Fabrice Malartre

Ground penetrating radar application in a shallow marine Oxfordian limestone sequence located on the eastern flank of the Paris Basin, NE France

Abstract A Ground Penetrating Radar (GPR) survey has been carried out in Upper Jurassic limestones located on the eastern flank of the Paris Basin (NE France). The potential of the investigation method is assessed for delineating geologically meaningful stratifications in the shallow subsurface. The fundamentals of the GPR technique are described. Penetration depth and vertical resolution depends on the soil conditions, the characteristics of input signal and the configuration of the transmitter–receiver assembly. In the studied carbonates the penetration level is rather good and the electromagnetic signal reaches up to 1000 nanoseconds maximum (i.e. approximately 55 m). Several depositional units are outlined on the GPR profiles. Six different lithological units are recognised with distinct GPR reflection characteristics. The profiles illustrate the internal 3D organisation of the carbonate platform and its geometry. They provide detailed insight into the nature of an Oxfordian reefal build-up. The high-resolution subsurface model is directly calibrated with geological field observations and it results in a predictive 3D depositional working model. The GPR method is a non-destructive remote sensing technique that is cost effective. The method is considered complementary to other conventional high-resolution reservoir characterisation studies. It represents a powerful investigation tool in earth science studies concerning the imaging of the structure of the shallow subsurface.

Organic geochemistry in a sequence stratigraphic framework. The siliciclastic shelf environment of Cretaceous series, SE France

For a better understanding of siliciclastic shelf environments, correlation between sequence stratigraphy and organic geochemistry is used. Our study is focused on the Cretaceous deposits of Marcoule (Gard, France), particularly on a close-packed siltites layer (200-400 m thick), which is well characterized as a marine flooding facies of a single trangressive-regressive cycle. During the Uppermost Albian and the Lower Cenomanian, the stratigraphic data indicate a change in the depositional environment from offshore to shoreface. Organic geochemistry is used in order to characterize origin and variability of the organic matter in relation to the stratigraphic data. The study is carried out on core samples from 2 drill holes (MAR 203 and MAR 501). Analyses of the aliphatic and aromatic hydrocarbons were performed using GC-MS and focused on biomarker distributions. The biomarkers indicate a contribution of mixed terrestrial and marine organic matter. The changes in molecular signatures are related to variations in the source of organic matter (marine versus terrestrial), preservation conditions (largely influenced by clay and early diagenesis), environmental oxidation-reduction and acidic conditions as well as bioturbation. Various environmental zones, characterized by different molecular signatures, can be distinguished. Resin derived biomarkers can be assigned to higher plant material input and may reflect the evolution and diversity of Gymnospermae versus Angiospermae during the transgressive/regressive cycle. The relative sea-level variations are clearly correlated with the nature and the preservation of the organic matter. For example, the Pr/Ph and Pr/n-C 17 ratios as well as the regular steranes distributions underline the maximum flooding surface evidenced by other studies. We observe a good correlation between the organic data and sequence stratigraphy: changes in geochemical signatures reflect the 3rd order depositional cycles.

Paleoenvironments, paleoclimates and sequences of Westphalian deposits of Lorraine coal basin (Upper Carboniferous, NE France)

Facies and sequences of the Westphalian C are identified in cores and well logs of three boreholes and three seismic lines supplied by Conoco-Phillips from the Lorraine coal Basin. The lithofacies associations suggest various paleoenvironments and sequences during the Westphalian C. Decameter-thick sedimentary bodies display alluvial fan deposits in the northwestern border of the basin (Chaumont borehole). Decametric sedimentary bodies constituted either of conglomeratic and sandy facies with cylindrical shape in well logs represent braided river deposits, or alternations of fining and coarsening upward sequences with sandy, silty and clayey facies with bell and funnel shapes in well log correspond to meander river and lacustrine deltaic deposits in the Saulcy and Lorettes boreholes. Three fining upward third order sequences in the center of the basin in the Lorettes and Saulcy boreholes represent a period 1 with braided river deposits, a period 2 with flood plain, lake and meandering river deposits and a period 3 with anastomosed or meandering river deposits.nnPeriod 1 is correlated with a subsidence period in the basin and uplift of the borders, period 2 with the maximum fresh water flooding period with flood plain or lake deposits and period 3 with the filling period.nnThe seismic profiles of Conoco-Phillips confirm the tectonic structures described by previous authors in Lorraine Basin. We agree that this basin was a strike-slip basin as demonstrated by previous authors with depocenters near the South Hunsruck and Metz faults from the Westphalian to the Permian. Biomarkers show that paleoclimate changes (wet/dry) of weak amplitude in the equatorial climate could also modify the sedimentation of this basin and act on sequences of second order.

Interactions climat-eustatisme-tectonique. Les enseignements et perspectives du Crétacé supérieur (Cénomanien-Coniacien)

Abstract A recent detailed analysis of southeastern France upper Cretaceous series has evidenced that Cenomanian-Turonian and Turonian-Coniacian boundaries are marked by quick and large amplitude relative sea level changes. Comparisons with other sections in different worldwide basins are coincident with the observations pointed out in southeast France. We establish: (1) high-frequency synchronous events in different geodynamic settings, (2) the superposition of various hierarchically eustatic cycles i.e. the superimposition of high-frequency oscillations on a third-order trend. Two possible mechanisms responsible of these observations are emphasized and discussed: glacio-eustasy versus high-frequency tectonics.

