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Stephen P Hesselbo - One of the best experts on this subject based on the ideXlab platform.
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an early jurassic Sinemurian toarcian stratigraphic framework for the occurrence of organic matter preservation intervals ompis
Earth-Science Reviews, 2021Co-Authors: Micha Ruhl, Luis V Duarte, Ricardo L Silva, Stephen P Hesselbo, Grant D Wach, Driss Sadki, Juan J Gomez, Darragh Oconnor, Bruno RodriguesAbstract:Abstract Lower Jurassic sedimentary successions in the Atlantic margin basins include several organic-rich intervals, some with source rock potential; time-equivalent units are also identified in on- and offshore areas worldwide. Despite decades of research, it is still unclear which mechanisms lead to the deposition of organic-rich sediments during the Early Jurassic. The objectives of this study are to construct a detailed temporal and geographical framework of Sinemurian–Toarcian organic matter preservation intervals (OMPIs; subdivided into local, regional, and superregional) and roughly constrain the relationship of OMPIs with the Lower Jurassic δ13C record. This survey combines an in-depth analysis of literature on the distribution of organic-rich facies in the Sinemurian–Toarcian with new geochemical studies [total organic carbon (TOC) and organic matter pyrolysis] from selected outcrop sections from Portugal, Spain, and Morocco. Strong local control on OMPIs during most of the Sinemurian is suggested. Regionally widespread organic-rich facies are associated with the most negative δ13C values of the broad Sinemurian–Pliensbachian negative carbon isotopic trend recorded in organic matter (including the Sinemurian–Pliensbachian Boundary Event). Pliensbachian OMPIs are expressive in the areas bordering the proto-Atlantic Ocean and are often linked with positive δ13C excursions and short-lived warm intervals, but OMPIs are also defined for the Late Pliensbachian cool interval. Early Toarcian superregional OMPIs are associated with some of the most pronounced δ13C excursions of the Mesozoic. Toarcian maximum TOC content occurs with the positive δ13C (recovery) trend following the δ13C negative shift typically linked with the Early Toarcian Oceanic Anoxic Event (T-OAE), supporting the notion that peak carbon sequestration/ocean anoxia post-dated the main phase of carbon input into the atmosphere, as also suggested by recent modelling efforts. However, additional superregional OMPIs predate and postdate the T-OAE, indicating that conditions favouring preservation of organic matter (increased productivity and/or enhanced preservation) during the Early Toarcian were not restricted to the T-OAE interval. The compilation of Sinemurian–Toarcian OMPIs presented in this paper demonstrates that organic-rich intervals of regional and superregional expression in the Lower Jurassic sedimentary record are ubiquitous and may even be more numerous than in the Cretaceous. Considering the association of some of the Sinemurian, Pliensbachian, and Toarcian (not taking into account the T-OAE related OMPIs) regional and superregional OMPIs with well-defined carbon isotopic excursions, it is here suggested that these hold the same relevance as the secondary OAEs of the Cretaceous, such as the Valanginian OAE (Weissert Event), Hauterivian OAE (Faraoni Event), and Late Aptian–Early Albian OAE (OAE 1b cluster).
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million year scale alternation of warm humid and semi arid periods as a mid latitude climate mode in the early jurassic late Sinemurian laurasian seaway
Climate of The Past, 2021Co-Authors: Thomas Munier, James B Riding, Stephen P Hesselbo, Clemens V Ullmann, Jeanfrancois Deconinck, Pierre Pellenard, Cedric Bougeault, Mathilde Mercuzot, Annelise Santoni, Emilia HuretAbstract:Abstract. Clay mineral and stable isotope (C, O) data are reported from the upper Sinemurian (Lower Jurassic) of the Cardigan Bay Basin (Llanbedr–Mochras Farm borehole, northwestern Wales) and the Paris Basin (Montcornet borehole, northern France) to highlight the prevailing environmental and climatic conditions. In both basins, located at similar palaeolatitudes of 30–35∘ N, the clay mineral assemblages comprise chlorite, illite, illite–smectite mixed layers (R1 I-S), smectite, and kaolinite in various proportions. Because the influence of burial diagenesis and authigenesis is negligible in both boreholes, the clay minerals are interpreted to be derived from the erosion of the Caledonian and Variscan massifs, including their basement and pedogenic cover. In the Cardigan Bay Basin, the variations in the proportions of smectite and kaolinite are inversely related to each other through the entire upper Sinemurian. As in the succeeding Pliensbachian, the upper Sinemurian stratigraphic distribution reveals an alternation of kaolinite-rich intervals reflecting strong hydrolysing conditions and smectite-rich intervals indicating a semi-arid climate. Kaolinite is particularly abundant in the upper part of the obtusum zone and in the oxynotum zone, suggesting more intense hydrolysing conditions likely coeval with warm conditions responsible for an acceleration of the hydrological cycle. In the north of the Paris Basin, the succession is less continuous compared to the Cardigan Bay Basin site, as the oxynotum zone and the upper raricostatum zone are either absent or highly condensed. The clay assemblages are dominantly composed of illite and kaolinite without significant stratigraphic trends, but a smectite-rich interval identified in the obtusum zone is interpreted as a consequence of the emersion of the London–Brabant Massif following a lowering of sea level. Following a slight negative carbon isotope excursion at the obtusum–oxynotum zone transition, a long-term decrease in δ13Corg from the late oxynotum–early raricostatum zones is recorded in the two sites and may precede or partly include the negative carbon isotope excursion of the Sinemurian–Pliensbachian Boundary Event, which is recognised in most basins worldwide and interpreted to signify a late pulse of the Central Atlantic Magmatic Province volcanism.
