Papers by Jean-françois Deconinck
Paleoceanography and paleoclimatology, Jun 1, 2020
Astrochronology depends on the faithful record of insolation forcing in climatic proxies, includi... more Astrochronology depends on the faithful record of insolation forcing in climatic proxies, including the carbon isotope composition measured on bulk carbonates (δ 13 C carb). In marginal basins close to carbonate platforms, the source of carbonate is varied, which can impact the record of the astronomical cycles in the δ 13 C carb signal. We compare here the δ 13 C carb values together with detrital and weathering proxies before and during a crisis in the platform carbonate production (Weissert event, Valanginian,~135 Ma) to document how a change in the carbonate source can affect the record of the orbital forcing by the carbon isotope system. The level of burial diagenesis was insufficient to alter the clay mineral assemblages, which are linked to cyclic changes in weathering conditions. The δ 13 C carb values correspond to the values measured in other parts of the basin, which experienced various levels of burial diagenesis, suggesting that they also reflect a paleoenvironmental signal. In marl beds, the δ 13 C carb values increase with detrital and kaolinite content, suggesting that humid/arid cycles controlled the evolution of the δ 13 C carb signal in marl beds. Before the Weissert event, the δ 13 C carb values in the limestone beds increase with CaCO 3 content and arid conditions. This can reflect the change of type of carbonate produced in shallow-marine environments and exported to the basin. These environmental changes disrupted the record of the eccentricity cycles in the δ 13 C carb signal. The sources of carbonate must therefore be clearly identified and documented before using the δ 13 C carb series for orbital tuning in hemipelagic areas close to carbonate platforms. Plain Language Summary The Milankovitch cycles are periodic motions of the Earth's orbit at the origin of cyclic climatic changes recorded in strata. Regular decimetric alternations between marl and limestone strata deposited in deep seas are notably caused by humid-arid cycles orbitally induced, which usually take~20,000 yr to be deposited. Counting these strata cycles allows the duration of the geological periods to be calculated. The so-called astronomical timescales depend on the faithful stratal record of the Milankovitch cycles. Carbon isotopes are used to build astronomical timescales despite sources of carbon are varied and often unconstrained. We compare here proxies from the continental weathering and erosion to the marine carbonate production recorded in marl-limestone alternations. We show here that the different sources of carbonates-produced by organisms with variated ecological needs-disrupt the record of the Milankovitch cycles in the carbon isotopes. The sources of carbon in sediments have to be compared to additional climatic proxies before being used for astronomical timescales. In addition, we propose models to explain how the Milankovitch cycles can be recorded and disrupted in the proxies studied here.
The Late Pliensbachian Event (LPE), in the Early Jurassic, is associated with a perturbation in t... more The Late Pliensbachian Event (LPE), in the Early Jurassic, is associated with a perturbation in the global carbon cycle (positive carbon isotope excursion (CIE) of ~ 2 ‰), cooling of ~5°C, and the deposition of widespread regressive facies. Cooling during the Late Pliensbachian has been linked to enhanced organic matter burial and/or disruption of thermohaline ocean circulation due to North Sea doming. Orbital forcing had a strong influence on the Pliensbachian environments and recent studies show that the terrestrial realm and the marine realm in and around the Cardigan Bay Basin were strongly influenced by orbital climate forcing. In the present study we build on the previously published data for long eccentricity cycle E459 ± 1 and extend the palaeoenvironmental record to include E458 ± 1. We explore the environmental and depositional changes on orbital time scales for the Mochras core during the onset of the LPE. Clay mineralogy, XRF elemental analysis, isotope ratio mass spectrometry, and palynology are combined to resolve systematic changes in erosion, weathering, fire, grain size and riverine influx. Our results indicate distinctively different environments before and after the onset of the LPE positive CIE, and show increased physical erosion relative to chemical weathering. We also identify 5 swings in the climate, in tandem with the 405 kyr eccentricity minima and maxima. Eccentricity maxima are linked to precessionally repeated occurrences of a semi-arid, monsoonal climate with high fire activity and relatively coarser fraction of terrestrial runoff. In contrast, 405 kyr minima in the Mochras core are linked to a more persistent, annually wet climate, low fire activity, and relatively finer grained deposits across multiple precession cycles. The onset of the LPE +ve CIE did not impact the expression of the 405 kyr in the proxy records, however, during the second pulse of lighter carbon (12 C) enrichment, the clay minerals record a change from dominant chemical weathering to dominant physical erosion.
