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2016-01-29 - Colloque/Présentation - poster - Anglais - 1 page(s)

Dupont Nicolas , Quinif Yves , Dubois Caroline , Kaufmann Olivier , "Speleogenesis by alterite erosion within ghost-rock features in the Ardenne Allochton (Sprimont syncline, East Belgium)" in 5th International Geologica Belgica Meeting, Mons, Belgique, 2016

  • Codes CREF : Sciences de l'ingénieur (DI2000), Géologie (DI1411), Sédimentologie (DI1415), Sciences de la terre et du cosmos (DI1400)
  • Unités de recherche UMONS : Géologie fondamentale et appliquée (F401)
  • Instituts UMONS : Institut de Recherche en Science et Ingénierie des Matériaux (Matériaux), Institut des Sciences et du Management des Risques (Risques)

Abstract(s) :

(Anglais) Ghost-rock karstification consist in the in-situ partial dissolution of carbonate rocks forming volumes of residual material (alterite) within the fresh rock. In-situ alterite volumes determine geometric features called ghost-rock features (GRF). Cavities may develop in a later phase by the internal erosion of in-situ alterite within GRF. This process of creating cave networks has been recently demonstrated experimentally. Evidence of GRF has been discovered in the Sprimont syncline, composed of lower-Carboniferous limestones. Several stages of weathering were highlighted in the Correux quarry, in the Ourthe Formation encrinite and the cherty limestone of Yvoir Formation. The most spectacular phenomena consist in two caves exposed in the northern front of the quarry. These caves are formed in a highly weathered part of the Yvoir Formation limestone. They are partly filled by detrital sediments. By place, flowstones seal in-situ alterite (both floor and walls) and detrital fillings. The highest stalagmitic flowstone was dated by uranium disequilibrium series, giving ages ranging from 53,851±2493 yBP to 61,542±1235 yBP (isotopic stage 4). Several facts strongly indicate that these cavities are formed within pre-existing weathered corridors. The walls of the caves are made of friable in-situ alterite. One of the cave is clearly located in the upper part of a GRF. Considering the shapes of the caves, these GRF would be formed along slightly N-S fractures. This fracture direction is common in the Sprimont syncline. To form the caves in the pre-existing ghost-rock features, friable parts of the alterite were eroded by underground streaming. This is comforted by several observations. The erosion left pillars of in-situ alterite, and one of them is conserved by a recent detrital filling. The later erosion of in-situ alterite below a stalagmitic flowstone has been observed. Moreover, limestone alteration products (i.e. weathered crinoids fragments) were found within the detrital fillings, mixed with typical minerals from upstream mid-Devonian formations. These facts suggest for the first time a direct evidence to link ghost-rock karstification to the formation of cave systems in the Ardenne Allochton.