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Luis V Duarte - One of the best experts on this subject based on the ideXlab platform.
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late Pliensbachian early toarcian palaeoenvironmental dynamics and the Pliensbachian toarcian event in the middle atlas basin morocco
International Journal of Coal Geology, 2020Co-Authors: Bruno Rodrigues, João Graciano Mendonça Filho, Ricardo L. Silva, Driss Sadki, Joalice De Oliveira Mendonça, Luis V DuarteAbstract:Abstract Geochemical and palynofacies analysis of 38 samples from the Middle Atlas Basin (Ait Moussa and Issouka sections, Morocco) allowed to investigate sea-level changes, climate, and tectonics and impact on depositional environments in the westernmost Tethyan Gondwana-margin during the Late Pliensbachian–Early Toarcian and the Pliensbachian–Toarcian Event (Pl–Toa Event). The studied sections from the Middle Atlas Basin have low total organic carbon contents. Overall, kerogen assemblages are dominated by the Phytoclast Group, thus showing a strong terrestrial affinity and some degree of proximity to the source. Deposition occurred dominantly in oxic and proximal environments. Upper Pliensbachian kerogen assemblages from Ait Moussa are dominated by terrestrial particles and agree with the overall regressive character of the sedimentary succession. Uppermost Pliensbachian–lowermost Toarcian kerogen assemblages from Ait Moussa show an increase in marine particles. Considering the overall sedimentological context of the Middle Atlas Basin, these kerogen assemblages are interpreted to reflect local variation in accommodation space (driven by different sedimentation rates or tectonic compartmentalization) or ecological conditions (such as nutrient availability, temperature, turbidity, etc). In the Early Toarcian, above a major regional discontinuity and at the beginning of the Pl–Toa Event, increases in Botryococcus sp., AOM, and terrestrial palynomorphs suggest episodes of coastal erosion associated with transgression, likely driven by a combination of eustatic/tectonic changes and warmer and more humid climates leading to an increase in continental weathering and fluvial runoff. On the other hand, increases in sporomorphs and pollen grains occurring in tetrads and agglomerates indicate regressive episodes associated with increased sedimentation rates driven by enhanced continental weathering and fluvial runoff. This study shows the strong relationship between sea-level and the combined response of litho-, hydro-, and biosphere during the Early Toarcian, with implications to understand organic productivity and organic matter accumulation and preservation in the Tethys Ocean during the Pl–Toa Event.
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Late Pliensbachian–Early Toarcian palaeoenvironmental dynamics and the Pliensbachian–Toarcian Event in the Middle Atlas Basin (Morocco)
International Journal of Coal Geology, 2020Co-Authors: Bruno Rodrigues, João Graciano Mendonça Filho, Ricardo L. Silva, Driss Sadki, Joalice De Oliveira Mendonça, Luis V DuarteAbstract:Abstract Geochemical and palynofacies analysis of 38 samples from the Middle Atlas Basin (Ait Moussa and Issouka sections, Morocco) allowed to investigate sea-level changes, climate, and tectonics and impact on depositional environments in the westernmost Tethyan Gondwana-margin during the Late Pliensbachian–Early Toarcian and the Pliensbachian–Toarcian Event (Pl–Toa Event). The studied sections from the Middle Atlas Basin have low total organic carbon contents. Overall, kerogen assemblages are dominated by the Phytoclast Group, thus showing a strong terrestrial affinity and some degree of proximity to the source. Deposition occurred dominantly in oxic and proximal environments. Upper Pliensbachian kerogen assemblages from Ait Moussa are dominated by terrestrial particles and agree with the overall regressive character of the sedimentary succession. Uppermost Pliensbachian–lowermost Toarcian kerogen assemblages from Ait Moussa show an increase in marine particles. Considering the overall sedimentological context of the Middle Atlas Basin, these kerogen assemblages are interpreted to reflect local variation in accommodation space (driven by different sedimentation rates or tectonic compartmentalization) or ecological conditions (such as nutrient availability, temperature, turbidity, etc). In the Early Toarcian, above a major regional discontinuity and at the beginning of the Pl–Toa Event, increases in Botryococcus sp., AOM, and terrestrial palynomorphs suggest episodes of coastal erosion associated with transgression, likely driven by a combination of eustatic/tectonic changes and warmer and more humid climates leading to an increase in continental weathering and fluvial runoff. On the other hand, increases in sporomorphs and pollen grains occurring in tetrads and agglomerates indicate regressive episodes associated with increased sedimentation rates driven by enhanced continental weathering and fluvial runoff. This study shows the strong relationship between sea-level and the combined response of litho-, hydro-, and biosphere during the Early Toarcian, with implications to understand organic productivity and organic matter accumulation and preservation in the Tethys Ocean during the Pl–Toa Event.
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Mechanisms and drivers of belemnite body-size dynamics across the Pliensbachian-Toarcian crisis.
Royal Society open science, 2019Co-Authors: Patrícia Rita, Luis V Duarte, Paulina Nätscher, Robert Weis, Kenneth De BaetsAbstract:Body-size reduction is considered an important response to current climate warming and has been observed during past biotic crises, including the Pliensbachian–Toarcian crisis, a second-order mass ...
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R script from Mechanisms and drivers of belemnite body-size dynamics across the Pliensbachian–Toarcian crisis
2019Co-Authors: Patrícia Rita, Luis V Duarte, Paulina Nätscher, Robert Weis, Kenneth De BaetsAbstract:Body-size reduction is considered an important response to current climate warming and has been observed during past biotic crises, including the Pliensbachian–Toarcian crisis, a second-order mass extinction. However, in fossil cephalopod studies, the mechanisms and their potential link with climate are rarely investigated and palaeobiological scales of organization are not usually differentiated. Here, we hypothesize that belemnites reduce their adult size across the Pliensbachian–Toarcian boundary warming event. Belemnite body-size dynamics across the Pliensbachian–Toarcian boundary in the Peniche section (Lusitanian Basin, Portugal) were analysed based on the newly collected field data. We disentangle the mechanisms and the environmental drivers of the size fluctuations observed from the individual to the assemblage scale. Despite the lack of a major taxonomic turnover, a 40% decrease in rostrum volume is observed across the Pliensbachian–Toarcian boundary, before the Toarcian Oceanic Anoxic Event where belemnites go locally extinct. The pattern is mainly driven by a reduction in adult size of the two dominant species, Pseudohastites longiformis and Passaloteuthis bisulcata. Belemnite-size distribution is best correlated with fluctuations in a palaeotemperature proxy (stable oxygen isotopes); however, potential indirect effects of volcanism and carbon cycle perturbations may also play a role. This highlights the complex interplay between environmental stressors (warming, deoxygenation, nutrient input) and biotic variables (productivity, competition, migration) associated with these hyperthermal events in driving belemnite body size.