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carbon and oxygen isotope records from the southern eurasian seaway following the triassic jurassic boundary parallel long term enhanced carbon burial and seawater warming
Earth-Science Reviews, 2020Co-Authors: Stephen P Hesselbo, Clemens V Ullmann, Christoph Korte, Anders L EbbesenAbstract:Abstract Fossil shells of benthos and nektobenthos have been shown to be faithful recorders of seawater carbon- and oxygen-isotope geochemistry, and thus also useful to track the relationship between carbon cycle and palaeotemperature. In this study we present an extensive dataset from Lower Jurassic (Hettangian and lower Sinemurian) mollusc and brachiopod hard parts collected from biostratigraphically well-calibrated UK coastal outcrops (Bristol Channel and Hebrides basins). These basins lay palaeogeographically in the southern part of the Laurasian Seaway that connected the Tethys and Boreal oceans. All samples have been subject to screening for diagenesis on the basis of elemental composition, light microscopy, and SEM observations. In the case of some localities within the Hebrides Basin, alteration by hydrothermal systems around Paleogene intrusions has led to re-setting of carbonate oxygen isotopes, but the original carbon isotope values from the shells are largely preserved. Above the prominent and apparently short-lived, ~3 per mil δ13Ccarb amplitude positive carbon-isotope excursion (CIE) that occurs immediately above the Triassic-Jurasic (T-J) boundary (in the tilmanni ammonite biozone), a pronounced negative CIE (the so-called Main Negative CIE) spans the entire Hettangian Stage. At the Hettangian-Sinemurian boundary, and through the lower Sinemurian, the carbon-isotope values of the skeletal carbonate again trend towards progressively more positive values, but representing a time of several million years. The heaviest δ13Ccarb values of about +4.3 per mil are evident towards the top of the lower Sinemurian, and are comparable with values observed from the tilmanni Zone, and from the lower Toarcian, higher in the Jurassic. This long-term positive hump, which confirms trends derived from bulk organic matter carbon-isotope records, is supporting evidence of prolonged enhanced organic carbon burial that is inferred to have occurred in the extensive system of lacustrine and marine rifts that traversed a fragmenting Pangaea after emplacement of the Central Atlantic Magmatic Province. In parallel, oxygen-isotope values of the skeletal carbonate show a continuous downward trend from the lower part of the Hettangian (~ −1 per mil δ18Ocarb in the planorbis Zone) to the top of the lower Sinemurian (~ −2.5 per mil δ18Ocarb in the higher turneri Zone). Oxygen-isotope values may be interpreted as due to gradually increasing palaeotemperature, and/or addition of a meteoric or cryospheric water component; in the case of the Laurasian Seaway, palaeoceanographic and palaeoecological considerations point towards a dominant palaeotemperature signal. Consequently, any atmospheric carbon-dioxide drawdown effect on global palaeotemperatures, as suggested by progressively increasing δ13Ccarb values, and assuming a constant silicate weathering sink, was more than counterbalanced in the seaway by regional processes that led to significantly warmer bottom water temperatures.
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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: Micha Ruhl, Hugh C Jenkyns, Stephen P Hesselbo, 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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orbital pacing of the early jurassic carbon cycle black shale formation and seabed methane seepage
Sedimentology, 2017Co-Authors: Weimu Xu, Micha Ruhl, James B Riding, Stephen P Hesselbo, Hugh C JenkynsAbstract:The Early Jurassic (ca 201 to 174 Ma) was marked by a series of rapid perturbations in climate, the environment and global geochemical cycles, which have been linked to volcanic outgassing and the release of biogenic or thermogenic methane into the ocean–atmosphere system. The state of the global carbon cycle and prevailing climatic and environmental conditions that existed at this time are, however, poorly constrained. Here, mudrocks of the Lower Sinemurian Arietites bucklandi ammonite Biozone at coastal exposures at Kilve, Somerset, UK, have been studied. This succession includes laminated organic-rich black shales, which are present throughout the Bristol Channel Basin, and coincides with a 2 to 3‰ negative carbon-isotope excursion, distinct changes in inferred land vegetation and abundant marine prasinophytes (green algae). The event itself does not represent a single perturbation of the regional environment, but follows in a sequence of eccentricity-modulated, precession-paced perturbations that occur throughout the preceding Hettangian stage, with the periodic formation of organic-rich laminated black shales in the Bristol Channel Basin. However, the Early Sinemurian event studied herein is more extreme in nature, with sedimentary total organic carbon values of 5 to 11% persisting over about 2 m, representing ca 100 kyr, possibly in phase with short (ca 100 kyr) and long (ca 405 kyr) eccentricity forcing. The formation of methane-seep carbonate-cemented mounds took place relatively soon after the deposition of laminated black shales. Biogenic methane probably formed in response to microbial methanogenesis in the organic-rich black shale, which was subsequently channelled to the sediment–water interface approximately 5 m above the source bed, and ca 200 kyr after cessation of formation of the black shale.
