A detailed study of calcareous nannoplankton from 11 upper Miocene to Holocene cores recovered by the D/V Glomar Challenger in the Sigsbee abyssal plain at Site 3, Leg 1 of the JOIDES Deep Sea Drilling Project, was conducted with the use of optical and scanning electron microscopes. Results show the presence of 8 of the 11 nannoplankton zones established for the late Neogene by Martini. The zones present, from youngest to oldest, are: Emiliania huxleyi zone, Gephyrocapsa oceanica zone, Pseudoemiliania lacunosa zone, Discoaster surculus zone, Reticulofenestra pseudoumbilica zone, Discoaster asymmetricus zone, Ceratolithus tricorniculatus zone, and Discoaster quinqueramus zone. Three of Martini's zones were not detected because there was no core coverage for the intervals w ere they most likely would be present. These include two late Pliocene zones, Discoaster brouweri zone and Discoaster pentaradiatus zone, and the Late Miocene Ceratolithus rugosus zone.

A total of 84 species was recognized; however, a sizable part of the assemblages consists of reworked specimens. Nearly 70% of the species present in the Pleistocene assemblage are reworked; in pre-Pleistocene sediments, 25-50% are reworked. Relative abundances of individuals vary considerably throughout the 11 cores, but only 2 samples of the 88 examined were found to be entirely barren of nannofossils. Late Neogene calcareous nannoplankton from the Sigsbee abyssal plain occur in a succession of zones that agrees with the Neogene Standard Zonation sequence; they are also comparable to nannofossil assemblages known from continental shelf deposits in the Gulf Coast region.

End_of_Article - Last_Page 617------------