Earth and Atmospheric Sciences, Department of


Date of this Version



Published in Proceedings of the Ocean Drilling Program, Scientific Results (1998) volume 159: 413-431. Paper number 32. J. Mascle, G.P. Lohmann and M. Moullade, editors. Copyright 1998, Ocean Drilling Program. Used by permission.


Paleogene sections on the Côte d’Ivoire-Ghana Marginal Ridge in the eastern Atlantic Ocean, sampled at three sites during Ocean Drilling Program Leg 159, are shown to have calcareous nannofossil assemblages in distinct packages of (sub)zones separated by hiatuses or barren sediments. The packages are different at each of the sites; all fall within the interval from late Paleocene Zone CP6 to latest Oligocene Subzone CN1a inclusive. Three packages (CP9b–CP11, CP13, and CP19) on the crest of the Marginal Ridge at Site 960, four (CP7–CP9b, CP11, CP13–?CP15, and CP17–CN1a) at nearby Site 959 on the shoulder of the Marginal Ridge, and only two (CP6–CP8a, and CP10) at the deeper Site 961, on the southern tip of the Marginal Ridge, were identified. The Paleogene section at Site 960 is thinner and less complete than at Site 959, but it is thinnest and least complete at Site 961. Conditions during most of the Paleogene were strikingly different near the crest of the Marginal Ridge (most affected by changes in sea level) compared with those on its lower slopes (where bottom currents were probably more effective in removing sediments or preventing sedimentation in an already sediment-starved area).

Hiatuses on the crest of the Marginal Ridge are more frequent than on its shoulder where the nannofossil succession is interrupted by intervals with seemingly barren sediments instead. Two short hiatuses at Site 960 are almost coincident with, and probably related to, major falls in the global sea level of ~125 m during the earliest middle Eocene (also coeval with a hiatus at Site 959 and elsewhere in the Atlantic), and of ~60 m during the latest Oligocene. An intervening hiatus at the same site (middle Eocene–lower Oligocene section virtually being missing) corresponds with a period of strongly fluctuating global sea level, which included three major falls.