Namurian

Carboniferous rocks had a great impact on the landscape and industrialisation of western Europe, hence a distinction between ‘Carboniferous limestone’ and ‘Coal Measures’ since the dawn of geological science. André Dumont (1852) and Omalius d’Halloy (1853) already distinguished a ‘Houiller sans houille’ (Coal Measures without coal), subsequently named ‘Namurian’ by Purves in 1883. Whereas the lower boundary was quite clear – the quick transition from carbonates to siliciclastics – the boundary of the Namurian with the overlying coal-rich Coal Measures was subject to different interpretations and miscorrelations. International status of the Namurian as a chronostratigraphical stage was acquired in 1927 at the first International Carboniferous Congress, as part of a general classification scheme for the West European Carboniferous. Boundaries were based on ammonoid biozonation, selected to coincide with major events affecting the regional lithological framework. The twofold subdivision of the Carboniferous, Dinantian - Silesian or Mississippian – Pennsylvanian Subsystems, has been a matter of debate since the second Carboniferous Congress in 1935. Dinantian and Silesian were ratified for the Lower and Upper Carboniferous in 1971 although the western European Upper Carboniferous was not considered very suitable for intercontinental correlation, due to its position in the Variscan closure zone of the Pangaea supercontinent. The definition in 1985 of a Mid-Carboniferous Boundary and GSSP at Arrow Canyon, Nevada paved the way to adoption of Mississippian and Pennsylvanian Subsystems for the Lower and Upper Carboniferous in 1999. As a consequence, the status of the Namurian stage has been reduced to a regional European Stage. This decision has also practical consequences as the Namurian straddles this Mid-Carboniferous Boundary. Actually, the time span for the Namurian is 326.4 – 315 Ma and the accepted GTS age for the Mid-Carboniferous boundary is 318.1 Ma. The lower part of the Namurian is equivalent to the Mississippian Serpukhovian stage, the upper part of the Namurian is equivalent to part of the Pennsylvanian Bashkirian stage. Application of the global time scale in western Europe is hindered, however, by poor correlation potential of the fossil record and by insufficient radiometric dating. Continued use of the Namurian stage is allowed, on condition that global equivalents are indicated, and that ambiguous terms such as Lower and Upper Carboniferous are avoided, except when related to historic concepts

Chokerian

The Chokier alum shales, exposed in the Meuse valley between Namur and Liège (Belgium), were defined by d’Omalius d’Halloy in 1853 as the lower unproductive unit of the Carboniferous coal measures. From this original concept, both a lithostratigraphic and a chronostratigraphic unit were defined. The Formation of Chokier returned to d’Omalius d’Halloy’s original ‘houiller sans houille’ concept (Paproth et al., 1983). The intermediate ‘assise de Chokier’ (Stainier, 1901) reflected a hybrid litho-bio construction by using synchronous marine incursions or goniatite bands for subdivision and basin-wide correlation. The ‘assise de Chokier’ became equivalent to the Namurian A, encompassing the Eumorphoceras and Homoceras goniatite zones, defined as the lower subdivision of the Namurian Stage at the first Carboniferous Congress in Heerlen, 1927. The Chokierian chronostratigraphic stage - with type section located in the UK - was defined by Hodson (1957), splitting the Sabdenian (or Homoceras) stage of Bisat (1928). The Chokierian formed a step in a coherent system of goniatite stages, whose applicability on regional, northwest European scale has not been questioned. The Chokierian received the status of an international faunal stage – necessarily as a substage to the Namurian - at the Sheffield Carboniferous Congress in 1967. Chokierian and Alportian are transitional stages in the faunal turnover that characterises the difference between the lower and upper Carboniferous. Following the definition of a Mid-Carboniferous Boundary GSSP in 1985 and acceptance of the Mississippian – Pennsylvanian as the basic subdivision of the Carboniferous, the Chokierian is used as a Regional Stage on current ICS Geological Time Scales. The Chokierian was initially correlated with the Misissippian Subsystem and Serpukhovian stage. Re-assessment of the duration of the Namurian substages and goniatite – conodont correlation suggest to shift the Chokierian to the Pennsylvanian Subsystem and Bashkirian Stage. Exact position of the Mid-Carboniferous Boundary is probably very near the base of the Chokierian. According to recommendation by SCCS, the preferred use of the Chokierian is as a European Substage of the Namurian

The 'Maagdentoren' of Zichem (Belgium) : damage assessment of ferruginous sandstone by X-ray tomography

