Unconformity between a Late Miocene-Pliocene accretionary prism (Nishizaki Formation) and Pliocene trench-slope sediments (Kagamigaura Formation), central Japan

Abstract : Unconformities provide key geological evidence of a major tectonic event, a period without the deposition of sediment, or an environmental change (e.g. Tomkeieff 1962). In particular, an unconformity between an accretionary prism and trench-slope sediments at the toe of a plate-subduction margin provides information on the temporal and spatial evolution of tectonic processes during accretion (e.g. Strasser et al. 2009). Recently excavated outcrop at the southern tip of the Boso Peninsula, central Japan (Figs 1-3), contains an unconformity between a Late Miocene-Pliocene accretionary prism (the Nishizaki Formation) and Pliocene trench-slope sediments (the Kagamigaura Formation). There are major differences in the amount of clockwise rotation associated with multiple collisions of the Izu-Bonin Island Arc as well as tectonic structure between these formations (Yamamoto & Kawakami 2005).