Paleontological and microfacial features of the Las Chacritas Formation (Middle Ordovician), Central Precordillera, San Juan Province, Argentina

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

Évora - Portugal

Congreso; I Congresso Ibérico de Paleontología-XVI Jornadas de la Sociedad Española de Paleontología; 2000

Sociedad Española de Paleontología

ABSTRACT: The regional correlation and tectosedimentary significance of an upper Arenigian-lower Llanvirnian carbonate sequence of the Las Chacritas Formation, 55 m thicknes, outcropping at the sierra de La Trampa, San Juan Precordillera, Argentina, is analysed. The age of this sequence has been established on the basis of its conodonts contents, which indicate the Leonodus variabilis Zone. At the base the Las Chacritas Formation overlay conformably limestones of the San Juan formation (Arenigian), and at the top is overlain in paraconcordance by calcareous black shales of the Las Aguaditas Formation (Lower Caradocian). Las Chacritas Formation is composed mainly of limestones, mudstones, marls and wackestones. This sequence includes in the middle part a conspicuous slumped level, which is also recorded in others equivalent units of the Precordillea, such as Las Aguaditas Formation, at its type locality and Gualcamayo Formation at the Villicum range. We suggest that such slumped level is coeval for all this units, as a result of a tecto-sedimentary event, this way, the slumped level can be considered as useful level for correlation.