Stratigraphy and first dating of the Las Arcas Formation in the Santa Maria Valley, Salta Province, Argentina

SPAGNUOLO, C.M.; GEORGIEFF, S.M.; RAPALINI, A.E.

Mendoza

Congreso; 18th International Sedimentological Congress; 2010

International Association of Sedimentologists

The Santa María Valley is a tectonic NNW-SSE depocenter located in NE Catamarca, NW Tucumán and SE Salta. It is limited by the Aconquija Ranges and the Cumbres Calchaquíes to the east and to the west by the Quilmes Ranges. The general stratigraphy of this region begins with a Lower Cambrian to Precambrian metamorphic and igneous basement (Ruiz Huidobro 1966, Toselli and Rossi 1998, Toselli et al 1999) and continues with the Cenozoic strata. The Cenozoic units are composed by the Saladillo Formation (Paleogene; Galván and Ruiz Huidobro 1965; Bossi et al. 2001) and the Santa María Group (Neogene; Ruiz Huidobro 1960, Galván and Ruiz Huidobro 1965) divided into the San José, Las Arcas, Chiquimil, Andalhuala and Corral Quemado Formations. Above them lies the Yasyamayo Formation and Quaternary deposits. The study was carried out in the Las Arcas Formation in the Totoritas Creek that is a tributary creek of the Santa María River in southern Salta Province. The outcrops begin with yellow-greenish mudstones of the San José Formation that passes transitionally to siltstones and sandstones red beds belonging to the Las Arcas Formation. A ~820m stratigraphic log was measured and sampled on this unit. The column begins with red fine lacustrine sediments which gradually passes into orange-red coarse sandstones and conglomerates. According to the stratigraphic correlation Las Arcas Formation has been assigned as Middle-Upper Miocene. In the outcrops of the Totoritas Creek, at 47 m from the base of the first red bed a tuff is intercalated in the siltstones strata. This tuff was dating by Ar-Ar method and the results indicate an age between 8.79 +/- 0.14Ma. A magnetostratigraphic study is also being carried out in the Las Arcas Formation. The preliminary results suggest the presence of a magnetic component carried by ilmenohematites and titanomagnetites. These studies will give information about the age of the unit, deposition timing and sedimentary rates. Bossi, G.E., Georgieff, S.M., Gavriloff, I.J.C., Ibañez, L.M. and Muruaga, C.M. (2001). Cenozoic evolution of the intramontane Santa María basin, Pampean Ranges, northwestern Argentina. Journal of South American Earth Sciences, 14, 725-734. Galván, A. and Ruiz Huidobro, O. (1965). Geología del Valle de Santa María. Estratigrafía de las formaciones mesozoica-terciarias. Acta Geológica Lilloana, 7, 217-230. Ruíz Huidobro, O. (1960). Descripción Geológica de la Hoja 8e, Chicoana, Provincia de Salta. Boletín de la Dirección Nacional de Geología y Minería 89, 1-46, Buenos Aires. Ruíz Huidobro, O. (1966). Contribución a la geología de las Cumbres Calchaquíes y Sierra del Aconquija (Tucumán–Catamarca). Acta Geológica Lilloana, 8, 215pp. Toselli, J.A. and Rossi, J.N. (1998). El basamento metamórfico- ígneo de las Sierras Pampeanas de la Provincia de Tucumán. In: Geología de Tucumán (Eds. Gianfrancisco, M., Puchulu, M.E., Durango de Cabrera, J. and Aceñolaza, G.F.). Colegio de Graduados en Ciencias Geológicas de Tucumán, pp. 47–56. Toselli, J.A., López, J.P. and Sardi, F.G. (1999). El basamento metamórfico en Cumbres Calchaquíes noroccidentales, Aconquija, Ambato y Ancasti: Sierras Pampeanas. In: Relatorio XIV Congreso Geológico Argentino (Eds. González Bonorino, G., Omarini, R. and Viramonte). Geología del Noroeste Argentino, 1, 73–79.