The Noreán Formation is found in the northern part of the Eastern Ranges of the Colombian Andes, stretching from the Cesar Department in the north, towards the Serranía de San Lucas in Bolívar to the Santander Massif in Santander in the south. The formation forms the economic basement in the southern Lower Magdalena Valley (VIM) and the northern Middle Magdalena Valley (VMM). The formation is interpreted as characteristic of an important explosive volcanic phase, the materials of which were deposited in a graben setting of the Middle Magdalena Valley. The Early Jurassic basin was covered by a shallow sea and in part drained by rivers and lakes. The basin at time of deposition was bordered by a volcanic arc, characterized by basaltic to calc-alkaline magmas. The formation also comprises less than thin very fine to fine sandstone beds constituting quartz (90 to 60 %), feldspars (10 to 40 %) and lithic fragments (1-2 %).