Maastrichtian

The stratotype of the Maastrichtian Stage named by the Belgian geologist André Dumont in 1849 is situated in the Netherlands at the St Pietersberg.The original description of the "Maastricht Limestone"? is quoted and the successive historical interpretations of the Maastrichtian Stage are outlined. The Maastrichtian Stage in Belgium is then presented in three areas: the Liège-Limburg region, the Mons Basin, and outliers at Orp-Jauche, Orp-le-Petit, as well as Hockai and some other Hautes Fagnes outcrops

Biostratigraphy and events at the Campanian-Maastrichtian Boundary

Problems related to stages, bioevents, ecoevents and stage boundaries as well as their mutual relationships are briefly discussed. Subsequently, a review is made of the data on the Campanian-Maastrichtian boundary as currently accepted and defined in the Boreal and Tethyan realms

The global bio-events at the Cenomanian-Turonian transition in the reduced Bahloul Formation of Bou Ghanem (central Tunisia)

In central Tunisia, the thickness of the Bahloul Formation varies generally between 20 to 40 m such as for example, respectively, at wadi Smara near Kalaat Senan and at wadi Bahloul near Maktar. The thickness is also of several tens metres at Koudiat el Azreg near Jerissa and at Tajerouine. In these sites where the thickness of the Bahloul Formation is dilated, in addition to five geochemical events (δ¹³C), nine bio-events were defined near the Cenomanian-Turonian transition, successively in ascending order: 1. LO Rotalipora cushmani, 2. Heterohelix bio-event, 3. FO Pseudaspidoceras pseudonodosoides, 4. LO P. pseudonodosoides, 5. LO Thalmanninella multiloculata, 6. “filaments” bio-event, Cenomanian-Turonian transition, 7. FO Watinoceras sp., 8. FO Pseudaspidoceras flexuosum, 9. FO Helvetoglobotruncana helvetica. Even though the Bahloul Formation in the Bou Ghanem site is only 7.7 m thick (from which only 2.4 m of laminated black limestones), all nine marker bio-events were recorded, almost in the same order except some small differences. A good number of these bio-events are global as they are also present at Pueblo (Colorado, USA), the stratotype for the base of the Turonian stage. Consequently, at a global scale, it is possible to place the Cenomanian-Turonian boundary with one or several of these bio-events, with a good level of confidence

Zones d'ammonites et de foraminifères du Vraconnien au Turonien : Une comparasion entre les domaines boréal et téthysien (NW Europe / Tunisie centrale)

Depuis la fin du 19ème siècle, l'intervalle comprenant l'Albien supérieur élevé, le Cénomanien, le Turonien et le Coniacien basal a été subdivisé d'abord en zones d'ammonites puis, à partir du milieu du 20ème siècle, en zones de foraminifères planctoniques, deux groupes de macro- et de microfossiles particulièrement efficaces en bio-chronostratigraphie grâce à leur taux d'évolution rapide. Toutefois, des différences de compositions fauniques entre le domaine boréal (Europe du Nord-Ouest) et le domaine téthysien (Méditerranée) ont longtemps empêché des corrélations précises entre ces deux domaines. Aujour-d'hui, dans un intervalle de temps couvrant environ 16 millions d'années, on dénombre 29 zones d'am-monites en domaine téthysien contre 24 en domaine boréal parmi lesquelles 16 sont communes aux deux domaines. Pour les foraminifères planctoniques, on compte 11 zones en domaine téthysien et 10 en domaine boréal, dont 7 communes.Since the end of the 19th century the interval comprising the uppermost Upper Albian, the Cenomamian, the Turonian and the basal Coniacian has been subdivided, first into ammonite zones, then, beginning in the middle of the 20th century, into zones of planktonic foraminifera. These two groups, one macrofossil, the other microfossil, are particularly effective for bio-chronostratigraphy thanks to their rapid rates of evolution. But differences in the faunal makeup between the Boreal domain (northwestern Europe) and the Tethyan domain (Mediterranean) have for a long time hindered precise correlation of the two domains. Today, in a time interval covering about 16 million years, there are 29 ammonite zones in the Tethyan domain versus 24 in the Boreal one, of which 16 are common to both domains. For the planktonic foraminifera the Tethyan domain has 11 zones, the Boreal domain 10, with 7 in common

Zonation by ammonites and foraminifers of the Vraconnian-Turonian interval: A comparison of the Boreal and Tethyan domains (NW Europe / Central Tunisia)

