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Hugh C Jenkyns - One of the best experts on this subject based on the ideXlab platform.

  • a southern hemisphere record of global trace metal drawdown and orbital modulation of organic matter burial across the cenomanian turonian Boundary ocean drilling program site 1138 kerguelen plateau
    Sedimentology, 2017
    Co-Authors: Alexander J Dickson, Hugh C Jenkyns, Matthew Sakerclark, Cinzia Bottini, Elisabetta Erba, F Russo, Olga Gorbanenko, Bernhard David A Naafs, Richard D. Pancost
    Abstract:

    Despite its assumed global nature, there are very few detailed stratigraphic records of the late Cenomanian to the early Turonian Oceanic Anoxic Event 2 from the Southern Hemisphere. A highly resolved record of environmental changes across the Cenomanian–Turonian Boundary interval is presented from Ocean Drilling Program Site 1138 on the central Kerguelen Plateau (southern Indian Ocean). The new data lead to three key observations. Firstly, detailed biostratigraphy and chemostratigraphy indicate that the record of Oceanic Anoxic Event 2 is not complete, with a hiatus spanning the onset of the event. A decrease in glauconite and highly weathered clays after the onset of Oceanic Anoxic Event 2 marks the end of the hiatus interval, which can be explained by a relative sea-level rise that increased sediment accommodation space on the Kerguelen Plateau margin. This change in depositional environment controlled the timing of the delayed peak in organic-matter burial during Oceanic Anoxic Event 2 at Site 1138 compared with other Oceanic Anoxic Event 2 locations worldwide. A second key observation is the presence of cyclic fluctuations in the quantity and composition of organic matter being buried on the central Kerguelen Plateau throughout the latter stages of Oceanic Anoxic Event 2 and the early Turonian. A close correspondence between organic matter, sedimentary elemental compositions and sediments recording sea-floor oxygenation suggests that the cycles were mainly productivity-driven phenomena. Available age-control points constrain the periodicity of the coupled changes in sedimentary parameters to ca 15 to 50 ka, suggesting a link between carbon burial and astronomically forced climatic variations (precession or obliquity) in the Southern Hemisphere mid-latitudes both during, and after, Oceanic Anoxic Event 2: fluctuations that were superimposed on the impact of global-scale processes. Finally, trace-metal data from the non-sulphidic black shale unit at Site 1138 provide the first evidence from outside of the proto-North Atlantic region for a global drawdown of seawater trace-metal (Mo) inventories during Oceanic Anoxic Event 2. This article is protected by copyright. All rights reserved.

  • Planktonic foraminiferal biostratigraphy and assemblage composition across the Cenomanian-Turonian Boundary interval at Clot Chevalier (Vocontian Basin, SE France)
    Cretaceous Research, 2016
    Co-Authors: Francesca Falzoni, Maria Rose Petrizzo, Andrew S Gale, Hugh C Jenkyns, Harilaos Tsikos
    Abstract:

    The Cenomanian-Turonian Boundary interval is generally considered a critical time for planktonic foraminifera due to the environmental perturbations associated with Oceanic Anoxic Event 2. However, only the rotaliporids became extinct at the onset of the event, whilst several lineages evolved and/or diversified. This remarkable morphologic plasticity is often overlooked in the literature, partly because a number of stratigraphic sections have only been studied in thin-section due to the degree of lithification of the samples. Improved documentation of the morphological variability of planktonic foraminifera and better defined species concepts are required in order to improve biostratigraphy, particularly as Helvetoglobotruncana helvetica is an unreliable marker for the base of the Turonian. At the same time, detailed study of the planktonic foraminiferal response to OAE 2 demands a more profound knowledge of the assemblage composition. We present new biostratigraphic, taxonomic, and quantitative data for planktonic foraminiferal species from the Clot Chevalier section (Vocontian Basin, SE France), with the aim of (1) providing a detailed biostratigraphic analysis of the section, (2) documenting the morphological plasticity of specimens in this time interval and stabilizing species concepts, and (3) identifying promising markers to improve the resolution of the present biozonation and allow regional correlation. Samples were processed with acetic acid to extract isolated planktonic foraminifera. Assemblages were assigned to the upper Cenomanian Rotalipora cushmani Zone and to the uppermost Cenomanian-lowermost Turonian Whiteinella archaeocretacea Zone. Planktonic foraminiferal bioevents and assemblage composition identified at Clot Chevalier are compared with the well-studied Pont d'Issole section located ca. 15 km to the NE, highlighting similarities and differences in the species occurrences that may complicate the stratigraphic correlation between the two sections. The results of our study support the validity and common occurrence of species that have been misidentified and/or overlooked in the literature (i.e., Dicarinella roddai, Praeglobotruncana oraviensis, Marginotruncana caronae) and indicate that primitive marginotruncanids evolved before the onset of OAE 2, although species diversification occurred only after the event. Moreover, we believe that the first appearance of P. oraviensis might represent a promising bioevent for approximating the Cenomanian/Turonian Boundary, after calibration with bio- and chemostratigraphically well-constrained sections. Finally, we describe three new trochospiral species, named ". Pseudoclavihedbergella" chevaliensis, Praeglobotruncana pseudoalgeriana and Praeglobotruncana clotensis.

  • black shale deposition atmospheric co2 drawdown and cooling during the cenomanian turonian oceanic anoxic event
    Paleoceanography, 2011
    Co-Authors: Ian Jarvis, Hugh C Jenkyns, John S Lignum, Darren R Grocke, Martin A Pearce
    Abstract:

    [1] Oceanic Anoxic Event 2 (OAE2), spanning the Cenomanian-Turonian Boundary (CTB), represents one of the largest perturbations in the global carbon cycle in the last 100 Myr. The δ13Ccarb, δ13Corg, and δ18O chemostratigraphy of a black shale–bearing CTB succession in the Vocontian Basin of France is described and correlated at high resolution to the European CTB reference section at Eastbourne, England, and to successions in Germany, the equatorial and midlatitude proto-North Atlantic, and the U.S. Western Interior Seaway (WIS). Δ13C (offset between δ13Ccarb and δ13Corg) is shown to be a good pCO2 proxy that is consistent with pCO2 records obtained using biomarker δ13C data from Atlantic black shales and leaf stomata data from WIS sections. Boreal chalk δ18O records show sea surface temperature (SST) changes that closely follow the Δ13C pCO2 proxy and confirm TEX86 results from deep ocean sites. Rising pCO2 and SST during the Late Cenomanian is attributed to volcanic degassing; pCO2 and SST maxima occurred at the onset of black shale deposition, followed by falling pCO2 and cooling due to carbon sequestration by marine organic productivity and preservation, and increased silicate weathering. A marked pCO2 minimum (∼25% fall) occurred with a SST minimum (Plenus Cold Event) showing >4°C of cooling in ∼40 kyr. Renewed increases in pCO2, SST, and δ13C during latest Cenomanian black shale deposition suggest that a continuing volcanogenic CO2 flux overrode further drawdown effects. Maximum pCO2 and SST followed the end of OAE2, associated with a falling nutrient supply during the Early Turonian eustatic highstand.

  • stepwise extinction of larger foraminifers at the cenomanian turonian Boundary a shallow water perspective on nutrient fluctuations during oceanic anoxic event 2 bonarelli event
    Geology, 2008
    Co-Authors: Mariano Parente, Hugh C Jenkyns, Gianluca Frijia, Matteo Di Lucia, Richard G Woodfine, Francesco Baroncini
    Abstract:

    A two-step pattern in the extinction of larger foraminifers is recorded in the upper Cenomanian shallow-water carbonates of the southern Apennines (Italy). The first step eliminated the alveolinids, the most extreme oligotrophs, and reduced dramatically the diversity of larger foraminifers. The second step wiped out the few survivors, seemingly able to tolerate mesotrophic conditions, leaving a disaster fauna dominated by small heterotrophs. This pattern of extinction parallels the ecological succession of shallow-water benthic foraminiferal assemblages along a gradient of increasing nutrient availability. High-resolution carbon isotope stratigraphy shows that the extinction of alveolinids was contemporaneous with the extinction of rotaliporid planktic foraminifers, the drowning of certain Tethyan carbonate platforms, and an episode of thermal instability recorded in sea-surface temperature in the open ocean. Ocean stratification, during the first phase of Oceanic Anoxic Event 2, would have promoted oligotrophic conditions in surface tropical waters and maximum diversity of larger foraminifers. Following this, ocean overturning caused by surface-water cooling is credited with delivering to shallow-water environments the excess nutrient loads previously stored at depth, triggering the environmental changes leading to stepwise extinction of larger foraminifers.

  • carbon isotope stratigraphy recorded by the cenomanian turonian oceanic anoxic event correlation and implications based on three key localities
    Journal of the Geological Society, 2005
    Co-Authors: Maria Rose Petrizzo, Hugh C Jenkyns, Harilaos Tsikos, Astrid Forster, Elisabetta Erba, Ben Walsworthbell, Sadat Kolonic, Premoli I Silva, Marianne Baas
    Abstract:

    We present new, detailed carbon-isotope records for bulk carbonate, total organic carbon (TOC) and phytane from three key sections spanning the Cenomanian–Turonian Boundary interval (Eastbourne, England; Gubbio, Italy; Tarfaya, Morocco), with the purpose of establishing a common chemostratigraphic framework for Oceanic Anoxic Event (OAE) 2. Isotope curves from all localities are characterized by a positive carbon-isotope excursion of c . 4‰ for TOC and phytane and c . 2.5‰ for carbonate, although diagenetic overprinting appears to have obliterated the primary carbonate carbon-isotope signal in at least part of the Tarfaya section. Stratigraphically, peak δ 13 C values for all components are followed by intervals of high, near-constant δ 13 C in the form of an isotopic plateau. Recognition of an unambiguous return to background δ 13 C values above the plateau is, however, contentious in all sections, hence no firm chemostratigraphic marker for the end-point of the positive isotopic excursion can be established. The stratigraphically consistent first appearance of the calcareous nannofossil Quadrum gartneri at or near the Cenomanian–Turonian Boundary as established by ammonite stratigraphy, in conjunction with the end of the δ 13 C maximum characteristic of the isotopic plateau, provides a potentially powerful tool for delimiting the stratigraphic extent and duration of OAE 2. This Oceanic Anoxic Event is demonstrated to be largely, if not wholly, confined to the latest part of the Cenomanian stage.

Andrew S Gale - One of the best experts on this subject based on the ideXlab platform.

  • cretaceous albian turonian calcareous nannofossil biostratigraphy of the onshore cauvery basin southeastern india
    Cretaceous Research, 2021
    Co-Authors: Sudeep Kanungo, Paul R. Bown, Andrew S Gale
    Abstract:

    Abstract A suite of outcrop samples from the Cauvery Basin belonging to the mudrock-claystone dominated Karai Formation were analysed for nannofossil biostratigraphy in two newly measured sections at Karai and Garudamangalam. The age of the Karai Section is interpreted as early Albian to early Turonian, whereas the Garudamangalam Section is interpreted as late Albian to late Cenomanian. The Albian ‘BC’ zones of Bown et al. (1998) are applicable in both sections, whereas the Cenomanian and Turonian ‘UC’ zones of Burnett (1998), are only partially applicable, due to some problematic primary and secondary markers. The Albian-Cenomanian Boundary appears to be continuous and is approximated in both sections using the FO of lower Cenomanian ammonites of the M. mantelli Zone. The Cenomanian-Turonian Boundary interval is incomplete in the two sections, with a hiatus of ~0.66 myr, indicated by the absence of the upper Cenomanian Nannofossil Zone UC5. The nannoplankton assemblages are composed of broadly cosmopolitan taxa, despite the relatively high-latitude setting of SE India during the Albian (~45°S), which is reflected in the common occurrence of biogeographically bipolar taxa such as Repagulum parvidentatum and Seribiscutum primitivum. The palaeobiogeographic affinity of the nannoplankton, however, does not bear a distinct Austral stamp, as typical Austral taxa, such as Sollasites falklandensis and Zeugrhabdotus kerguelenensis are very rare in the studied sections. The early appearance of Crucibiscutum hayi in the lower Albian, and Gartnerago segmentatum in the upper Albian in the Cauvery Basin suggests that these two species may have originated in southern high latitudes before migrating to the northern Boreal regions. Four new calcareous nannofossil species, Calculites karaiensis, Loxolithus bicyclus, Manivitella fibrosa and Tranolithus simplex are described.

