Biostratigraphy and Paleoenvironmental Evolution of the Colorado Basin, South Atlantic Ocean

JUAN PABLO PÉREZ PANERA; DIANA RONCHI; GLADYS ANGELOZZI; JUAN PABLO LOVECCHIO; LYDIA CALVO MARCILESE; MARÍA LUCIANA HIRIART; LEONARDO TÓRTORA; NORBERTO CALARAMO; CARLOS DANIEL CUCINIELLO; OTTONE, GUILLERMO

Congreso; AAPG INTERNATIONAL CONFERENCE AND EXHIBITION; 2019

AAPG

The Colorado basin is a sedimentary trough perched in the Argentinean shelf that formed in the early Mesozoic due to the breakup of SW Gondwana. The main synrift depocenters remain undrilled but presumably host continental sediments. The South Atlantic Ocean breakup in the Early Cretaceous triggers the drift phase, with fluvial sedimentation along most of the basin. Marine sedimentation starts during the Campanian, with a major Atlantic flooding. This contribution focuses on the paleoenvironmental evolution of the basin since this event. New analyses and sample reexaminations in 15 of the 27 exploration wells were integrated into a local biostratigraphic scheme for the late Campanian ? Neogene series. Nine foraminifera and fifteen calcareous nannofossil biozones are proposed. Four major sedimentary cycles, bounded by regional unconformities, were identified. They are characterized by lithology, seismic pattern, and micropaleontological content. The first cycle is represented, at well locations, by Early to Late Cretaceous continental deposits. The second cycle records two pulses of a regional marine ingression in the late Campanian - early Maastrichtian and in the late Maastrichtian ? early Paleocene. The later generates a wide epicontinental sea under high-stress environmental conditions, and reached up to the Neuquén basin. A regional unconformity is related to this transgression and denotes the Cretaceous/ Paleogene boundary. The Eocene ? early Oligocene third sedimentary cycle records a new transgression with neritic marine sedimentation across the basin. The diachronous character of this cycle is given by its bounding hiatus and unconformities that span different time intervals across the basin. Finally, the late Oligocene - Miocene sedimentary cycle involves two transgressions that correlate with major events recorded in Patagonia: latest Oligocene ? early Miocene (Patagoniense) and middle to late Miocene (Entrerriense). During the late Miocene, the regressive phase produces the migration of marine clinoforms on the shelf under open marine conditions.