Abstract:
A quantitative study of late Tertiary and Quaternary calcareous nannofossils from DSDP/ODP Sites 664, 659, 608, 609, 610 in the Northeast Atlantic was carried out to reconstruct the development of the nannofossil assemblage during the last 5.2 million years. Species of Reticulofenestra and Gephyrocapsa, Pseudoemiliania lacunosa and Emiliania huxleyi are the main components of the nannofossil assemblage. Eight developmental stages of the nannofossil assemblage are distinguished based on changes in the main composition of the nannofossil assemblage. In the Pliocene, the assemblage is dominated by Reticulofenestra species. In the Quaternary, the assemblage is characterized by frequently alternating dominance of P. lacunosa and Gephyrocapsa species. Changes in the assemblage during the Quaternary were more rapid and abrupt than in the Pliocene. Today, the recently evolved E. huxleyi is the dominant species. The changes in nannofossil development are seen as the result of major evolutionary changes in the dominant species within the members of the family Nochaerbdaceae. The nannofossil assemblage shows a number of geographical variations throughout the eight stages. In the early Pliocene, Discoaster spp. and Sphenolithus spp. were common in low latitudes and rare in high latitudes; in the late Quaternary, G. oceanica and G. margereli were abundant in low latitudes, whereas G. caribbeanica was prominent in high latitudes. Small latitudinal variations in the assemblage were related to small paleo-oceanographic variations from low to high latitude; whereas large differences between the study sites reflect different paleo-oceanographic conditions between the north and the south.