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Stratigraphic analysis of cored and geophysically logged boreholes in the Kasterlee-Geel-Retie-Mol-Dessel area of the Belgian Campine has established the presence of two lithostratigraphic units between the classical Diest and Mol Formations, geometrically related to the type Kasterlee Sand occurring west of the Kasterlee village and the study area. A lower ‘clayey Kasterlee’ unit, equivalent to the lithology occurring at the top of the Beerzel and Heist-op-den-Berg hills, systematically occurs to the east of the Kasterlee village. An overlying unit has a pale colour making it lithostratigraphically comparable to Mol Sand although its fine grain size, traces of glauconite and geometrical position have traditionally led stratigraphers to consider it as a lateral variety of the type Kasterlee Sand; it has been named the ‘lower Mol’ or ‘Kasterlee-sensu-Gulinck’ unit in this study. In the present analysis, the greenish glauconitic Kasterlee Sand in its hilly stratotype area evolves eastwards into the lower ‘clayey Kasterlee’ unit and possibly also into an overlying ‘lower Mol’ or ‘Kasterlee-sensu-Gulinck’ unit, although it is equally possible that the latter unit has an erosive contact and therefore is stratigraphically slightly younger than the type Kasterlee Sand west of the Kasterlee village. A lateral extension of this detailed stratigraphic succession into the faulted zone of east Limburg is proposed.

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Quartz veins in the early Variscan Monts d'Arré e slate belt (Central Armorican Terrane, Western France), have been used to determine fluid-flow characteristics. A combination of a detailed structural analysis, fluid inclusion microthermometry and stable isotope analyses provides insights in the scale of fluid flow and the water-rock interactions. This research suggests that fluids were expelled during progressive deformation and underwent an evolution in fluid chemistry because of changing redox conditions. Seven quartz-vein generations were identified in the metasedimentary multilayer sequence of the Upper Silurian to Lower Devonian Plougastel Formation, and placed within the time frame of the deformation history. Fluid inclusion data of primary inclusions in syn-to post-tectonic vein generations indicate a gradual increase in methane content of the aqueous-gaseous H 2 O-CO 2 -NaCl-CH 4 -N 2 fluid during similar P-T conditions (350-400°C and 2-3.5 kbar). The heterogeneous centimetre-to metre-scale multilayer sequence of quartzites and phyllites has a range of oxygen-isotope values (8.0-14.1& Vienna Standard Mean Ocean Water), which is comparable with the range in the crosscutting quartz veins (10.5-14.7& V-SMOW). Significant differences between oxygen-isotope values of veins and adjacent host rock (D = )2.8& to +4.9& V-SMOW) suggest an absence of host-rock buffering on a centimetre scale, but based on the similar range of isotope values in the Plougastel Formation, an intraformational buffering and an intermediate-scale fluid-flow system could be inferred. The abundance of veins, their well-distributed and isolated occurrence, and their direct relationship with the progressive deformation suggests that the intermediate-scale fluid-flow system primarily occurred in a dynamically generated network of temporarily open fractures.

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