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Supplementary material from "Mechanisms and drivers of belemnite body-size dynamics across the Pliensbachian–Toarcian crisis"
2019Co-Authors: Patrícia Rita, Luis V Duarte, Paulina Nätscher, Robert Weis, Kenneth De BaetsAbstract:Body-size reduction is considered an important response to current climate warming and has been observed during past biotic crises, including the Pliensbachian–Toarcian crisis, a second-order mass extinction. However, in fossil cephalopod studies, the mechanisms and their potential link with climate are rarely investigated and palaeobiological scales of organization are not usually differentiated. Here, we hypothesize that belemnites reduce their adult size across the Pliensbachian–Toarcian boundary warming event. Belemnite body-size dynamics across the Pliensbachian–Toarcian boundary in the Peniche section (Lusitanian Basin, Portugal) were analysed based on the newly collected field data. We disentangle the mechanisms and the environmental drivers of the size fluctuations observed from the individual to the assemblage scale. Despite the lack of a major taxonomic turnover, a 40% decrease in rostrum volume is observed across the Pliensbachian–Toarcian boundary, before the Toarcian Oceanic Anoxic Event where belemnites go locally extinct. The pattern is mainly driven by a reduction in adult size of the two dominant species, Pseudohastites longiformis and Passaloteuthis bisulcata. Belemnite-size distribution is best correlated with fluctuations in a palaeotemperature proxy (stable oxygen isotopes); however, potential indirect effects of volcanism and carbon cycle perturbations may also play a role. This highlights the complex interplay between environmental stressors (warming, deoxygenation, nutrient input) and biotic variables (productivity, competition, migration) associated with these hyperthermal events in driving belemnite body size.
Jean-louis Dommergues - One of the best experts on this subject based on the ideXlab platform.
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Carbon-isotope events during the Pliensbachian (Lower Jurassic) on the African and European margins of the NW Tethyan Realm
Newsletters on Stratigraphy, 2020Co-Authors: Mathilde Mercuzot, Christian Meister, Jean-louis Dommergues, Cédric Bougeault, Pierre Pellenard, Nicolas Thibault, Francois Baudin, Olivier Mathieu, Christophe Durlet, Ludovic BruneauAbstract:Early Jurassic palaeoenvironments and palaeoclimates, based on chemostratigraphy, have been extensively studied for the northern Tethyan margin. For the first time, high-resolution chemostratigraphy for the entire Pliensbachian is proposed for the African Tethyan margin (Morocco), and compared with new sections from the European Tethyan margin (France). Precise ammonite determinations, completed by calcareous nannofossil distribution, provide an accurate biostratigraphic framework from the Upper Sinemurian to the Upper Pliensbachian. Bulk inorganic carbon (δ13Ccarb) and organic carbon (δ13Corg) isotope signals are used to characterise and compare carbon-cycle trends in the Central High Atlas Basin (Amellago-Ikis section, Morocco), the Paris Basin (Montcornet borehole, France), and the Subalpine Basin (Serre-Poncon section, France). Comparison of this new dataset with previously published geochemical data from European basins confirms the existence of five distinct carbon-isotope events, synchronous at the scale of the NW Tethyan Realm: (1) a clear –2‰ negative excursion of δ13Ccarb and δ13Corg, corresponding to the Sinemurian–Pliensbachian Boundary Event (SPBE), probably associated with a massive release of light carbon by volcanism and hydrothermalism during the breakup of Pangea; (2) a positive excursion (+1 to +1.5‰) in the Valdani and Luridum subzones (Ibex Zone), reflecting increased organic matter storage under warm climate conditions; (3) a broadly negative event from the Davoei Zone to the lower part of the Margaritatus Zone, associated with major oceanographic reorganisation in a transgressive context, and possible enhanced hydrothermalism related to the opening of the Hispanic corridor; (4) a positive carbon excursion (+2‰) during the Subnodosus and Gibbosus subzones (Margaritatus Zone), corresponding to the Late Pliensbachian Event (LPE), associated with organic matter storage; (5) an end-Margaritatus–Spinatum negative excursion, associated with sea-level fall, probably driven by glacio-eustasy. This new high-resolution carbon-isotope dataset highlights the synchroneity of carbon-cycle trends throughout the NW Tethyan Realm. Several major isotopic events, prior to those of the Toarcian, must therefore have occurred at a supra-regional to global scale during the Pliensbachian, involving significant internal and external geodynamic mechanisms.
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Climatic and palaeoceanographic changes during the Pliensbachian (Early Jurassic) inferred from clay mineralogy and stable isotope (C-O) geochemistry (NW Europe).
