Genesis and rank distribution of Upper Carboniferous coal basins in the Cantabrian Mountains, Northern Spain

A coals (Rr < 6.0%). The regional rank distribution can be correlated with the increase in the thermal effect observed from Westphalian to the Stephanian coals, and from the Cantabrian Zone to the West Asturian-Leonese Zone. These rank variations are related to the thermal processes caused by the emplacement of some major faults, and granitoids and mafic rocks in upper crustal levels and the subsequent development of the regional methamorphic contact aureoles.