Abstract

The basement terrane of the La Gloria-Presa Rodríguez area includes Upper Jurassic and/or Lower Cretaceous intermediate-composition volcanic and derived epiclastic rocks, gabbro, granodiorite, and quartz monzonite. The post-batholithic sequence consists of conglomerates of the Upper Cretaceous Redonda Formation (new name); shales, mudstones, and sandstones of the Upper Cretaceous Rosario Formation; conglomerates, sandstones, mudstones and shales of the Eocene Buenos Aires and Delicias Formations (new names); sandstones and basalts of the Miocene Rosarito Beach Formation; and Pliocene-Pleistocene capping conglomerates and sandstones.

The Upper Cretaceous Redonda Formation is composed of moderately rounded cobbles of quartzite, felsite porphyry, and volcanic breccia deposited on a high-relief Lower Cretaceous basement. The Eocene Delicias Formation is divided into a lower mudstone and an upper sandstone member. The sandstone member contains a brackish-water fauna with abundant Potamides and Ostrea. The overlying Buenos Aires Formation is divided into a lower conglomerate member and an upper sandstone member. The sandstone member contains an abundant megafauna, including characteristically tropical marine species of Turritella, Ficopsis and Tellina.

The structural history of the area includes deformation and erosion of the Lower Cretaceous metavolcanic and granitic rocks followed by persistent relative stability. The overlying younger strata exhibit only low inclinations, in part to the southwest, and in part to the northeast. Post-batholithic strata are cut by numerous high-angle, northeast-southwest-trending, normal faults. Several related small anticlines and synclines are developed in the area.

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