According to its original definition, the Artes Formation is formed by the ensemble of continental, red mudstones and sandstones interbedded with conglomerates resting on top of the marine deposits of the Bartonian to Priabonian Santa Maria Croup. However, detailed mapping clearly shows that those marine rocks are laterally equivalent to distal alluvial fan facies of the "Artes type". On the basis of our present sedimentological knowledge these facies can not be differentiated from those forming the Artes Formation sensu stricto .Therefore, we propose a new definition for the entire formation that includes its subdivision into two members