Geological record and sedimentology of the Palaeozoic oolitic ironstone deposits in Western Europe. Spatial relationships with the Linienbandkeramik settlements (LBK) in Belgium.

Mined since prehistoric times, oolitic ironstones (OIS) were a very important world source of iron
from 1850 to 1945: hereafter they have been progressively replaced by the Precambrian Banded Iron-
Formations (BIF). OIS are iron-rich sedimentary rocks bearing ferruginous ooids. They consist of at
least 15% iron. In Western Europe, their overall depositional environment is that of a shallow shelf,
most often located close to the transition from non-marine to marine environments. Their main age
range is concentrated within the Ordovician through Devonian and the Jurassic through Paleogene.
Proterozoic occurrences are known but these occur outside Europe. The host rocks of the ironstones
are predominantly clastic, whereas the host sediment of the ferruginous ooids can be either clastic or
carbonate or both. The OIS occur at the top of coarsening and shoaling upward cycles. They represent
condensed deposits and transgressive system tracts. Numerous oolitic ironstone deposits are
interpreted as tempestites or as intertidal deposits.
It is generally agreed that ferruginous ooids formed in shallow marine water conditions, near the
water-sediment interface, with repeated reworking of the sediment. Such an environment implies
oxidizing conditions, the sedimentary iron being in the ferric state. The exact source of the iron is still
a matter of discussion and speculation, just as the primary or secondary origin of the ferruginous
ooids. Besides hematite (or goethite), also siderite, Fe-dolomite and berthierine/chamosite are present
in the OIS as iron-bearing minerals. Due to weathering processes the carbonate matrix is often
removed, the iron is released and oxidized, whereas the ferrous silicates are converted into ferric
oxides or ferric hydroxides. Many old mining activities are based on occurrences of this weathered
ore. The latter material has also strong staining properties.
1. Germany
OIS are outcropping in the Eifel area. The latter is part of the Ardenno-Rhenish Massif and lies in the
eastern extension of the Neufchateau Synclinorium, south of the Ardenne Anticlinorium (enclosing the
Cambro-Ordovician Stavelot-Venn inlier). The general structure of the Eifel corresponds to an
intensively folded and faulted synclinorium In the center of this synclinorium, outcrops of OIS occur
on both flanks of successive synclines that are individually named (from the north to the south): the
Sötenicher Mulde, the Blankenheimer Mulde the Rohrer Mulde, the Dollendorfer Mulde, the
Ahrdorfer Mulde and the Hillesheimer Mulde. Two important stratigraphic levels with IOS are known
and they coincide more or less with the Lower-Middle Devonian boundary (Uppermost Emsian-
Lowermost Eifelian). These OIS represent excellent marker beds for geological mapping.
2. The Netherlands
There is no outcrop of OIS in this country.
3. Belgium
Oolitic iron ores were formed during different periods in Belgium: the Lochkovian (Lower Devonian,
Dinant Synclinorium, restricted to the Belgian-French border), the Givetian (Middle Devonian, Dinant
Synclinorium), the Frasnian (Upper Devonian, Dinant Synclinorium), the Famennian (Upper
Devonian, Namur S., Dinant S. & Vesdre S.) and the Toarcian-Aalenian (Jurassic, Lorraine area, Paris
Basin – called “minette ore”). The most important OIS level is the Lower Famennian one. It has been
intensively mined until the middle of the 20th century, essentially in the Namur Synclinorium, between
the cities of Namur and Huy. In this area, its important thickness (until 1.85m) and the number of
layers triggered the development of an important economic activity. Outcrops were restricted to the
tributaries of the Meuse River. The Famennian oolitic ironstone facies change from north to south by a
gradual decrease in the number of layers, in their thickness, grain size, ooid concentration, clast size
and iron content. They represent also excellent lithostratigraphical marker beds. The clay-dolomitic
matrix is being progressively replaced by a calcitic cement. The other Devonian OIS levels are not of
great economic importance, they were only mined locally, to supply smith’s working places. Due to
surface mining, outcrops are now very rare, and often indicated by a light depression in the topography
only.
4. Grand-Duchy of Luxembourg
OIS are restricted to the Jurassic (Aalenian-Lower Bajocian) in the NW part of the Paris Basin. This
essentially goethitic ore (“minette”) was intensively mined in the three adjacent country borders area
(FR-BE-LU). No OIS levels in the Lower Devonian are outcropping in the northern part of the Grand
Duchy.
5. France
Numerous OIS layers are known in France at several stratigraphical levels, but a lot of them cannot be
considered as a real ore. Paleozoic OIS belonging to the Armorican Massif were mined in the
Normandy area (Urville Fm, Llanvirn, Middle Ordovician) and in the Bretagne area (Arenig, Lower
Ordovician). In Normandy, OIS do outcrop inside several synclines (e.g. May and Urville Sy.), as one
thick composite layer. 
The spatial relationships of the different oolitic ironstone levels with the Linienbandkeramik
settlements (LBK) in the studied area, will be presented.