ESTRATIGRAFIA DEL ORDOVICICO DEL RIO DE LAS CHACRITAS, SIERRA DE LA TRAMPA, PRECORDILLERA CENTRAL DE SAN JUAN, ARGENTINA.

PERALTA, SILVIO H.; HEREDIA, S.E.; BERESI, M.S.

Salta

Congreso; XIV Congreso Geológico Argentino; 1999

Asociación Geológica Argentina

            An overview focused on the stratigraphic features of the Ordovician, post-San Juan Formation, outcropping in the La Trampa range, Central Precordillera of San Juan Province, Argentina, is given in this paper. New data and reports in progress are presented in this contribution. On the other side, recurrent problems concerning to the litho and biostratigraphy of the Ordovician unites are discussed. On the basis of this data, in the Las Chacritas river and the Las Tunas sections, a new Late Arenigian-Early Llanvirnian lithostratigraphic unite is recognised, which bears conodonts of the Lenodus variabilis Zone. Such unite named Las Chacritas Formation, 54 m in thickness, is composed mainly of carbonate deposits, overlaying in stratigraphic discontinuity (paraconformity) the limestones of the San Juan Formation, which is Arenigian in age. At the tope, the contact with the basal deposits of the overlaying Las Aguaditas Formation, lower Caradoc in age, is an erosional surface. On the basis of the biostratigraphic data, the carbonate succession of the Las Chacritas Formation is correlative with Lower Member of the Gualcamayo Formation, however, from a lithostratigraphic point of view, strong differences there are between both unites. On the other hand, the overlaying mixed (marly-siliciclastic) Lower Caradocian deposits can be certainly correlated with the Las Aguaditas Formation, take in account their litho and biostratigraphic features.