Global and Planetary Change, 2017Co-Authors: Cédric Bougeault, Jean-louis Dommergues, Pierre Pellenard, Jean-françois Deconinck, Stephen P. Hesselbo, Ludovic Bruneau, Théophile Cocquerez, Rémi Laffont, Emilia Huret, Nicolas ThibaultAbstract:The Early Jurassic was broadly a greenhouse climate period that was punctuated by short warm and cold climatic events, positive and negative excursions of carbon isotopes, and episodes of enhanced organic matter burial. Clay minerals from Pliensbachian sediments recovered from two boreholes in the Paris Basin, are used here as proxies of detrital supplies, runoff conditions, and palaeoceanographic changes. The combined use of these minerals with stable isotope data (C-O) from bulk carbonates and organic matter allows palaeoclimatic reconstructions to be refined for the Pliensbachian. Kaolinite/illite ratio is discussed as a reliable proxy of the hydrological cycle and runoff from landmasses. Three periods of enhanced runoff are recognised within the Pliensbachian. The first one at the Sinemurian-Pliensbachian transition shows a significant increase of kaolinite concomitant with the negative carbon isotope excursion at the so-called Sinemurian Pliensbachian Boundary Event (SPBE). The Early/Late Pliensbachian transition was also characterised by more humid conditions. This warm interval is associated with a major change in oceanic circulation during the Davoei Zone, likely triggered by sea-level rise; the newly created palaeogeography, notably the flooding of the London-Brabant Massif, allowed boreal detrital supplies, including kaolinite and chlorite, to be exported to the Paris Basin. The last event of enhanced runoff occurred during the late Pliensbachian (Subnodosus Subzone of the Margaritatus Zone), which occurred also during a warm period, favouring organic matter production and preservation. Our study highlights the major role of the London Brabant Massif in influencing oceanic circulation of the NW European area, as a topographic barrier (emerged lands) during periods of lowstand sea-level and its flooding during period of high sea-level. This massif was the unique source of smectite in the Paris Basin. Two episodes of smectite-rich sedimentation (‘smectite events’), coincide with regressive intervals, indicating emersion of the London Brabant Massif and thus suggesting that an amplitude of sea-level change high enough to be linked to glacio-eustasy. This mechanism is consistent with sedimentological and geochemical evidences of continental ice growth notably during the Latest Pliensbachian (Spinatum Zone), and possibly during the Early Pliensbachian (late Jamesoni/early Ibex Zones).
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Ammonites from the Apoderoceras beds (Early Pliensbachian) in São Pedro de Muel (Lusitanian Basin, Portugal).
Bulletin of Geosciences, 2012Co-Authors: Christian Meister, Jean-louis Dommergues, Rogério RochaAbstract:The lowermost Portuguese Pliensbachian is characterized by the association of Apoderoceras dunrobinense Spath, Tragophylloceras numismale (Quenstedt) and Vicininodiceras aff. mouterdei Donovan. This ammonite fauna indicates the lower part of the Jamesoni Chronozone (lower to middle Taylori Subchronozone). Thanks to the numerous specimens collected, the ontogeny and variability of A. dunrobinense Spath, could also be investigated. The paleogeographical distribution of these ammonites underlines the close connections between the Lusitanian Basin and the Euroboreal seas during the Early Pliensbachian.
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The Pliensbachian ammonites of the Algarve Basin (Portugal) and their palaeobiogeographical significance for the “Iberia-Newfoundland” conjugate margins
Swiss Journal of Geosciences, 2011Co-Authors: Jean-louis Dommergues, Christian Meister, Rogério B. RochaAbstract:A review of the Pliensbachian ammonite faunas of the Algarve Basin is given covering their taxonomy, stratigraphy and palaeobiogeography (palaeobiodiversity). This review is based on both an extensive revision of the previously collected and/or published material and on new finds precisely located within the ammonite succession. This new material allows us to clarify the variations within the most abundant species—a new species Reynesocoeloceras elmii nov. sp. is described—and to improve our understanding (palaeobiodiversity, palaeobiogeography and bio- or chrono-stratigraphy) of the two single known Pliensbachian fossiliferous assemblages in the Algarve Basin. The first of these assemblages is relatively diverse and is ascribed to the upper half of the Luridum Subchronozone. The second assemblage is less diversified and probably partly condensed. It is broadly attributed to the upper half of the Stokesi Subchronozone. Despite the newly collected ammonites and extensive prospecting, our knowledge of the Pliensbachian ammonite faunas of the Algarve remains fragmentary. Therefore, it is difficult to propose an incontrovertible extensive palaeobiogeographical interpretation for these faunas, but it seems that Tethyan (Mediterranean) affinities were of major importance whereas there were probably no NW European influences via the Lusitanian Basin.
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Ammonite diversity and its palaeobiogeographical structure during the early Pliensbachian (Jurassic) in the western Tethys and adjacent areas
Palaeogeography Palaeoclimatology Palaeoecology, 2009Co-Authors: Jean-louis Dommergues, Emmanuel Fara, Christian MeisterAbstract:The early Pliensbachian (Early Jurassic) is known as a time of marked provincialism in the marine realm, notably between the Mediterranean Tethys and North–West Europe. In order to test this observation quantitatively, we compiled 104 locality-level species lists from those areas based on a comprehensive revision of early Pliensbachian ammonites. With this dataset, we also explore the relationship between ammonite richness and biogeography at the scale of the sub-chronozone during the early Pliensbachian. Using various multivariate statistics and rarefaction techniques, we show that: (i) there is a sharp contrast between the NW European (NWE) and the Mediterranean (MED) provinces, although there is some mixing in Austroalpine and Pontic ammonite faunas; (ii) species richness in the MED province is about twice that in the NWE province for each chronozone; (iii) ammonite species richness tends to decrease during the early Pliensbachian, especially at the Ibex–Davoei transition; and (iv) the NWE and MED sensu stricto provinces both record the same pattern of variations in richness despite the fact that their taxonomic compositions have virtually nothing in common at the species level. We suggest that the low ammonite richness of the Davoei chronozone may be related to a coeval warming of seawaters, but that this was insufficient to affect the sharp palaeobiogeographic contrast between the two provinces. This persistent compartmentalisation probably reflects a major palaeogeographical structure, such as an emerged or near-emerged barrier running from the Betic range to the Brianconnais ridge. Overall, it seems that the diversity and distribution of early Pliensbachian ammonite species were simultaneously controlled by climate, palaeogeography and eustasy.
Stephane Bodin - One of the best experts on this subject based on the ideXlab platform.
