Samir Shafik,2 David K. Watkins,3 and Im Chul Shin4


The distribution of calcareous nannofossils in the upper Cenozoic sections sampled at four sites in the eastern equatorial Atlantic Ocean during Ocean Drilling Program (ODP) Leg 159 is documented here. A virtually complete upper Cenozoic sequence of nannofossil (sub)zones is identified at Site 959 on the shoulder of the Côte d’Ivoire-Ghana marginal ridge, with proxies for the rare marker species being employed. Hiatuses within the middle and upper Miocene are detected at two other sites on the same ridge, being more clearly defined at Site 960 on the crest of the ridge. Two of these hiatuses are of regional significance. A middle Miocene hiatus, based on a truncated Zone CN4, absent Zone CN5, and reduced Zone CN6, could probably be related to a major change in the depositional regime at Site 959, when a mid-Cenozoic series of short episodes of deposition of non-calcareous sediments ended. A late Miocene hiatus, based on the absence of Subzone CN8a in all sites on the ridge, is seemingly coeval with another one previously documented in oceanic sections elsewhere. Two other late Miocene hiatuses, based on the absence of Subzones CN7a and CN9a, coupled with a very thin Zone CN6, indicate a sediment starvation of the ridge during much of the middle and late Miocene. The timing of the hiatuses suggests a correspondence with major falls in sea level.

1Mascle, J., Lohmann, G.P., and Moullade, M. (Eds.), 1998. Proc. ODP, Sci. Results, 159: College Station, TX (Ocean Drilling Program).
2Australian Geological Survey Organization, GPO Box 378, Canberra ACT 2601, Australia. sshafik@agso.gov.au
3Department of Geology, University of Nebraska-Lincoln, Lincoln, NE 69588-0340 U.S.A.
4Korea Ocean Research Institute, Ansan, P.O. Box 29, Seoul, 325-600 Korea.