Miocene diatom biostratigraphy of the Atlantic sector of the Southern Ocean

Four ODP sites located between 64°S and 41°S in the eastern Atlantic sector ofthe Southern Ocean were investigated to refine the Miocene diatom biostratigraphic zonation tied to the geomagnetic chronology. The Miocene diatom stratigraphy from two sites located on Maud Rise (ODP Leg 113) is revised considering the progress in diatom biostratigraphic research, diatom taxonomy and magnetostratigraphic age assignment during the past 10 years. A new diatom zonation was erected for Site 1092 (ODP Leg 177) located on Meteor Rise integrating a magnetostratigraphic interpretation of the shipboard data. This zonation was also applied to Site 1088 (ODP Leg 177) located on Astrid Ridge. The study is focused to Middle and Upper Miocene sequences. It reveals latitudinal differentiations in stratigraphic species ranges and species occurrence pattern that are related to latitudinal differences in surface water masses reflecting the climatic development of the Antarctic cryosphere. Considering the latitudinal differences two stratigraphic zonations are proposed that are applicable to the northern and southern zone ofthe Southern Ocean, respectively. The southern Southern Ocean Miocene diatom biostratigraphic zonation consists of 16 zones in which 11 represent new or modified zones. The northern biostratigraphic zonation contains 10 diatom zones allowing a stratigraphic resolution in the range of 0.2-2 Myr. This paper also includes the taxonomic transfer of seven Miocene diatom taxa from genus Nitzschia Hassal to Fragilariopsis Hustedt.