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See detailVariations in stratigraphic and reservoir properties adjacent to the Mid-Paleocene sequence boundary, Campo section, Pyrenees, Spain
Da Silva, Anne-Christine ULg; Loisy, Corinne; Cerepi, Adrian et al

in Sedimentary Geology (2009), 219

The Paleocene of the Campo section, Spain has different sedimentological characteristics above and below the Mid-Paleocene Unconformity. Beneath the unconformity sediments are dominated by evaporitic ... [more ▼]

The Paleocene of the Campo section, Spain has different sedimentological characteristics above and below the Mid-Paleocene Unconformity. Beneath the unconformity sediments are dominated by evaporitic carbonates and collapse breccias. Above it they are characterized by continental detrital beds alternating with paleosols. Different subaerial features are observed and correspond to different porosity values, pore–throat sizes and micrite morphologies. Unexposed or intertidal facies have low porosity, low throat–pore size (mesoporosity) and well preserved rhombic crystals. Intermediate exposed facies (paleosols) possess medium porosity, medium pore–throat size (microporosity) and mainly micro-rhombic crystals. Finally, the facies corresponding to high exposure intensity and to evaporitic original facies presents high porosity, permeability, large pore–throat size and rounded micritic crystals. These observations show that the emersion phase caused important dissolution, especially when associated with an easily dissolved original lithofacies. [less ▲]

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See detailMagnetic susceptibility evolution and sedimentary environments on carbonate platform sediments and atolls, comparison of the Frasnian from Belgium and Alberta, Canada
Da Silva, Anne-Christine ULg; Potma, Ken; Weissenberger, John A. W. et al

in Sedimentary Geology (2009), 214

Magnetic susceptibility (MS) measurements on carbonate rocks are considered as a proxy for impurities delivered to the carbonate environments. In the absence of strong climatic or tectonic variations ... [more ▼]

Magnetic susceptibility (MS) measurements on carbonate rocks are considered as a proxy for impurities delivered to the carbonate environments. In the absence of strong climatic or tectonic variations, bulk MS values have been linked to sea level variations, because sea-level fall increases clastic supply and therefore increases magnetic mineral deposition. In this paper we explore the relationship between the average magnitude of bulk MS, with shallowing-up sequences and facies evolution in different Devonian carbonate complexes. Similarities and differences between these parameters have been scrutinized in carbonate attached platform and detached platforms (mounds and/or atolls) from Belgium and Canada. In the carbonate attached platforms from Belgium and Canada, the MS patterns are directly related to depositional environment. Mean MS values increase from the most distal towards the most proximal facies and towards the top of the majority of fourth-order shallowing-up sequences. These trends are in agreement with theoretical background (MS increases with regression). In the Belgian detached platform, the average MS pattern generally shows an opposite behaviour of that observed in the attached carbonate platforms. Average MS decreases towards the most proximal facies and towards the top of a majority of the fourth-order shallowing-up sequences. This behaviour can be explained by the influence of sedimentary rate and water agitation during deposition. A high sedimentary rate will dilute the magnetic minerals in the atoll facies and the highwater agitation during deposition may be expected to have prevented the deposition of the magnetic grains. So, the combination of these two effects will result in the observed low values in the atoll crown and lagoonal facies. In the Canadian detached platform, MS is mainly negative. This means that the limestones are very pure. The technique does not appear to be appropriate in these rocks. The variations of average MS behaviour by platform type can imply difficulties in correlating carbonates from different settings. A comparison of time equivalent mound and platform deposits shows that after an important regressive surface, the MS values are increasing for the platform deposits and decreasing for the mound. So MS evolution can be in complete opposition (caused by highly different sedimentary rates) in different depositional settings. The MS signal preserved in carbonate rocks is probably mainly related to 1) varying clastic supplies; 2) varying carbonate accumulation rates (dilution of the magnetic minerals by high carbonate production) and 3) potentially diagenesis. [less ▲]

