Eocene to Quaternary benthic foraminifers and paleobathymetry of the Izu-Bonin Arc, Legs 125 and 126

Benthic foraminifers obtained from ODP Sites 782, 786, 790, 791 and 792 were examined. The results indicate total basement uplift in the inner part of the Bonin arc-trench system since late Oligocene and total basement subsidence in the outer part of the system since late Eocene. The last occurrence (LO) of Stilostomella spp. and Pleurostomella spp. and the first occurrence (FO) of Bulimina aculeata d'Orbigny occurred consistently at 0.7 Ma at all three arc proximal sites (790, 791 and 792). This fact is taken to suggest a change of water mass, from one originating from the central part of the ocean to that originating from ocean-margin areas at that time. -from Author