Journal of the Geological Society
New microfossil and magnetostratigraphical data as well as geochemical and clay mineral weatherin... more New microfossil and magnetostratigraphical data as well as geochemical and clay mineral weathering indices are documented from the uppermost Jurassic Owadów–Brzezinki palaeontological site in central Poland. The newly discovered chitinoidellid assemblage of the lowermost part of the section and the previously documented assemblage from the middle part of the section are assigned, respectively, to the uppermost Dobeni and Boneti Subzones of the Chitinoidellidae Zone. The same part of the succession is correlated to the magnetosubzone M20n.2n. The new data allow refinement of the Tithonian stratigraphical scheme including an assignment of the upper part of the Boreal Zarajskites Subzone of the Scythicus (Panderi) ammonite Zone to the Upper Tithonian and its correlation with the lowermost part of Tethyan Microcanthum ammonite Zone and the lower portion of the M20n.2n magnetosubzone. The data show that the Fittoni/Albani ammonite zone boundary should likely be placed within the Boneti S...
HAL (Le Centre pour la Communication Scientifique Directe), Sep 1, 2016
345 pagesNational audienceCet ouvrage présente les processus sédimentaires, de l’érosion jusqu’à ... more 345 pagesNational audienceCet ouvrage présente les processus sédimentaires, de l’érosion jusqu’à la transformation en roche, en passant par le transport et le dépôt. Il associe les aspects descriptifs des sédiments et roches sédimentaires et leurs processus de formations à travers quelques exemples choisis. Les méthodes d’observations des roches sédimentaires et les techniques avancées de la pétrographie sédimentaire sont décrites (coloration, cathodoluminescence, diffraction X, Microscopie électronique...). De nombreuses photographies de terrain, d’échantillons macroscopiques et de lames minces permettent d’appréhender la discipline à différentes échelles. L'utilisation des différentes roches sédimentaires en tant que géoressources exploitables est également abordée. De nombreux exercices, accompagnés d’un corrigé détaillé, complètent l’ouvrage
FIG. 16. — Ostracods from Guadalupian-Lopingian boundary interval in South China: A, Kirkbya sp. ... more FIG. 16. — Ostracods from Guadalupian-Lopingian boundary interval in South China: A, Kirkbya sp. 1, right lateral view of complete carapace, P6M3757, sample 11CHAO172; B, Kirkbya sp. 2, left lateral view of left valve, P6M3758, sample 11CHAO164; C, Kirkbya sp. 3, left lateral view of left valve, P6M3759, sample 11CHAO166; D, Kirkbya sp. 4, left lateral view of left valve, P6M3760, sample 11CHAO158; E, Kirkbya sp. 5, left lateral view of left valve, P6M3776, sample 11CHAO88; F, G, Reviya cf. subsompongensis Chitnarin, 2008; F, right lateral view of right valve, P6M3762, sample 11CHAO167; G, right lateral view of right valve, P6M3763, sample 11CHAO166; H, Neoamphissites sp. 1, left lateral view of left valve, P6M3764, sample 11CHAO169; I, J, Kegelites sp. 1; I, left lateral view of complete carapace, P6M3765, sample 11CHAO81; J, left lateral view of complete carapace, P6M3766, sample 11CHAO99; K, L, Kindlella sp. 1; K, right lateral view of complete carapace, P6M3767, sample 11CHAO150...