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See detailMineralogical signatures of Lake Baikal sediments: Sources of sediment supplies through Late Quaternary
Fagel, Nathalie ULg; Thamo-Bozso, Edith; Heim, Birgit

in Sedimentary Geology (2007), 194(1-2), 37-59

The mineralogical composition of Late Quaternary sediments was investigated in three piston cores recovered on elevated plateaus in Lake Baikal: on Continent Ridge, a northern extension of Academician ... [more ▼]

The mineralogical composition of Late Quaternary sediments was investigated in three piston cores recovered on elevated plateaus in Lake Baikal: on Continent Ridge, a northern extension of Academician Ridge in the North Basin; on the Posolsky Bank near the Selenga Delta; and on the Vydrino Shoulder in the South Basin. The sediments are alternating biogenic diatom-rich muds and terrigenous silty clays, with sandy layers occurring in the southern (Vydrino) core. Core stratigraphy is based on AMS C-14 dates on pollen, diatom zonation, and magnetic record correlation: the 6-10 m long cores cover the last similar to 40 kyr in Vydrino, similar to 60 kyr in Posolsky and similar to 185 kyr in Continent Ridge. The bulk, clay (< 2 mu m) and sand (63-200 mu m) mineral signatures are compared with the mineralogical assemblages identified in river sediments and rocks sampled in the Selenga watershed and surface sediments collected in the various sub-basins. Spatial variability in the bulk mineral signature mainly reflects the sediment location relative to the lake margin. The complex clay mineral assemblages are more distinctive in terms of source-area. The clay signature of Vydrino core differs from the two other sites, in its high illite content. The Posolsky assemblage is consistent with the Selenga River clay mineral signature. The Continent Ridge clay assemblage is highly variable, reflecting mixing of several sources including a more proximal contribution than the Barguzin or even the Selenga tributaries. The similar homblende-dominated heavy mineral compositions of the Continent Ridge and Posolsky Bank sediments reflect the homogenous granitoid signature of the watersheds of the eastern side of Lake Baikal. In contrast, in the Southern Basin, the sediments from Vydrino Shoulder are mica-dominated, recording local sedimentary and metamorphic detritus supplies by numerous small rivers. Besides the control of sediment supply by the Selenga River, our data emphasize the significant influences of the Lake Baikal coastal margins in South and North Basin. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

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See detailImpregnation method for detecting annual laminations in sediment cores: An overview
Boes, Xavier; Fagel, Nathalie ULg

in Sedimentary Geology (2005), 179(3-4), 185-194

Annually laminated sediments can provide an absolute time scale (by varve counting) and a high-resolution palaeoclimate information (from varve thickness). Both types of information may be directly ... [more ▼]

Annually laminated sediments can provide an absolute time scale (by varve counting) and a high-resolution palaeoclimate information (from varve thickness). Both types of information may be directly measured from sediment core surfaces. In this paper, we stress that varve counting and varve thickness measurements derived from fresh core surfaces could not systematically reveal the internal sedimentary structure, even if assisted by high resolution image analysis. We present an example of a homogeneous sediment core for which the varves were only observable after core impregnation and polishing steps. Because the impregnation methods are not yet standardized, the aim of this paper is to give an updated review of the methodology. In this review, we present the major critical points during impregnation steps. In particular, we focus on all of the post-treatment sediment disturbances that can alter the laminated micro-structure and, consequently, varve measurements. Finally, we propose a modified impregnation protocol, especially adapted for tracking varved intervals in long cores. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailFacies architecture and diagenesis of Belgian Late Frasnian carbonate mounds
Boulvain, Frédéric ULg

in Sedimentary Geology (2001), 145(3-4), 269-294

Late Frasnian Petit-Mont Member carbonate mounds occur in the southern pail of the Dinant Synclinorium and in the Philippeville Anticline (SW Belgium). These mounds are 30 to 80 m thick and 100 to 250 m ... [more ▼]