  • turonian ammonites from northwestern aquitaine france
    Cretaceous Research, 2016
    Co-Authors: James W Kennedy, Andrew S Gale
    Abstract:

    Abstract The position of the Cenomanian-Turonian Boundary is established for the first time in Charente-Maritime, northwestern Aquitaine (France), on the basis of ammonite occurrences and the δ13C isotope curve, corresponding to Oceanic Anoxic Event 2, that straddles the Boundary. The earliest Turonian ammonites recognised are a monospecific occurrence of the early early Turonian pseudotissotiine Bageites bakui Zaborski, 1998, previously known only from northern Nigeria. Newly collected material and well-preserved specimens from existing collections supplement previous records, and include species of Placenticeras, Morrowites, Kamerunoceras, Romaniceras (Romaniceras), Spathites (Jeanrogericeras), Mammites, Fagesia, Neoptychites, Choffaticeras (Leoniceras), Collignoniceras and Lecointriceras. These confirm the presence of the upper lower Turonian nodosoides Zone and the lower middle Turonian turoniense and kallesi zones/subzones of authors.

  • Planktonic foraminiferal biostratigraphy and assemblage composition across the Cenomanian-Turonian Boundary interval at Clot Chevalier (Vocontian Basin, SE France)
    Cretaceous Research, 2016
    Co-Authors: Francesca Falzoni, Maria Rose Petrizzo, Andrew S Gale, Hugh C Jenkyns, Harilaos Tsikos
    Abstract:

    The Cenomanian-Turonian Boundary interval is generally considered a critical time for planktonic foraminifera due to the environmental perturbations associated with Oceanic Anoxic Event 2. However, only the rotaliporids became extinct at the onset of the event, whilst several lineages evolved and/or diversified. This remarkable morphologic plasticity is often overlooked in the literature, partly because a number of stratigraphic sections have only been studied in thin-section due to the degree of lithification of the samples. Improved documentation of the morphological variability of planktonic foraminifera and better defined species concepts are required in order to improve biostratigraphy, particularly as Helvetoglobotruncana helvetica is an unreliable marker for the base of the Turonian. At the same time, detailed study of the planktonic foraminiferal response to OAE 2 demands a more profound knowledge of the assemblage composition. We present new biostratigraphic, taxonomic, and quantitative data for planktonic foraminiferal species from the Clot Chevalier section (Vocontian Basin, SE France), with the aim of (1) providing a detailed biostratigraphic analysis of the section, (2) documenting the morphological plasticity of specimens in this time interval and stabilizing species concepts, and (3) identifying promising markers to improve the resolution of the present biozonation and allow regional correlation. Samples were processed with acetic acid to extract isolated planktonic foraminifera. Assemblages were assigned to the upper Cenomanian Rotalipora cushmani Zone and to the uppermost Cenomanian-lowermost Turonian Whiteinella archaeocretacea Zone. Planktonic foraminiferal bioevents and assemblage composition identified at Clot Chevalier are compared with the well-studied Pont d'Issole section located ca. 15 km to the NE, highlighting similarities and differences in the species occurrences that may complicate the stratigraphic correlation between the two sections. The results of our study support the validity and common occurrence of species that have been misidentified and/or overlooked in the literature (i.e., Dicarinella roddai, Praeglobotruncana oraviensis, Marginotruncana caronae) and indicate that primitive marginotruncanids evolved before the onset of OAE 2, although species diversification occurred only after the event. Moreover, we believe that the first appearance of P. oraviensis might represent a promising bioevent for approximating the Cenomanian/Turonian Boundary, after calibration with bio- and chemostratigraphically well-constrained sections. Finally, we describe three new trochospiral species, named ". Pseudoclavihedbergella" chevaliensis, Praeglobotruncana pseudoalgeriana and Praeglobotruncana clotensis.

  • sea level change carbon cycling and palaeoclimate during the late cenomanian of northwest europe an integrated palaeoenvironmental analysis
    Cretaceous Research, 2006
    Co-Authors: Silke Voigt, Andrew S Gale, Thomas Voigt
    Abstract:

