Pleistocene biostratigraphy, chronostratigraphy and paleocirculation of the southeast pacific central water core RC 11-220

Abstract

An 11-m core, RC 11-220, raised from a depth of 2,950 m in the unstudied Southeast Pacific Central Water of the Tuamotu Ridge (14° 49′S 139° 58′W) received paleontologic and paleoecologic analysis. Eight biostratigraphic horizons were recognized (6 planktonic foraminiferal, 1 coccolithophorid and the discoaster extinction) defining the core as continuous through the basal Pleistocene. The Globorotalia truncatulinoides (d'Orbigny) datum was approached but not encountered. The core has an estimated average sedimentation rate of 0.60 cm/10 3 years. Extrapolation from two paleomagnetic datums (Brunhes/Matuyama, ca. 0.69 Ma and the top of the Olduvai, ca. 1.61 Ma) indicates the age of the core bottom to be ca. 1.87 Ma. Based on the evidence recorded in RC 11-220 and our knowledge of the circulation patterns at the core site today, the following paleocirculation model is proposed. The total carbonate and coarse fraction data indicate a relatively constant depositional pattern and productivity. In addition, judging from the faunal dominance and the distributional pattern of key species such as Globigerinoides ruber (d'Orbigny), Globigerinoides sacculifer (Brady) and Globigerinita glutinata (Egger), a minor shift in the salinity regime is suggested while temperature remained relatively constant. On the average, salinity was slightly higher during the first approximate million years and was somewhat reduced during the last million years B.P. The major conclusion of this study however is that the character of the surface South Central Pacific Waters remained relatively constant throughout the Pleistocene.