Sedimentology and sequence stratigraphy of the Agrio Formation (Late Valanginian-earliest Barremian) and the closure of the Mendoza Group to the North of the Huincul High

Abstract

The Agrio Formation (late Early Valanginian-earliest Barremian) is an environmentally complex marine and continental succession that involves unconformities and flooding surfaces that respond to tectonic thermal subsidence. Internally, the Pilmatué member contains five 3rd order sequences eustatically controlled. The Avilé Member starts over a regional unconformity that is the result of erosion and bypass by tectonic quiescence and only punctuated subsidence permits to explain the abnormal thickness in some areas. The Agua de la Mula Member starts with an isochronous and geologically instantaneous inundation which is better explained by tectonic subsidence rather than global eustatism. It contains four sequences but of 4th order. It also shows a sedimentary input from the east in some areas, largely neglected in the literature. The Chorreado Member, from a sequence stratigraphy point of view, is part of the Mendoza Group as it does not represent a basin expansion after a minor unconformity during the Barremian. Contrarily, the unconformity that marks the base of the Troncoso Member of the Huitrín Formation is an evidence of intense regional basin reorganization. The depocentres in the discussed intervals and units shift to the northwest while the thickness in proximal areas in the two marine members of the Agrio Formation point out to accommodation space created by tectonism. This is the first sequence stratigraphic model for the interval in two decades after the first absolute ages and latest biozone calibration provided for the Agrio Formation.