Intermittent Formation, Sedimentation and Deformation History of Cenozoic Forearc Basins along the Northwestern Pacific Margins as an Indicator of Tectonic Scenarios

Abstract

This chapter examines the basin‐filling stratigraphy and major unconformity events of the Cenozoic forearc basins in the NE Japan, SW Japan, Ryukyu and Izu‐Bonin forearc territories along the northwestern Pacific margins to obtain information on the back‐ ground tectonic scenarios along the plate subduction zones. The forearc basin type and tectonic history are characteristic for each forearc territory, reflecting the differences in plate tectonic processes. Several major unconformity events seem to be synchronous for a forearc territory or whole forearc territories around Japan, suggesting that these events originated from more or less wider scale plate tectonic events. In the NE Japan forearc territory, the Oligocene unconformity can be the largest events, which transformed the forearc basin styles from the trench slope break‐uplifted, fluvial system‐dominated type to the tensional, deeper marine sloped type. In the SW Japan and Ryukyu forearc ter‐ ritories, the latest Oligocene to Middle Miocene gap was the transformation phase from the Palaeogene Shimanto‐type forearc and accretionary complex, to the Neogene compressive, sloped to ridged forearc basins, developments of which have been interrupted by several unconformity events possibly related to changes in plate tectonic condition. These transformations of the forearc basin styles may reflect the changes in plate tectonic conditions in the northwestern Pacific region.