Geological Setting and Genesis of Coticules (Spessartine Metapelites) in the Lower Ordovician of the Stavelot Massif, Belgium
Journal of the Geological Society, London, Vol. 143, 1986, pp. 253-258, 8 figs, 2 tables Printed in Northern Ireland Geological setting and genesis of coticules (spessartine metapelites) in the Lower Ordovician of the Stavelot Massif, Belgium J. LAMENS’, F. GEUKENS’ & W. VIAENE2 Instituut voor Aardwetenschappen, Katholieke Universiteit Leuven, Redingenstraat 16, B-3000 Leuven, Belgium ’Afdeling Fysico-Chemische Geologie, Katholieke Universiteit Leuven, Celestijnenlaan 200C, B-3030 Heverlee, Belgium Abstract: The LowerOrdovician in the CaledonianStavelot Massif (Belgium) containsa coticule member, probablyArenig in age, composed of redhematite-rich shales alternating with thin yellowish coticulebeds. These coticules are fine-grained highly manganiferousmetamorphic rocks mainly composed of spessartine garnet, mica and quartz. Similar rocks of about the same age occur in several localities along the Appalachian and Caledonian fold belts. The Belgian coticules are thought to haveoriginated from marly sediments which had beendeposited rapidly, probably by density currents, and in which CaCO, had been diagenetically replaced by MnCO,. During metamorphism, spessartine garnets- were formed from this MnCO, and mica. Manganese and iron are thought to have originated from volcanic-exhalative processes. The Stavelot Massif is one of the five Caledonian Massifs in could be used as a key lithology for correlation along the Belgium. It consists of MiddleCambrian to Lower Appalachian and Caledonian fold belts. Similar rocks have Ordovician strata (Fig. 1, Table 1). The southeastern partof also been described from older (Precambrian) and younger the Stavelot Massifis at a low metamorphicgrade. The strata(Roy & Purkait 1968; Vearncombe 1983; Minnigh LowerOrdovician of the Stavelot Massifis called 1979). Most of these spessartine-rich rocks, however, have “Salmian”.It has been subdivided into Salmian 1 (Sml), morequartz and less mica than the Belgian coticules.
[Show full text]