Clemens V Ullmann - One of the best experts on this subject based on the ideXlab platform.
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million year scale alternation of warm humid and semi arid periods as a mid latitude climate mode in the early jurassic late Sinemurian laurasian seaway
Climate of The Past, 2021Co-Authors: Thomas Munier, James B Riding, Stephen P Hesselbo, Clemens V Ullmann, Jeanfrancois Deconinck, Pierre Pellenard, Cedric Bougeault, Mathilde Mercuzot, Annelise Santoni, Emilia HuretAbstract:Abstract. Clay mineral and stable isotope (C, O) data are reported from the upper Sinemurian (Lower Jurassic) of the Cardigan Bay Basin (Llanbedr–Mochras Farm borehole, northwestern Wales) and the Paris Basin (Montcornet borehole, northern France) to highlight the prevailing environmental and climatic conditions. In both basins, located at similar palaeolatitudes of 30–35∘ N, the clay mineral assemblages comprise chlorite, illite, illite–smectite mixed layers (R1 I-S), smectite, and kaolinite in various proportions. Because the influence of burial diagenesis and authigenesis is negligible in both boreholes, the clay minerals are interpreted to be derived from the erosion of the Caledonian and Variscan massifs, including their basement and pedogenic cover. In the Cardigan Bay Basin, the variations in the proportions of smectite and kaolinite are inversely related to each other through the entire upper Sinemurian. As in the succeeding Pliensbachian, the upper Sinemurian stratigraphic distribution reveals an alternation of kaolinite-rich intervals reflecting strong hydrolysing conditions and smectite-rich intervals indicating a semi-arid climate. Kaolinite is particularly abundant in the upper part of the obtusum zone and in the oxynotum zone, suggesting more intense hydrolysing conditions likely coeval with warm conditions responsible for an acceleration of the hydrological cycle. In the north of the Paris Basin, the succession is less continuous compared to the Cardigan Bay Basin site, as the oxynotum zone and the upper raricostatum zone are either absent or highly condensed. The clay assemblages are dominantly composed of illite and kaolinite without significant stratigraphic trends, but a smectite-rich interval identified in the obtusum zone is interpreted as a consequence of the emersion of the London–Brabant Massif following a lowering of sea level. Following a slight negative carbon isotope excursion at the obtusum–oxynotum zone transition, a long-term decrease in δ13Corg from the late oxynotum–early raricostatum zones is recorded in the two sites and may precede or partly include the negative carbon isotope excursion of the Sinemurian–Pliensbachian Boundary Event, which is recognised in most basins worldwide and interpreted to signify a late pulse of the Central Atlantic Magmatic Province volcanism.
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carbon and oxygen isotope records from the southern eurasian seaway following the triassic jurassic boundary parallel long term enhanced carbon burial and seawater warming
Earth-Science Reviews, 2020Co-Authors: Stephen P Hesselbo, Clemens V Ullmann, Christoph Korte, Anders L EbbesenAbstract:Abstract Fossil shells of benthos and nektobenthos have been shown to be faithful recorders of seawater carbon- and oxygen-isotope geochemistry, and thus also useful to track the relationship between carbon cycle and palaeotemperature. In this study we present an extensive dataset from Lower Jurassic (Hettangian and lower Sinemurian) mollusc and brachiopod hard parts collected from biostratigraphically well-calibrated UK coastal outcrops (Bristol Channel and Hebrides basins). These basins lay palaeogeographically in the southern part of the Laurasian Seaway that connected the Tethys and Boreal oceans. All samples have been subject to screening for diagenesis on the basis of elemental composition, light microscopy, and SEM observations. In the case of some localities within the Hebrides Basin, alteration by hydrothermal systems around Paleogene intrusions has led to re-setting of carbonate oxygen isotopes, but the original carbon isotope values from the shells are largely preserved. Above the prominent and apparently short-lived, ~3 per mil δ13Ccarb amplitude positive carbon-isotope excursion (CIE) that occurs immediately above the Triassic-Jurasic (T-J) boundary (in the tilmanni ammonite biozone), a pronounced negative CIE (the so-called Main Negative CIE) spans the entire Hettangian Stage. At the Hettangian-Sinemurian boundary, and through the lower Sinemurian, the carbon-isotope values of the skeletal carbonate again trend towards progressively more positive values, but representing a time of several million years. The heaviest δ13Ccarb values of about +4.3 per mil are evident towards the top of the lower Sinemurian, and are comparable with values observed from the tilmanni Zone, and from the lower Toarcian, higher in the Jurassic. This long-term positive hump, which confirms trends derived from bulk organic matter carbon-isotope records, is supporting evidence of prolonged enhanced organic carbon burial that is inferred to have occurred in the extensive system of lacustrine and marine rifts that traversed a fragmenting Pangaea after emplacement of the Central Atlantic Magmatic Province. In parallel, oxygen-isotope values of the skeletal carbonate show a continuous downward trend from the lower part of the Hettangian (~ −1 per mil δ18Ocarb in the planorbis Zone) to the top of the lower Sinemurian (~ −2.5 per mil δ18Ocarb in the higher turneri Zone). Oxygen-isotope values may be interpreted as due to gradually increasing palaeotemperature, and/or addition of a meteoric or cryospheric water component; in the case of the Laurasian Seaway, palaeoceanographic and palaeoecological considerations point towards a dominant palaeotemperature signal. Consequently, any atmospheric carbon-dioxide drawdown effect on global palaeotemperatures, as suggested by progressively increasing δ13Ccarb values, and assuming a constant silicate weathering sink, was more than counterbalanced in the seaway by regional processes that led to significantly warmer bottom water temperatures.
