ABSTRACT As the operator of several exploratory blocks in ultradeep waters, Petrobras was responsible for many presalt oil discoveries in Santos Basin such as Tupi, Carioca, Guará, and Iara. In partnership with the National Petroleum, Natural Gas and Biofuels Agency (ANP), Petrobras drilled well 2-ANP-2A, which resulted in the Libra discovery. In 2013, Libra was offered in the first bidding round executed by the Brazilian government under the new Production Sharing Contract for presalt areas. The winning consortium is comprised of Petrobras (operator), Shell, Total, CNOOC (China National Offshore Oil Corporation), CNPC (China National Petroleum Corporation), and PPSA (Pré-Sal Petróleo S.A.). The Libra discovery is sitting over a structural trap of about 550 km 2 (212 mi 2 ) closure at the Aptian top reservoirs level presenting a maximum oil column that can reach up to 900 m (2953 ft). The main reservoirs are lacustrine carbonates, deposited from the Neobarremian until the Aptian. Preliminary estimates indicate a volume of oil in place between 8 and 12 billion BOE. The development proposed for Libra started with Phase 0, in 2014, and is focused on information gathering, including appraisal wells, extended well tests (EWT), early production systems (EPS), and a pilot project. Phase 1 encompasses the definitive production systems and is expected to start in 2022 and finish in 2030.

Abstract Stratigraphic correlations from wells tied to high resolution seismic data offer specific constraints for interpreting tectonic events. Paleogeographic models based on these interpretations can be used to define the paleobathymetry of a basin at specific points in time and space, providing critical constraints on the rifting and subsidence history that are not available from regional structural interpretations. Based on detailed work undertaken to define the play characteristics of the Campos basin, we propose a new subsidence history for the critical presalt to salt transition time. Mapping of the “synrift” to “sag” transitional stratigraphy indicates a significant erosional unconformity at the base salt level across the outer Campos hinge in the southern Campos basin that results in the removal of the uppermost presalt section and portions of the underlying coquina section. We propose that this erosional unconformity truncates presalt stratigraphy where the basin has undergone short wavelength differential subsidence due to ductile extension within the lower crust. The uppermost presalt interval is therefore a late synrift deposit, as opposed to postrift “sag” infill of accommodation created by thermal relaxation of thinned crust. Well correlation within a sequence stratigraphic framework has identified three regionally correlative flooding surfaces and corresponding sequences within the coquina section that can be mapped with good confidence on 3D PSDM data, and extend across the hinge. These indicate a broad, shallow-water lacustrine depositional environment for the coquina and provide an upper limit on the age of differential subsidence. Halokinetic sequences seen in the postsalt section in the Campos basin imply that the original salt thickness was significantly greater downdip of the hinge, which required that enhanced subsidence occurred no later than the end of salt deposition, providing a lower limit on the age of differential subsidence. Our interpretation of subsidence localized at the Campos hinge by extension expressed within the ductile lower crust of the Campos basin is supported by deep seismic imaging that places the zone of maximum crustal thinning, defined by an abrupt shallowing of the Moho reflection, beneath the hinge zone. The localization of extension and subsidence creates a monocline that is subject to erosion just prior to evaporite deposition in the Campos basin. The differential subsidence across the hinge provides the accommodation for thick evaporites in the outer Campos basin, while the inner Campos basin has only thin evaporite deposits due to the lack of accommodation.

Crowleys Ridge in southeastern Missouri preserves Cretaceous to Eocene marginal marine sediments deposited in the northwestern portion of the Mississippi Embayment. Sandwiched between the Paleocene Porters Creek Formation and the uppermost Cretaceous Owl Creek Formation is the Paleocene Clayton Formation. Four trenches were excavated and a complete section of Clayton Formation was sampled at a large strip mine in Stoddard County, Missouri. The Clayton at this location consists of 185 cm of graded deposit, the lower part of which includes large Owl Creek rip-up clasts containing layers of microtektites, invertebrate fossils, and abundant terrestrial and marine palynomorphs. Driller's logs and electric logs covering ∼9000 km 2 were reviewed. Well data confirm the consistent thickness and lithology of the Clayton Formation in this part of the Mississippi Embayment. Based on sedimentological and palynological data from this study, the Clayton Formation in the northwestern Mississippi Embayment appears to be a megatsunami deposit resulting from post-impact effects (early Paleocene) associated with the Chicxulub impact event.