The Paleocene–early Eocene interval is punctuated by a series of transient warming events known as hyperthermals that have been associated with changes in the carbon isotope composition of the ocean-atmosphere system. Here we present and discuss a detailed record of calcareous nannofossil and foraminiferal assemblages coupled with high-resolution geochemical, isotopic, and environmental magnetic records across the middle Ypresian at the Contessa Road section (Gubbio, Italy). This allows characterization of the Eocene Thermal Maximum 3 (ETM3, K or X) and recognition of four minor (I1, I2, J, L) hyperthermals. At the Contessa Road section, the ETM3 is marked by short-lived negative excursions in both δ 13 C and δ 18 O, pronounced changes in rock magnetic properties, and calcium carbonate reduction. These changes coupled with the moderate to low state of preservation of calcareous nannofossils and planktonic foraminifera, higher FI and agglutinated foraminifera values, along with a lower P/(P + B) ratio (P—planktonic; B—benthic) and coarse fractions provide evidence of enhanced carbonate dissolution during the ETM3. A marked shift toward warmer and more oligotrophic conditions has been inferred that suggests unstable and perturbed environmental conditions both in the photic zone and at the seafloor.

Abstract The recent surge of exploration activities over distal margins, with the acquisition of more and more high-quality and deep seismic data, has led to enhance concepts of the deformation and subsidence history of passive margins in general and sheared margins in particular. The French Guiana sheared margin is very narrow. The thinning of the upper crust is accommodated by few major faults relayed by well-expressed transfer zones, giving a general oblique trend to the margin. Another possible effect of the shear component during the rifting is the presence in the distal domain of a Moho high. Its exhumation is coeval with the emplacement of a deltaic system coming from the Demerara Plateau, evidencing a probably important early subsidence of the margin. This early subsidence in the late-rifting stage is increased during the early drifting, when the thinned crust reached its isostatic/thermal equilibrium in the Cenomano-Turonian before suffering an important Late Cretaceous sedimentation load. In the Palaeogene, starving of the margin and significant uplifts in the Guiana Craton are observed, possibly resulting from the rise of the Purus Arch (Andes fore-bulge?). Finally, the Amazon deposition by the Late Miocene–Pliocene provoked a large subsidence in the distal domain.

Abstract The study focuses on the offshore Guyana–Suriname–French Guiana region. It draws from seismic, well, gravimetric and magnetic data. They indicate that the continental break-up along the western margin of the Demerara Plateau took place during the Callovian–Oxfordian, associated with the Central Atlantic opening, and accommodated by normal faults. The continental break-up in the SE offshore Guyana accommodated by strike-slip faults was coeval. The continental break-up along the NE and eastern margins of the Demerara Plateau took place during the late Aptian–Albian, associated with the opening of the Equatorial Atlantic, and accommodated by dextral strike-slip and normal faults, respectively. Different spreading vectors of the Central and Equatorial Atlantic required development of the Accommodation Block during the late Aptian/Albian–Paleocene in their contact region, and in the region between the Central Atlantic and its southernmost portion represented by the Offshore Guyana Block, which were separated from each other by the opening Equatorial Atlantic. Its role was to accommodate for about 20° mismatch between the Central and Equatorial Atlantic spreading vectors, which has decreased from the late Aptian/Albian to Paleocene down to 0°. Differential movements between the Central and Equatorial Atlantic oceans were also accommodated by strike-slip faults of the Guyana continental margin, some active until the Paleocene.

Abstract We describe an examination of two lines of evidence, tectono-structural evolution and hydrocarbon geochemistry, of asymmetric opening of the Atlantic Equatorial Margin. Our structural mapping used compilations of geophysical data and a review of both published literature and oil company public presentations. Geochemically, we accessed regional non-exclusive oil studies of the conjugate margins of Africa and South America, plus considerable published material. A group of non-exclusive oils was refined to 286, which clustered into five families, all represented along the NE Brazil margin but only one along the West African Transform (WAT) margin. Multiple lacustrine-sourced oils were seen around the South Atlantic, including NE Brazil, but a rich, oil-prone lacustrine source was not indicated offshore Ivory Coast and Ghana. Despite minor evidence of mixed source, possibly lacustrine stringers within an alluvial to marine setting, the predominant source is marine Cretaceous (Cenomanian–Turonian and possibly Albian). We find that opening asymmetry (a) biased the location of lacustrine (Early to mid-Cretaceous prerift to early synrift) source rocks to the NE Brazil margin and (b) locally narrowed the width of the optimal marine (Mid-Late Cretaceous postrift) WAT Margin source kitchens. Burial of the latter has aggravated the risk of late charge from light (condensate and gas) hydrocarbons.