Geological setting and genesis of coticules (spessartine metapelites) in the Lower Ordovician of the Stavelot Massif, Belgium

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Abstract
The Lower Ordovician in the Caledonian Stavelot Massif (Belgium) contains a coticule member, probably Arenig in age, composed of red hematite-rich shales alternating with thin yellowish coticule beds. These coticules are fine-grained highly manganiferous metamorphic 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 have originated from marly sediments which had been deposited rapidly, probably by density currents, and in which CaCO 3 had been diagenetically replaced by MnCO 3. During metamorphism, spessartine garnets were formed from this MnCO 3 and mica. Manganese and iron are thought to have originated from volcanic-exhalative processes.