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.

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.