Oolitic ironstones as event-stratigraphical marker beds within the Upper Devonian of the Ardenno-Rhenish Massif

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Abstract
Summary: Seven stratigraphically distinct, Clinton-type oolitic ironstones occur in the Upper Devonian of the Ardenne shelf, south of the London-Brabant Massif. They occur at the lithofacies boundary of succeeding lithological units and represent condensed deposits associated with hardgrounds and shoaling upward sequences. Microfacies analysis points to storm-generated concentration, removal and subsequent transport of the ferruginized allochems. The ironstones represent excellent marker beds which can be traced over several tens of kilometres on the palaeoshelf. Conodonts provide further evidence for the allochtonous character of the allochems and have enabled precise dating and correlation of each ironstone level with synsedimentary volcanic and tectonic events in the Rhenish Massif. Although the source of the iron is still a matter of discussion, lateritic weathering is not accepted here; instead, volcanism and evapotranspiration processes might represent potential sources for the iron in the studied ironstones.

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