Mollusks of the Upper Jurassic (upper Oxfordian-lower Kimmeridgian) shallow marine Minas Viejas Formation, northeastern Mexico

• First detailed record of marine invertebrates from the Upper Jurassic Minas Viejas Formation.
• Stratigraphy and paleogeography of ammonites, bivalves and gastropods.
• Taxa are predominantly endemic to the ancient Gulf of Mexico, some show affinities to the European Tethys.

We present the first systematic description of Late Jurassic (late Oxfordian-early Kimmeridgian) invertebrates from the shallow marine Minas Viejas Formation of northeastern Mexico. The unit was generally considered to be extremely poor in fossils, due to an overall evaporitic character. The collection described here includes three taxa of ammonites, 10 taxa of bivalves and five taxa of gastropods. The fossils were discovered near Galeana and other localities in southern Nuevo León and northeastern San Luis Potosí, in thin-bedded marly limestones intercalated between gypsum units. Due to complex internal deformation of the sediments, fossils used for this study cannot be assigned to precise layers of origin. However, the taxa identified suggest a Late Jurassic (late Oxfordian–early Kimmeridgian) age for these fossil-bearing layers and allow us, for the first time, to assign a biostratigraphic age to Upper Jurassic strata in the region underlying the La Caja and La Casita formations.

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