    A new high resolution sea-level curve for the Late Cenomanian M. geslinianum Zone has been generated using sequence stratigraphic analysis on transects through the margins of the Anglo-Paris Basin in the UK and Saxony Basin in Germany. Transgressive sediments that bury a rocky shoreline in the Dresden area have proved particularly useful in determining both the absolute amount of sea-level change and the rate of rise. After a brief fall at the base of the M. geslinianum Zone, sea level rose rapidly through the higher part of the zone, resulting in an overall short term eustatic rise of 22–28 m. Biostratigraphy and carbon isotope stratigraphy have enabled detailed correlations to be made between marginal locations and thick, relatively complete, basinal successions. The basinal successions at Eastbourne, UK, and Grobern, Germany, provide both geochemical proxies for palaeoenvironmental change, including oxygen and carbon isotope records, and an orbital timescale graduated in precession and eccentricity cycles. Integration of the sea-level history with palaeoclimate evolution, palaeoceanography and changes in carbon cycling allows a detailed reconstruction of events during the Late Cenomanian. Orbital forcing on long eccentricity maxima provides the underlying drive for these changes, but amplification by tectonic events and feedback mechanisms augmented the orbital effects and made the Cenomanian/Turonian Boundary Event distinctive. In particular, variations in atmospheric CO2 caused by oceanic drawdown and a brief period of intense volcanic outgassing resulted respectively in short term cooling and warming events. The magnitude and high rates (up to 1 m/1 kyr) of sea-level rise are diagnostic of glacioeustasy, however improbable this may appear at the height of the Cretaceous greenhouse.

  • stratigraphy of the upper cenomanian lower turonian chalk succession at eastbourne sussex uk ammonites inoceramid bivalves and stable carbon isotopes
    Cretaceous Research, 2005
    Co-Authors: Andrew S Gale, James W Kennedy, Silke Voigt, Ireneusz Walaszczyk
    Abstract:

    Thirty-one ammonite, and eight inoceramid bivalve taxa are recorded from the Cenomanian-Turonian Boundary interval at Eastbourne, Sussex, in southern England, and correlated with the d 13 C isotope record in carbonate and organic carbon. New ammonite records from Western Europe include the North American species Cunningtoniceras arizonense Kirkland and Cobban, 1986, Tarrantoceras (Sumitomoceras) conlini Wright and Kennedy, 1981, Puebloites corrugatus (Stanton, 1894) and Euomphaloceras costatum Cobban, Hook and Kennedy, 1989. The ammonites allow definition of three Late Cenomanian (C. guerangeri, M. geslinianum, N. juddii) and three Turonian (W. devonense, F. catinus, M. nodosoides) zones. The inoceramid study enables recognition of the Mytiloides puebloensis Zone, and allows us to demonstrate the absence of the Mytiloides hattini Zone at Eastbourne. The first occurrence of M. puebloensis Walaszczyk and Cobban, 2000, is coincident with that of the ammonite genus Watinoceras, as in the United States Western Interior, and allows precise placement of the Cenomanian-Turonian Boundary in the Anglo-Paris Basin for the first time. We present stable carbon isotope data through the succession, including the first d 13 Corg record for the UK Chalk. The positive Cenomanian-Turonian Boundary carbon isotope excursion at Eastbourne is reflected in the d 13 Ccarb record by an overall stepwise increase in values, whereas the d 13 Corg record displays distinct minima at times of d 13 Ccarb plateaux. Each plateau precedes the following d 13 C increase recorded in both the carbonate and the organic carbon curves. The distinct pattern in the organic and carbonate d 13 C records results in three intervals that show marked increases in the isotopic fractionation between organic and inorganic carbon. We use a combination of carbon isotope, ammonite and inoceramid data to develop a detailed correlation with the proposed CeT stratotype at Pueblo, Colorado, which has a resolution close to that of Milankovitch precession cycles. 2005 Elsevier Ltd. All rights reserved.

Delphine Desmares - One of the best experts on this subject based on the ideXlab platform.

  • roveacrinids crinoidea roveacrinida from the cenomanian turonian of southwest algeria saharan atlas and guir basin
    Annales De Paleontologie, 2017
    Co-Authors: Bruno Ferré, Madani Benyoucef, Kaddour Mebarki, Delphine Desmares, Loic Villier, Luc G Bulot, Houcine Boumediene Benachour, Lionel Marie, Jacques Sauvagnat
    Abstract:

