« FAMENNE-ARDENNE » REFERS TO THE GEOLOGICAL AND GEOMORPHOLOGICAL UNITS OF THE GEOPARK.
1. To the south, the ARDENNE : Lower Devonian shale, sandstone and puddingstone.
2. In the centre, CALESTIENNE : Givetian and Frasnian limestone.
3. To the north, the FAMENNE depression : Famenne shales.
To the far north of the Geopark, in the Terre de Durbuy, a brief incursion into the Condroz, folded rocks from the Famennian Stage and Carboniferous Period. The geological history of the Geopark is divided into 5 phases.
1. SEDIMENTATION. During the Devonian and Lower Carboniferous : deposits in horizontal layers on the seabed.
2. DIAGENESIS. Compaction of the sediments and formation of rocks : sandstone, shales, limestone.
3. TECTONICS. Circa 325 Ma, formation of a mountain chain (the Variscan chain), containing folds such as the Durbuy anticline and joints.
4. EROSION. Formation of a vast flat surface (peneplain). Followed, during the Secondary and early Tertiary, by chemical attack on the rock in a hot, humid climate. Formation of ghost-rocks or weathered limestone, precursors of caves.
5. REJUVENATION. Second half of the Tertiary, uplift of the Ardenne base, incision of rivers to form valleys and formation of caves from eroded ghost-rocks.
FIG 1 Palaeographic map of the world showing the location of the continents during the Givetian stage (Scotese 2014). Belgium is located along the Tropic of Capricorn.
FIG 2 Simplified geological map.
FIG 3 Chronostratigraphic scale or geologic timescale, focusing on the Devonian and Carboniferous. The Earth’s history has been broken down into various subdivisions : era, system, stage. The Eifelian, Givetian, Frasnian and Famennian were defined in the late 19th century on the basis of a description of the reference profiles located not far from the Geopark, in Eifel, Givet, Frasnes or in the Famenne respectively.
FIG 4 A 24 hours Earth’s history.
FIG 5 Durbuy anticline.