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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: Micha Ruhl, Hugh C Jenkyns, Stephen P Hesselbo, 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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Sinemurian-Pliensbachian calcareous nannofossil biostratigraphy and organic carbon isotope stratigraphy in the Paris Basin: calibration to the ammonite biozonation of NW Europe.
Palaeogeography Palaeoclimatology Palaeoecology, 2017Co-Authors: Leonie Peti, Marie-emilie Clémence, Christoph Korte, Nicolas Thibault, Pierre Pellenard, Cedric Bougeault, Jean-louis Dommergues, Mads E. Jelby, Clemens V UllmannAbstract:The biostratigraphy of Sinemurian to lower Toarcian calcareous nannofossils has been investigated in the Sancerre-Couy core (Paris Basin), which contains a mixed assemblage of species with affinities to the northern and southern areas of the peri-tethyan realm, thus allowing for the use and calibration of the Mediterranean Province (Italy/S France) and NW Europe (UK) biozonation schemes. This study is based on semi-quantitative analyses of the calcareous nannofossil assemblage performed on 145 samples and the recorded bioevents are calibrated to the NW European Ammonite Zonation and to a new organic carbon isotope curve based on 385 data points. The main bioevents, i.e. the first occurrences of Parhabdolithus liasicus, Crepidolithus pliensbachensis, Crepidolithus crassus, Mitrolithus lenticularis, Similiscutum cruciulus sensu lato, Lotharingius hauffii, Crepidolithus cavus and Lotharingius sigillatus as well as the last occurrence of Parhabdolithus robustus, have been identified. However, we show that a large number of standard biostratigraphic markers show inconsistent occurrences at the base and top of their range, possibly accounting for some of the significant discrepancies observed between the different domains. In addition to the nine main bioevents used for the biozonation of the core, we document an additional 50 distinct bioevents, evaluate their reliability and discuss their potential significance by comparison to previous studies. A total of five significant negative organic carbon isotope excursions are identified and defined in the Paris Basin including the well-documented Sinemurian–Pliensbachian boundary event. One positive excursion is further defined in the Pliensbachian interval. Our calibration of high-resolution calcareous nannofossil biostratigraphy to ammonite biostratigraphy and organic carbon isotopes represents a new stratigraphic reference for the Lower Jurassic series.
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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, Hugh C Jenkyns, Stephen P Hesselbo, Linda A Hinnov, 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.
Luis V Duarte - One of the best experts on this subject based on the ideXlab platform.
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an early jurassic Sinemurian toarcian stratigraphic framework for the occurrence of organic matter preservation intervals ompis
Earth-Science Reviews, 2021Co-Authors: Micha Ruhl, Luis V Duarte, Ricardo L Silva, Stephen P Hesselbo, Grant D Wach, Driss Sadki, Juan J Gomez, Darragh Oconnor, Bruno RodriguesAbstract:Abstract Lower Jurassic sedimentary successions in the Atlantic margin basins include several organic-rich intervals, some with source rock potential; time-equivalent units are also identified in on- and offshore areas worldwide. Despite decades of research, it is still unclear which mechanisms lead to the deposition of organic-rich sediments during the Early Jurassic. The objectives of this study are to construct a detailed temporal and geographical framework of Sinemurian–Toarcian organic matter preservation intervals (OMPIs; subdivided into local, regional, and superregional) and roughly constrain the relationship of OMPIs with the Lower Jurassic δ13C record. This survey combines an in-depth analysis of literature on the distribution of organic-rich facies in the Sinemurian–Toarcian with new geochemical studies [total organic carbon (TOC) and organic matter pyrolysis] from selected outcrop sections from Portugal, Spain, and Morocco. Strong local control on OMPIs during most of the Sinemurian is suggested. Regionally widespread organic-rich facies are associated with the most negative δ13C values of the broad Sinemurian–Pliensbachian negative carbon isotopic trend recorded in organic matter (including the Sinemurian–Pliensbachian Boundary Event). Pliensbachian OMPIs are expressive in the areas bordering the proto-Atlantic Ocean and are often linked with positive δ13C excursions and short-lived warm intervals, but OMPIs are also defined for the Late Pliensbachian cool interval. Early Toarcian superregional OMPIs are associated with some of the most pronounced δ13C excursions of the Mesozoic. Toarcian maximum TOC content occurs with the positive δ13C (recovery) trend following the δ13C negative shift typically linked with the Early Toarcian Oceanic Anoxic Event (T-OAE), supporting the notion that peak carbon sequestration/ocean anoxia post-dated the main phase of carbon input into the atmosphere, as also suggested by recent modelling efforts. However, additional superregional OMPIs predate and postdate the T-OAE, indicating that conditions favouring preservation of organic matter (increased productivity and/or enhanced preservation) during the Early Toarcian were not restricted to the T-OAE interval. The compilation of Sinemurian–Toarcian OMPIs presented in this paper demonstrates that organic-rich intervals of regional and superregional expression in the Lower Jurassic sedimentary record are ubiquitous and may even be more numerous than in the Cretaceous. Considering the association of some of the Sinemurian, Pliensbachian, and Toarcian (not taking into account the T-OAE related OMPIs) regional and superregional OMPIs with well-defined carbon isotopic excursions, it is here suggested that these hold the same relevance as the secondary OAEs of the Cretaceous, such as the Valanginian OAE (Weissert Event), Hauterivian OAE (Faraoni Event), and Late Aptian–Early Albian OAE (OAE 1b cluster).
