Continental Eocene of Mendoza: new data and biostratigraphic implications

VERA, BÁRBARA; TUNIK, MAISA; CERDEÑO, ESPERANZA

Mendoza

Congreso; IV International Paleontological Congress; 2014

Among the Cenozoic vertebrates of Mendoza Province (Argentina) listed by Pascual and de la Fuente, the authors referred to some fossils collected by the geologist Estanislao Kozlowski in the area named Agua de Flores, Malargüe Department. These remains were considered belonging to the Family Oldfieldthomasiidae (Notoungulata) and are housed in the Museo de La Plata (MLP 96-VIII-15-1, two right mandibles: one with m1-m2 and other with two broken teeth; and MLP 96-VIII-15-2, a calcaneum, an astragalus, and vertebrae). In an unpublished report, Kozlowski described two separated geologic sections in the area, Agua de Flores I and II, and mentioned some isolated mammal bones from the base of the Laguna Blanca Group, a unit considered to be late Oligocene. However, the specimen MLP 96-VII-15-1 was determined as aff. Peripantostylops (Henricosborniidae), a notoungulate known in Cañadón Vaca (Chubut Province), a locality considered to represent the Vacan South American Land Mammal Age (lower-middle Eocene). Based on this background, since 2008, we began to explore the outcrops surrounding the area between Puesto Agua de Flores and Puesto Agua de Isaac, distant approximately 8 km from each other and located at the east of Sierra Cara Cura. Recently, near Agua de Isaac, we recovered other isolated specimens from a tuffaceous sandstone 2 m thick, located 108 m above the angular unconformity that separates the Malargüe and Laguna Blanca Groups. This last unit can be correlated with the pre-orogenic sequence of Silvestro and Atencio, previously set on the Oligocene based on the age of overlying basalts. The new fossils (housed in the Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales, Mendoza) include a maxillary fragment (IANIGLA-PV 85) bearing two brachydont teeth (P3-P4?) with close roots and a large, irregular central fossette, a mandibular symphysis lacking teeth (IANIGLA-PV 83) and a fragment of bone (IANIGLA-PV 82). Despite their bad preservation, the teeth resemble the morphology of Eocene notoungulates from Patagonia as it happened with MLP 96-VIII-15-1. Besides, the astragalus MLP 96-VIII-15-2 shows also an oldfieldthomasiid appearance. The presence of these notoungulate remains with Eocene affinities would therefore change the span of the pre-orogenic stage of the basin in the Malargüe fold and trust belt. Besides, it constitutes a new record for the Paleogene of Mendoza Province and Argentina, and an interesting novelty for further geologic, paleontological and biostratigraphic studies.