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two phased collapse of the shallow water carbonate factory during the late Pliensbachian toarcian driven by changing climate and enhanced continental weathering in the northwestern gondwana margin
Earth-Science Reviews, 2020Co-Authors: Francoisnicolas Krencker, Rowan C Martindale, Lahcen Kabiri, Alicia Fantasia, Jan Danisch, Mohamed El Ouali, Stephane BodinAbstract:Abstract The end Pliensbachian–Toarcian is characterized by several carbon-cycle perturbations and faunal turnovers (e.g., ammonites and foraminifera), which are most likely triggered by pulses of the Karoo-Ferrar-Chon Aike large igneous province. The majority of information about these events is based on detailed studies of sites deposited in deep-water settings, which leaves vast uncertainties about the expression of, and response to, these events in shallow-marine ecosystems. Here, we present a comprehensive assessment of paleoclimatic impacts on neritic depositional environments from the latest Pliensbachian through the middle Toarcian in the central High Atlas Basin, Morocco, and compare those with changes observed in coeval neritic environments within the western Tethyan realm. A total of four new stratigraphic sections were investigated in the southern part of central High Atlas Basin and these new sections are synthesized with six previously published sections, distributed over eight localities. Correlations between sections are based on biostratigraphy, chemostratigraphy and lithostratigraphy. In Morocco, two episodes of carbonate factory shutdown are observed, spanning the Pliensbachian/Toarcian boundary and the Polymorphum/Levisoni transition. Each carbonate factory collapse correlates to well-documented environmental disturbances during the latest Pliensbachian–middle Toarcian interval, including the Toarcian Oceanic Anoxic Event (T-OAE). Moreover, each episode of carbonate factory shutdown coincides with an interval characterized by a significant increase of coarse siliciclastic input in the basin, further demonstrating the link between global warming, increased continental weathering, and ecosystem turnovers. Furthermore, these two episodes of carbonate factory shutdown are each followed by episodes of renewed carbonate production, showing the resilience of the neritic carbonate factory in this region. The first recovery interval, occurring during the late Polymorphum Zone, is associated with a mixed siliciclastic‑carbonate system. The second episode of carbonate recovery quickly follows the shutdown associated with the onset of the T-OAE. It is associated with an abiotic-dominated carbonate production mode, resulting in an elevated ooid production. A full recovery of biotic carbonate production only occurs in the late stage of the T-OAE. Although biotic turnover occurs at both events, from a shallow-marine perspective, the major biotic and abiotic crisis occurred at the Pliensbachian/Toarcian boundary and not during the T-OAE. This is in contrast to the deep-marine record, where the T-OAE is often inferred to be the most significant event. An enhanced hydrological cycle and the subsequent increase of continental nutrient shedding might have triggered the most severe changes of the carbonate productivity at the Pliensbachian/Toarcian transition; whereas, ocean acidification and increased storm activity likely played a significant role at the onset of the T-OAE.
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Two-phased collapse of the shallow-water carbonate factory during the late Pliensbachian–Toarcian driven by changing climate and enhanced continental weathering in the Northwestern Gondwana Margin
Earth-Science Reviews, 2020Co-Authors: Francoisnicolas Krencker, Rowan C Martindale, Lahcen Kabiri, Alicia Fantasia, Jan Danisch, Mohamed El Ouali, Stephane BodinAbstract:Abstract The end Pliensbachian–Toarcian is characterized by several carbon-cycle perturbations and faunal turnovers (e.g., ammonites and foraminifera), which are most likely triggered by pulses of the Karoo-Ferrar-Chon Aike large igneous province. The majority of information about these events is based on detailed studies of sites deposited in deep-water settings, which leaves vast uncertainties about the expression of, and response to, these events in shallow-marine ecosystems. Here, we present a comprehensive assessment of paleoclimatic impacts on neritic depositional environments from the latest Pliensbachian through the middle Toarcian in the central High Atlas Basin, Morocco, and compare those with changes observed in coeval neritic environments within the western Tethyan realm. A total of four new stratigraphic sections were investigated in the southern part of central High Atlas Basin and these new sections are synthesized with six previously published sections, distributed over eight localities. Correlations between sections are based on biostratigraphy, chemostratigraphy and lithostratigraphy. In Morocco, two episodes of carbonate factory shutdown are observed, spanning the Pliensbachian/Toarcian boundary and the Polymorphum/Levisoni transition. Each carbonate factory collapse correlates to well-documented environmental disturbances during the latest Pliensbachian–middle Toarcian interval, including the Toarcian Oceanic Anoxic Event (T-OAE). Moreover, each episode of carbonate factory shutdown coincides with an interval characterized by a significant increase of coarse siliciclastic input in the basin, further demonstrating the link between global warming, increased continental weathering, and ecosystem turnovers. Furthermore, these two episodes of carbonate factory shutdown are each followed by episodes of renewed carbonate production, showing the resilience of the neritic carbonate factory in this region. The first recovery interval, occurring during the late Polymorphum Zone, is associated with a mixed siliciclastic‑carbonate system. The second episode of carbonate recovery quickly follows the shutdown associated with the onset of the T-OAE. It is associated with an abiotic-dominated carbonate production mode, resulting in an elevated ooid production. A full recovery of biotic carbonate production only occurs in the late stage of the T-OAE. Although biotic turnover occurs at both events, from a shallow-marine perspective, the major biotic and abiotic crisis occurred at the Pliensbachian/Toarcian boundary and not during the T-OAE. This is in contrast to the deep-marine record, where the T-OAE is often inferred to be the most significant event. An enhanced hydrological cycle and the subsequent increase of continental nutrient shedding might have triggered the most severe changes of the carbonate productivity at the Pliensbachian/Toarcian transition; whereas, ocean acidification and increased storm activity likely played a significant role at the onset of the T-OAE.
