HR: 09:15h
AN: PP31F-06    [Abstracts]
TI: Faunal Change of Benthic Foraminifera to the Glacial Events during the Mid-Oligocene Interval in the Eastern Equatorial Pacific Sites (ODP Leg 199)
AU: * Takata, H
EM: yuu@soc.shimane-u.ac.jp
AF: ReCCLE, Shimane University, 1060 Nishikawatsu, Matsue, 690-8504, Japan
AU: Nomura, R
EM: nomura@edu.shimane-u.ac.jp
AF: Faculty of Education, Shimane University, 1060 Nishikawatsu, Matsue, 690-8504, Japan
AB: Deep-sea paleoceanographic environments considerably varied in the late Paleogene, in response to the fluctuation of the Antarctic ice volume and to the potentials of deep water formation in the Southern Ocean. Several glacial events with stable oxygen isotopic shift occurred during the Oligocene. Recently, many Oligocene paleoceanographic studies of Site 1218, ODP Leg 199 (the eastern equatorial Pacific Ocean) have been carried out (Coxall et al., 2005; Wade and Palike, 2004; Palike et al., 2006). These studies suggested that various orbital forcing, particularly long eccentricity and ~1.2 m.y.-obliquity amplitude modulation, affected not only glacial events but also the carbonate compensation depth or surface carbonate production via weathering process. Because the drilled section of this site contains well-preserved foraminifera in almost all samples, this section provides the opportunity for conducting a detailed study of faunal change to the Oligocene glacial events. The objectives of our study are to investigate the mid-Oligocene faunal succession (27.0 to 30.5 Ma) of benthic foraminifera and to consider their relation to paleoceanographic changes in the eastern equatorial Pacific Ocean. Based on a factor analysis to benthic foraminiferal fauna at Sites 1218 and 1219 (112 samples), three factor assemblages were recognized. The Factor 2 assemblage is characterized by typical deep-sea taxa under Oligotropic condition, such as Oridorsalis umbonatus, Cibicidoides spp. and Gyroidinoides spp., whereas the Factor 1 assemblage, characterized by Nuttallides umbonifer that is related to Southern Ocean deepwater flow and / or carbonate undersaturation of deep waters. Factor 1 assemblage was common around four glacial events (76Ol-C11r, 73Ol-C10m, 70Ol-C10n and 67Ol-C9n (Palike et al., 2006)). In addition, dominance of the assemblage became continuously after the 73Ol-C10m. Such occurrence suggests that influence of Southern Ocean deepwater flow and/or carbonate undersaturation at this site was increased in every glacial event during the mid-Oligocene interval. In contrast, the Factor 2 assemblage was observed temporally within the dominance of the Factor 1 assemblage in the glacial events. It seems to be caused by enhanced carbonate production from ocean surface that may be related to orbital cycles. Therefore, the changes of both the characteristics of the deep watermass and surface carbonate production due to orbital forcing are responsible to abyssal benthic foraminifera during the mid-Oligocene in the eastern equatorial Pacific Ocean.
DE: 4944 Micropaleontology (0459, 3030)
DE: 9355 Pacific Ocean
DE: 9606 Paleogene
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting