STRATIGRAPHIC FRAMEWORK AND FACIES CHANGES IN THE HIRNANTIAN-RHUDDANIAN TRANSITION SAN JUAN, PRECORDILLERA ARGENTINA: PALEOENVIRONMENTAL AND TECTOSEDIMENTARY SIGNIFICANCE

JESSICA GÓMEZ SÁNCHEZ; SILVIO PERALTA; BERESI MATILDE S.

PUERTO MADRYN, CHUBUT

Congreso; XXI CONGRESO GEOLÓGICO ARGENTINO; 2022

Asociacion Geológica Argentina

The Hirnantian-Rhuddanian transition is registered in the Central Precordillera, at the basal part of the La Chilca Formation (Late Hirnantian-Early Wenlock) and, in the Eastern Precordillera at the upper part of the Don Braulio Formation (Late Hirnantian-Llandovery). La Chilca Formation is recognized from the Jáchal River area to the north, up to the north of the San Juan River and consists of a storm-dominated thickening-coarsening upward siliciclastic succession bounded by transgressive surfaces. This unit overlies marine deposits from the Late Ordovician age, in the northern sector of the basin (Los Azules, Las Aguaditas and Don Braulio formations), and of Early Ordovician age (San Juan Formation) in the southern sector of the basin. At the top is para conformably overlain by the Los Espejos Formation (Middle-Upper Silurian). The Braulio Formation crops out on the eastern  flank of the Villicum range; it is made up of a siliciclastics hallow-water succession, with Hirnantian glacimarine diamictites at the base, and ferruginous oolitic bars of Llandovery age at the upper part. In this work, a brief stratigraphic and lithofacial analysis of the theOrdovician-Silurian transition is carried out in the Talacasto, Don Braulio Creek and the Cerro La Chilca areas, in order to provide information related to the palaeogeography of the Early Paleozoic basin of Precordillera.