Michel Vanguestaine

A new geological map of the Brabant Massif, Belgium

A new geological map, mostly subcrop, of the Brabant Massif is presented, based on a revised lithostratigraphy of the outcrop area and on recently acquired palaeontological and lithological data from boreholes in the concealed area. New interpretations of magnetic and gravity data are used to extend the lithostratigraphical units into areas with few or no boreholes. A structural model of the western, northern and southern parts of the Brabant Massif is presented. The main anticlinal axis plunges towards the west-northwest, its core comprising Upper Precambrian (?) to Lower Cambrian terrigenous rocks which outcrop in the southeast. To the north of the main axis, younger rocks appear in regular succession, but to the southwest this picture is complicated by the occurrence of a second anticlinal structure and by a subparallel magmatic arc.

Espèces zonales d'Acritarches du Cambro-trémadocien de belgique et de l'Ardenne française

Abstract Nine acritarch zones are recognized in the Cambro-Tremadocian of Belgium and the French Ardennes. The author gives the main characteristics of these zones as well as an estimation of their position relative to the international chronostratigraphic scale. The zonation is based on the stratigraphic ranges of easily identifiable species, eight of which are new: Micrhystridium, lanceolatum, Priscogalea chevronensis, Leiosphaeridia fumiana, Lophosphaeridium bacilliferum, L. ? kryptoradiatum, Revinotesta microspinosa, Dictyotidium hasletianum and Polyedryxium ? pentagonale . Their description necessitated the establishment of a new genus: Revinotesta . The author proposes two new specific combinations and defines his concept of the genera Priscogalea, Cymatiogalea and Lophosphaeridium .

Review of the stratigraphy of the Ordovician in the Brabant Massif, Belgium

A review of isolated data from the literature and our own observations make it possible to establish a model of the stratigraphical history of the Ordovician on the southern margin of the Brabant Massif. The succession is composed of seven informal formations, totalling a minimum of 2500 m of sediments, mainly comprising mudstones, siltstones and sandstones. This succession is compared and partly correlated with the sections observed in the adjoining areas, in the Bande de Sambre-et-Meuse, the Stavelot and Rocroi Massifs and the Remscheid–Altena and Ebbe anticlines (western Germany).

The Late Cambrian acritarch Cristallinium randomense: morphology, taxonomy and stratigraphical extension

The holotype of Cristallinium randomense Martin and other figured specimens are re-examined. The processes are often grouped as those of typical Vulcanisphaera species. Probable connections between Cristallinium and Vulcanisphaera are indicated. These genera form a plexus in which Retisphaeridium is also possibly involved. A complete bibliographical list of C. randomense is provided. Few published specimens are demonstrated to belong to this species. As a consequence, some stratigraphical dates, based on the restricted Late Cambrian range of the species, are questioned. The new combination Retisphaeridium ovillense (Cramer and Diez de Cramer) Vanguestaine nov. comb. is proposed.

Ordovician and Silurian acritarch assemblages from the west Leinster and Slievenamon areas of southeast Ireland.

The Lower Palaeozoic sequences west of the Leinster Granite and in the Slievenamon Inlier of southeast Ireland have been palynologically re-investigated. Most of the productive samples yielded sufficient identifiable acritarchs for positive stratigraphical age determinations for several of the formations. The samples also include rare cryptospores, scolecodonts and tubular structures. Previous work in the area west of the Leinster Granite proposed an unbroken succession from Early Ordovician Ribband Group turbidites and volcanics passing up conformably to Early Ordovician to Late Silurian Kilcullen Group. The new palynological data clearly show that the Kilcullen Group in this area is entirely Silurian (Llandovery-early Wenlock) in age, also results obtained from the same group at Slievenamon confirm the previously reported Silurian age. Ordovician acritarchs found in the Kilcullen Group of both study areas are reworked and range in age from late Tremadoc to Llanvirn. The new data reveal a major stratigraphic break between the Ribband Group dated as Early and Middle Ordovician and the Silurian Kilcullen Group. This major break extends some hundreds of kms southwest to the Dingle Peninsula and possibly equates with a similar discontinuity in the Isle of Man to the northeast. This break would thus appear to be a major feature within the northwestern Avalonian margin sequence.

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.

Cambrian palynology of the Bray Group in County Wicklow and South County Dublin, Ireland

Abstract The Cambrian Bray Group of southeast Ireland crops out in several areas, with its biostratigraphic dating generally poorly constrained. In its principal outcrop, that of the Bray–Wicklow district, a sparse, poorly preserved acritarch assemblage was recorded some years ago, suggesting a late Early to early Middle Cambrian age. In the present study 58 samples were collected for palynological investigation from throughout the group, of which four were productive. The productive samples occur in a geographically small area and lie within a 120-m-thick part of the Bray Head Formation which forms the upper part of the 4500-m-thick Bray Group. The palynological material is characterised by an abundance of Skiagia species of which Skiagia orbicularis (Volkova, 1968) Downie, 1982 is the most frequent. Particular attention was paid to the possible presence of the Middle Cambrian stratigraphic markers Cristallinium cambriense (Sklavikova, 1968) Vanguestaine, 1978 and Eliasum llaniscum Fombella, 1977. Our findings are that C. cambriense is not present and the occurrence of E. llaniscum cannot be definitely demonstrated. The presence and diversity of the Skiagia complex and the absence of the former taxa is indicative of a mid–late Early Cambrian age.

A Middle Cambrian age for the Ediacara-type fauna from the Booley Bay Formation, County Wexford, Ireland: new acritarch data and their implications

Ten years ago a well-preserved Ediacara-type fauna was recorded for the first time in sediments at the type section of the Lower Palaeozoic Booley Bay Formation in County Wexford, Ireland (Crimes et alii, 1995). Four microfossil samples were collected from mudstones intercalated in sandstone beds. These yielded an acritarch fauna that (Moczydlowska & Crimes, 1995) considered to indicate a late Late Cambrian age for the Ediacara-type fauna. They proposed that this find extended the known stratigraphic range of Ediacara-type fauna from the Neoproterozoic to the Late Cambrian, rather than to the Middle Cambrian as had been indicated previously (Conway Morris, 1993).