FIG. 15. — Ostracods from Guadalupian in South China: A, B, Geffenina posterodorsospina? Chitnari... more FIG. 15. — Ostracods from Guadalupian in South China: A, B, Geffenina posterodorsospina? Chitnarin, 2012; A, left lateral view of complete carapace, P6M3742, 11CHAO80; B, right lateral view of complete carapace, P6M3743, 11CHAO80; C, Knoxitidae sp. 1, right lateral view of complete carapace, P6M3744, sample 11CHAO171; D, Knoxiella sp. 1, right lateral view of complete carapace, P6M3745, sample 11CHAO156; E, F, Knoxiella sp. 2; E, left lateral view of complete carapace, P6M3746, sample 11CHAO80; F, right sublateral view of complete carapace, P6M3747, sample 11CHAO80; G, Permoyoungiella? sp. 1, right lateral view of right valve, P6M3748, sample 11CHAO172; H, Kirkbyoidea sp. 1, left lateral view of left valve, P6M3749, sample 11CHAO166; I, Kirkbyoidea sp. 2, left lateral view of left valve, P6M3750, sample 11CHAO168; J, Kirkbyoidea sp. 3, right lateral view of right valve, P6M3751, sample 11CHAO167; K, L, Roundyella? sp. 1; K, left lateral view of left valve, P6M3752, sample 11CHAO168;...
FIG. 13. — Ostracods from Guadalupian-Lopingian boundary interval in South China: A, Silenites? s... more FIG. 13. — Ostracods from Guadalupian-Lopingian boundary interval in South China: A, Silenites? sp. 1, right lateral view, P6M3714, sample 11CHAO173; B, Silenites? sp. 2, right lateral view, P6M3715, sample 11CHAO172; C, Silenites? sp. 3, right lateral view, P6M3716, sample 11CHAO97; D, Silenites? sp. 4, right lateral view, P6M3717, sample 11CHAO87; E, Silenites? sp. 5, right lateral view, P6M3718, sample 11CHAO91; F, Silenites? sp. 6, right lateral view, P6M3719, sample 11CHAO95; G, Waylandella sp. 1, right lateral view, P6M3720, sample 11CHAO165; H, Basslerella sp. 1, left lateral view, P6M3721, sample 11CHAO173; I, Basslerella sp. 2, left lateral view, P6M3722, sample 11CHAO173; J, Basslerella sp. 3, right lateral view, P6M3723, sample 11CHAO173; K, Basslerella? sp. 4, left lateral view, P6M3724, sample 11CHAO171; L, Basslerella sp. 5, right lateral view, P6M3725, sample 11CHAO171; M, Basslerella sp. 6, right lateral view, P6M3726, sample 11CHAO171; N, Basslerella sp. 7, right la...
The Early Jurassic was characterized by major climatic and environmental perturbations which can ... more The Early Jurassic was characterized by major climatic and environmental perturbations which can be seen preserved at high resolution on orbital timescales. The Early Jurassic is a period of overall global warmth, and therefore serves as a suitable modern-day analogue to understand changes in the Earth System. Presently, Earth’s climate is warming and the frequency of large wildfires appears to be increasing. Recent research has indicated that Quaternary deposits reveal that wildfires respond to orbital forcings; however, to date no study has been able to test whether wildfire activity corresponds to changes over Milankovitch timescales in the deep past. A high-resolution astrochronology exists for the Upper Pliensbachian in the Llanbedr (Mochras Farm) borehole (NW Wales). Ruhl et al. (2016) show that elemental concentration recorded by hand-held X-ray fluorescence (XRF), changes mainly at periodicities of ~21,000 year, ~100,000 year and ~400,000 year, and which can be related to vi...
