The postglacial transgressive conglomerate in the Hirnantian of the central precordillera, Argentina

BERESI, MATILDE S; PERALTA, SILVIO H.; GÓMEZ JÉSSICA

Novosibirsk, Siberia

Simposio; 13 th International Symposium on the Ordovician System; 2019

Trofimuk Inst. petroleum Geology; Russian Academy of Sciences; Novosibirsk State University

Hirnantian deposits of the Argentine Precordillera at the Talacasto area are represented by the conglomerate of the basal Salto Macho Member (B. Baldis et al., 1984) of the La Chilca Formation. The Ordovician-Silurian boundary is recorded in these deposits (A. Cuerda et al., 1988). The basal conglomerate of the La Chilca Formation represents a post-glacial Hirnantian transgression and this event is recognizable in other localities within the lower part of the La Chilca Formation. The deposition of the conglomerate took place before the graptolite-based persculptus Zone during a rapid post-glacial sea-level rise. It was first described at the Baños de Talacasto section by H. Marchese (1972). The conglomerate level is cover by black, greenish-grey and yellowish shale, whit graptolites of Hirnantian to Llandovery age (A. Cuerda et al., 1988; Lenz et al., 2003). The sedimentological and stratigraphic analysis of the conglomerate level has been carried out in three sections in the Talacasto locality: Quebrada Poblete Sur (PS), Quebrada Ancha (QA) and Baños de Talacasto (BT). The sedimentary sequence was interpreted on the basis of lithofacies, vertical stacking patterns, body geometry, vertical and horizontal strata relations and fossil content according to existing models.The sections (Fig 1) were correlated and analyzed with the transgression of the late Ordovician, according to proposed models (H.Clifton, 2003)