Late Frasnian Petit-Mont Member carbonate mounds occur in the southern pail of the Dinant Synclinorium and in the Philippeville Anticline (SW Belgium). These mounds are 30 to 80 m thick and 100 to 250 m in diameter. They are embedded in shale, nodular shale and argillaceous limestone. Based on facies mapping of 14 buildups and related off-mound sediments, these mounds typically started from below the photic and storm wave base zones and builtup into shallow water environments. Above an argillaceous limestone substrate, the first carbonate mound facies consists of spiculitic wackestone with stromatactis (PM1), which becomes progressively enriched in crinoids and corals (PM2), then in peloids, stromatoporoids and cyanobacteria (PM3). PM4 consists of algal-coral-peloid wackestone and packstone with green algae and thick algal coatings, A core of algal and microbial bindstone (PM5) sporadically occurs within large mounds. The uppermost part of these mounds may show a recurrence of facies PM2 and PM1. PM1 to PM3 are coloured red by hematite derived from microaerophilic iron bacteria; PM4 and PM5 are grey. The transition from the aphotic to the cyanobacterial photic zone is recorded in the succession PM2-PM3; the transition from the cyanobacterial to the green algal photic zone is recorded by PM3-PM5. Storm wave base was reached within PM3 and fair-weather wave base within PM5. This paleobathymetric interpretation suggests a depth of 100-150 in during initial establishment of PM1. Three types of mounds can be distinguished on the basis of geometry and facies architecture: (1) "Les Bulants"-type mounds display a continuous vertical facies succession (PM2-3-4-5) and low relief, (2) although exhibiting the same facies succession as "Les Bulants", "Les Wayons"-type mounds show a distinct relief with steep flanks and bioclastic talus; (3) "St.-Remy" mounds consist exclusively of PM1 and PM2, bioclastic flank deposits are not observed. From (1) to (3), these mound types represent successive deepening down a ramp. Biostratigraphic correlation on a regional scale provides good evidence that relative sea-level changes largely controlled lateral and vertical transitions of facies. Beyond that, hypoxic conditions are indicated by the sponge and iron-bacteria consortium in lower parts of the mounds. This is in agreement with the general assumption of stratified water masses during Late Frasnian, preceding the prominent Lower Kellwasser crisis. Cementation began with a radiaxial synsedimentary cement. A fringe of meteoric phreatic cement, initially nonluminescent, then with a bright orange luminescence, occurs in all mounds. It is contemporaneous with a nonluminescent pervasive cement of grainstones deposited in littoral areas. Differentiation between the (reducing) mounds and the (oxidizing) littoral area resulted from better aquifer circulation in sedimentary bodies close to the recharge area. Late burial cements occlude all the remaining porosity and are contemporaneous with the opening of the Variscan fracture system. (C) 2001 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailIron bacterial and fungal mats, Bajocian stratotype (Mid-Jurassic, northern Normandy, France)
Préat; Mamet, B.; De Ridder, C. et al

in Sedimentary Geology (2001), 137

The Oolithe ferrugineuse de Bayeux Formation is located at the historical Bajocian stratotype of Sainte-Honorine-des-Pertes, north of Bayeux, Normandy. The condensed formation ranges from the base of the ... [more ▼]

