Edouard Poty

Upper Devonian and Mississippian foraminiferal and rugose coral zonations of Belgium and northern France: a tool for Eurasian correlations

The radiation of early Carboniferous foraminifers and rugose corals following the Devonian–Carboniferous crisis offers the best tool for high-resolution correlations in the Mississippian, together with the conodonts in the Tournaisian, notably in the Namur–Dinant Basin. However, some of the guides are facies-controlled and an integrated approach combining biostratigraphy, sedimentology and sequence stratigraphy is critical to identify delayed entries, potential stratigraphic gaps and to avoid diachronous correlations. The main difficulty is in correlating shallow and deeper water facies at any given time. In existing zonations, the Visean part of the scheme is always more detailed, reflecting the widespread development of shallow-water platforms in the early Visean which created conditions more suitable for foraminifers and rugose corals over large areas. In contrast, the Tournaisian zones, less well documented, reflect unfavourable environmental conditions in the lower ramp (Dinant Sedimentation Area) and pervasive dolomitization of the inner ramp (Condroz and Namur Sedimentation Areas). Recent progress in understanding the Belgian early Carboniferous sequence stratigraphy and lithostratigraphy, and revision of the biostratigraphy of the key sections, strongly modify former biostratigraphic interpretations. Improvements mainly concern the latest Devonian, the late Tournaisian and the early Visean. The late Devonian and the Tournaisian are equated with foraminifer zones DFZ1 to DFZ8 and MFZ1 to MFZ8 respectively. The Visean correlates with zones MFZ9 to MFZ14. Zone MFZ15 straddles the Visean–Namurian boundary and Zone MFZ16 is the youngest Mississippian zone. The rugose corals allow the recognition of ten zones, RC0 to RC9, covering the Strunian (late Famennian) to Serpukhovian interval. Discrepancies with former zonations are discussed. The Moliniacian Stage is emended to restore the coincidence between its base and that of the Visean.

Pre-permian Sedimentation in Nw Europe - Pre-permian Depositional-environments Around the Brabant Massif in Belgium, the Netherlands and Germany

Abstract Pre-Permian sedimentation in northwestern Europe has been controlled by the structural evolution of this area. Cambro-Silurian deposition has been influenced by partly synsedimentary movements (among others Ordovician-Silurian uplift south of the Brabant/Condroz zone, such as the Stavelot-Venn Massif). Presence, respectively absence of important late Caledonian deformation has subdivided northwestern Europe into three major sedimentary environments during the Devono-Carboniferous: the Caledonian fold belt and the Cornwall-Rhenish Basin which are separated by the Belgo-Dutch platform. Subsequently, the Hercynian or Variscan orogenies have gradually reduced the sedimentary area and produced the overall withdrawal of the marine environment. Eventually, large-scale overthrusts - such as the Dinant Nappe - masked parts of the original sedimentary basins.

Late Frasnian phillipsastreid biostromes in Belgium

Abstract In the Belgian Namur-Dinant Basin the boundary between the Lustin Formation and the Aisemont Formation (in the Lower rhenana conodont Biozone) corresponds to a fall followed by a rise in sea level, leading to the first recorded late Frasnian coral crisis. The Aisemont Formation records a transgressive-regressive cycle. Prior to the crisis most of the colonial rugose corals were members of the Family Disphyllidae, but these were largely replaced by corals belonging to the Phillipsastraeidae. Among these Frechastraea colonized all environments of the basin and was the main constructor of a biostromal reef in its northern-most proximal area, in the fair-weather wave zone. Corals did not encrust each other and therefore were not firmly attached, but they hug tightly the substrate (a dead coral colony) and rest closely on it to resist to the turbulence of waves. During the Silurian and Devonian, up until the late Frasnian crisis, shallow-water reefs in turbulent water were usually built by encrusting stromatoporoids, whereas rugose corals were restricted to waters of lower energy. Indeed, they were unable to encrust substrates, unlike stromatoporoids and post-Palaeozoic scleractinians, and to live in turbulent habitats. In Belgium argillaceous sedimentation prevented the development of stromatoporoids and provided an opportunity for the corals to colonize empty niches and to construct biostromes in relatively high-energy environments. At the same time Alveolites and stromatoporoids were dominant in a mid-proximal environment below the fair-weather wave base, but within the storm wave zone, where they also constructed biostromes.

