Abstract
The depositional age and sedimentary environment of the Pleistocene succession beneath the Tokushima Plain in southwestern Japan remain poorly understood, even though it includes key marker beds and age constraints that are crucial for understanding the history of the basin. We identified brackish–marine beds and constructed the chronostratigraphy of the subsurface Pleistocene strata using analyses of tephra layers, the electric conductivity (EC) and pH of muddy sediments, and diatom and pollen fossils in borehole cores from the southeastern Tokushima Plain. We correlated four tephra layers to the G9L , Naruohama-IV (Nh-IV), Kakuto (Kkt), and Ata-Torihama (Ata-Th) tephra layers, based on major and trace element compositions and the refractive index values of glass shards. High EC, brackish–marine diatoms, and pollen assemblages highlighted five brackish–marine beds, which were deposited during highstands in marine isotope stages (MISs) 11 to 5e. The marine beds corresponding to MISs 11, 9, and 5e (or 7) occur in subsurface Pleistocene strata in the northern part of the plain, and thus provide age constraints on the evolution of the Tokushima Plain.
