Sequence-stratigraphical scheme for the Neopalaeozoic units of the Calingasta-Uspallata basin in the western flank of the Precordillera

Abstract

The Upper Palaeozoic Majaditas, Hoyada Verde / El Paso and Tres Saltos Formation (Precordillera of western Argentina) were selected to build a sequence stratigraphic framework due to the existence of laterally extensive and thick exposed sections, unconformable contact with pre-Carboniferous basement, and the presence of fossils and glacially-influenced intervals. The key surfaces used were: a) sequence boundaries, characterized by drastic basinward facies shift, b) initial flooding surfaces, accompanied by landward facies shift, and c) maximum flooding surfaces or intervals, representing the maximum landward expansion of marine conditions. Fining- and coarsening-upward stacking patterns were used to define the transgressive (TST) and highstand (HST) system tracts. Sequence I rests unconformably on basement. The basal section consists of glacially-influenced deposits of a lowstand wedge. In the Hoyada Verde Formation, glacial deposits are capped by a striated boulder pavement, indicative of ice abrasion on the shelf, in turn overlain by thin-bedded diamictites (early TST), followed by IRD (ice-rafted detritus) - free mudstones with fossils (late TST). Sequence II is bound by an erosional unconformity that reflects a drastic basinward shift in facies: coarse-grained sandstones and conglomerates rest on open marine mudstones and fine-grained sandstones of Sequence I. This surface coincides with the contact between the Hoyada Verde Formation (and equivalent El Paso Formation) and the Tres Saltos Formation, east of Barreal, and the contact between the Diamictitico and Rojo I Members of the Majaditas Formation farther south. The HST is dominated by coarsening-upward successions in the Rojo II and Superior Members of the Majaditas Formation. Majaditas Formation further south. A large scale, fining- to coarsening-upwards vertical stacking pattern evolution indicates the passage from the TST to HST. The HST is dominated by coarsening upward successions or parasequences, as exemplified in the Miembro Rojo II and Superior Members of the Majaditas Formation.