Continuous sedimentary gradients are only crudely expressed by standard facies and microfacies methods which are more appropriate to situations where changes occur in relatively discrete steps. In carbonate sediments and rocks, continuous gradients are often represented by the arrangement of component grain types in a relay, that is, a systematic shifting of the relative importance of the components. Subdivision of such relays into (micro)facies can only be arbitrary. Correspondence analysis is shown to be useful for detecting, isolating and describing relays. Particular use is made of the arch effect in which samples and components from data sets with a strong unidimensional structure (a relay) plot in the form of an arch in the plane of the first two factor axes. A relay index, indicating the position of samples in the relay, can be extracted from the analysis and plotted on maps and stratigraphic logs to reveal details of the sedimentary gradient in areal and/or stratigraphic context. Examples are given from: (i) Recent shallow‐marine carbonate sediments from northern Norway, illustrating a relatively simple depositional setting where surface sediments are viewed in plan; and (ii) Lower Carboniferous carbonates of southwest England, representing a more complex regional study of a particular stratigraphic interval viewed in cross‐section. In both examples the relays can be related to identifiable environmental gradients.

The National Subcommission on the Stratigraphy of the Lower Palaeozoic of Belgium has evaluated the previous and present definitions of the Cambrian, Ordovician and Silurian lithostratigraphical units (groups, formations and members) and presents in this paper the results of this evaluation. Some of these units described in published or unpublished documents are considered to be junior synonyms of previously described units. Other units were given a higher or lower ranking. Units that are too thin or too thick were abandoned. The Subcommission reached agreement on the validity and usefulness of all the units that are described below. For each of them, a lithological and sedimentological description is given, the area of distribution and possible facies changes, the thickness of the unit, the arguments for the age determination, some remarks about the history of the definitions, and the names of units considered to be junior synonyms. In the Brabant Massif 32 formations are (re) defined and described, in the Condroz inlier 18 formations, in the Stavelot Massif 3 groups, 8 formations and 8 members, with an additional formation with an unspecified Mid Ordovician-earliest Devonian age, in the Rocroi Massif 3 groups, 7 formations and 2 members, in the Givonne Inlier 4 formations and in the Serpont Inlier 2 formations. The formations are shown in chronostratigraphical tables with a colour encoding the dominant lithology or sedimentology.

Six paleogeographic sedimentation areas (s. a.) are recognized in the Namur-Dinant Basin: (1) the Hainaut s. a., (2) the Namur s. a., (3) the Condroz s. a., (4) the Dinant s. a., (5) the Visé-Maastricht s. a., and (6) the southern Avesnois s. a. (only in northern France). Together with the sea-level variations (third-order sequences), local controls influenced the nature of the sedimentary deposits, so the lithostratigraphic successions in each sedimentation area are distinctive. The depositional setting was that of a carbonate platform which evolved from a ramp in the early Tournaisian to a rimmed shelf during the early Viséan and then to a regionally extensive shelf during the middle and late Viséan. Before the Livian, open marine fades were developed to the south, but from the Livian onwards open marine facies were restricted to the north while evaporites developed in the south. This inversion of the normal pattern was probably related to an early phase of Variscan shortening. Dinantian biostratigraphy is mainly based upon foraminifera, rugose corals and conodonts. Fifty formations (including members), 3 groups and 2 informal lithostratigraphic units are briefly described.

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Abstract:The Aïn Settara section (Kalaat Senan, central Tunisia) shows a continuous and well exposed marl-limestone alternation, extending from the Upper Maastrichtian to the basal Danian. The section reveals the superposition of several cycles, which correspond to the combined astro-climatic effect of both eccentricity and precession. Based on the ~100-kyr eccentricity and the ~21-kyr precession cycles, a floating chronometric scale is proposed. Thanks to this scale, the sedimentary and biological events of the section are dated with respect to the Cretaceous-Paleogene (K-Pg) boundary taken as the reference. Highlighting the very stable 405-kyr eccentricity cycle allows on one side to confirm the relevance of the established time scale and on the other side to determine the phase of this important signal with respect to the K-Pg boundary event.

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The primary and early diagenetic components of carbonate rocks are commonly arranged systematically in a sort of 'relay' along a gradient formed by one or several environmental factors. Such a relay, if present, can be revealed by the optimization of a matrix of similarity coefficients. The technique presented uses presencelabsence data and is simple and rapid. An illustration is given using data from some Dinantian limestones in southwest Britain.KEY WORDS. Similarity matrix Jaccard coefficients Relay effect Limestone petrography Carbonate components Dinantian