Late Cretaceous turbidite-contourite mixed system on the Argentine Margin: palaeoceanographic and conceptual implications

Mixed or hybrid turbidite-contourite systems are formed by the interaction between downslope and alongslope processes. These systems are characterized by a variability and complexity of features. Globally, several mixed systems have been recognized in the Cenozoic record, however their representation in the Mesozoic remains severely understated. This issue is aggravated if we consider that the Mesozoic oceanic circulation is still poorly understood today. Argentina has one of the largest margins in the world, formed during the E-W breakup of Gondwana and diachronous opening of the South Atlantic Ocean, from south to north. This margin is characterized by an extensive Cretaceous turbidite-contourite system, which offers a key sedimentary record to understand past bottom-current dynamics and their interaction with turbidity currents. Thus, the objectives of this work are: 1) to identify significant modifications and physiographic features in the Cretaceous sedimentary stacking pattern, 2) to discriminate the mechanisms responsible for the formation and evolution of each feature and 3) to study the relationship with the main regional and palaeoceanographic events. This study is based on newly acquired broadband seismic reflection data and established well data. The mixed system in the Argentine Margin comprises 23 downslope elongated mounds on the lower continental slope and rise. The drift mounds are characterized by asymmetric morphologies, with a smooth aggradational NE side and a steep eroded SW side, separated by large individual channels that start at the continental shelf/upper slope and cut through the margin's topography. The interpretation and integration of these results aims to propose a conceptual model for depositional mixed systems and clarify the role and influence of bottom-current versus turbidity currents.