Estratigrafía de las rocas metasedimentarias (Neoproterozoico-Cámbrico) de la Sierra de Mojotoro, Cordillera Oriental Argentina

the basement of argentine eastern cordillera is an heterogeneous succession of siliciclastic and chemical rocks of neoproterozoic-early cambrian age, identified as the "precambrian basement" (keidel, 1910) underlying with angular unconformity the cambrian and ordovician deposits of the mesón and santa victoria groups. the unit was defined as the puncoviscana formation (turner, 1960) in the santa victoria range, and assigned to the neoproterozoic-cambrian (mirré and ace？olaza, 1972) due to the presence of oldhamia, a trace fossil of the lower cambrian. however, the puncoviscana formation s.l. (ace？olaza and ace？olaza, 2005) is often adopted to identify all the basement of eastern cordillera, representing a heterogeneous group of rocks affected by low-grade metamorphism. the basement of the mojotoro range is part of the 1a tecto-metamorphic zone, as defined by willner (1990). they are part of a near-surface structural level in which the sedimentary characteristics and the original microfabric could be studied in detail (fig. 1). from structural, stratigraphic and mineralogical information, a discontinuity (fault) could be inferred, and a new early cambrian stratigraphic unit named the guachos formation (moya, 1998) in the mojotoro range can be defined. the main purpose of this contribution is to characterize the similarities and differences between the stratigraphic units of the basement in the mojotoro range (lower-middle cambrian) in order to assess their relative stratigraphic position. the metamorphic grade was established from the cartographic material and sedimentological, petrographical and mineralogical characterization, and enabled the identification of three stratigraphic units (fig. 1): the chachapoyas, the alto de la sierra and the guachos formations. satellite images and aerial photographs were used to build up a map of the studied area, with structures, lithologic contacts and sampling sites placed using gps. the compositional studies of the field sample