The predominantly conglomeratic sandstone formation with interbedded shales dates to the Late Cretaceous period; Cenomanian-Maastrichtian epochs and has a maximum thickness of 2,700 metres (8,900 ft).

The Santos Formation is 1,275 to 2,700 metres (4,183 to 8,858 ft) thick,[1] and consists of reddish lithic conglomerates and sandstones, interbedded with grey shales and reddish clays.

These facies are interbedded and change laterally into the Itajai-Açu and Juréia Formations.

The depositional environment is thought to be transitional continental to marginal marine, ranging from alluvial to braided rivers and deltas.

Biostratigraphic data indicate a Late Cretaceous age (Cenomanian-Maastrichtian).