Six new Tertiary lithostratigraphic units, each one corresponding to a separate stratigraphic sequence,
have been recognized in the southeast border of the Duero Basin (north of the Somosierra - Ayllón Sierra).
The age of these units is Paleogene-Late Miocene (Turolian) to Pliocene. The lower units are synorogenic,
consequence of the tectonic uplift on the Central System while the upper units are postorogenic. These
units are correlated with other ones of equal regional scale and well known age in the Duero Basi