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stratigraphic distribution and paleoecological significance of early jurassic Pliensbachian toarcian lithiotid coral reefal deposits from the central high atlas of morocco
Palaeogeography Palaeoclimatology Palaeoecology, 2019Co-Authors: Hannahmaria R Brame, Nicholas P Ettinger, Irena Debeljak, Raphael Vasseur, Bernard Lathuiliere, Rowan C Martindale, Lahcen Kabiri, Stephane BodinAbstract:Abstract During the Early Jurassic, a group of large, aberrant bivalves called lithiotids proliferated in proximal, shallow marine environments. These lithiotids formed bioherms and extensive biostromes in the western and southern margins of the Tethys Ocean as well as eastern Panthalassa. In the Central High Atlas of Morocco, Pliensbachian and Toarcian (Lower Jurassic) lithiotid and lithiotid-coral reefal deposits occur within carbonate and mixed carbonate/siliciclastic neritic depositional settings. This study describes the stratigraphic distribution, taxonomy, and architecture of these lithiotid-rich deposits. The studied lithiotid and lithiotid-coral deposits from Morocco occur in sheltered, near-shore lagoons along tropical carbonate ramps and platforms. These facies are abundant in upper Pliensbachian strata as well as in the early Toarcian. The persistence and similarity of lithiotid-coral buildups across the stage boundary indicate that these ecosystems were not significantly affected by the Pliensbachian/Toarcian extinction in Morocco (at least, not until the Toarcian Oceanic Anoxic Event). In both the upper Pliensbachian and lower Toarcian, lithiotids (Lithioperna and Cochlearites) are frequently associated with phaceloid corals (Retiophyllia in the Pliensbachian and Phacellophyllia and Archaeosmiliopsis in the Toarcian) and solitary corals (Haimeicyclus and Archaeosmilia) as well as other corals and bivalves (Gervilleioperna, Mytiloperna, Opisoma, and rare megalodontids); however, the spatial distribution of taxa is patchy. The close association of lithiotid bivalves and corals is rarely documented in the literature, and lithiotid-coral reefal deposits are rare. Thus, these Moroccan biostromes and bioherms that record the interaction of corals and lithiotids are of particular scientific importance. Furthermore, multiple generations and successions of lithiotid-coral framestones can be observed in both Pliensbachian and Toarcian strata, which provide insight into the evolution of these communities and their resilience to ecosystem perturbations. Despite the success of lithiotid-coral communities in the Pliensbachian and Toarcian, these ecosystems were decimated by the Toarcian Oceanic Anoxic Event and never recovered.
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Orbital chronology of the Pliensbachian - Toarcian transition from the Central High Atlas Basin (Morocco)
Newsletters on Stratigraphy, 2017Co-Authors: Stephane Bodin, Francoisnicolas Krencker, Mathieu Martinez, Emanuela MattioliAbstract:The Pliensbachian-Toarcian transition has been studied in depth for the major environmental changes and the marine invertebrate biodiversity crisis observed at that time. Despite a large number of studies performed, the time frames provided for this interval show large discrepancies from author to author. Major environmental changes occurring at that time impacted the sedimentation pattern and sedimentation rates, making uncertain the construction of time scales. Here, we provide a new astrochronological framework based on an expanded hemipelagic section from the Central High Atlas Basin (Morocco). delta C-13 and CaCO3 measurements performed on the studied section allowed the construction of an orbital time scale based on the 405-kyr eccentricity and the obliquity cycles. This orbital time scale is then compared to the Peniche section (GSSP of the Toarcian Stage) in order to limit the effects of eventual condensation and erosion events on the construction of the orbital time scale. The duration of the early Toarcian Polymorphum Zone is then assessed at 0.9-1.0 myr, while the interval from the base of the Toarcian Stage to the FO of C. superbus is assessed at 0.51 myr. This long duration of the Polymorphum Zone highlights the fact that numerous sections in Europe are affected by long-term condensation and hiati around the Pliensbachian Toarcian transition. Finally, we also explore the potential of the Central High Atlas basin to provide a refined time scale for the late Pliensbachian. Preliminary data lead to a duration assessment of the NJ5b calcareous nannofossil zone of at least 2.07 myr, and to a mean duration of the Emaciatum ammonite zone of 2.05 myr. These durations are similar to 1 myr longer than the durations proposed in the Geological Time Scale 2012, which illustrates the potential of the Central High Atlas Basin for calibrating the Pliensbachian times.
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perturbation of the carbon cycle during the late Pliensbachian early toarcian new insight from high resolution carbon isotope records in morocco
Journal of African Earth Sciences, 2016Co-Authors: Stephane Bodin, Tim Kothe, Rene Hoffmann, Francoisnicolas Krencker, Emanuela Mattioli, Ulrich Heimhofer, Lahcen KabiriAbstract:Abstract Preceding the early Toarcian Oceanic Anoxic Event by ∼1 Myr, the Pliensbachian–Toarcian boundary event is in many aspects as severe and disturbing for the environment as its better-studied successor. Both events are associated with rapid and pronounced global warming, major faunal and floral turnover, increased hydrological cycling and dramatic collapses of carbonate production. To better characterize the Pliensbachian–Toarcian boundary event, a high-resolution, paired carbonate and organic matter carbon isotope survey of three sections from the Central High Atlas Basin of Morocco has been undertaken. A pronounced negative shift in the carbonate carbon-isotope record, not paralleled by a similar excursion in the organic carbon, can be linked to the collapse of the neritic carbonate factory in the earliest Toarcian. These results show that, contrary to the Toarcian Oceanic Anoxic Event, a rapid and massive injection of 13 C-depleted carbon into the atmosphere is not responsible for the environmental perturbations observed during the Pliensbachian–Toarcian boundary event. However, input of isotopically non-depleted carbon such as mantle source CO 2 into the atmosphere as a potential cause for the Pliensbachian–Toarcian boundary event cannot be excluded. This would most probably be sourced from an early pulse of the Karoo–Ferrar Large Igneous Province.
Stephen P. Hesselbo - One of the best experts on this subject based on the ideXlab platform.