Basin Research, 2018
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2017
High-resolution clay mineralogical investigations were conducted on the Permian-Triassic (P-Tr) c... more High-resolution clay mineralogical investigations were conducted on the Permian-Triassic (P-Tr) carbonate-and siliceous rocks from the Shangsi section, South China. The clay mineralogy is dominated by illite and illite/smectite mixed-layers (I/S) throughout the sampled section with subordinate chlorite and vermiculite emerging from bed 24 (approaching the End-Permian mass extinction horizon-EPME) onwards. Positive correlations of clay fraction with mainly land-derived TiO 2 and magnetic susceptibility (MS) indicate a primary continental origin of the clay minerals. Rock-Eval pyrolysis analysis, palynomorph coloration, Scanning electron microscope(SEM) and Transmission Electron Microscope(TEM) observations, all suggest that the rocks experienced thermal diagenesis which mainly promotes illitization processes of smectite clay minerals while
Geologische Rundschau, 1995
An interdisciplinary approach based on highresolution physical stratigraphy, biostratigraphy, org... more An interdisciplinary approach based on highresolution physical stratigraphy, biostratigraphy, organic matter analysis and clay mineralogy has been applied to the mixed siliciclastic/carbonate Kimmeridgian/ Tithonian deposits of the Boulonnais (north-western France). These rocks are the age-equivalents of some of the offshore marine source rocks of the North Sea and were deposited in an overall storm-dominated homoclinal ramp setting which may represent one of the most shore-proximal sediments of this age cropping out in northwestern Europe. Comparison with data from the Yorkshire, Dorset, Lorraine and Aquitaine areas allows the discrimination of three major transgressiveregressive sediment packages with disconformities of interregional extent: (1) from the Baylei Zone to top Eudoxus Zone; (2) from the Autissiodorensis Zone to base Scitulus Zone; (3) from the upper Scitulus Zone to the Pectinatus Zone. The lower two regionally correlative disconformities correspond to the sequence boundaries at the top of the Eudoxus Zone and the top of the Autissiodorensis Zone, formed by high-frequency relative sea-level variations during the periods of maximum transgression of the platform. The latter disconfortuity (the P1 nodule bed) reflects a major tectonically induced reorganization of the northwest European intrashelf sedimentary basin, characterized by a shift in both the location of the main depocentre and the sources of sediment production.
Bulletin de la Société Géologique de France, 2007
On the eastern edge of the Aquitaine Basin, the Lias-Dogger transition and the events, which occu... more On the eastern edge of the Aquitaine Basin, the Lias-Dogger transition and the events, which occurred during this time interval are studied in the Quercy sedimentary basin. Stratigraphic correlations are proposed using a biochronological calibration based on the determination of numerous ammonites and brachiopods. Facies analyses using statistical processing integrate the presence of faults and tectonic compartments and lead to reconstruction of palaeoenvironments in space and time. The paper includes the description of system tracts following Haq et al. [1987] and Vail et al. [1991], and twelve palaeogeographic maps of the area studied. The objectives are to distinguish the various allocyclic and autocyclic factors controlling sedimentation and to show the impact of the Mid-Cimmerian tectonic event on the evolution of the basin.
Journal of Sedimentary Research, 2010
Examination of petrophysical properties (acoustic velocity, porosity, permeability, and density) ... more Examination of petrophysical properties (acoustic velocity, porosity, permeability, and density) and petrographical characteristics (texture, facies composition, and diagenesis) of more than 250 core plugs from the Middle Jurassic carbonates of the eastern Paris Basin provides insights into the parameters controlling acoustic velocities in relatively low-porosity carbonate rocks (W , 20%). The pore-type observations reveal distinct acoustic velocities in samples with intergranular macropores and samples with micropores in subhedral micrite, such that velocities in microporous mudstonewackestone (lagoonal) deposits are greater than in macroporous grainstone (shoal) samples, at a given porosity range (15-20%). The standard Wyllie and Raymer transforms fit very well with the linear regression between acoustic velocity and porosity from mudstone or lagoonal facies. Marls and fine-grained deposits interpreted as lagoonal facies include statistically significant correlation (r = 0.9) between velocity and porosity. However, the data suggest that the wide scatter in velocityporosity relationship from grainstones are not the result of different sorting, grain size, pore type, dolomite content, or clay content. Instead, early cementation greatly influences acoustic properties during diagenesis, and are interpreted to account for the high variability of velocities over a given porosity range. Specifically, at a given porosity, acoustic velocities in compacted grainstone that did not undergo early cementation are higher than in early-cemented grainstone. Petrographic observations suggest that early cementation limits mechanical compaction, creating a heterogeneous medium from the earliest stages of diagenesis (non-touching grains, preservation of intergranular macropores that are partially to totally filled by later blocky calcite cement). The abundant interfaces between micritized ooids, early cement fringes, and blocky calcites in grainstones may induce significant wave attenuation. As a result, the standard time-average equations fail to predict the effect of diagenetic features such as early cementation on sonic velocity. Conversely, an absence of early cementation favors mechanical compaction, grain-to-grain contact, and suturing. The result is a homogeneous micritized grainsupported network that may facilitate wave propagation. Through demonstration of the key role of early cementation in the explanation of variability in acoustic properties, the results of this study illustrate the complicated factors influencing velocity transforms in carbonates (Wyllie and Raymer), i.e., classical tools for predicting reservoir properties. These insights on the interpretation of Vp and the refinement of velocityporosity transforms in grainstone units may be broadly applicable to enhancing seismic-based exploration in carbonate successions.
