Key sequence stratigraphic surfaces along a basin margin: the Late Paleozoic successions of the Calingasta-Uspallata basin, west Argentina

LÓPEZ GAMUNDÍ, O.; CISTERNA, G.A.; STERREN, A.F.; LÓPEZ GAMUNDÍ, C.; VERGEL, M.M.

Esquel

Simposio; VII Simposio Argentino del Paleozoico Superior-SAPS; 2018

Late Paleozoic successions exposed along the western flank of the Precordillera at the latitude of Barreal and further south are characterized by Mid Carboniferous glacial marine and glacially-influenced sediments (Sequence I) followed by shallow marine, sand-rich deposits (Sequence II). A sequence stratigraphic framework proposed for these successions (López-Gamundí and Martínez, 2003), recently confirmed and refined by biostratigraphic studies, isanchored on the presence of key surfaces. A basal sequence boundary (SB I), overlain by clastsupported, boulder to pebbly conglomerates with striated clasts (i.e. El Paso and Majaditas formations), rests unconformably on Lower Paleozoic metasedimentary basement. A postlgacial flooding interval (FI), characterized by mud-prone deposits (Hoyada Verde, El Paso and Majaditas Formations), is temporally constrained by two well diversified faunas of Late Serpukhovian?Bashkirian age, the Levipustula Fauna and the coeval Aseptella Tuberculatella/Rhipidomella-Micraphelia Fauna (Cisterna et al., 2017), and associated palynomorphs (Vergel et al., 2016). The succession between SB I and FI shows a vertical retrogradational stacking which indicates a drastic landward facies shift that culminates with a maximum flooding surface (MFI). Sequence II (i.e. Tres Saltos Formation, upper half of the Majaditas Formation) is bound at its base by an erosional unconformity (SB II) that reflects a basinward shift in facies associated with a drastic decrease of accommodation space: coarse- tomedium-grained sandstones and subordinate conglomerates rest on open marine mudstones and fine-grained sandstones of Sequence I. The rest of the Sequence II is dominated by shallow marine (inner shelf) to littoral sand-prone deposits.