LAUSR

Abstract During the Late Cretaceous, the Austral-Magallanes Basin (AMB) records the change from a thermal subsidence post-rift stage to a retroarc foreland basin scenario. The lower-Upper Cretaceous Puesto El Moro Formation (PMF) was deposited during the configuration of the foreland AMB. The aims of this contribution are: (i) to define the sedimentary paleoenvironments that are recorded by the PMF deposits and their spatio-temporal distribution, and (ii) to reconstruct the paleogeographic configuration and distributions of the sedimentary environments in the AMB during the early-Late Cretaceous onset of the foreland system. Based on detailed sedimentological observations and analysis of architectural elements, we divide the PMF into three informal sections. The lower section of the PMF represents a shallowing-upward estuary bay succession. The middle section of the PMF is characterized by braided and high-sinuosity meandering fluvial systems, flowing toward the southwest. Finally, the upper section of the PMF corresponds to a distributive fluvial system flowing toward the southwest. The PMF accumulated synchronously with the estuarine-fluvial Mata Amarilla Formation (MAF) located to the east of the study area. The results obtained in this contribution suggest that the type and vertical stacking of sedimentary paleoenvironments of the PMF could be correlated with the contemporary MAF. A subsurface dataset supported by the oil industry indicates the occurrence of the SE-trending Piedra Clavada High inside the northern AMB. We interpret that this topographic high controlled, during the Late Cretaceous, the types and distribution of sedimentary paleoenvironments of the AMB, indicating that an important compartmentalization of the basin occurred during the beginning of the foreland stage. The northern part of the AMB is divided into the Cardiel-Tres Lagos sub-basin and the Foredeep main depocentre.