Permian fusulinids from Cobachi, central Sonora, Mexico

Abstract

Upper Paleozoic rocks in the Cobachi area of central Sonora, Mexico, include the Picacho Colorado and La Vuelta Colorada formation of Carboniferous?-Permian age. A 155 m carbonate succession of the Picacho Colorado Formation, exposed on the east side of Cerro Picacho Colorado, a few kilometers southeast of Cobachi, consists of pinkish and reddish limestone, cherty limestone with some recrystallization, and bioclastic gray limestone. Crinoids, bryozoa, brachiopods and foraminifers are present indicating a marine shallow water shelf depositional environment. Well preserved fusulinaceans occur near the top of the section, but are scarce, partially silicified, and poorly preserved in the middle part and the base of the section. Skinnerella cobachiensis n. sp., Paraskinnerella cf. P. durhami, Parafusulina P. cf. P. multisepta and three unnamed species of Parafusulina of early Permian (Leonardian) age are described from this succession. The fusulinacean assemblage from this area has affinities with forms found in rocks with similar age in east central California, west Texas, southeast Mexico, and Central and South America.