Late Cretaceous marine transgressions in Ecuador and northern Peru: A refined stratigraphic framework

Study of ammonites and bivalves along selected sections on the Andean margin of northern Peru and Ecuador has made it possible to recognize correlatable marine transgressions and propose a refined stratigraphic framework for the Upper Cretaceous of the region. Six maximum flooding events are recognized: latest Turonian-early Coniacian (major event), late Coniacian-early Santonian, early Campanian, mid Campanian-early late Campanian (major event), early Maastrichtian (major event), and terminal early Maastrichtian. Most of these events can be correlated with global eustatic sea level rises, but their relative manifestations indicate that the Andean margin already was being deformed by the late Cretaceous 'Peruvian' tectonic events. The onset of fine-grained clastic sedimentation in the Oriente and East Peruvian basins in the mid Turonian-earliest Coniacian is taken as the first event of the 'Peruvian' phase. The Campanian regional transgression in the Peruvian-Ecuadorian forearc zones concealed the 'Peruvian' deformational event. The latter caused a paleogeographic upheaval, as indicated by the subsequent development of a NNE-trending forearc basin, which extended from Paita in northwestern Peru to northern Ecuador. In the forearc zones, only short-lived transgressions are recorded in the late Campanian and early Maastrichtian as a result of nearly continuous tectonic activity. This activity culminated with a significant tectonic event in the late Maastrichtian that caused a widespread hiatus.