Oligocene-lower Miocene calcareous nannofossil biostratigraphy of ODP Leg 154 hole 929A from the western equatorial Atlantic at the Ceara Rise.

摘要

The Ocean Drilling Program (ODP) Leg 154 in the western equatorial Atlantic cored Paleocene - Holocene strata at Site 929 on the Ceara Rise. The calcareous nannofossil biostratigraphy of the Oligocene -- lower Miocene sequence at Hole 929A is a necessary compliment to shipboard analysis. The analysis of Hole 929A samples presented here yielded 9 biozones defined by 10 nannofossil datums. Of these datums, two first occurrences (FO) and eight last occurrences (LO) were distinguished according to the Martini (1971) Zonation scheme. Based on quantitative analysis 21 genera and 79 species were identified in this section. The assemblages have abundances from rare to very abundant with moderate to good preservation and overgrowth on the lower Miocene discoasters.;The Ceara Rise and the analogous Sierra Leone Rise are located on opposite sides of the equatorial Atlantic Ocean and are bounded by the same fracture zones. The Ceara Rise is on the western side, whereas the Sierra Leone Rise is in the eastern side. The two sites, Site 929 and Site 366, on these two rises were correlated via their nannofossils. However, because of poor preservation at Site 366 the zonal boundaries between NN3/NN2, NN1/ NP25, and NP22/NP21 are not well detailed. The relative abundance (%) of the total assemblages and their sedimentation rates in the western equatorial Atlantic were also calculated, and those for Hole 929A were generally higher.