Integrated stratigraphy of the Upper Hauterivian to Lower Barremian Agua de la Mula Member of the Agrio Formation, Neuquen Basin, Argentina

The Upper Hauterivian to Lower Barremian Agua de la Mula Member of the Agrio Formation (Neuquen Basin, Argentina) was studied applying an integrated stratigraphic approach and facies analysis. The ammonite biostratigraphy of the member has been improved based on bed-by-bed collecting. The already defined biozones (Spitidiscus riccardii, Crioceratites schlagintweiti, Crioceratites diamantensis and Paraspiticeras groeberi) were recognized, precisely related to the succession, and further refinement was proposed. Sequences of different order are built by stacked starvation/dilution (s/d) sequences, regarded here as sixth-order sequences with only two components that can be unequivocally distinguished: the lower starvation hemisequence and the upper dilution hemisequence. Pro- and retrogradational stacking pattern of s/d sequences define supra-ordinate sequences. The sequence-stratigraphic analysis resulted in the subdivision of the member into four main depositional sequences (dsAM-1 to -4) and several subordinate sequences. Previously published sequence stratigraphic charts of the Neuquen Basin did not relate sedimentary sequences to biozones, and are hence not comparable to the scheme presented here and other charts. Our study shows a good agreement with the sequence-chronostratigraphic scheme of european basins, thus arguing in favour of a predominantly eustatic control on sequence development during the Late Hauterivian to early Barremian. A latest early Barremian age is proposed for the almost ammonite-barren upper part of the Agrio Formation, based on correlations of sequence boundaries.