduction to the south of the Eo-Cimmerian accretionary belt. Rift reactivation, with significant thinning of the continental lithosphere, occurred in the Aalenian. Despite the strong Alpine tectonic overprinting, some structural data confirms that the extension trend was east-west (almost parallel to the active margin) resulting in the formation of a series of pull-apart basins in the GC and the South Caspian region behind the Eastern Pontides-Lesser Caucasus subduction-related volcanic belt. In Bajocian times, subduction-related volcanic activity largely expanded from the Eastern Pontides-Lesser Caucasus to encompass the Transcaucasus, the southern part of GC and the Crimea region. Such widening of the volcanic arc was probably due to a shallowing of the northward subducting slab. In the back-arc GC region, this signalled the onset of the post-rift stage. The return of the slab to normal steepness resulted in subsidence in the back-arc region and in the GC with extensive accommodation space creation. This was subsequently filled by the Late Jurassic, Cretaceous and Cenozoic sedimentary successions.
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