Ibaraki University, Japan

Detailed oxygen isotope stratigraphy using benthic foraminifers (Bolivina robusta, Bulimina aculeata and Melonis pompilioides) from cored hemipelagic mudstones enables the lower Pleistocene Otadai and Umegase Formations of the Kazusa Group in the Boso Peninsula, central Japan, a turbidite sequence with high depositional rate (average depositional rate of hemipelagic mudstone: 0.9 m/k.y.), to be correlated with astronomically tuned pelagic sequences. Remarkable correlation between this isotope curve and those from DSDP Site 607 from the North Atlantic, and ODP Site 677 and Site 849 from the tropical Pacific is well demonstrated magnetostratigraphically based on the Jaramillo normal Subchronozone. Numerical age model can be addressed to each oxygen isotope event in the studied sequence applying the age for correlative event in the deep sea sequence. As a result of this study, the ages of events are determined as follows; 1) the first occurrence of Gephyrocapsa parallela: 1038-1041 ka, 2) the marker tephra layers O7, O11, O12 and O16: 1050-1056 ka, 1067-1070 ka, 1073-1078 ka and 1101-1105 ka, respectively, 3) the base of the Jaramillo normal Subchronozone: 1068-1084 ka, and 4) the boundary between the Otadai and Umegase Formations: 1011-1017 ka. The maximum error of the age determination is about 6 k.y.. Average sedimentary rates of turbidite sandstones, hemipelagic mudstones and total sediments are 1.9 m/k.y., 0.9 m/k.y. and 2.8 m/k.y., respectively.