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orbital pacing and secular evolution of the early jurassic carbon cycle
Proceedings of the National Academy of Sciences of the United States of America, 2020Co-Authors: Stephen P. Hesselbo, Micha Ruhl, Hugh C Jenkyns, Marisa Storm, Clemens V Ullmann, Melanie J Leng, James B RidingAbstract:Global perturbations to the Early Jurassic environment (∼201 to ∼174 Ma), notably during the Triassic–Jurassic transition and Toarcian Oceanic Anoxic Event, are well studied and largely associated with volcanogenic greenhouse gas emissions released by large igneous provinces. The long-term secular evolution, timing, and pacing of changes in the Early Jurassic carbon cycle that provide context for these events are thus far poorly understood due to a lack of continuous high-resolution δ13C data. Here we present a δ13CTOC record for the uppermost Rhaetian (Triassic) to Pliensbachian (Lower Jurassic), derived from a calcareous mudstone succession of the exceptionally expanded Llanbedr (Mochras Farm) borehole, Cardigan Bay Basin, Wales, United Kingdom. Combined with existing δ13CTOC data from the Toarcian, the compilation covers the entire Lower Jurassic. The dataset reproduces large-amplitude δ13CTOC excursions (>3‰) recognized elsewhere, at the Sinemurian–Pliensbachian transition and in the lower Toarcian serpentinum zone, as well as several previously identified medium-amplitude (∼0.5 to 2‰) shifts in the Hettangian to Pliensbachian interval. In addition, multiple hitherto undiscovered isotope shifts of comparable amplitude and stratigraphic extent are recorded, demonstrating that those similar features described earlier from stratigraphically more limited sections are nonunique in a long-term context. These shifts are identified as long-eccentricity (∼405-ky) orbital cycles. Orbital tuning of the δ13CTOC record provides the basis for an astrochronological duration estimate for the Pliensbachian and Sinemurian, giving implications for the duration of the Hettangian Stage. Overall the chemostratigraphy illustrates particular sensitivity of the marine carbon cycle to long-eccentricity orbital forcing.
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Climatic and palaeoceanographic changes during the Pliensbachian (Early Jurassic) inferred from clay mineralogy and stable isotope (C-O) geochemistry (NW Europe).
Global and Planetary Change, 2017Co-Authors: Cédric Bougeault, Jean-louis Dommergues, Pierre Pellenard, Jean-françois Deconinck, Stephen P. Hesselbo, Ludovic Bruneau, Théophile Cocquerez, Rémi Laffont, Emilia Huret, Nicolas ThibaultAbstract:The Early Jurassic was broadly a greenhouse climate period that was punctuated by short warm and cold climatic events, positive and negative excursions of carbon isotopes, and episodes of enhanced organic matter burial. Clay minerals from Pliensbachian sediments recovered from two boreholes in the Paris Basin, are used here as proxies of detrital supplies, runoff conditions, and palaeoceanographic changes. The combined use of these minerals with stable isotope data (C-O) from bulk carbonates and organic matter allows palaeoclimatic reconstructions to be refined for the Pliensbachian. Kaolinite/illite ratio is discussed as a reliable proxy of the hydrological cycle and runoff from landmasses. Three periods of enhanced runoff are recognised within the Pliensbachian. The first one at the Sinemurian-Pliensbachian transition shows a significant increase of kaolinite concomitant with the negative carbon isotope excursion at the so-called Sinemurian Pliensbachian Boundary Event (SPBE). The Early/Late Pliensbachian transition was also characterised by more humid conditions. This warm interval is associated with a major change in oceanic circulation during the Davoei Zone, likely triggered by sea-level rise; the newly created palaeogeography, notably the flooding of the London-Brabant Massif, allowed boreal detrital supplies, including kaolinite and chlorite, to be exported to the Paris Basin. The last event of enhanced runoff occurred during the late Pliensbachian (Subnodosus Subzone of the Margaritatus Zone), which occurred also during a warm period, favouring organic matter production and preservation. Our study highlights the major role of the London Brabant Massif in influencing oceanic circulation of the NW European area, as a topographic barrier (emerged lands) during periods of lowstand sea-level and its flooding during period of high sea-level. This massif was the unique source of smectite in the Paris Basin. Two episodes of smectite-rich sedimentation (‘smectite events’), coincide with regressive intervals, indicating emersion of the London Brabant Massif and thus suggesting that an amplitude of sea-level change high enough to be linked to glacio-eustasy. This mechanism is consistent with sedimentological and geochemical evidences of continental ice growth notably during the Latest Pliensbachian (Spinatum Zone), and possibly during the Early Pliensbachian (late Jamesoni/early Ibex Zones).
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astronomical constraints on the duration of the early jurassic Pliensbachian stage and global climatic fluctuations
Earth and Planetary Science Letters, 2016Co-Authors: Micha Ruhl, James B Riding, Stephen P. Hesselbo, Linda A Hinnov, Hugh C Jenkyns, Marisa Storm, Daniel Minisini, Clemens V Ullmann, Melanie J LengAbstract:The Early Jurassic was marked by multiple periods of major global climatic and palaeoceanographic change, biotic turnover and perturbed global geochemical cycles, commonly linked to large igneous province volcanism. This epoch was also characterised by the initial break-up of the super-continent Pangaea and the opening and formation of shallow-marine basins and ocean gateways, the timing of which are poorly constrained. Here, we show that the Pliensbachian Stage and the Sinemurian–Pliensbachian global carbon-cycle perturbation (marked by a negative shift in δ13Cδ13C of 2–4‰2–4‰), have respective durations of ∼8.7 and ∼2 Myr. We astronomically tune the floating Pliensbachian time scale to the 405 Kyr eccentricity solution (La2010d), and propose a revised Early Jurassic time scale with a significantly shortened Sinemurian Stage duration of 6.9±0.4 Myr6.9±0.4 Myr. When calibrated against the new time scale, the existing Pliensbachian seawater 87Sr/86Sr record shows relatively stable values during the first ∼2 Myr of the Pliensbachian, superimposed on the long-term Early Jurassic decline in 87Sr/86Sr. This plateau in 87Sr/86Sr values coincides with the Sinemurian–Pliensbachian boundary carbon-cycle perturbation. It is possibly linked to a late phase of Central Atlantic Magmatic Province (CAMP) volcanism that induced enhanced global weathering of continental crustal materials, leading to an elevated radiogenic strontium flux to the global ocean.
