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,; VERGEL, M.M

Esquel

Simposio; VII SAPS - VII SIMPOSIO ARGENTINO DEL PALEOZOICO SUPERIOR; 2018

Late Paleozoic successions exposed along the western flank of the Precodillera 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), and recently confirmed and refined by biostratigraphic studies, is anchored on the presence of key surfaces. A basal sequence boundary (SB I) overlain by clast-supported, boulder to pebbly conglomerates, occasionally with striated clasts, rests unconformably on basement (i.e. El Paso and Majaditas Formations). A postglacial 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 interval 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 by an erosional unconformity (SB II) that reflects a basinward shift in facies associated with a drastic decrease of accommodation space: coarse- to medium-grained sandstones and subordinate conglomerates rest on open marine mudstones and fine-grained sandstones of Sequence I.