    Abstract In the southwestern part of Algeria, the Cenomanian-Turonian marine deposits build up a prominent ledge in a perched syncline (Ksour Mountains, western Saharan Atlas) or at high radius of curvature (Guir Basin). The petrographical analysis of the Cenomanian-Turonian deposits of the Ksour Mountains and of the Guir Basin reveals unexpected assemblages of roveacrinoidal ossicles comparable with those formerly reported from the Tinrhert area. For the first time, isolated ossicles of genuine and undisputable Roveacrinidae are illustrated. Three sections, Djebel Rhoundjaia (western Saharan Atlas), Berridel and Kenadsa (Guir Basin), were scrutinized to recognize the microcrinoidal sections within the carbonate microfacies and to compile the successive occurrence of respective roveacrinid taxa (besides the classical search for standard index microfossils) in an attempt to pinpoint more precisely the position of the Cenomanian-Turonian Boundary (C/T B). These assemblages are particularly morphologically and taxonomically diverse with three species of genus Roveacrinus and one of genus Orthogonocrinus . The presence of Saccocomidae ( Applinocrinus ) is especially unusual in such stratigraphic levels. The relative abundance and diversity of Roveacrinidae evidence a peak when approaching the C/T B. Such an event is recurring in the latest Cenomanian in various Tethyan and Atlantic areas. These fluctuations are consistent with a high surface-water productivity just before the C/T B.

  • the cenomanian turonian Boundary event on the moroccan atlantic margin agadir basin stable isotope and sequence stratigraphy
    Palaeogeography Palaeoclimatology Palaeoecology, 2010
    Co-Authors: Mohamed Jati, Serge Ferry, Daniele Grosheny, Moussa Masrour, Mohamed Aoutem, Nourrisaid Icame, Francois Gauthierlafaye, Delphine Desmares
    Abstract:

    Abstract Correlations of four sections, constrained by stable isotope stratigraphy and micropalaeontology, along a 80 km-long, E/W-oriented transect from the western High-Atlas to the present-day coast (Taghazoute), show that the Cenomanian–Turonian Boundary event (CTBE) occurred within shallow-water, oyster-bearing limestones and marls, and not in the overlying black shale. The age of the laminated shale is early Turonian as the planktonic marker Helvetoglobotruncana helvetica is found from its first centimetres upward. The underlying deposits hosting the CTBE event are bounded by two unconformities interpreted as emersion surfaces, and represent the strongest seawardshifts of facies in the local Cenomanian sedimentary wedge. The δ 13 C anomaly is only recorded in the coastal Taghazoute section, not in other sections landward, meaning that the CTBE occurred here during a short transgressive phase within an overall regressive trend. The lower Turonian black shale of the Taghazoute section is transgressive onto the second unconformity and pass landward to white, evenly laminated, chert-bearing mudstones, then to bioturbated mudstones in the easternmost sections of the transect (western High-Atlas).

  • high resolution stratigraphic record constrained by volcanic ash beds at the cenomanian turonian Boundary in the western interior basin usa
    Cretaceous Research, 2007
    Co-Authors: Daniele Grosheny, Delphine Desmares, Bernard Beaudoin, Silvia Gardin, Francois Gauthierlafaye
    Abstract:

    Five altered volcanic-ash beds have been correlated in the Cenomanian–Turonian Boundary interval through the US Western Interior Basin over tens of thousands of square kilometres. Using these independent chronostratigraphic marker-beds to constrain the other classic stratigraphic records such as limestone bed by bed correlations, peaks within the δ13C isotope excursion and a few other key biological events, a regional correlation scheme has been obtained between seven sections from Arizona to Kansas and northwards to South Dakota. On the basis of this high resolution scheme, we show that the last occurrences of the planktonic foraminiferid Rotalipora cushmani as well as the first occurrence of Helvetoglobotruncana helvetica are strongly diachronous, the Whiteinella archaeocretacea Partial Range Zone, in which the Cenomanian–Turonian Boundary is located, being reduced to almost nothing, particularly at Pueblo (Colorado). At this type section, the δ13C isotope excursion presents strongly negative values in the limestone beds, suggesting that they are of diagenetic origin. In spite of this, the onset and most of the fine-scale features of the carbon-isotope excursion identified at Pueblo are recognised over long distances even in the more coastal sections where bed by bed correlations become more difficult. As suggested by our scheme, differences observed between supposedly continuous sections could be related to hiatuses in the sedimentary record. Such gaps could explain the disappearance of some fine-scale features of the δ13C isotope excursion. If this interpretation is correct, one hiatus may have been as long as 850 Kyrs.

