Coal forming environments in the tectonically controlled intermontane Stephanian Cévennes coal basin (Massif central, France) show a complex interelationship between structural and sedimentological features. The ...Coal forming environments in the tectonically controlled intermontane Stephanian Cévennes coal basin (Massif central, France) show a complex interelationship between structural and sedimentological features. The study of the general structural features and the geometry of the coal beds developed during the different stages in the evolution of the basin, and the spatial relation of the lithofacial units to the early tectonic activities, lead the authors to suggest the following model. The synsedimentary faults that occurred as both intrabasinal and marginal faults controlled not only the spatial distribution, shape and thickness of the detrital rock units and coal seams, but also caused the inversion of the tectonic style. The marginal faults exercised important controls on the geometry of the basin and the distribution of lithofacial units. However due to the subsidence of the central part of the basin and the depocenter, and the to differences in the timing and intensity of the displacement the coal enrichment zones shifted both vertically and laterally. This eventually resulted in the inversion of the whole tectonic framework from semi graben through graben to a new semi graben. The style and rate of the tectonic movement and basin filling that occurred in the Stephanian Cévennes coal basin were in turn closely linked with the tectonic movement in the surrounding area. Therefore the authors propose that the environment and processes of coal formation in this basin are closely linked to its tectonic evolution.展开更多
During late Westphalian and early Stephanian(late Moscovian)times there was a progressive westward withdrawal of the coal swamps from across Euramerica,eventually being restricted mainly to the basins of the Interior ...During late Westphalian and early Stephanian(late Moscovian)times there was a progressive westward withdrawal of the coal swamps from across Euramerica,eventually being restricted mainly to the basins of the Interior Province of North America.These changes can be correlated with the northwards migration of the Variscan Front that disrupted landscapes and drainage patterns.The resulting better-drained substrates caused localised change in the swamp vegetation from being lycopsid-to fern-dominated.Compared with the lycopsids,the ferns had non-determinate growth that produced less biomass per unit area,as well as producing vegetation with a more closed canopy,factors which combined to reduce overall evapo-transpiration.This in turn caused localised reductions in rainfall,which further affected the ability of the lycopsids to dominate the swamp vegetation.By Asturian times,most European coal swamps had mixed lycopsid-fern and fern dominated vegetation,eventually to be replaced by predominantly conifer and cordaite dryland vegetation.Lycopsid-dominated coal swamps persisted only in the westernmost parts of Euramerica,in the coalfields of the Interior Province of the USA,but even here they had disappeared by middle-late Cantabrian times.This tectonically-driven decline in the Euramerican coal swamps was probably responsible for an annual increase in atmospheric CO_(2) of c.0.37 ppm,and may have been implicated in the marked increase in global temperatures near the Moscovian-Kasimovian boundary,and the onset of the Late Pennsylvanian nonglacial interval.展开更多
文摘Coal forming environments in the tectonically controlled intermontane Stephanian Cévennes coal basin (Massif central, France) show a complex interelationship between structural and sedimentological features. The study of the general structural features and the geometry of the coal beds developed during the different stages in the evolution of the basin, and the spatial relation of the lithofacial units to the early tectonic activities, lead the authors to suggest the following model. The synsedimentary faults that occurred as both intrabasinal and marginal faults controlled not only the spatial distribution, shape and thickness of the detrital rock units and coal seams, but also caused the inversion of the tectonic style. The marginal faults exercised important controls on the geometry of the basin and the distribution of lithofacial units. However due to the subsidence of the central part of the basin and the depocenter, and the to differences in the timing and intensity of the displacement the coal enrichment zones shifted both vertically and laterally. This eventually resulted in the inversion of the whole tectonic framework from semi graben through graben to a new semi graben. The style and rate of the tectonic movement and basin filling that occurred in the Stephanian Cévennes coal basin were in turn closely linked with the tectonic movement in the surrounding area. Therefore the authors propose that the environment and processes of coal formation in this basin are closely linked to its tectonic evolution.
文摘During late Westphalian and early Stephanian(late Moscovian)times there was a progressive westward withdrawal of the coal swamps from across Euramerica,eventually being restricted mainly to the basins of the Interior Province of North America.These changes can be correlated with the northwards migration of the Variscan Front that disrupted landscapes and drainage patterns.The resulting better-drained substrates caused localised change in the swamp vegetation from being lycopsid-to fern-dominated.Compared with the lycopsids,the ferns had non-determinate growth that produced less biomass per unit area,as well as producing vegetation with a more closed canopy,factors which combined to reduce overall evapo-transpiration.This in turn caused localised reductions in rainfall,which further affected the ability of the lycopsids to dominate the swamp vegetation.By Asturian times,most European coal swamps had mixed lycopsid-fern and fern dominated vegetation,eventually to be replaced by predominantly conifer and cordaite dryland vegetation.Lycopsid-dominated coal swamps persisted only in the westernmost parts of Euramerica,in the coalfields of the Interior Province of the USA,but even here they had disappeared by middle-late Cantabrian times.This tectonically-driven decline in the Euramerican coal swamps was probably responsible for an annual increase in atmospheric CO_(2) of c.0.37 ppm,and may have been implicated in the marked increase in global temperatures near the Moscovian-Kasimovian boundary,and the onset of the Late Pennsylvanian nonglacial interval.
