Relationship between hydrocarbon generation–expulsion and deformation in an exhumated Early Cretaceous kitchen in the Austral-Magallanes Basin, southern Patagonia

Abstract

We characterized the thermal evolution of the exhumated hydrocarbon kitchen of the Rio Mayer Formation (Lower Cretaceous) in the Austral-Magallanes Basin in two profiles outcropping in the southern Patagonian Andes.We integrated data from fluid inclusion, organic petrology, geochemistry and apatite fission track studies into a one-dimensional basin and petroleum system model to evaluate the timing of hydrocarbon generation–expulsion processes. At the Estancia La Federica locality (internal fold–thrust belt domain), the lower organic-rich interval of the Rio Mayer Formation at present day conditions is in the oil window, with the development of natural fractures filled with fibrous calcite crystals. By contrast, at the Estancia Cristina locality (basement domain), the unit is in the dry gas window with natural fractures filled with granular calcite andquartz. The kitchens began the generation–expulsion processes from the west (Early Cretaceous) to east (Late Cretaceous–Eocene) – that is, from the basement to the internal and external fold–thrust belt domains. The advance of the orogenic wedge deactivated and exhumated these kitchens from west to east. The western kitchen was deactivated during the Late Cretaceous,whereas the eastern kitchen was deactivated during the Eocene. These successive compressional pulses conditioned the eastward migration of the hydrocarbon generation front and favoured the charge of reservoirs located in thewestward (foreland) region. The results of this study emphasize the importance of considering the temporal activation of source kitchens related to Andean deformation in our understanding of the basin-scale controls on source rock evolution and the development of petroleum systems.