REVISION ESTRATIGRAFICA DEL NEOGENO DE LAS HUAYQUERIAS DE MENDOZA SEPTENTRIONAL, ARGENTINA

Marcelo R. Yrigoyen

Abstract


Several radimetric ages of mineral separates of tuffaceous horizons interbedded in the mammal-bearing Late Cenozoic formations of Mendoza province (west-central Argentina) were published by Marshall el al. in 1986. The oldest one belongs to the top of the Late Miocene Huayquerías Formation, correctly dated with an average age of 5.8 ± 0.1 Ma by sample LGM 236. The stratigraphic position of other two dated tuffs; erroneously assigned to the Tunuyán Formation, was the objective of our detailed geologic and stratigraphic revision of the Río Seco de la Salada area. The main conclusions of that field survey, as well as other observations derived from regional systematic detailed mapping also carried in the Huayquerías de San Carlos and Huayquerías del Este region are summarized as follows: l. The deposition of the Tunuyán Formation, with not yet known radimetric dating, is of an Early Pliocene age, probably between 5.5 Ma and 3.8 Ma. 2. The Procyonidae Chapalmalania altaefrontis Kraglievich & de Olazábal was collected near the middle section of the Tunuyán Formation belonging to the Chapadmalalian Land-Mammal Age; 3. The Marshall el al. dated tuff LGM 233, with an average age of 2.6 ± 0.1 Ma belongs to the Lower La Represa Member of the Bajada Grande Formation; 4. The Marshall el al. dated tuff LGM 235, with an average of 2.4 ± 0.3 Ma, belongs to the Middle Member of the Bajada Grande Formation, of Late Pliocene age; 5. The Glyptodontidae Plohophorus yrigoyeni Castellanos was collected in the La Represa Member of the Bajada Grande Formation; 6. The Mesotheriidae Pseudotypotherium subinsigne Rovereto was collected by Dessanti (1946) in the lower section of the Tunuyán Formation, belonging to the Montehermosan Land-Mammal Age; 7. The fossiliferous Bajada Grande Formation of the Huayquerías region is equivalent to the Mogotes Formation of the Pilona-Tupungato region, both formations of a Late Pliocene age; 8. Within the Cenozoic non marine section cropping out in the Huayquerías region two erosional and slightly angular unconformities are exposed. The first one between the Huayquerías Formation and the Tunuyán Formation; the second one between the Tunuyán Formation and the El Quemado Tilloid Member or between the Tunuyán Formation and La Represa Member of the Bajada Grande Formation when the Tilloid was not deposited.

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