35. MESOZOIC BIOSTRATIGRAPHIC, PALEOENVIRONMENTAL, AND PALEOBIOGEOGRAPHIC SYNTHESIS, EQUATORIAL ATLANTIC¹

M. Moullade,² D.K. Watkins,³ F.E. Oboh-Ikuenobe,⁴ J.-P. Bellier,⁵ E. Masure,⁵ A.E.L. Holbourn,⁶ J. Erbacher,⁷ W. Kuhnt,⁶ T. Pletsch,⁶ M.A. Kaminski,⁸ R. Rauscher,⁹ S. Shafik,¹⁰ O. Yepes,⁴ J. Dejax,¹¹ J.M. Gregg,⁴ I.C. Shin,¹² and M. Schuler⁹

ABSTRACT

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.

¹Mascle, J., Lohmann, G.P., and Moullade, M. (Eds.), 1998. Proc. ODP, Sci. Results, 159: College Station, TX (Ocean Drilling Program).
²Laboratoire de Micropaléontologie et de Géologie Marines, CNRS UMR 6526 et GDR 88, Université de Nice-Sophia Antipolis, Parc Valrose, 06108 Nice Cedex 2, France. moullade@unice.fr
³Department of Geology, University of Nebraska, Lincoln, NE 68588-0340, U.S.A.
⁴Department of Geology and Geophysics, University of Missouri-Rolla, Rolla, MO 65409-0410, U.S.A.
⁵Laboratoire de Micropaléontologie, URA CNRS 1761, Université Pierre et Marie Curie, 4 place Jussieu, 75252 Paris Cedex 05, France.
⁶Geologisch-Paläontologisches Institut der Christian-Albrechts-Universität zu Kiel, Olshausenstrasse 40, D-24118 Kiel, Federal Republic of Germany.
⁷Institut u. Museum für Geologie/Paläontologie der Universität Tübingen, Sigwartstrasse 10, D-72076, Tübingen, Federal Republic of Germany.
⁸Research School of Geological and Geophysical Sciences, Birkbeck College and University College London, Gower Street, London WC1E 6BT, United Kingdom.
⁹Centre de Géochimie de la Surface (CNRS), 1 rue Blessig, 67084 Strasbourg Cedex, France.
¹⁰Marine Science and Petroleum Geology Program, Australian Geological Survey Organization, GPO Box 378, Canberra, ACT 2601, Australia.
¹¹Laboratoire de Paléontologie, Museum National d’Histoire Naturelle, 8 rue Buffon, 75005 Paris, France.
¹²Korea Ocean Research and Development Institute, Ansan, P.O. Box 29, Seoul 425-600, Korea.