Abstract The main objective of this study was to investigate secondary migration in the A¸u Formation, including reconstruction of migration pathways, estimation of velocity of the migration fronts, and identification of key variables controlling the migration process. The Potiguar Basin in northeastern Brazil is an appropriate geologic setting for studying secondary migration. Almost all of the oil accumulated in the onshore A¸u sandstones was generated from offshore pods of active source rocks in the Alagamar Formation and has migrated laterally for long distances. The A¸u Formation, which is the main carrier bed and reservoir of this petroleum system, dips seaward as a regional monocline structure, with gentle folds, normal faults, and facies changes. In this study, we reconstructed the history of secondary migration using basin-scale modeling of 8272 grid cells. Rock and fluid properties used in this investigation are those typically found in most of the oil accumulations in the A¸u Formation. Petroleum migration pathways and economic oil accumulations in the Alagamar–Acu petroleum system were controlled by northeast–southwest structural noses at the top of the A¸u Formation. Estimated ratios of oil displacement for the earlier oil migration fronts range from 3.0 to 7.0 cm/year. Oil in the main onshore accumulations of the Potiguar Basin may have been trapped between 1 and 5 m.y after the beginning of secondary migration. Significant loss of petroleum may have occurred along seepages from onshore outcrops of the A¸u Formation.

Abstract This work integrates the available geological information and geochronology data for the Cretaceous–Recent magmatism in the South Atlantic, represented by onshore and offshore magmatic events, including the oceanic islands along the transform faults and near the mid-ocean ridge. The analysis of the igneous rocks and their tectonic settings allows new insights into the evolution of the African and Brazilian continental margins during the South Atlantic opening. Following the abundant volcanism in the Early Cretaceous, the magmatic quiescence during the Aptian–Albian times is a common characteristic of almost all Brazilian and West African marginal basins. However, rocks ascribed to the Cabo Granite (104 Ma) are observed in NE Brazil. In West Africa, sparse Aptian–Albian ages are observed in a few coastal igneous centres. In the SE Brazilian margin, an east–west alkaline magmatic trend is observed from Poços de Caldas to Cabo Frio, comprising igneous intrusions dated from 87 to 64 Ma. Mafic dyke swarms trending NW also occur in the region extending from the Cabo Frio Province towards the Central Brazilian Craton. On the West African side, Early Cretaceous–Recent volcanism is observed in the Walvis Ridge (139 Ma), the St Helena Ridge (81 Ma) and the Cameroon Volcanic Line (Early Tertiary–Recent). Volcanic islands such as Ascencion (1.0–0.65 Ma), Tristão da Cunha (2.5–0.13 Ma) and the St Helena islands (12 Ma) most probably correspond to mantle plumes or hot spots presently located near the mid-Atlantic spreading centre. Within the South America platform and deep oceanic regions, the following volcanic islands are observed: the Rio Grande Rise (88–86 Ma), Abrolhos (54–44 Ma), the Vitória–Trindade Chain (no age), Trindade (2.8–1.2 Ma) and Fernando de Noronha (12–1.5 Ma). There are several volcanic features along the NW–SE-trending Cruzeiro do Sul Lineament from Cabo Frio to the Rio Grande Rise, but they have not been dated. The only known occurrence of serpentinized mantle rocks in the South Atlantic margin is associated with the Saint Peter and Saint Paul Rocks located along the São Paulo Fracture Zone. The Cameroon Volcanic Line in NW Africa is related to the magmatism that started in the Late Cretaceous and shows local manifestations up to the Present. The compilation of all available magmatic ages suggests an asymmetrical evolution between the African and South America platforms with more pre-break-up and post-break-up magmatism observed in the Brazilian margin. This is most likely to have resulted from the different geological processes operating during the South Atlantic Ocean opening, shifts in the spreading centre, and, possibly, the rising and waning of mantle plumes. Supplementary material: A complete table with radiometric dates that have been obtained by universities, government agencies and research groups is available at: www.geolsoc.org.uk/SUP18596

Abstract The continental shelf adjacent to the northern coast of Rio Grande do Norte State, northeastern Brazil, represents a modern, highly dynamic mixed siliciclastic-carbonate shelf system developed in shallow water (< 60 m). Sediment dynamic processes are driven by waves, winds, tides, and the west- to northwest-directed North Brazil Current. This high-energy setting is associated with the presence of highly variable seabed features. This paper describes the spatial distribution of the mapped bedforms, in order to relate them to sedimentary processes and physical characteristics of the environment, and to the sedimentary history of this shoreline-shelf system. In a novel approach, the integrated data set presented here includes remote sensing, bathymetric, oceanographic, hydroacoustic, and sedimentologic data supported by diving. In addition, the high-energy mixed siliciclastic-carbonate shelf system contains a different sedimentary inventory than most well-studied siliciclastic or carbonate shelf environments. A variety of bedforms, which range from kilometers to tens of centimeters in scale, is present in the study area. Sediment reworking is accountable for the recent formation and migration of mobile bedforms which are superimposed on older relict structures. The integrated approach led to the identification of six main groups of large-scale bedforms: (I) very large longitudinal dunes, (II) very large transverse dunes, (III) small dunes, (IV) isolated shallow-marine sand bodies, (V) submerged beachrock chains, and (VI) incised-valley systems. The continental shelf off Rio Grande do Norte has experienced regressions and transgressions during the last glacial cycles. Outside the incised valley of the Rio Açu a continuous strong reflector, identified in all boomer profiles, represents the most recent sea-level lowstand surface that separates Pleistocene deposits below from early Holocene deposits above. During the Holocene sea-level rise, at least two beachrock lines formed at 20 m and 10 m of modern water depth.

Abstract The French national meteorite collection of the Muséum National d'Histoire Naturelle (MNHN) represents one of the richest collections in the world in terms of its historical heritage and scientific value, particularly for samples of observed falls (512). In fact, early meteoritic research was dominated by French 18th and 19th century scientists such as René Just Haüy, Auguste Daubrée, Stanislas Meunier and Alfred Lacroix. They all contributed, along with Jean Orcel and Paul Pellas in the last 80 years, to form this exceptional collection. The fall at L'Aigle in 1803 led to the recognition of the nature of meteorites and the promotion of the science of meteoritics by Jean-Baptiste Biot. The first catalogue of the meteorite collection elaborated by Cordier in 1837 contained 43 specimens. The collection now contains about 3385 specimens representing 1343 distinct meteorites, to which can be added at least 3000 tektites and numerous specimens of impactites, casts, artificial samples and thin sections. France has the greatest number of meteorite falls by surface unit and by number of inhabitants, with 70 distinct meteorite falls recovered. The collection offers a diverse range of meteorites such as those containing rare presolar grains, the famous carbonaceous chondrite Orgueil (fall, 14 May 1864), the first martian meteorite, Chassigny (fall, 3 October 1815) and Ensisheim (fall, 7 November 1492), which is one of the two oldest observed and documented meteorites and the first meteorite to be registered in the catalogue. The MNHN collection represents a resource that is particularly appreciated by the scientific community.