Emmanuelle Puceat - One of the best experts on this subject based on the ideXlab platform.

  • nitrogen and carbon cycle perturbations through the cenomanian turonian oceanic anoxic event 2 94 ma in the vocontian basin se france
    Palaeogeography Palaeoclimatology Palaeoecology, 2020
    Co-Authors: Julien Danzelle, Laurent Riquier, Francois Baudin, Christophe Thomazo, Emmanuelle Puceat
    Abstract:

    Abstract Oceanic Anoxic Event 2, spanning the Cenomanian-Turonian Boundary, was an episode of major perturbations in global biogeochemical cycles, characterized by the widespread burial of organic carbon in both oceans and epicontinental basins. In the Vocontian Basin (SE France), this event was expressed by the deposition of the Niveau Thomel, a succession of interbedded dark shales, grey marls and bioturbated carbonates as observed in the Lambruisse section. Analyses of the total organic carbon (TOC) content, combined with the concentrations of redox-sensitive trace elements, revealed that conditions fluctuated from oxic to suboxic-anoxic during the deposition of the Niveau Thomel. Transient periods of deoxygenation were related to perturbations in nutrient cycling reflected by near-zero to negative δ15N signatures indicative of increased diazotrophy. The development of deoxygenated conditions in the Vocontian Basin was likely preconditioned by hydrographically restricted conditions, as confirmed by Mo vs. U enrichments, reducing bottom-water ventilation associated with water-column stratification. Intervals of reoxygenation were likely linked to climate-induced changes. In particular, a phase of regional or global cooling associated with a drop in pCO2, called the Plenus Cold Event (PCE) resulted in vigorous reoxygenation of the Vocontian Basin.

  • thermal evolution of cretaceous tethyan marine waters inferred from oxygen isotope composition of fish tooth enamels
    Paleoceanography, 2003
    Co-Authors: Emmanuelle Puceat, Christophe Lecuyer, Simon M F Sheppard, Gilles Dromart, Stephane Reboulet, Patricia Grandjean
    Abstract:

    [1] The evolution of subtropical (30–35°N) upper ocean temperatures through the Cretaceous is inferred from the oxygen isotope compositions of 64 fish teeth (enamel) coming from the western Tethyan platform. Mean δ18O values of 22‰ at the Berriasian-Valanginian Boundary decrease, with oscillations to 18.5‰ around the Cenomanian-Turonian Boundary, and progressively increase to 21.5‰ by the end of the Cretaceous. The similarity of this oxygen isotope curve for bioapatites from platform environments with those for foraminifera and bulk carbonates that were deposited in deeper waters and at other paleolatitudes indicates that they record global climatic signals. Major cooling events at the million-year scale can be distinguished: (1) at the Berriasian-Valanginian Boundary and (2) during the earliest Late Valanginian. A third cooling event is detected during the earliest Aptian. These events, already proposed as icehouse interludes during the lower Cretaceous, are also recorded at subtropical latitudes. A progressive warming is identified from the Aptian to the Cenomanian-Turonian interval that corresponds to a thermal optimum, and then upper ocean temperatures decreased to the Maastrichtian. Minimum isotopic temperatures range from 15°C to 28°C, assuming a δ18Oseawater of −1‰, for an ice-free world. Taking more realistic δ18Oseawater values of ∼0‰ for tropical waters, during glacial periods (within the Berriasian-Valanginian interval, and earliest Aptian) or with above average salinities (possibly the Maastrichtian), temperatures are increased by 4–5°C. Temperature differences between climatic extremes of the Valanginian and Cenomanian-Turonian are estimated to have been 10°C. Latitudinal thermal gradients for the Albian-Cenomanian, Turonian, and Maastrichtian were 0.2–0.3°C/° latitude and thus weaker than modern oceanic values at about 0.4°C/° latitude.

Thierry Adatte - One of the best experts on this subject based on the ideXlab platform.

