Abstract The western margin of Australia provides a regional latitudinal and climatic gradient from the macrotidal tropical north to the microtidal temperate south, modulated by the poleward-flowing warm Leeuwin Current. Coral-reef systems, discontinuously developed during the late Tertiary-Quaternary, vary from fringing reefs to isolated reefs which rise from deep-ramp settings. Quaternary evolution of the reef systems is being documented using regional mapping, seismic imaging, coring and U-series dating. The well-constrained sea-level data from the Houtman Abrolhos carbonate platforms (at 28–29° S) have also been applied to the less known North West Shelf reefs. The Ningaloo fringing reef at 20–22° S records Holocene and last-interglacial phases of reef growth in a tectonically stable environment. It overlies Tertiary carbonates of the Cape Range, which is flanked by uplifted Plio-Pleistocene terraces and reefs. Scott Reef (at 14° S) is a macrotidal, isolated reef which overlies a carbonate platform and a major gas discovery. Seismic profiles reveal a last-interglacial (ca. 125,000 year) reef system, but reefs which apparently grew to sea-level are 30 m below present sea-level, indicating significant subsidence in the late Quaternary. Contemporary reefs grew during the Holocene in the accommodation space provided by subsidence and are up to 35 m thick. The Rowley Shoals (15–17° S) comprise one of the most perfect morphological series of reefs known, and these emergent, annular reefs rise from depths of 200–400 m. Seismic profiles suggest that late Quaternary subsidence has been an important control on reef growth, while differential subsidence has influenced reef morpho1ogy. Differential geomorphic and physical process settings, seismic stratigraphy, sea-level history, and subsidence are keys to patterns of reef growth which can be seen as responses to these controls.

Abstract The Brazilian tropical north shelf (BT N shelf) and the Brazilian tropical northeast shelf (BT NE shelf) along the Atlantic Ocean display unique conditions for tropical passive margins. Together they encompass approximately 3000 km in length, extending from Cape Orange in the north to Abrolhos Bank in the south. Both the north and NE shelves are very shallow and highly energetic systems. The first one is subject to energetic forcing from a number of different sources, including near-resonant semi-diurnal tides, large buoyancy flux from the Amazon River discharge, wind stress from the northeasterly trade winds and strong along-shelf flow associated with the North Brazil Current. The second one is subject to the full strength of the westerly-flowing South Equatorial Current, combined with high winds, moderate–high tidal range and/or waves. The BT N shelf is the largest shelf in Brazil, and is mostly covered with siliciclastic mud and sands because of the enormous water and sediment discharge from the Amazon River. In contrast, the BT NE shelf is narrow and open, and almost entirely covered by carbonate sediments due to the small amount of freshwater and sediment input.

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