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Garrido A.C., Parent H. (2017) Lithofacies and age of the Quintuco Formation (Lower Cretaceous) in the Mallín Quemado area (Sierra de la Vaca Muerta, Neuquén Basin, Argentina). Stratigraphic and depositional implications // Boletín del Instituto de Fisiografía y Geología, 87. Pp. 1-16.
A detailed lithostratigraphic study of the Quintuco Fm in the Cerro Mallín Quemado area (Sierra de la Vaca Muerta) has provided the opportunity to review the conflictive diversity of interpretations proposed in the last 40 years for this unit. In the study area the Quintuco Fm shows a heterolithic succession about 80 m-thick. This succession is composed of interbedded sandy mudstones, wacky sandstones and fine to medium-grained sandstones in a coarsening-upwards arrangement. Thin coquiniferous levels occur interestratified towards the medium and upper parts of the stratigraphic column. The underlying offshore Vaca Muerta Fm-facies, developed under euxinic to anoxic conditions change gradually towards the dysoxic, storm waves-influenced conditions of the offshore transition zone of the Quintuco Fm-facies. Upwards the Quintuco Fm passes gradationally to shoreface sandy deposits of the Mulichinco Fm. The transition between both units is defined in a short section of the sedimentary column. The Quintuco Fm can be clearly recognized, and differentiated from the contiguous units, following the lithologic characterization of the original definition. There are important discrepancies in its determination among the authors. The main source of these discrepancies has been the use of biostratigraphic, chronostratigraphic and/or sequencestratigraphic criteria. once recognized the lithostratigraphic unit from the observed lithology in the section, the ammonites collected from there were studied in order to date these rocks and to establish regional time-correlation. These ammonites indicate the Quintuco Fm in the study area is Berriasian in age. This age was obtained from the chronostratigraphic zones estimated from the ammonite biostratigraphy of the studied section. Towards northern positions in the basin, e.g. Pampa Tril area, the age of the Quintuco Fm is early Valanginian. This pattern of the units becoming younger towards north reflects the shoreline progradation towards the basin.