  • stratigraphy of the cenomanian turonian oceanic anoxic event oae2 in shallow shelf sequences of ne egypt
    Cretaceous Research, 2011
    Co-Authors: Ahmed M Elsabbagh, Thierry Adatte, Gerta Keller, Abdel Aziz Tantawy, Hassan Khozyem, Jorge E Spangenberg, B. Gertsch
    Abstract:

    Abstract Two shallow water late Cenomanian to early Turonian sequences of NE Egypt have been investigated to evaluate the response to OAE2. Age control based on calcareous nannoplankton, planktic foraminifera and ammonite biostratigraphies integrated with δ 13 C stratigraphy is relatively good despite low diversity and sporadic occurrences. Planktic and benthic foraminiferal faunas are characterized by dysoxic, brackish and mesotrophic conditions, as indicated by low species diversity, low oxygen and low salinity tolerant planktic and benthic species, along with oyster-rich limestone layers. In these subtidal to inner neritic environments the OAE2 δ 13 C excursion appears comparable and coeval to that of open marine environments. However, in contrast to open marine environments where anoxic conditions begin after the first δ 13 C peak and end at or near the Cenomanian–Turonian Boundary, in shallow coastal environments anoxic conditions do not appear until the early Turonian. This delay in anoxia appears to be related to the sea-level transgression that reached its maximum in the early Turonian, as observed in shallow water sections from Egypt to Morocco.

  • middle and late cenomanian oceanic anoxic events in shallow and deeper shelf environments of western morocco
    Sedimentology, 2010
    Co-Authors: B. Gertsch, Thierry Adatte, Gerta Keller, Abdel Aziz Tantawy, Zsolt Berner, Haydon P. Mort, Dominik Fleitmann
    Abstract:

    The response of shallow-water sequences to oceanic anoxic event 2 and mid-Cenomanian events 1a and 1b was investigated along the west African margin of Morocco north of Agadir (Azazoul) and correlated with the deep-water sequence of the Tarfaya Basin (Mohammed Beach) based on biostratigraphy, mineralogy, phosphorus and stable isotopes. In the deeper Mohammed Beach section results show double peaks in delta 13C(org) for mid-Cenomanian events 1a and 1b (Rotalipora reicheli biozone, lower CC10a biozone), the characteristic oceanic anoxic event 2 delta 13C excursion (Rotalipora cushmani extinction, top of CC10a biozone) and laminated (anoxic) black shale. In the shallow environment north of Agadir, a fluctuating sea-level associated with dysoxic, brackish and mesotrophic conditions prevailed during the middle to late Cenomanian, as indicated by oyster biostromes, nannofossils, planktonic and benthonic foraminiferal assemblages. Anoxic conditions characteristic of oceanic anoxic event 2 (for example, laminated black shales) did not reach into shallow-water environments until the maximum transgression of the early Turonian. Climate conditions decoupled along the western margin of Morocco between mid-Cenomanian event 1b and the Cenomanian-Turonian Boundary, as also observed in eastern Tethys. North of Agadir alternating humid and dry seasonal conditions prevailed, whereas in the Tarfaya Basin the climate was dry and seasonal. This climatic decoupling can be attributed to variations in the Intertropical Convergence Zone and in the intensity of the north-east trade winds in tropical areas.

  • the late hauterivian faraoni oceanic anoxic event in the western tethys evidence from phosphorus burial rates
    Palaeogeography Palaeoclimatology Palaeoecology, 2006
    Co-Authors: Stéphane Bodin, Alexis Godet, Karl B. Föllmi, Jean Vermeulen, Nicolas Fiet, Hubert Arnaud, Andre Strasser, Thierry Adatte
    Abstract:

    In the uppermost Hauterivian sediments of the western Tethys, a short-lived anoxic event (Faraoni event) is documented both in the form of an interval enriched in organic matter (pelagic realm) and in a condensed interval enriched in glauconite and phosphate (shelf realm). This latter interval represents the onset of a drowning episode on the Helvetic carbonate platform along the northern tethyan margin that lasted throughout the early Barremian. This drowning episode marks a turning point in the way the platform carbonate factory functioned: during the Hauterivian carbonate production was dominated by heterozoans, whereas during the late Barremian a photozoan assemblage developed that is preserved in the so-called Urgonian limestone. The late Hauterivian Faraoni oceanic anoxic event is of particular interest because it is not accompanied by a major positive shift in y 13 C unlike other oceanic anoxic events during the Cretaceous (Valanginian, early Aptian, Cenomanian–Turonian Boundary). We have analyzed four (hemi-)pelagic sections with regards to their phosphorus content to better understand the palaeoceanographic conditions related to this anoxic event and the associated changes in the shallow-water carbonate factory. The sections are