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shallow marine carbon and oxygen isotope and elemental records indicate icehouse greenhouse cycles during the early jurassic
Paleoceanography, 2011Co-Authors: Christoph Korte, Stephen P. HesselboAbstract:[1] For much of the Mesozoic record there has been an inconclusive debate on the possible global significance of isotopic proxies for environmental change and of sequence stratigraphic depositional sequences. We present a carbon and oxygen isotope and elemental record for part of the Early Jurassic based on marine benthic and nektobenthic molluscs and brachiopods from the shallow marine succession of the Cleveland Basin, UK. The invertebrate isotope record is supplemented with carbon isotope data from fossil wood, which samples atmospheric carbon. New data elucidate two major global carbon isotope events, a negative excursion of ∼2‰ at the Sinemurian–Pliensbachian boundary, and a positive excursion of ∼2‰ in the Late Pliensbachian. The Sinemurian–Pliensbachian boundary event is similar to the slightly younger Toarcian Oceanic Anoxic Event and is characterized by deposition of relatively deepwater organic-rich shale. The Late Pliensbachian strata by contrast are characterized by shallow marine deposition. Oxygen isotope data imply cooling locally for both events. However, because deeper water conditions characterize the Sinemurian–Pliensbachian boundary in the Cleveland Basin the temperature drop is likely of local significance; in contrast a cool Late Pliensbachian shallow seafloor agrees with previous inference of partial icehouse conditions. Both the large-scale, long-term and small-scale, short-duration isotopic cycles occurred in concert with relative sea level changes documented previously from sequence stratigraphy. Isotope events and the sea level cycles are concluded to reflect processes of global significance, supporting the idea of an Early Jurassic in which cyclic swings from icehouse to greenhouse and super greenhouse conditions occurred at timescales from 1 to 10 Ma.
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the global boundary stratotype section and point gssp for the base of the Pliensbachian stage lower jurassic wine haven yorkshire uk
Episodes, 2006Co-Authors: Christian Meister, Jean-louis Dommergues, Stephen P. Hesselbo, Martin Aberhan, Joachim Blau, Susanne Feistburkhardt, Ernie A Hailwood, Malcolm B Hart, Mark W Hounslow, Mark HyltonAbstract:Following votes by the Pliensbachian Working Group, the Jurassic Subcommission and the International Commission on Stratigraphy, IUGS rati.ed the proposed Global Boundary Stratotype Section and Point (GSSP) for the base of the Pliensbachian Stage (Lower Jurassic) at the base of bed 73b in the Wine Haven section, Robin Hood's Bay, Yorkshire Coast, UK. This level contains the characteristic ammonite association Bifericeras donovani Dommergues and Meister and Apoderoceras sp. Complementary data include: a) Strontium-isotope stratigraphy, based on analysis of belemnites which yield a calcite 87Sr/86Sr ratio for the boundary level of 0.707425 and data supporting interpretation of continuous sedimentation; b) Belemnite oxygen-isotope data indicate a signi.cant temperature drop (~5 oC) across the boundary at this locality; c) A Transgressive Systems Tract (TST) initiated in the Aplanatum Subzone (uppermost Sinemurian) continues into the Lowermost Pliensbachian (Taylori Subzone); it forms part of a transgressive facies cycle sensu Graciansky et al. (1998); d) The Upper Sinemurian to lowermost Pliensbachian at Wine Haven section has a predominantly normal magnetic polarity, but two discrete reversed polarity magnetozones are present. The .rst spans much of the latest Sinemurian Aplanatum Subzone. It terminates <0.5m below the Sinemurian-Pliensbachian boundary and may prove a valuable chronostratigraphic marker. The second extends from the latest Oxynotum Subzone probably through to the lower part of the Raricostatum Subzone.
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Carbon-isotope events during the Pliensbachian (Lower Jurassic) on the African and European margins of the NW Tethyan Realm
Newsletters on Stratigraphy, 2020Co-Authors: Mathilde Mercuzot, Christian Meister, Jean-louis Dommergues, Cédric Bougeault, Pierre Pellenard, Nicolas Thibault, Francois Baudin, Olivier Mathieu, Christophe Durlet, Ludovic BruneauAbstract:Early Jurassic palaeoenvironments and palaeoclimates, based on chemostratigraphy, have been extensively studied for the northern Tethyan margin. For the first time, high-resolution chemostratigraphy for the entire Pliensbachian is proposed for the African Tethyan margin (Morocco), and compared with new sections from the European Tethyan margin (France). Precise ammonite determinations, completed by calcareous nannofossil distribution, provide an accurate biostratigraphic framework from the Upper Sinemurian to the Upper Pliensbachian. Bulk inorganic carbon (δ13Ccarb) and organic carbon (δ13Corg) isotope signals are used to characterise and compare carbon-cycle trends in the Central High Atlas Basin (Amellago-Ikis section, Morocco), the Paris Basin (Montcornet borehole, France), and the Subalpine Basin (Serre-Poncon section, France). Comparison of this new dataset with previously published geochemical data from European basins confirms the existence of five distinct carbon-isotope events, synchronous at the scale of the NW Tethyan Realm: (1) a clear –2‰ negative excursion of δ13Ccarb and δ13Corg, corresponding to the Sinemurian–Pliensbachian Boundary Event (SPBE), probably associated with a massive release of light carbon by volcanism and hydrothermalism during the breakup of Pangea; (2) a positive excursion (+1 to +1.5‰) in the Valdani and Luridum subzones (Ibex Zone), reflecting increased organic matter storage under warm climate conditions; (3) a broadly negative event from the Davoei Zone to the lower part of the Margaritatus Zone, associated with major oceanographic reorganisation in a transgressive context, and possible enhanced hydrothermalism related to the opening of the Hispanic corridor; (4) a positive carbon excursion (+2‰) during the Subnodosus and Gibbosus subzones (Margaritatus Zone), corresponding to the Late Pliensbachian Event (LPE), associated with organic matter storage; (5) an end-Margaritatus–Spinatum negative excursion, associated with sea-level fall, probably driven by glacio-eustasy. This new high-resolution carbon-isotope dataset highlights the synchroneity of carbon-cycle trends throughout the NW Tethyan Realm. Several major isotopic events, prior to those of the Toarcian, must therefore have occurred at a supra-regional to global scale during the Pliensbachian, involving significant internal and external geodynamic mechanisms.