Since the end of the 19th century the interval comprising the uppermost Upper Albian, the Cenomamian, the Turonian and the basal Coniacian has been subdivided, first into ammonite zones, then, beginning in the middle of the 20th century, into zones of planktonic foraminifera. These two groups, one macrofos-sil, the other microfossil, are particularly effective for bio-chronostratigraphy thanks to their rapid rates of evolution. But differences in the faunal makeup between the Boreal domain (northwestern Europe) and the Tethyan domain (Mediterranean) have for a long time hindered precise correlation of the two domains. Today, in a time interval covering about 16 million years, there are 29 ammonite zones in the Tethyan domain versus 24 in the Boreal one, of which 16 are common to both domains. For the planktonic foraminifera the Tethyan domain has 11 zones, the Boreal domain 10, with 7 in common.Depuis la fin du 19ème siècle, l'intervalle comprenant l'Albien supérieur élevé, le Cénomanien, le Turonien et le Coniacien basal a été subdivisé d'abord en zones d'ammonites puis, à partir du milieu du 20ème siècle, en zones de foraminifères planctoniques, deux groupes de macro- et de microfossiles particulièrement efficaces en bio-chronostratigraphie grâce à leur taux d'évolution rapide. Toutefois, des différences de compositions fauniques entre le domaine boréal (Europe du Nord-Ouest) et le domaine téthysien (Méditerranée) ont longtemps empêché des corrélations précises entre ces deux domaines. Aujourd'hui, dans un intervalle de temps couvrant environ 16 millions d'années, on dénom-bre 29 zones d'ammonites en domaine téthysien contre 24 en domaine boréal parmi lesquelles 16 sont communes aux deux domaines. Pour les foraminifères planctoniques, on compte 11 zones en domaine téthysien et 10 en domaine boréal, dont 7 communes

Définition des unités chronostratigraphiques mondiales et échelle des temps : pour des conventions simples et limitées favorisant la mise en oeuvre des connaissances disponibles

Ce travail discute quatre aspects de la terminologie stratigraphique considérés comme inappropriés et propose des améliorations concernant : (1) le système de double terminologie avec des termes propres pour chacun des aspects temporel et géométrique des corps de roche ; (2) l’assertion selon laquelle le Point Stratotypique Mondial (PSM) définit la base d’un étage qui coïncide avec le sommet de l’étage précédent au lieu de tout simplement : la limite d’étage ; (3) la répugnance devant la désignation de sections additionnelles (auxiliaires) qui accroîtraient la connaissance d’un PSM et pourraient ainsi élargir le domaine de corrélation immédiate ; (4) le système actuel de subdivision différent pour le Précambrien (limites définies par des âges) et pour le Phanérozoïque (limites définies par des PSM) est accepté mais un troisième système (des limites propres à chaque outil de corrélation) est proposé pour les dépôts âgés de 3 à 5 Ma. Par ailleurs, si le travail encourage l’utilisation universelle d’un nombre restreint de conventions, il met en garde contre une prolifération de celles-ci pour des unités qui, en devenant plus courtes, deviennent plus malaisées à reconnaître. On souligne enfin que la distinction doit rester très claire entre ces conventions qui sont une affaire d’administration et de consensus et la connaissance, un domaine où la libre expression des opinions est indispensable

The Cretaceous-Palaeogene (K/P) boundary in the Aïn Settara section (Kalaat Senan, Central Tunisia): lithological, micropalaeontological and geochemical evidence

The Cretaceous-Palaeogene (K/P) boundary, until recently known as the "Cretaceous-Tertiary" or K/T boundary, is well exposed at Aïn Settara in the Kalaat Senan area (Central Tunisia), 50 km south of the El Kef section. Micropalaeontological and geochemical studies led to the identification of six main features tentatively named "events", which characterise the K/P boundary interval, and of which at least two (B and C) have global significance. The lowermost event A located at about 14 cm below the base of the Dark Boundary Clay is marked by a sudden increase in tiny bioturbations, by small nodules and a few macrofossils, a 50% drop in calcareous nannofossil abundance and an increase in Scytinascias (organic linings of foraminifera). It is thought to witness a slowdown in sedimentation. Event B is characterised by a burrowed surface, separating the ca 60-cm thick Dark Boundary Clay from the underlying Aïn Settara marls. It indicates an episode of nondeposition, just before a major change in lithology from marls to clays, corresponding to a major flooding. No substantial palaeontological changes have been recorded in relation to this event. Event C is characterised by maximum concentrations of Ir and Ni-rich spinels, which have been observed in platy nodules, similar to the level at El Kef (K/P boundary sensu ODIN, 1992). It coincides with a major extinction in planktonic foraminiferal species (71%) and a 60% drop in nannofossil abundance. The change in lithology (occurrence of small ripples and channel-like structures) recorded at event D, a few cm up-section, might be related to a locally recorded storm activity. Events E and F, which are situated higher up in the Dark Boundary Clay, are mainly determined by palaeontological changes (palynomorphs and nannofossils), probably resulting from small sea-level variations. The coincidence of the cosmic markers with the major biotic changes at event C pleads for the asteroid impact hypothesis. Their disjunction from the base of the Dark Boundary Clay shows that the change of lithology usually used to determine the K-P boundary is distinct from the major extinction (in the planktonic realm), classically referred to this boundary and linked to the presence of cosmic markers. These results argue the need for the revaluation of the K-P boundary GSSP at El Kef. It is suggested to redefine the K-P boundary at the level of coincidence of the major biotic changes and the cosmic markers