... Le stockage de déchets radioactifs en couches géologiques profondes. Benjamin Brigaud ( Auteu... more ... Le stockage de déchets radioactifs en couches géologiques profondes. Benjamin Brigaud ( Auteur correspondant. ) 1 , Jean-François Deconinck 1 , Christophe Durlet 1 , Pierre Pellenard 1 , Jacques Thierry 1 , Alain Trouiller, Benoît Vincent 2. (2009). ...
Proceedings of the Ocean Drilling Program, 150 Scientific Results, 1996
Tektite-bearing sediment was recovered from the New Jersey continental slope (1123 m water depth)... more Tektite-bearing sediment was recovered from the New Jersey continental slope (1123 m water depth) by the Ocean Drilling Program (ODP) at Site 904. The biostratigraphy, mineralogy, and geochemistry of Site 904 tektites and enclosing sediment permit us to interpret their source and the sequence of events that led to their deposition. The tektites of Site 904 occur within upper Eocene (Zones P15, NP19/20) biosiliceous chalks. The tektites are concentrated in three well-defined laminae that occur in a 5-cm-thick section (Interval 150-904A-45X-2, 84.5-89.5 cm). Tektites are abundant between the laminae and occur sporadically, above and below the layers, through a 24-cm-thick section (Interval 150-904A-45X-2, 79-103 cm). Small-sized tektites (<63 µm) occur rarely above the 24-cm-thick interval for another 19 cm (Interval 150-904A-45X-2, 60-79 cm). Grain-size distribution indicates that the tektites and associated detrital minerals fine upward. The coarse-grained fractions occur in the bottom and middle laminae and the fine-grained fractions are concentrated in the upper lamina. Because benthic foraminifer assemblages are bathyal, turbidity currents originating in shallow water could not have deposited the tektites and detrital minerals. The abundance of planktonic versus benthic foraminifers also argues against displacement of sediment from shallow water. Site 904 tektites, as at Deep Sea Drilling Project (DSDP) Site 612, are associated with shock metamorphosed minerals and are considered to be an impact ejecta. Gravity settling of the ejecta through the air and the water column is the proposed depositional process. The structures and deformation features contained in the sediment that yielded the tektites indicate that deposition of the ejecta on the New Jersey continental slope was influenced by mass-wasting and gravity-flow processes. These processes are interpreted to have occurred as a result of disturbances to the seafloor and water column by tsunami and possibly shock-generated waves. Biostratigraphic and major oxide analyses correlate the upper Eocene tektites of Site 904 to those of Site 612, to the Exmore breccia at Exmore, Virginia, and to the North American strewn field. The range in the major oxide composition suggest that the tektites originated from a single but heterogeneous source.
Clay Minerals, 1988
The clay-mineralogical assemblages of Purbeckian carbonate sediments of the Swiss and French Jura... more The clay-mineralogical assemblages of Purbeckian carbonate sediments of the Swiss and French Jura Mountains are often composed of illite and interstratified illite-smectite. These illitic minerals occur mainly in thin layers of green marls which show evidence of subaerial exposure and mark the top of shallowing-upward sequences. X-ray diffraction, chemical and thermal analyses coupled with transmission electron microscopy suggest that the Purbeckian illitic minerals replaced smectite in intermediate continental-marine environments. The transition from smectite to illite and interstratified illite-smectite probably resulted from repeated cycles of wetting by marine waters and subsequent drying in hypersaline environments, under a hot Purbeckian climate.
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Papers by Jean-françois Deconinck