Abstract
Regression-and-transgression boundaries (RTBs) were defined in Miocene strata of the Yatsuo area (RTBs Y1, Y2, and Y3) in a backarc basin, the Mizunami area (RTBs M1, M2, and M3) in an intra-arc basin, and the Kakegawa area (RTBs K1 and K2) in a forearc basin, across central Honshu, Japan. The sedimentary successions of the Yatsuo and Mizunami areas consist of coastal-shelf deposits, and the RTBs are recorded as unconformities or ravinement surfaces. In the Kakegawa area, the middle of a turbidite section (RTB K1) and an erosional surface (RTB K2) in thick mudstone might represent maximum regressions.The recognized RTBs were formed in Miocene time, except for RTB M3 in Pliocene time. The Miocene RTBs can be correlated within four time zones by means of magnetostratigraphy ; Zone Jmi1 (RTB K1) in Chron C5Dn (17.62-17.28 Ma), Zone Jmi2 (RTBs Y1, M1, and K2) in Chron C5Br (16.01-15.16 Ma), Zone Jmi3 (RTBs Y2 and M2) in Subchron C5Bn1r (15.03-14.89 Ma), and Zone Jmi4 (RTB Y3) between 14.89 and 12.3±1.9 Ma. The synchronicities of the RTBs in Zones Jmi2 and Jmi3 in the different tectonic settings suggest that the RTBs were formed by regional sea-level changes.