Palynofacies of marginal marine deposits: the rhaetian of the east margin of the Massif Central (France)

Abstract The methodology presented concerns the definition of palynofacies. It develops 3 procedure stages based on multivariate analyses: 1 — define the palynomaceral facies, 2 — define and compare palynomorph facies with palynomaceral facies and 3 — exploit the two precedent categories of facies. The study deals with Rhaetian sedimentary cycles corresponding to the western limit boundary of the southeastern France intracratonic basin. Rhaetian strata are representative of paralic depositional environments, overlying Triassic fluvial deposits. On the palynomaceral sequence, that is revealed by multivariate analyses, the most buoyant particles are the needle-like phytoclasts. Crevasse splays, dewatering, drowned soils and restricted wave-influenced deposit facies yield them. The less buoyant particles are the black massive or polygonal phytoclasts. They were produced by crevasses, deltaic shales, distributary channels, palaeosoils, sheet-floods, shoals and shoreface facies. The bisaccate pollen Ovalipollis and the nonsaccate pollen Circumpolles are associated with needle-like particles. They are linked to deltaic shales, restricted deposits sheet-floods, shoal, shoreface and storm facies. The marine element Dapcodinium is not related to a particular palynomaceral type but could be compared to the lowest buoyant phytoclast. Deltaic plain and back-shoal lagoonal facies favour the concentration of Dapcodinium . The distribution of the small size dinoflagellate cysts ( Dapcodinium ) and large size dinoflagellate cysts ( Rhaetogonyaulax ) emphasizes the role of the size in the floatation competence. Base level-rises and highs are marked by amalgamated bioclastic deposits, fluvial channel fills, mixed siliciclastic-bioclastic amalgamated shoals, storm deposits or ravinement surfaces. Needle-like particles, Ovalipollis and Circumpolles are associated to these deposits. Base level-falls are represented by crevasse splay deposits, fluvial stream incisions, non-incising fluvial channels, sheet flood and stacked palaeosol facies. Black roundish or equidimensional translucent phytoclasts, Rhaetogonyaulax , short-spine Micrhystridium (acritarch) and smooth-walled spores are associated with these facies. In addition to to the energy factor, the water depth constrains both phytoclast and palynomorph sedimentation.

Palynofacies variations in a carbonate ramp system environment (Upper Muschelkalk, NE France)

This study analyses variations in the size of black woody phytoclast and palynofacies types of shallow subtidal environments evolving to deeper subtidal environments, of latest Illyrdian-latest Fassanian age (Upper Muschelkalk). Some of the results display some discrepancies between elevated particle sizes that were supposedly deposited in a relative proximal source and the rich veryhachid palynofacies that are thought to represent distal marine environments. A case study of the succession in the Heming quarry, located in the Alsace-Lorraine trough (southwestern part of the intracratonic Germanic basin) reveals that : (1) the palynological assemblages are dominated by acritarchs belonging to micrhystridids, disaccate pollen and woody phytoclasts; (2) the abundance of phytoclasts, sporomorphs and marine groups is not correlated with lithologies; (3) the length of the processes of micrhystridids is not a useful parameter in defining palynofacies types. In carbonate ramp environments, many factors could have confused the palynological signals such as high-energy events and the water level on which the nutrient supply depended pro parte. All these factors seem to have been governed by climatic or tectono-eustatic events.

Reconstruction of outer shelf paleoenvironments in the Turonian–Coniacian of Southeast France (micropaleontology – sedimentology:: local and global controlling factors

Abstract Micropaleontological analysis and sedimentological studies were undertaken on the Turonian to the Coniacian strata of the western part of the Vocontian Basin near Nyons, Southeast France, in order to understand the evolution of paleoenvironments. Microfacies examination shows an alternation of two types of deposits: (1) sediments dominated by abundant sponge spicules, echinoderm fragments and quartz packstones–wackestones, suggesting a shallow water environment, and (2) sediments dominated by abundant calcispheres and planktic foraminifera, providing evidence of a deeper water environment. The biostratigraphy is based on a systematic analysis of planktic foraminifera (about 50 taxa). The first appearance of Dicarinella primitiva , associated with Marginotruncana tarfayaensis and Marginotruncana sinuosa , indicates the beginning of the Coniacian. Ostracoda corroborate the Coniacian age given by planktic foraminifera. Amongst the benthic foraminifera, Nodosariidae, Verneuilinidae and Eggerellidae are the most common families represented by the fauna. The qualitative and quantitative changes of benthic and planktic foraminifera population parameters provide precise information about the paleoenvironmental conditions (paleobathymetry, sediment composition, dissolved oxygen). The biological system reflects high-frequency sea level fluctuations. A possible glacially and/or tectonically induced mechanism is discussed in order to explain this kind of variations.