The ferruginous sandstone of the gothic “Maagdentoren” is suffering from a specific biological deterioration process triggered by perforating activities of mason bees. The damage due to these perforations causes extensive loss of material, so that a durable conservation of such degraded stone blocs becomes questionable. In order to evaluate the conservation possibilities of stone blocs damaged by perforating mason bees, an investigation of the internal structure by means of X-ray tomography was carried out. This investigation revealed that the cumulative effect of the digging work by multiple generations of mason bees may result in networks of perforations. Bioturbated sandstones were found to be most suitable for attack by mason bees because of morphological and geometrical compatibility between the original layered burrowings by marine organisms and those by the mason bees. As a conclusion the conservation is not recommended of sandstone blocs for which the load bearing capacity is endangered by the branched and layered perforations

Stratigraphic interpretation of the Tohogne borehole (province de Luxembourg). Devonian - Carbinoferous transition

The Tohogne borehole section, from the Lower Tournaisian into the Upper Famennian, has a remarkable micropalaeontological content (conodonts, foraminifers, spores) which enabled a detailed subdivision of these strata. New data in biostratigraphy and systematic palaeontology and palaeogeographic implications are presented, as well as correlations with reference sections

Microfossils and depositional environment of late Dinantian carbonates at Heibaart (Northern Belgium)

The core intervals of five boreholes in the Dinantian carbonates of the Heibaart area in northern Belgium have been investigated on their microfossil contents and lithofacies. The foraminifers suggest an early Warnantian age. No conodonts have been recovered. Twenty-eight species of ostracodes are described, two of them being new : Bairdia robinsoni nov. sp. and Rectobairdia conili nov. sp. The carbonates consist of bioclastic wackestones, bioclastic-peloid grainstones and algal bindstones. The depositional environment varied from an open marine shelf lagoon in the earliest Warnantian (Cf 6a zone) to very shallow lagoons with a restricted water circulation in the Cf 6a - ß zone. The extreme large size of the ostracode species recovered from the Cf 6a - ß zone is not characteristic of the very shallow lagoon environment. Extremely large ostracodes have also been recognized in other carbonate facies of Dinantian age

Damage assessment of ferruginous sandstone by X-ray tomography : the 'Virgin Tower' of Zichem (Belgium)

The ferruginous sandstone of the Gothic “Virgin Tower” is suffering from a specific biological deterioration process triggered by perforating activities of mason bees. The damage due to these perforations causes extensive loss of material, so that a durable conservation of such degraded stone blocks becomes questionable. In order to evaluate the conservation possibilities of stone blocks damaged by perforating mason bees, an investigation of the internal structure by means of X-ray tomography was carried out. This investigation revealed that the cumulative effect of the digging work by multiple generations of mason bees may result in networks of perforations. Bioturbated sandstones were found to be most suitable for attack by mason bees because of morphological and geometrical compatibility between the original layered burrowings by marine organisms and those by the mason bees. As a conclusion, the conservation is not recommended of sandstone blocks for which the load bearing capacity is endangered by the branched and layered perforations

Investigation of the Degradation Phenomena of the Luxembourg Sandstone in the Royal Museum for Central Africa (Belgium)

The Royal Museum for Central Africa in Tervuren was built in the beginning of the 20th century. The outer walls and ornamental elements were almost exclusively constructed in massive blocks of Luxembourg sandstone, a stone well suited as building material. Despite the stated good quality, the facades locally suffer from exposure to weathering. Moreover, certain zones show severe damage due to rain water infiltration originating from defects in the water evacuation system which is entirely hidden within the walls. As a consequence, important damage to the sandstone blocks in the form of crack-formation, scaling, spalling and (salt) staining, is noticed. This paper presents the results of an investigation carried out in the framework of the restoration strategy aiming to explain degradation and damage phenomena in relation to the properties and varieties of Luxembourg sandstone. Detailed visual observations with regard to the architectural concept was followed by a sampling plan and a test program. Physical and microscopic analysis allowed to establish the relationship between rock type, colour and weathering effects. The test program consisted of the determination of physical and mineralogical properties, hardness profiles obtained by means of the portable DRMS device (Drilling Resistance Measurement System), ultrasound velocity measurements and the determination of the actual salt contamination. The strengthening effect of a number of consolidation tests, using tetraethoxysilane (TEOS), was also evaluated by means of hardness profiles

Mechelen-Zennegat Archeologisch onderzoek in het kader van het Sigmaplan voor de deelzone Zennegat-Battenbroek

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