Ammonite fauna and biostratigraphy of the Jurassic in Sierra de Reyes (Mendoza, Argentina)

The biostratigraphically important ammonitina of Sierra de Reyes, southernmost Mendoza province, eastern margin of the central part of the Neuquén Basin are identified and key taxa are illustrated. Sierra de Reyes is a north-south oriented brachyanticline, with a nucleus of Upper Triassic-Lower Jurassic volcanics and continental beds, and Middle-Upper Jurassic marine strata at its western and eastern limbs. Three and five sections were studied on the western and eastern slopes, respectively, and 79 fossiliferous localities were sampled. A succession of 16 bio- and chronostratigraphic units was identified, spanning the interval from the Aalenian to the Oxfordian, resting on top of Upper Triassic-Lower Jurassic volcanics and continental beds and capped by the gypsum of the Auquilco Formation. Most of these zones are widely recognized in the southern Andes. The zonation is as follows: 1: Bredyia manflasensis Assemblage Zone, Lower to Middle Aalenian; 2: Westermanniceras groeberi Assemblage Zone, Middle Aalenian; 3: Malarguensis Standard Zone, Upper Aalenian to Lower Bajocian; 4: Singularis Standard Zone, lower Lower Bajocian; 5: Giebeli Standard Zone, middle Lower Bajocian; 6: Humphriesianum Standard Chronozone, upper Lower Bajocian; 7: Rotundum Standard Chronozone, Lower Upper Bajocian; 8-10: Morphoceras gulisanoi Assemblage Zone; 9: Cadomites-Tulitidae mixed assemblage, (? Lower-) Middle, and Upper Bathonian; 10: Steinmanni Standard Zone Uppermost Bathonian, with one local horizon: Stehnocephalites gerthi horizon; 11: Vergarensis Zone, Bathonian Callovian boundary; 12: Bodenbenderi Zone, Lower Callovian; 13: Proximum Standard Zone, uppermost Lower Callovian); 14: Rehmannia patagoniensis Horizon, Middle Callovian; 15: Peltoceratoides – Parawedekindia Assemblage Zone, Upper Callovian-Lower Oxfordian; 16: Perisphinctes-Araucanites Assemblage Zone, upper Lower and Middle Oxfordian.