Sedimentary facies of incised-valley fill deposits near the transgression-to-regression turnaround point

Abstract

This study examines the sedimentary characteristics and accumulation rates of incised-valley fill deposits in the inland region of the Nobi Plain, focusing on their relationship with sea-level and climate changes. A 23-meter-long core sample (UK core) from Ushiki was analyzed, revealing six sedimentary units (UK1–UK6). Units UK1–UK3 represent fluvial-to-marine transitions, while UK4–UK6 reflect regressive environments. The accumulation rates correspond to the rates of glacial sea-level changes. Peat formation around 4 ka indicates a shift to wetland conditions. This study underscores the distinctive features near the transgression-regression transition zone.