Preliminary petrographic analysis from conglomerate olistoliths of the Rinconada Formation (Emsiano-Eifeliano?), Villicum Range, Eastern Precordillera, San Juan province.

HAMMAR, MARÍA VERÓNICA; PERALTA, SILVIO H.

San Juan, Argentina

Workshop; Field Meeting Project IGCP 499 (IUGS-UNESCO) ?Devonian land-sea interaction: evolution of ecosystems and climate?, p. 109-112. San Juan, Argentina.; 2007

Universidad Nacional de San Juan-Universidad Nacional Tucumán

A petrographic analysis of clasts from allochthonous conglomerate blocks included in the sedimentary mélange (olistostrome) of the Rinconada Formation, (Emsian- Eifelian?) has been performed. The study has been done in the stratigraphic section outcropping in the Rio del Alto Creek, on the eastern slope of the Villicum Eastern Precordillera, San Juan Province. Therein, a more or less continuous Early Paleozoic marine succession outcrops which is made up by the Early Ordovician fossiliferous limestone of the San Juan Formation, (Tremadoc to Darriwil), then the graptolite-rich black shale of the Darriwilian Gualcamayo Formation, 39 m thick, which is paraconformably overlay by the siliciclastic early Sandbian La Cantera Formation, which in turn is paraconformably overlain whether by coarse-grained Katian deposits of the La Pola Formation, 47m thick, or by the basal glaci-marine diamictite of the Hirnantian-Llandovery Don Braulio Formation.In agree with the petrographic data obtained from this study, no metamorphic clast have been recognized, in the conglomerate olistholiths of the Rinconada Formation in the El Alto Creek. Clast population is dominated by magmatic (mostly volcanic) and sedimentary (mostly siliciclastic and carbonate) composition. Siliceous clasts (quartz and chert) are accesories. A mixing up of intrabasinal with extrabasinal clasts is inferred from the occurrence of well preserved limestone gravel and blocks and also chert in allochthonous conglomeratic blocks.