Abstract The Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE2) is the last major OAE of the Mesozoic and probably the best studied. In marine rocks around the Gulf of Mexico it is associated with a variety of different environments, from well-oxygenated carbonate platforms to anoxic, organic-rich outer shelf environments and un-studied basinal muds. This paper reviews the current level of knowledge about the geographic distribution and stratigraphic expression of OAE2 in the Gulf of Mexico in order to synthesize this disparate data and attempt to draw some conclusions about regional oceanography during this critical interval of the Cretaceous. A large number of localities with varying local redox states have been tied to OAE2, including the Valles-San Luis Potosí and Guerrero-Morelos platforms in southern Mexico, deep shelf sites in northern Mexico, the well-studied outcrops and cores of west Texas on the Comanche platform, cores and wells along the Barremanian-Albian shelf margin of south Texas, geophysical data in the East Texas basin, cores in the Marine Tuscaloosa Formation of Louisiana, Alabama, and Mississippi, and deep wells in the deep water Gulf of Mexico. The distribution of anoxic sediments at these sites during OAE2 appears to be determined by water depth. Shallow sites, like the Mexican carbonate platforms and the Comanche platform of Texas, are oxygenated during the event. Deeper shelf sites, like the south Texas Rio Grande submarine plateau and the noncarbonate platform parts of the Mexican shelf, are anoxic and enriched in organic carbon; it seems likely that this trend continues across the rest of the Cretaceous Gulf shelf, although data is sparse. Whether this oxygen minimum zone only impacts the deeper parts of the shelf or extends all the way to the basin floor is the most significant outstanding question about OAE2 in the Gulf of Mexico.

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 The IGUANES cruise took place in May 2013 on the R/V L’Atalante along the Demerara passive transform margin off French Guiana and Surinam. Seismic, multibeam and chirp acquisitions were made. Piston cores were collected for pore geochemistry and sedimentology. A mooring was deployed on the sea-bottom for 10 months (temperature, salinity, turbidity and current measurements). This new dataset highlights the lateral variability of the 350 km-long Guiana–Surinam transform margin due to the presence of a releasing bend between two transform segments. The adjacent Demerara Plateau is affected by a 350 km-long giant slide complex. This complex initiated in Cretaceous times and was regularly reactivated until recent times. Since the Miocene, contourite processes seem to be active due to the onset of the North Atlantic Deep Water (NADW) bottom current. A main NADW water vein flows towards SE, eroding slide headscarps and allowing the deposition of contourite drifts. Numerous depressions looking like comet tails or comet scours record this flow. Some of those were interpreted before the cruise as active pockmarks. Pore geochemistry and core analysis do not show any evidence of present-day gas seepage.

Abstract The Demerara Plateau is located on the northeast South America continental margin between 5° and 10° North, marking the northwest corner of the equatorial segment of the Atlantic Ocean. It is conjugate to the Guinea Plateau on the African margin, which rifted from the Demerara during the Early Cretaceous opening of the Central Atlantic. Published studies of the Demerara Plateau are focused on its Cretaceous history, when the northern edge of the platform was formed by trans-tensional deformation along Atlantic transform faults, and its eastern edge by extensional deformation during rifting. The platform itself is commonly interpreted as a continental block left behind following South Atlantic rifting. Seismic data across the plateau reveal significant compressional deformation beneath an Albian unconformity. We suggest that this deformation is the result of early opening of the South Atlantic, with a rotation pole located close to the present-day Amazon delta. Allowing for this compression in plate reconstructions of the South Atlantic results in restorations which do not require large amounts of intracontinental deformation in South America, and, consequently, in a relatively simple plate model for the South Atlantic.

Abstract: Recent studies indicate that the bulk (80%) of Deccan trap eruptions occurred over a relatively short time interval in magnetic polarity C29r, whereas multiproxy studies from central and southeastern India place the Cretaceous-Tertiary (KT) mass extinction near the end of this main phase of Deccan volcanism suggesting a cause-and-effect relationship. Beyond India multiproxy studies also place the main Deccan phase in the uppermost Maastrichtian C29r below the KTB (planktic foraminiferal zones CF2-CF1), as indicated by a rapid shift in 187 Os/ 188 Os ratios in deep-sea sections from the Atlantic, Pacific and Indian Oceans, coincident with rapid climate warming, coeval increase in weathering, a significant decrease in bulk carbonate indicative of acidification due to volcanic SO 2 , and major biotic stress conditions expressed in species dwarfing and decreased abundance in calcareous microfossils (planktic foraminifera and nannofossils). These observations indicate that Deccan volcanism played a key role in increasing atmospheric CO 2 and SO 2 levels that resulted in global warming and acidified oceans, respectively, increasing biotic stress that predisposed faunas to eventual extinction at the KTB.