The Minas Viejas Formation consists of carbonates and sulfates that are the first evidence of marine incursion into northeastern Mexico during the Late Jurassic (Oxfordian). In the area southwest of Galeana, Nuevo Leon, this evaporite sequence is intensively deformed, but a consistent stratigraphic succession and separation of two members is recognizable. In addition to the Las Minas Member that was defined by Gtte (1988), we introduce the La Primavera Member. Our data suggest that only one largely evaporitic succession exists in the region and that the terms Minas Viejas and Olvido are synonyms for the same stratigraphic unit. Lateral and vertical changes of facies in the Minas Viejas Formation are the result of syndepositional normal faulting and relate to the onset of sea-floor spreading in the Gulf of Mexico. Alkaline volcanic rocks occur in the La Primavera Member of the Minas Viejas Formation. This Oxfordian volcanism is hitherto undescribed in the area and links the tectonostratigraphic evolution of northeastern Mexico to early sea-floor spreading in the Gulf of Mexico. In addition, barite deposits in the Galeana area likely are related to this Late Jurassic volcanism. Barite mineralization is restricted mainly to stratigraphic levels older than the alkaline volcanism in the Minas Viejas Formation and is not the result of magmatism of Tertiary age. Apparently, carbonatite magmatism that provided the source for barium by hydrothermal activity was associated with Late Jurassic volcanism.