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a calcareous nannofossil and organic geochemical study of marine palaeoenvironmental changes across the Sinemurian pliensbachian early jurassic 191 ma in portugal
Palaeogeography Palaeoclimatology Palaeoecology, 2016Co-Authors: Julien Plancq, Emanuela Mattioli, Luis V Duarte, Bernard Pittet, Francois Baudin, Myriam Boussaha, Vincent GrossiAbstract:The Sinemurian/Pliensbachian boundary (~ 191 Ma) is acknowledged as one of the most important steps in the radiation of planktonic organisms, especially primary producers such as dinoflagellates and coccolithophores. To date, there is no detailed study documenting changes in planktonic assemblages related to palaeoceanographic changes across this boundary. The aim of this study is to characterize the palaeoenvironmental changes occurring across the Sinemurian/Pliensbachian boundary at the Sao Pedro de Moel section (Lusitanian Basin, Portugal) using micropalaeontology and organic geochemistry approaches. Combined calcareous nannofossil assemblage and lipid biomarker data document for a decrease in primary productivity in relation to a major sea-level rise occurring above the boundary. The Lusitanian Basin was particularly restricted during the late Sinemurian with a relatively low sea level, a configuration that led to the recurrent development of black shales. After a sharp sea-level fall, the basin became progressively deeper and more open during the earliest Pliensbachian, subsequently to a major transgression. This sea-level increase seems to have been a global feature and could have been related to the opening of the Hispanic Corridor that connected the Tethys and palaeo-Pacific oceans. The palaeoceanographic and palaeoclimatic changes induced by this opening may have played a role in the diversification of coccolithophores with the first occurrence or colonization of Tethyan waters by placolith-type coccoliths.
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spatial characterization of the late Sinemurian early jurassic palaeoenvironments in the lusitanian basin
Palaeogeography Palaeoclimatology Palaeoecology, 2014Co-Authors: Myriam Boussaha, Emanuela Mattioli, Bernard Pittet, Luis V DuarteAbstract:Abstract The upper Sinemurian of the Lusitanian Basin (Portugal) is characterized by the deposition of carbonates (dolomitic limestones, limestones), sometimes enriched in organic matter (total organic carbon up to 22%). The main goal of this study is to understand the distribution of carbonates and organic matter-rich sediments in space and time, and to characterize the context of their deposition at the basin scale. Three sections located along a proximal–distal transect in the Lusitanian Basin and dated from the oxynotum to raricostatum ammonite zones (upper Sinemurian) have been studied for their microfacies and sedimentary structures, and correlated by means of ammonite and calcareous nannofossil biostratigraphy, and sequence stratigraphy. The proximal part of the basin is dominated by carbonates whereas organic-rich sediments and marl-limestone alternations are common in the distal part. Microfacies analysis shows a trend from high- to low-energy environments, which reflects a deepening trend in most of the basin within the raricostatum ammonite Zone. A forced regression took place in the earliest Pliensbachian, which is likely related to tectono-eustasy. This particular surface can be correlated at the regional level, to several basins of the western Tethys. The presence of black shales in the distal part of the basin and of framboidal pyrite in the proximal part is interpreted as resulting from an episode of pervasive dysoxia/anoxia at the basin scale during this time interval. The basin recorded conditions varying from dysoxic/anoxic phases in times of water column stratification, to full oxygenation in times of intense mixing by storms, attested by the presence of storm-related sedimentary structures in some carbonate-rich deposits. The occurrence of upper Sinemurian sediments rich in organic matter in other basins, in England and Spain, in the same time interval (upper Sinemurian, raricostatum ammonite Zone) suggests that palaeoclimatic and palaeogeographic conditions were prone to the development of a supraregional dysoxia/anoxia.
