In intermontane coal basins the organic matter maturation rate varies greatly with geodynamic conditions. The Stephanian basin of the Cevennes is a small hyperthermic basin which underwent early major faulting. The Westphalian-Stephanian basin of the Lorraine is larger, with minor early tectonic activity.In the Cevennes basin, coalification was controlled during the filling stage by basement topographic irregularities and heat-flow distribution in fault zones. The Rouvergue paleohorst acted as a hot zone. In the Lorraine basin, heterogeneity in coal-rank distribution is directly linked to variations in geothermal conductivity, which depends on lithology and mainly on the dip of the strata.In intermontane coal basins, geothermal gradients vary significantly in space and time. Hyperthermic conditions are characteristic of the filling stage and are chiefly linked to heat-flow circulation controlled by lineaments. In the Lorraine basin, present geothermal gradients are distinctly higher along anticlinal axes than along syncline axes. This characteristic is mainly concerned with coalification of younger seams which underwent major post-folding maturation.The geothermal history of intermontane coal-basins is polyphase. During successive filling, folding and covering stages, maturation conditions varied considerably, depending on where the coal seams were situated in the basin and also according to their stratigraphic position.
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- Polyphase Coalification in French Intermontane Coal Basins of the Late Carboniferous
X. B. Liu
- Springer Berlin Heidelberg