The Oolithe ferrugineuse de Bayeux Formation is located at the historical Bajocian stratotype of Sainte-Honorine-des-Pertes, north of Bayeux, Normandy. The condensed formation ranges from the base of the Humphriesianum Zone to the Parkinsoni Zone and is divided into four beds of decimetric scale. Three main microfacies are present: (1) oncoid rudstones, (2) ooid bioclastic packstones and (3) silty burrowed wackestones/ packstones. Sedimentation took place in a very quiet environment, below the photic zone and below or near the storm wave base. The general setting is a distal carbonate ramp, its lower part characterized by hemipelagic sedimentation indicated by the presence of planktonic foraminifers. The inferred depth is around 100 m. Free oxygen concentration was low. Dysaerobic conditions are indicated by a scarcity of benthic macrofauna. Ferruginous structures are numerous in the first two microfacies, and absent in the last. Hematite staining is not uniform and follows many sedimentary patterns. Among the more widespread Fe structures are perforation infillings with endolithic microorganisms, microstromatolites, oncoids, ooids, blisters, coatings and hardgrounds. These structures can be associated and none are mutually exclusive. Hematite-coated filaments of different sizes and shapes are observed in the micrite matrix: the walls of various organisms; the calcite crystals associated with the Fe cortical laminations; the perforations and burrow; the hardgrounds; and microstromatolites. Petrographical and SEM examinations suggest that the laminated crusts (oncoids and hardgrounds) are formed by microbial iron mats dominated by filamentous bacteria and fungi. Seven types of microbes are recognized: filaments (five morphotypes), spheroidal bodies and stalked bodies. Filamentous microfossils of type 1 to 4 resemble the present-day filamentous bacteria (Beggiatoales and Cytophagaceae). Because of their large diameter and their branching nature, filaments of type 5 are possibly filamentous fungi. Another argument in favor of fungi is the presence of stalked and spheroidal bodies that resemble zoosporangia and oogonia of some Oomycota. In deep, calm and dysaerobic waters, many interfaces (e.g. between aerobic and dysaerobic waters) are present in the sediments. The stability of the soluble reduced state of iron (Fe2+) is higher at such interfaces, and many ferric iron-encrusted microbial fossils are observed. Iron could thus serve as an electron donor for microbial iron-oxidation processes. Other microbial iron deposition pathways are also possible. It appears that, regardless of geological age (Paleozoic, Mesozoic) and geographical location, the same microbiological mechanisms are probably responsible for the red color in calcareous stratified or unstratified bodies. The presence of fossilized iron-encrusted bacteria and fungi at interfaces may therefore serve as an indicator of anoxic to dysaerobic conditions in various paleo(micro)environments. [less ▲]

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See detailCLAY SEDIMENTATION IN THE JAPAN SEA SINCE THE EARLY MIOCENE - INFLUENCE OF SOURCE-ROCK AND HYDROTHERMAL ACTIVITY
Fagel, Nathalie ULg; André, Luc; CHAMLEY, H. et al

in Sedimentary Geology (1992), 80(1-2), 27-40

X-ray diffraction analyses have been carried out on 128 samples of Miocene to Quaternary sediments from ODP Sites 794, 795 and 797. Some clay fractions of samples from Site 797 have also been studied for ... [more ▼]

X-ray diffraction analyses have been carried out on 128 samples of Miocene to Quaternary sediments from ODP Sites 794, 795 and 797. Some clay fractions of samples from Site 797 have also been studied for rare earth elements and by Nd isotopic analyses. These three sites display similar lithological and clay assemblages (with dominant chlorite, illite and smectite) showing that the sedimentation was homogeneous throughout the whole Japan Sea Basin. Three mineralogical zones are recognized. The first zone (Lower Miocene sandy clay of Sites 794 and 797) is mainly composed of chlorite resulting from hydrothermal transformation of arc-derived smectite, due to sill injections during the initial oceanic spreading stage. The second zone (Lower Miocene to Lower Pliocene siliceous claystone and diatomaceous silty clay) is dominated by arc-derived smectite; the abundance of this mineral decreases upwards while illite and chlorite increase. This trend reflects a change of detrital source, from an eastern arc-derived source (epsilon(Nd)t > -3.3; variable LREE enrichment) to a western continental crust source (epsilon(Nd)t < -9.4; shale-like REE patterns); climatic modifications in the current dynamics are proposed as a cause for this change. The third zone (Upper Pliocene to Recent silty clay with minor diatom oozes) is characterized at Site 797 by increasing amounts of illite and chlorite. This reflects a more and more important western supply which is assumed to be related to tectonic rejuvenations of the Asian margin or climatic modifications affecting the alteration conditions or the current dynamics. At Sites 794 and 795, the more or less sharp supply of chlorite seems to be driven by the incipient subduction zone on the eastern margin of the Japan Sea. [less ▲]

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See detailPre-Permian sedimentation in NW Europe.
Bless, M.J.M.; Bouckaert, J; Conil, R et al

in Sedimentary Geology (1980), 27(1), 1-81

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