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dynamics of upper Sinemurian macrobenthic groups bivalves and brachiopods preserved in organic rich facies of the lusitanian basin western iberia
2014Co-Authors: Ricardo Paredes, Maria Jose Comasrengifo, Luis V DuarteAbstract:Bivalves and brachiopods are the most abundant macrobenthos of the upper Sinemurian marine assemblages preserved in the Lusitanian Basin (Portugal). The wide variety of life habits of the bivalves and the taxonomic diversity of both groups indicate that these elements should be taken into account for marine assemblages analysis. Although the basin contains many upper Sinemurian outcrops, those in the S. Pedro de Moel and Peniche areas are exceptionally fossil rich. The palaeontological content of the basin’s Agua de Madeiros Formation is well preserved and has provided taxonomic and quantitative data regarding the abundance of bivalves and brachiopods. This lithostratigraphic unit shows two distinct sequences of biofacies: (1) shallow-water and soft-bottomed assemblages; and (2) hemipelagic assemblages associated with organic-rich facies. The transition between them corresponds to faunal turnover in the basin, recorded in the Raricostatum Subchronozone. The transition is particularly clear in the S. Pedro de Moel area, but does not seem to be synchronous with that observed in the Peniche area.
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organic rich facies in the Sinemurian and pliensbachian of the lusitanian basin portugal total organic carbon distribution and relation to transgressive regressive facies cycles
Geologica Acta, 2010Co-Authors: Luis V Duarte, Ricardo L Silva, Luiz Carlos Veiga De Oliveira, Maria Jose Comasrengifo, Fernando SilvaAbstract:The upper Sinemurian to Pliensbachian series of the Lusitanian Basin (Portugal) correspond to marly limestone sediments rich in benthic and nektonic macrofauna. This sedimentary record includes several intervals of organicrich facies, which are particularly well developed in the western sectors of the basin. They correspond to grey and dark marls locally showing strong lamination (black shale type) and are recognized as one of the most important potential oil source rocks. This study shows the vertical and lateral distribution of these organic-rich intervals, supported by over 550 total organic carbon (TOC) determinations. The results presented reveal two important intervals, with several black shale occurrences, in the Oxynotum(?)–Raricostatum (Polvoeira Member of Agua de Madeiros Formation) and at the top of the Ibex-upper part of Margaritatus zones (top of the Vale das Fontes Formation), showing in the distal (western) sectors up to 22% and 15% TOC, respectively. TOC values decrease progressively towards the proximal sectors, the youngest organic-rich interval being the most expressive at the basin scale. This lateral TOC distribution, the facies stacking patterns and the decrease observed in benthic macrofauna confirm that these intervals are related to 2nd-order transgressive phases. 2nd-order regressive phases, developed during the uppermost Raricostatum and Spinatum zones respectively, show lower TOC values. TOC distribution combined with other stratigraphic and sedimentological parameters enabled seven facies maps to be created for the time interval studied. At the regional scale, this study shows for the first time the good similarity between the upper Sinemurian-Pliensbachian sedimentary successions of the Lusitanian and Basque- Cantabrian basins.
Hugh C Jenkyns - 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: Micha Ruhl, Hugh C Jenkyns, Stephen P Hesselbo, 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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carbon isotope anomalies and demise of carbonate platforms in the Sinemurian early jurassic of the tethyan region evidence from the southern alps northern italy
Geological Magazine, 2017Co-Authors: Daniele Masetti, Emanuela Mattioli, Hugh C Jenkyns, Billy Figus, Filippo Barattolo, Renato PosenatoAbstract:Despite its global impact on ecosystems, the Triassic/Jurassic boundary event had only a modest effect on the carbonate depositional systems of the Southern Alps, whereas a fundamental reorganization of the same palaeogeographic area took place during the Sinemurian Age. This paper investigates whether or not the well-documented demise of Sinemurian carbonate platforms in the Tethyan region was a response to a global event by examination of carbon-isotope anomalies in successions of different facies that record this interval of time. A chemostratigraphic transect from Lake Garda up to the eastern Italian border is illustrated by four stratigraphic sections; high-resolution (20 cm over key intervals) chemostratigraphic sampling allowed detection of a major negative δ13C anomaly of ~ 1.5‰, preceded by a positive excursion, both in shallow- and deep-water successions, over the stratigraphical range of the ammonite genus Arnioceras. A comparison with sections from the UK suggests that the positive excursion belongs to the turneri Zone and the succeeding negative excursion falls within the obtusum Zone. In the deep-water Belluno Basin, the negative anomaly occurs in a biogenic chert-rich unit recording the onset of mesotrophic conditions in the basin. In the platform-carbonate successions, this major negative carbon-isotope excursion is developed within a calcarenitic unit corresponding to the lowest occurrence of the foraminifer Paleomayncina termieri. This evidence for deepening and transgression across the carbonate platform suggests pre-conditioning for drowning. Hence, rather than tectonic subsidence alone, environmental factors may have aided the demise of Tethyan carbonate platforms during the Early Jurassic Sinemurian Age.
