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Cretaceous to Paleocene sediments from Ocean Drilling Program Sites 959 to 962 in the Côte d'Ivoire-Ghana Transform Margin yield a rich assemblage of dinoflagellate cysts, few acritarchs, spores and pollen, and 12 types of dispersed organic matter. Dinoflagellate cysts proved invaluable in the refinement of shipboard-generated age determinations for Turonian to Paleocene sediments and identification of the Cretaceous/Paleocene boundary at Site 959. A few spore and pollen taxa are of stratigraphic significance. All but two samples of the tectonized basal siliciclastic sediments are barren of dinoflagellate cysts at Sites 959 and 960, but a few samples yield a very low diversity assemblage of spores and pollen. Palynofacies analysis indicates that amorphous organic matter is the dominant organic component in the sediments. However, the tectonized siliciclastic sedments are richer in identifiable terrestrially derived components (wood, black debris, and cuticles) or amorphous organic matter of terrestrial origin. Samples immediately below post-Albian unconformity surfaces at Sites 959 to 961 are enriched in wood and black debris. Thermal alteration indices (TAI) were derived from semiquantitative assessment of spore and pollen colors and used to interpret the thermal maturation of the sediments. TAI values indicate (1) a mature to overmature stage (values >2.5, occasionally dark) for the tectonized basal siliciclastic sediments at all four sites; (2) a moderately mature stage (2− 2.5) for some Upper Cretaceous sediments at Sites 959, 960, and 962; and (3) an immature stage (<2) for the rest of the stratigraphic section. The most mature sediments were deposited during the syntransform phase of basin evolution. 1 Mascle, J., Lohmann, G.P., and Moullade, M. (Eds.), 1998. Proc. ODP, Sci. Results, 159: College Station, TX (Ocean Drilling Program).

Two outcrop sections from the Maastrichtian Colón and Mito Juan Formations were analyzed for dinoflagellate cyst biostratigraphy. Samples from the Río Molino section (Cesar-Ranchería Basin, Colombia) represent a subset of samples from the 240 mthick hemipelagic limestones and calcareous mudstones reported in Martínez's (1989) foraminiferal study. The upper Campanian, lower Maastrichtian and uppermost Maastrichtian intervals were identified in this section based on some significant dinocyst biostratigraphic events, which are in agreement with planktonic foraminiferal data. In ascending stratigraphic order these events include the lowest occurrence (LO) of Areoligera spp., LO of Senegalinium spp., highest occurrence (HO) of Trichodinium castanea, HO of Xenascus ceratioides, LO of Cerodinium diebelii, LO of Trithyrodinium evittii, HO of Odontochitina operculata, LO of Phelodinium tricuspe, HO of Palaeohystrichophora infusorioides, LO of Glaphyrocysta perforata, LO of Disphaerogena carposphaeropsis and LO of Manumiella seelandica.

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Part of the Earth Sciences CommonsThis Article is brought to you for free and open access by the Earth and Atmospheric Sciences, Department of at DigitalCommons@University of Nebraska -Lincoln. It has been accepted for inclusion in Papers in the Earth and Atmospheric Sciences by an authorized administrator of DigitalCommons@University of Nebraska -Lincoln. ABSTRACTCretaceous 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.