Origin of Dinantian zebra dolomites south of the Brabant-Wales Massif, Belgium
Version of Record online: 5 JAN 2002
Volume 45, Issue 4, pages 727–743, August 1998
How to Cite
NIELSEN, P., SWENNEN, R., MUCHEZ, PH. and KEPPENS, E. (1998), Origin of Dinantian zebra dolomites south of the Brabant-Wales Massif, Belgium. Sedimentology, 45: 727–743. doi: 10.1046/j.1365-3091.1998.00171.x
- Issue online: 5 JAN 2002
- Version of Record online: 5 JAN 2002
Zebra dolomites, characterized by a repetition of dark grey (a) and light (b) coloured dolomite sheets building up abbabba-sequences, occur in Dinantian strata from deep boreholes (> 2000 m) south of the Brabant-Wales Massif in Belgium. These zebra dolomite sequences are several tens of metres thick. The dark grey dolomite sheets (a) consist of non-planar crystals, 80–150 μm in diameter. These crystals display a mottled red–orange luminescence and are interpreted to be replacive in origin. The white dolomite sheets (b) consist of coarse crystalline nonplanar b1 dolomite, which evolves outwards into transparent saddle shaped b2 dolomite. The b1 dolomites possess a mottled red–orange luminescence similar to the a dolomites, while the saddle shaped b2 rims display red to dark brown luminescent-zones. The b1 dolomites are possibly partly replacive and partly cavity filling. Their b2 rims display criteria typical for a cement origin. Locally, cavities exist between two succeeding white dolomite sheets. These cavities make up ≈5% of the zebra rocks and are locally filled by saddle shaped ankerite and/or xenomorphic ferroan calcite.
Geochemical and fluid inclusion data (Th ≈ 120 °C) indicate a burial diagenetic origin for these zebra dolomites. The a and b1 dolomites are characterized by similar geochemical compositions and fluid inclusion data pointing toward a related origin. To explain the development of the zebra textures, suprahydrostatic pressures in conjunction with late Variscan tectonic compression are invoked. A model involving dolomitizing fluids expelled during the Variscan orogeny is proposed. An overpressured system is also invoked to explain the important porosity development, the creation of centimetre-scale subvertical displacements of the zebra pattern and the microfractures affecting the b1–b2 dolomite crystals.