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orbital pacing of the early jurassic carbon cycle black shale formation and seabed methane seepage
Sedimentology, 2017Co-Authors: Weimu Xu, Micha Ruhl, James B Riding, Stephen P Hesselbo, Hugh C JenkynsAbstract:The Early Jurassic (ca 201 to 174 Ma) was marked by a series of rapid perturbations in climate, the environment and global geochemical cycles, which have been linked to volcanic outgassing and the release of biogenic or thermogenic methane into the ocean–atmosphere system. The state of the global carbon cycle and prevailing climatic and environmental conditions that existed at this time are, however, poorly constrained. Here, mudrocks of the Lower Sinemurian Arietites bucklandi ammonite Biozone at coastal exposures at Kilve, Somerset, UK, have been studied. This succession includes laminated organic-rich black shales, which are present throughout the Bristol Channel Basin, and coincides with a 2 to 3‰ negative carbon-isotope excursion, distinct changes in inferred land vegetation and abundant marine prasinophytes (green algae). The event itself does not represent a single perturbation of the regional environment, but follows in a sequence of eccentricity-modulated, precession-paced perturbations that occur throughout the preceding Hettangian stage, with the periodic formation of organic-rich laminated black shales in the Bristol Channel Basin. However, the Early Sinemurian event studied herein is more extreme in nature, with sedimentary total organic carbon values of 5 to 11% persisting over about 2 m, representing ca 100 kyr, possibly in phase with short (ca 100 kyr) and long (ca 405 kyr) eccentricity forcing. The formation of methane-seep carbonate-cemented mounds took place relatively soon after the deposition of laminated black shales. Biogenic methane probably formed in response to microbial methanogenesis in the organic-rich black shale, which was subsequently channelled to the sediment–water interface approximately 5 m above the source bed, and ca 200 kyr after cessation of formation of the black shale.
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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, Hugh C Jenkyns, Stephen P Hesselbo, Linda A Hinnov, 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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the lower lias group of the hebrides basin
Scottish Journal of Geology, 1998Co-Authors: Stephen P Hesselbo, Michael Oates, Hugh C JenkynsAbstract:Synopsis The lower and greater part of the Lias Group of the Hebrides Basin comprises shallow-marine to marginal-marine mudstones, siltstones, sandstones and limestones arranged in unambiguous transgressive-regressive facies cycles. In the northern region of the basin, the strata were deposited in a series of half graben bounded on their western margins by major eastward-dipping normal faults developed principally during the Triassic. Interpretation of the palaeogeographic setting of the lower Lias is complicated because exposure of the sequences occurs in the vicinity of transfer zones that have subsequently acted as foci for Palaeocene igneous activity. The principal exposures have been measured or remeasured in this study, and detailed sedimentary logs are presented that incorporate previously unpublished ammonite determinations. In the northern part of the Inner Hebrides Trough (Skye–Pabay–Raasay area), two formations are recognized: the Broadford Formation and the Pabay Shale Formation. The Broadford Formation, as used in this study, is equivalent only to the ‘Lower Broadford Beds’ of previous authors. The Pabay Shale incorporates the former ‘Upper Broadford Beds’ and ‘Pabba Shale’ of previous usage. Two new predominantly arenaceous members of the Pabay Shale Formation are formally defined for the northern area: the Hallaig Sandstone Member (Lower Sinemurian; Semicostatum–Turneri Zones) occurs within the lower Pabay Shale and has its type locality at Hallaig Waterfall on Raasay; the Suisnish Sandstone Member (Upper Sinemurian–Lower Pliensbachian; Raricostatum – Jamesoni zones) occupies the middle part of the Pabay Shale Formation and has its type locality at Rubha Suisnish and in the cliffs along the southern shore of Loch Eishort, on Skye. In the southern area (Mull–Morvern) use of the terms ‘Lower Broadford Beds’ or ‘Upper Broadford Beds’ is also inappropriate. In Ardnamurchan, and to a limited extent in more northerly exposures, the Broadford Formation interdigitates with its more southerly offshore equivalent, the Blue Lias Formation. The Pabay Shale of the Ardnamurchan–Morvern–Mull area is recognized down to the junction with the Blue Lias. A sandstone unit is well developed at about the Lower Sinemurian–Upper Sinemurian boundary: it is here named the Torosay Sandstone Member of the Pabay Shale Formation and is incompletely exposed at several localities on the southeastern coast of Mull. Although no age-diagnostic fossils have been found within the sandstone, it must lie within the upper Obtusum Zone to lower Raricostatum Zone interval. Overall, there is a general trend from more proximal environments of deposition in the north and east, towards more distal environments in the south and west. This regional pattern is modulated by the localized occurrence of sand-rich, very proximal successions in the vicinity of the supposed transfer zones, such as the area immediately SE of the northern termination of the Camasunary Fault. Records from the Upper Glen-1 borehole, in NW Skye, show that the expanded lower Lias sequence in the centre of the Sea of the Hebrides–Little Minch Basin can be subdivided in a similar manner to that exposed in the Inner Hebrides Trough; for example, it shows the development of more sandy strata at about the Lower Sinemurian to Upper Sinemurian boundary. Like the Ardnamurchan section, it also shows an intercalation of the Broadford Formation and Blue Lias. The upper half of the Pabay Shale appears to be truncated in the borehole: it is debatable whether this resulted from erosion prior to deposition of the Scalpa Sandstone, from sediment starvation or, alternatively, intersection of the borehole by a normal fault.
Emanuela Mattioli - One of the best experts on this subject based on the ideXlab platform.
