Estratigrafía del Paleozoico Inferior de la Sierra de Las Crucecitas, Precordillera Central, San Juan

MESTRE, A.; GOMEZ, M.J.; HEREDIA, S.; MORENO, F.

Serie Correlación Geológica

INSUGEO

Año: 2021 vol. 37 p. 5 - 18

LOWER PALEOZOIC STRATIGRAPHY OF THE SIERRA DE LAS CRUCECITAS, CENTRAL PRECORDILLERA, SAN JUAN. The Lower Paleo- zoic shows a wide distribution in the Central Precordillera, it has been extensively studied, mainly in the north area of this morphostructural unit, however, to the southward the studies are scarce. The present contribution offers the first insight into the Lower Paleozoic stratigraphy on the western flank of the Sierra de Las Cruce- citas, which is located on the southern margin of the Bolson de Hualilán. In this area, the San Juan, La Chilca, Los Espejos, Talacasto and Punta Negra formations were recognized, but this study focuses on the first three units. The San Juan Formation is composed of light gray to medium gray limestone and the pulchrilamiloid Zondarella sp. is recognized as almost the only fossil component which represents the westernmost finding of this organism in the Precordillera. A late Dapingian-Darriwilian age is suggested for these levels based on their stratigraphic position and outcrop characteristics. Only the first few meters of the La Chilca Formation were surveyed. In the base of this unit was recognized a reddish-brown paraconglomerate with scattered angular to subangular chert clasts and cemented by silica and oxide-Fe, then follows a monotonous succession of siltstones and green shale. The Los Espejos Formation presents a coarsening-up and thickening-up arrange- ment, with shale and sandstones with bioclastic accumulation in the middle part, while in the upper part there are sinsedimentary deformation structures. These preliminary stratigraphic observations in this area provide valuable information about the distribution and composition of the Paleozoic units studied. However, detailed studies must be carried out to achieve a better understanding of its importance within the Paleozoic basins of the Precordillera.