Belgian substages as a basis for an international chronostratigraphic division of the Tournaisian and Viséan

The Tournaisian and Visean were formerly considered as series and in Belgium were divided into two (Hastarian and Ivorian) and three stages (Moliniacian, Livian and Warnantian), which are now considered as substages. The Belgian substages are based on conodonts and foraminifers, and incidentally on rugose corals, and are described here. Their boundaries, biostratigraphy and sequence stratigraphy are well detailed and clearly defined. The base of the Hastarian (lower Tournaisian) corresponds to the base of the Tournaisian (base of Carboniferous); the base of the Ivorian (upper Tournaisian) corresponds to the appearance of the conodont Polygnathus communis carina , a little above the last Siphonodella ; the base of the Moliniacian (lower Visean) corresponds to the base of the Visean stage defined by the first occurrence of the foraminifer Eoparastaffella simplex ; the Livian (middle Visean) corresponds to the foraminiferal MFZ12 Zone and is marked by the appearance of Koskinotextularia and Pojarkovella nibelis ; the base of the Warnantian (upper Visean) is marked by the appearance of Neoarchaediscus , Vissariotaxis , Planospirodiscus , and Palaeotextularia with a bilaminar wall, the index taxa of the MFZ13- Neoarchaediscus Zone. The up-to-date chronostratigraphic subdivision of the Tournaisian and Visean is not limited to Belgium and the surrounding areas. It can be applied through Eurasia as far as South China. The Belgian units could therefore be the basis for a future international division of the Tournaisian into two parts (Hastarian and Ivorian) and of the Visean into three parts (Moliniacian, Livian and Warnantian), corresponding to time intervals of c. 5–8 Ma.

Kellwasser horizons, sea-level changes and brachiopod–coral crises during the late Frasnian in the Namur–Dinant Basin (southern Belgium): a synopsis

Abstract In Belgium, the Lower Kellwasser Event (LKW) corresponds to the relative sea-level maximum of the first (‘Aisemont sequence’ (AS)) of the two late Frasnian third-order sequences that are recognized here, but the Upper Kellwasser Event (UKW) may have been triggered by a series of tsunamites. The end of the middle Frasnian carbonate platform and reefs is caused by the sea-level drop and emersion of the last middle Frasnian third-order sequence (‘Lion sequence’) in the Lower rhenana Zone. The end of the ‘Petit-Mont’ mudmound growth during the transgressive (TST) and highstand (HST) systems tracts of the AS was caused by sea-level fall and emersion at the top of this sequence. The coral and brachiopod extinction in the Upper rhenana Zone, during the second late Frasnian third-order sequence (‘Lambermont sequence’ (LS)), is progressive and due to the widespread development of the dysoxic and anoxic facies, before the UKW. Only the LS TST has been identified. No sea-level fall has been recognized in relation to the UKW or near the Frasnian–Famennian boundary. The late Frasnian extinctions are more likely to be related to the decrease in the atmospheric oxygen rate and its impact on marine environments and, to complete, the UKW.

A Preliminary-study of Ashgill Carbonate Beds From the Lower Part of the Fosses Formation (condroz, Belgium)

The sedimentology and palaeontology of carbonate beds in the lower part of the Fosses Formation (Ashgill of the Condroz area, central Belgium) have been investigated. Two depositional interpretations are suggested: deposition either near a platform-ramp margin as bioclastic turbidites and interbedded shales or on a shelf as a transgressive sequence following a regressive event. Faunal affinities with the Baltic area and Wales are confirmed, and the location of Belgium in the tropics during the Ashgill is supported by the calcareous algae and the coral fauna.

Dinantian Reefs underneath the Netherlands

Recently a new hydrocarbon exploration play concept has been presented far below the conventional targets of Permian or Pennsylvanian age. In a number of publications, examples were given of large, presumably carbonate, built ups, below the Netherlands th

Interaction between eustacy and block-faulting in the Carboniferous of the Visé-Maastricht area (Belgium, the Netherlands)

