Glacio-eustatic control on deep-marine clastic forearc sedimentation, Pliocene-mid-Pleistocene (c. 1180-600 ka) Kazusa Group, SE Japan

Glacio-eustasy has been shown to be a primary control on sedimentation in t he open ocean and along passive continental margins, but its importance in elastic-dominated deep-marine sequences at active plate margins remains poo rly understood. In order to test the relative importance of glacio-eustasy at tectonically active plate margins during times of substantial polar ice, a high-resolution delta(18)O and delta(13)C record from planktonic foramin ifera (Globorotalia inflata) was undertaken from the Plio-Pleistocene (c. 1 180-600 ka) Kazusa Group, a forearc basin fill, onland SE Japan. This was c ombined with a high-resolution study of the magnetic susceptibility, total organic carbon, and %CaCO3 in order to evaluate the response to any glacio- eustatic changes in continental-margin sedimentary processes. The sections reveal globally recognized glacial-interglacial cycles, with sandy interval s correlating with inferred glacials, suggesting that relative sea-level ch anges during glacial-interglacial cycles exerted the primary control on sed iment accumulation in the deep-marine forearc basin. Cross-spectral analysi s of delta(18)O and delta(13)C data from the inter-turbidite hemipelagic an d pelagic mudstones reveals Milankovitch control both at precession and ecc entricity modes, with a shift in their relative importance at about 900 ka. The results of this study have important implications for stratigraphers a nd sedimentologists because they show that at times when there is substanti al polar ice: (1) the main control on sediment accumulation at active plate margins is glacio-eustatic, and (2) support the sequence stratigraphic par adigm developed from passive continental margins that global sea-level chan ges exert a primary control on siliciclastic deposition.