Wave-planation surfaces in the mid-western East Sea (Sea of Japan): Indicators of subsidence history and paleogeographic evolution of back-arc basin

This study focuses on revealing the origin of deep-marine wave planation surfaces and its geomorphic and tectonic implications for the back-arc evolution based on multi-channel seismic reflection profiles acquired from the mid-western East Sea (Sea of Japan). On seismic reflection profiles, the wave-planation surfaces are recognized as continuous and high-amplitude single reflectors outlining the flattened top of submarine terraces or isolated topographic highs. The wave planation surfaces are classified into four types, depending on the geomorphic characteristics and origins of substratal landmasses, i.e., continental margin terrace (type-1), rifted continental fragment (type-2), volcanic edifices (type-3), and uplifted sedimentary successions (type-4), which have common origin of wave erosion near the sea level, but different subsidence history. The mean subsidence rate of wave-planated substratum is calculated by dividing the maximum depth of a wave-planation surface below modified datum sea level (D-E) by the time elapsed since the onset of subsidence (T). Information of local subsidence history enables reconstruction of paleogeographic evolution of mid-western East Sea during the Neogene-Quaternary time: (1) incipient continental rifting and onset of marine incursion (ca. 23-18 Ma); (2) progressive continental rifting and onset of wave planation (ca. 18-11 Ma); (3) final eruption of post-rift volcanoes (ca. 11 Ma); (4) uplifting of shelf-margin banks and onset of the Pliocene-Holocene volcanic activities (ca. 11-2.5 Ma); (5) change in the locus of volcanic eruption and cessation of contractile uplifting in the basin margin (ca. 2.5-0 Ma).