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carbon isotope anomalies and demise of carbonate platforms in the Sinemurian early jurassic of the tethyan region evidence from the southern alps northern italy
Geological Magazine, 2017Co-Authors: Daniele Masetti, Emanuela Mattioli, Hugh C Jenkyns, Billy Figus, Filippo Barattolo, Renato PosenatoAbstract:Despite its global impact on ecosystems, the Triassic/Jurassic boundary event had only a modest effect on the carbonate depositional systems of the Southern Alps, whereas a fundamental reorganization of the same palaeogeographic area took place during the Sinemurian Age. This paper investigates whether or not the well-documented demise of Sinemurian carbonate platforms in the Tethyan region was a response to a global event by examination of carbon-isotope anomalies in successions of different facies that record this interval of time. A chemostratigraphic transect from Lake Garda up to the eastern Italian border is illustrated by four stratigraphic sections; high-resolution (20 cm over key intervals) chemostratigraphic sampling allowed detection of a major negative δ13C anomaly of ~ 1.5‰, preceded by a positive excursion, both in shallow- and deep-water successions, over the stratigraphical range of the ammonite genus Arnioceras. A comparison with sections from the UK suggests that the positive excursion belongs to the turneri Zone and the succeeding negative excursion falls within the obtusum Zone. In the deep-water Belluno Basin, the negative anomaly occurs in a biogenic chert-rich unit recording the onset of mesotrophic conditions in the basin. In the platform-carbonate successions, this major negative carbon-isotope excursion is developed within a calcarenitic unit corresponding to the lowest occurrence of the foraminifer Paleomayncina termieri. This evidence for deepening and transgression across the carbonate platform suggests pre-conditioning for drowning. Hence, rather than tectonic subsidence alone, environmental factors may have aided the demise of Tethyan carbonate platforms during the Early Jurassic Sinemurian Age.
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a calcareous nannofossil and organic geochemical study of marine palaeoenvironmental changes across the Sinemurian pliensbachian early jurassic 191 ma in portugal
Palaeogeography Palaeoclimatology Palaeoecology, 2016Co-Authors: Julien Plancq, Emanuela Mattioli, Luis V Duarte, Bernard Pittet, Francois Baudin, Myriam Boussaha, Vincent GrossiAbstract:The Sinemurian/Pliensbachian boundary (~ 191 Ma) is acknowledged as one of the most important steps in the radiation of planktonic organisms, especially primary producers such as dinoflagellates and coccolithophores. To date, there is no detailed study documenting changes in planktonic assemblages related to palaeoceanographic changes across this boundary. The aim of this study is to characterize the palaeoenvironmental changes occurring across the Sinemurian/Pliensbachian boundary at the Sao Pedro de Moel section (Lusitanian Basin, Portugal) using micropalaeontology and organic geochemistry approaches. Combined calcareous nannofossil assemblage and lipid biomarker data document for a decrease in primary productivity in relation to a major sea-level rise occurring above the boundary. The Lusitanian Basin was particularly restricted during the late Sinemurian with a relatively low sea level, a configuration that led to the recurrent development of black shales. After a sharp sea-level fall, the basin became progressively deeper and more open during the earliest Pliensbachian, subsequently to a major transgression. This sea-level increase seems to have been a global feature and could have been related to the opening of the Hispanic Corridor that connected the Tethys and palaeo-Pacific oceans. The palaeoceanographic and palaeoclimatic changes induced by this opening may have played a role in the diversification of coccolithophores with the first occurrence or colonization of Tethyan waters by placolith-type coccoliths.
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spatial characterization of the late Sinemurian early jurassic palaeoenvironments in the lusitanian basin
Palaeogeography Palaeoclimatology Palaeoecology, 2014Co-Authors: Myriam Boussaha, Emanuela Mattioli, Bernard Pittet, Luis V DuarteAbstract:Abstract The upper Sinemurian of the Lusitanian Basin (Portugal) is characterized by the deposition of carbonates (dolomitic limestones, limestones), sometimes enriched in organic matter (total organic carbon up to 22%). The main goal of this study is to understand the distribution of carbonates and organic matter-rich sediments in space and time, and to characterize the context of their deposition at the basin scale. Three sections located along a proximal–distal transect in the Lusitanian Basin and dated from the oxynotum to raricostatum ammonite zones (upper Sinemurian) have been studied for their microfacies and sedimentary structures, and correlated by means of ammonite and calcareous nannofossil biostratigraphy, and sequence stratigraphy. The proximal part of the basin is dominated by carbonates whereas organic-rich sediments and marl-limestone alternations are common in the distal part. Microfacies analysis shows a trend from high- to low-energy environments, which reflects a deepening trend in most of the basin within the raricostatum ammonite Zone. A forced regression took place in the earliest Pliensbachian, which is likely related to tectono-eustasy. This particular surface can be correlated at the regional level, to several basins of the western Tethys. The presence of black shales in the distal part of the basin and of framboidal pyrite in the proximal part is interpreted as resulting from an episode of pervasive dysoxia/anoxia at the basin scale during this time interval. The basin recorded conditions varying from dysoxic/anoxic phases in times of water column stratification, to full oxygenation in times of intense mixing by storms, attested by the presence of storm-related sedimentary structures in some carbonate-rich deposits. The occurrence of upper Sinemurian sediments rich in organic matter in other basins, in England and Spain, in the same time interval (upper Sinemurian, raricostatum ammonite Zone) suggests that palaeoclimatic and palaeogeographic conditions were prone to the development of a supraregional dysoxia/anoxia.