Abstract

CICCIOLI, P.L.; LIMARINO, C.O.  and  MARENSSI, S.A.. New radiometric ages for the Toro Negro Fromation in the Sierra de los Colorados, northwestern Sierras Pampeanas. Rev. Asoc. Geol. Argent. [online]. 2005, vol.60, n.1, pp.251-254. ISSN 0004-4822.

New absolute ages derived from whole rock K/Ar dating of two vitric tuffs collected from the upper-middle part of the Toro Negro Formation in the outcrops of the Sierra de Los Colorados, Sierras Pampeanas Noroccidentales (La Rioja Province) are presented herein. The obtained values of 8,6 ± 0,3 Ma and 6,8 ± 0,2 Ma respectively, indicate an Upper Miocene age and challenge the previous Pliocene age proposed for this unit. The results presented here have a high degree of confidence because they do not show evidences of reworking, mixing with terrigenous clastics nor diagenetic alteration. The tuff levels were mapped and georeferenced using GPS coordinates and their close location in the stratigraphic column provides an additional control for the obtained ages.

Keywords : Toro Negro Formation; K/Ar ages; Upper Miocene; La Rioja Province.

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