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Ammonites from the Apoderoceras beds (Early Pliensbachian) in São Pedro de Muel (Lusitanian Basin, Portugal).
Bulletin of Geosciences, 2012Co-Authors: Christian Meister, Jean-louis Dommergues, Rogério RochaAbstract:The lowermost Portuguese Pliensbachian is characterized by the association of Apoderoceras dunrobinense Spath, Tragophylloceras numismale (Quenstedt) and Vicininodiceras aff. mouterdei Donovan. This ammonite fauna indicates the lower part of the Jamesoni Chronozone (lower to middle Taylori Subchronozone). Thanks to the numerous specimens collected, the ontogeny and variability of A. dunrobinense Spath, could also be investigated. The paleogeographical distribution of these ammonites underlines the close connections between the Lusitanian Basin and the Euroboreal seas during the Early Pliensbachian.
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The Pliensbachian ammonites of the Algarve Basin (Portugal) and their palaeobiogeographical significance for the “Iberia-Newfoundland” conjugate margins
Swiss Journal of Geosciences, 2011Co-Authors: Jean-louis Dommergues, Christian Meister, Rogério B. RochaAbstract:A review of the Pliensbachian ammonite faunas of the Algarve Basin is given covering their taxonomy, stratigraphy and palaeobiogeography (palaeobiodiversity). This review is based on both an extensive revision of the previously collected and/or published material and on new finds precisely located within the ammonite succession. This new material allows us to clarify the variations within the most abundant species—a new species Reynesocoeloceras elmii nov. sp. is described—and to improve our understanding (palaeobiodiversity, palaeobiogeography and bio- or chrono-stratigraphy) of the two single known Pliensbachian fossiliferous assemblages in the Algarve Basin. The first of these assemblages is relatively diverse and is ascribed to the upper half of the Luridum Subchronozone. The second assemblage is less diversified and probably partly condensed. It is broadly attributed to the upper half of the Stokesi Subchronozone. Despite the newly collected ammonites and extensive prospecting, our knowledge of the Pliensbachian ammonite faunas of the Algarve remains fragmentary. Therefore, it is difficult to propose an incontrovertible extensive palaeobiogeographical interpretation for these faunas, but it seems that Tethyan (Mediterranean) affinities were of major importance whereas there were probably no NW European influences via the Lusitanian Basin.
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Ammonite diversity and its palaeobiogeographical structure during the early Pliensbachian (Jurassic) in the western Tethys and adjacent areas
Palaeogeography Palaeoclimatology Palaeoecology, 2009Co-Authors: Jean-louis Dommergues, Emmanuel Fara, Christian MeisterAbstract:The early Pliensbachian (Early Jurassic) is known as a time of marked provincialism in the marine realm, notably between the Mediterranean Tethys and North–West Europe. In order to test this observation quantitatively, we compiled 104 locality-level species lists from those areas based on a comprehensive revision of early Pliensbachian ammonites. With this dataset, we also explore the relationship between ammonite richness and biogeography at the scale of the sub-chronozone during the early Pliensbachian. Using various multivariate statistics and rarefaction techniques, we show that: (i) there is a sharp contrast between the NW European (NWE) and the Mediterranean (MED) provinces, although there is some mixing in Austroalpine and Pontic ammonite faunas; (ii) species richness in the MED province is about twice that in the NWE province for each chronozone; (iii) ammonite species richness tends to decrease during the early Pliensbachian, especially at the Ibex–Davoei transition; and (iv) the NWE and MED sensu stricto provinces both record the same pattern of variations in richness despite the fact that their taxonomic compositions have virtually nothing in common at the species level. We suggest that the low ammonite richness of the Davoei chronozone may be related to a coeval warming of seawaters, but that this was insufficient to affect the sharp palaeobiogeographic contrast between the two provinces. This persistent compartmentalisation probably reflects a major palaeogeographical structure, such as an emerged or near-emerged barrier running from the Betic range to the Brianconnais ridge. Overall, it seems that the diversity and distribution of early Pliensbachian ammonite species were simultaneously controlled by climate, palaeogeography and eustasy.
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Ammonite diversity and its palaeobiogeographical structure during the early Pliensbachian (Jurassic) in the western Tethys and adjacent areas
Palaeogeography Palaeoclimatology Palaeoecology, 2009Co-Authors: Jean-louis Dommergues, Emmanuel Fara, Christian MeisterAbstract:14 pagesInternational audienceThe early Pliensbachian (Early Jurassic) is known as a time of marked provincialism in the marine realm, notably between the Mediterranean Tethys and North–West Europe. In order to test this observation quantitatively, we compiled 104 locality-level species lists from those areas based on a comprehensive revision of early Pliensbachian ammonites. With this dataset, we also explore the relationship between ammonite richness and biogeography at the scale of the sub-chronozone during the early Pliensbachian. Using various multivariate statistics and rarefaction techniques, we show that: (i) there is a sharp contrast between the NW European (NWE) and the Mediterranean (MED) provinces, although there is some mixing in Austroalpine and Pontic ammonite faunas; (ii) species richness in the MED province is about twice that in the NWE province for each chronozone; (iii) ammonite species richness tends to decrease during the early Pliensbachian, especially at the Ibex–Davoei transition; and (iv) the NWE and MED sensu stricto provinces both record the same pattern of variations in richness despite the fact that their taxonomic compositions have virtually nothing in common at the species level. We suggest that the low ammonite richness of the Davoei chronozone may be related to a coeval warming of seawaters, but that this was insufficient to affect the sharp palaeobiogeographic contrast between the two provinces. This persistent compartmentalisation probably reflects a major palaeogeographical structure, such as an emerged or near-emerged barrier running from the Betic range to the Briançonnais ridge. Overall, it seems that the diversity and distribution of early Pliensbachian ammonite species were simultaneously controlled by climate, palaeogeography and eustasy
