The geologic evolution of the Campos basin, offshore southeastern Brazil, is linked to Mesozoic rifting that separated Africa and South America. Lagoa Feia is the basal Lower Cretaceous synrift formation in the stratigraphic sequence of the basin. It formed in a complexly evolving system of rift lakes of variable size and chemistry, overlying and closely related to rift volcanics. Lacustrine limestone and shale and alluvial fan volcaniclastic conglomerates dominate. The lake sequence reaches thickness of 3500 m and is capped by marine evaporites.

Organic-rich lacustrine shale of the Lagoa Feia Formation is the main source rock for the oil discovered to date in the Campos basin. Pelecypod coquinas constitute the intraformational reservoirs within a limited region. Lacustrine shale also sources reservoirs in overlying Cretaceous platform carbonates and Cretaceous and Tertiary turbidites, including those of the giant Albacora and Marlim fields. Lagoa Feia strata compare well with younger lake deposits of the east African rift system, which provide useful analogs for development of exploration models in the Lagoa Feia.