This study is based on the data of some wells for exploration of oil and gas and the data of many shot holes for seismic survey. As a result of it, the Quaternary sediments developed in this area have been stratigraphically subdivided as follows:
thickness
A4: Bottom deposits of the present sea ?
A3: Sand and gravel 10m±
A2: Clay, peat and pumice 30m±
A1: Gravel, sand, clay and peat 30m±
S:Shikotsu volcanics
(20, 000years B. P.)
Shishinai Formation 50m±
Nopporo Formation 50m±
Characteristic change in distribution and arrangement of the Quaternary sediments in this area is thought to be due to three types of vertical movements, which differ distinctly with each other.
