Stratigraphy and fossil mammals from the Toro Negro Formation (Neogene), Vinchina Department, northwestern La Rioja Province, Argentina.

摘要

The Toro Negro Formation is exposed in the western range of the Sierra de Los Colorados, in the North-West of La Rioja Province, Argentina. The sequence in La Troya creek (type section) is composed by a succession of epiclastic and piroclastic deposits, where thick-bedded sandstones and mudstones with interbedded conglomeradic lenses and tuff levels predominate. The facies analysis suggests a fluvial depositional environment of sand bed braided rivers for the lower Member and high efficiency alluvial fans for the upper Member. The species recorded are: Proeuphractus limpidus Ameghino, Chorobates villosissimus (Rovereto) Reig, Paleuphractus sp. Bordas, Doellotatus inornatus (Rovereto) Castellanos, Lomaphorops corallinus Rovereto, Neuryurus cf. giganteus, cf. Urotherium sp. (Mammalia, Cingulata), Xyophorus aff. bondesioi Scillato Yane, cf. Plesiontegatheriii tit, cf. Proscelidodon sp. (Mammalia, Tardigrada), Abrocoma sp., Protabrocoma sp., Propediolagus sp. (Mammalia, Rodentia), Eoatichenia sp. (Mammalia, Litopterna). This faunistic association suggests: 1) Lower Pliocene age; 2) climate conditions that changed from and to warm-temperate, or the development of and areas in a general context of more humid conditions; 3) open areas of herbaceous and shrub vegetation and arbo-real formation probably existed; 4) the record of the nothrotherin Xyophorus aff. bondesioi is related to the faunistic and climatic changes during the Middle Miocene; 5) the existence of a zoogeographic connection between the subandean and Pampean regions during the Pliocene.