Stratigraphic framework and facies changes in the Hirnantian-Rhuddanian transition San Juan, Precordillera Argentina: paleoenviromental and tectosedimentary significance.

GÓMEZ SÁNCHEZ, JESSICA C.; PERALTA, S H; BERESI, M.S.

Trelew

Congreso; XXI Congreso Geológico Argentino; 2022

Asociación 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 toward south which consists of a storm-dominated thickening-coarsening upward siliciclastic succession bounded by transgressive surfaces. This unit overlies marine deposits from the Middle to Upper Ordovician age, in the northern sector of the basin (Los Azules, Las Aguaditas and Don Braulio formations), and of Lower-Middle Ordovician age (San Juan Formation) in the southern sector of the basin. At the top is paraconformably overlain by the Los Espejos Formation (Middle-Upper Silurian).The Don Braulio Formation crops out on the eastern flank of the Villicum range; it is made up of a siliciclastic shallow-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 Ordovician-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 paleogeography of the Early Paleozoic basin of Precordillera.