Upper Cretaceous, K/T boundary, and Paleocene agglutinated foraminifers from Hole 959D (Côte d'Ivoire-Ghana Transform Margin)

Upper Cretaceous agglutinated foraminifer assemblages from Hole 959D of Ocean Drilling Program (ODP) Leg 159, Côte d’Ivoire-Ghana Transform Margin, reflect the subsidence history and paleoceanography of the widening equatorial Atlantic gateway. Five benthic foraminifer assemblage types are recognized: (1) Santonian and the lowermost Campanian assemblages (Cores 159-959D-65R and 64R) are characterized by the occurrence of bathyal calcareous benthic foraminifers with an increasing proportion of agglutinated foraminifers. The disappearance of calcareous foraminifers and assemblages exclusively composed of organically cemented agglutinated forms in Section 159-959D-65R-3 reflects the subsidence of the seafloor below the calcite compensation depth (CCD); (2) lower Campanian "biofacies B" assemblages (Cores 159-959D-63R through 61R) are exclusively composed of low-diversity agglutinated foraminifers, accompanied by abundant and occasionally well-preserved radiolarian assemblages; (3) middle Campanian to upper Maastrichtian deposits (Cores 159-959D-59R through 49R) contain an exclusively agglutinated Rzehakina epigona biofacies, which is well-known from middle to deep bathyal sites along the North Atlantic margins; (4) a change in agglutinated foraminifer assemblage composition toward morphologies commonly observed in present infaunal habitats and the common occurrence of the presumably infaunal genus Spiroplectammina are observed in Core 159-959D-48R. This change in agglutinated foraminifer assemblages corresponds to the Tethyan early Paleocene "Spiroplectammina event;" (5) a diversified Paleocene "Lizard Springs type" assemblage is characterized by several diverse Rzehakina, Saccamina, and Haplophragmoides species. Assemblages from Cores 159-959D-48R through 44R display high species diversity and reflect the deepest (lower bathyal to upper abyssal) paleobathymetry. Ranges of agglutinated foraminifer marker species and occurrences of paleoceanographic events within this biostratigraphic framework are almost identical to those observed in the North Atlantic, in the Western Tethys, and along the conjugate Brazilian margin. These observations lead us to confirm that a deep-water circulation system common to the North and South Atlantic has been active at least since the Santonian

Mesozoic biostratigraphic, paleoenvironmental, and paleobiogeographic synthesis, equatorial Atlantic

Cretaceous sediments from Ocean Drilling Program Leg 159 on the Côte d’Ivoire-Ghana Marginal Ridge (CIGMR), eastern equatorial Atlantic, are characterized by distinct stratigraphic changes in sedimentary facies associated with changes in the composition of the clayey and organic fractions, as well as of the calcareous nannofossil, radiolarian, foraminiferal, and palynomorph assemblages. In the absence of reliable magnetostratigraphic information, an integrated biostratigraphy provides the only means used to calibrate the geologic history of the Leg 159 area. The existence of marine depositional environments as early as the late Aptian to early Albian close to the Leg 159 drill sites puts constraints on the timing of the opening of the equatorial Atlantic gateway. Marine sedimentation on the ridge suggests that the West African and South American cratons were largely detached at this segment of the margin by the middle to late Albian. During the Cenomanian to Coniacian the ridge appears to have remained in an elevated position with concurrent low deposition or condensation (Site 959), high carbonate debris accumulation (Site 960), and even erosion (Site 962). Total organic Carbon measurements and microfaunal data lead us to suggest that, following the early opening of the seaway during the Albian, circulation remained restricted in the fragmented sub-basins of the CIGMR. It probably was not until the Santonian that a deep-water connection and circulation system became established between the Central and the South Atlantic. The sedimentary and faunal record at Site 959 show that a rapid subsidence occurred during the Santonian, with sub-calcite compensation depth conditions maintained until and beyond the Cretaceous/Tertiary boundary

Biostratigraphie de la marge guinéenne : résultats préliminaires de la campagne Equa-marge I (1983)

Preliminary micropaleontological study, principally based on Fora-minifera, of nine deep sea cores taken from the marginal sedimentary Guinean plateau. Early and Middle Eocene, Middle and Late Mioeene, Early Pliocene ana Quaternary microfaunas have been found. The thin and rarely complete Quaternary beds overly various eroded older terms, either (more often) through a hiatus, or through a thin reworked zone. (Biostratigraphy of the Guinean margin : preliminary results from the EQUAMARGE I (1983) cruise.)Etude micropaléontologique préliminaire, essentiellement fondée sur les Foraminifères, de neuf carottes superficielles prélevées en eau profonde sur le plateau marginal sédimentaire de la Guinée. Des niveaux d'âge éocène inférieur, éocène moyen, miocène moyen, miocène terminal, pliocène inférieur et quaternaire ont pu être mis en évidence par les microfaunes. Le Quaternaire, de faible épaisseur et rarement complet, repose sur divers termes antérieurs érodés, soit (le plus souvent) par l'intermédiaire d'un hiatus, soit par une mince zone de remaniement.Marinho M., Mascle Jean, Moullade Michel, Robert Christian M., Saint-Marc Pierre. Biostratigraphie de la marge guinéenne : résultats préliminaires de la campagne Equa-marge I (1983). In: Géologie Méditerranéenne. Tome 11, numéro 1-2, 1984. C.A.M. IXe colloque africain de micropaléontologie. Paris, Museum d'Histoire Naturelle, du 3 au 6 octobre 1983. pp. 59-65

A geological field trip to the Cote d'Ivoire Ghana transform margin

During the Equanaute survey (June 1992), fourteen submersible dives were performed between 4950 and 2250 m water depths across the southern slope of the Cote d'Ivoire-Ghana Marginal Ridge (CIGMR), in the eastern Equatorial Atlantic. The CIGMR, a high-standing topographic marginal ridge along the Cote d'Ivoire-Ghana transform margin, is believed to result from a complex structural evolution due to the specific wrench-related rifting between Western Equatorial Africa and Northeastern Brazil, in Early Cretaceous times. In this paper we report and discuss geological observations made during dives, and sample analyses to resolve the lithology, paleoenvironmental conditions, age and origin of the CIGMR. The data help in better characterizing the different sedimentary and tectonic regimes which successively prevailed during the CIGMR formation and assessing the thermal regime operative during the fabrication and subsequent evolution of the margin. The thick sedimentary pile exposed along the southern CIGMR slope is made up of a repetitive elastic sequence indicative of a deltaic-to-prodeltaic environment. This sedimentary pile, of Early Cretaceous age, has recorded different stages of the transform margin structural evolution. (1) Syn-to post-lithification deformations first record extensional deformations related to the rifting of the adjacent northern divergent; margin segment (the Deep Ivorian Basin). (2) Wrench tectonics has, at a later stage, produced intense fracturing and participated in local folding; chiefly detected upslope. The integrated studies of geological samples and insitu observations obtained during the Equanaute survey support models. for transform margin evolution proposed mainly from geophysicaI data