The Visé–Maastricht sedimentation area (VSA) is situated at the eastern end of the Brabant Massif and suffered block-faulting tectonics during Lower Carboniferous time. The south edge of the VSA, the area corresponding now to the vicinity of Visé, comprised three main tectonic blocks: the Hermalle-sous-Argenteau, Souvré and Bombaye blocks. They were bounded to south by the Booze–Val-Dieu block. To the north, in the vicinity of Maastricht, blocks are not well differentiated and are referred to as the Maastricht block system. From the end of the Tournaisian, the latter evolved into a rapidly subsiding graben, recording mainly debris fl ows and limestone turbidites, whereas the southern blocks remained relatively high. Through much of Lower Carboniferous time, they were emergent, but during high eustatic sea levels, they were fl ooded and covered by limestone deposits. The differences in the nature and the age of the deposits between blocks result from the interaction between block-faulting and eustacy. In the VSA, the Upper Devonian and Lower Tournaisian (Hastarian) deposits are similar to those known in the north part of the Namur-Dinant Basin. But from the late Tournaisian (Ivorian), the uplift of the Booze–Val-Dieu block prevented all connections with the Namur-Dinant Basin and the VSA became linked with the Campine Basin. The Souvré block subsided from the latest Givetian to the late Frasnian and recorded a thick middle Frasnian limestone series, but was later emergent, so much that karstic cavities developed. The Souvré block was submerged for a short time at the top of the Tournaisian, during the very high highstand (HST) corresponding to eustatic sequence 4, and the caves fi lled up with sediments. The Hermalle-sous-Argenteau and the Bombaye blocks, situated respectively west and east of the Souvré block, evolved in the same way during the late Devonian. They subsided slightly from the earliest Tournaisian to the late Viséan (Warnantian), but usually remained emergent and recorded deposits only during times of high eustatic levels corresponding to the early Tournaisian (for the Bombaye block), the end of the Tournaisian (HST of sequence 4), the end of the early Viséan (HST of sequence 6), then the late Viséan (HST of sequences 9 and 10). In its southern part, the Hermalle-sous-Argenteau block recorded also lowermost Viséan limestones correlated with the highstand of the eustatic sequence 5, probably as a result of the tilting of the block to the south at this time. Kurzfassung: Der Sedimentationsraum Visé–Maastricht (VSA) befi ndet sich am östlichen Ende des Brabanter Massivs und ist im Unterkarbon durch „block-faulting“-Tektonik geprägt. Das südliche Ende des VSA, heute die Umgebung von Visé umfassend, kann in drei tektonische Blöcke untergliedert werden: Hermalle-sous-Argenteau-Block, Souvré-Block und Bombaye-Block. Diese werden nach Süden vom Booze–Val-Dieu-Block begrenzt. Im Norden, in der Umgebung von Maastricht, können einzelne Blöcke nicht differenziert werden und sind daher zum Maastricht-Block-System zusammengefasst. Ab dem Ende des Tournaisiums entwickelt sich das Maastricht-Block-System in einen hoch subsidenten Graben, in dem hauptsächlich Schuttströme und Calciturbidite abgelagert werden, während die südlichen Blöcke zeitgleich relativ hoch gelegen verbleiben. Für die meiste Zeit des Unterkarbons sind diese Gebiete aufgetaucht, aber sie wurden während hoher Meeresspiegelstände überfl utet und Karbonate lagerten sich ab. Die Unterschiede in der Art und dem Alter der Ablagerungen zwischen den einzelnen Blöcken resultieren aus dem Zusammenspiel von „block-faulting“ und eustatischen Meeresspiegelschwankungen. Im VSA sind die Ablagerungen des Oberdevons und unteren Tournaisiums (Hastarium) vergleichbar mit den altersgleichen Ablagerungen des nördlichen Namur-Dinant-Beckens. Aber ab dem oberen Tournaisium (Ivorium) verhindert das Aufsteigen des Booze–Val-Dieu-Blocks die Verbindung von VSA und dem Namur-Dinant-Becken und der VSA wurde an das Campine-Becken angeschlossen. Der Souvré-Block war vom höchsten Givetium bis zum oberen Frasnium subsident und mächtige mittelfrasnische Kalksteine wurden abgelagert. Diese wurden später herausgehoben und ein Karstsystem entwickelte sich. Der Souvré-Block wurde im höchsten Tournaisium wieder kurzeitig überfl utet und in den Karstsystemen wurde unter marinen Bedingungen Z. dt. Ges. Geowiss., 162/2, p. 117–126, 6 figs. Article Stuttgart, June 2011