Evaluation of Regular Depth Distribution and Geologic Structural Mapping of Quaternary Marine Clay Beds in the Osaka Plain, Japan.

Abstract

The Quaternary stratigraphy on subsurface geology of the Osaka Plain has been mainly built up with drilling cores sampled by 13 deep drilling investigations for ground subsidence countermeasures and the analysis of activity on Quaternary faults. Meanwhile, seismic reflection surveys in the Osaka Plain have been carried out along 13 lines. Depth sections of the seismic surveys provided much additional information on the subsurface geological structure. But, the correlation between the depth section and the litho-stratigraphy of the Quaternary formation in the Osaka Plain was not complete. The upper part of the Quaternary formation in the Osaka plain intercalates 21 marine clay beds. The depth distribution of these marine clay horizons can be explained with a linear relation with the standard probability curve on base depth distribution at the OD-1 drilling site. This linear relation is used for the correlation between the reflectors in the depth section of the seismic survey and the base horizon of the each marine clay bed. The result of the correlation can be applied for the mapping on subsurface geologic structure in the Osaka Plain. The author tried to make geologic structure contour map of the horizons of the main marine clay beds. These Quaternary marine clay beds have been correlated with the oxygen isotope record from deep sea cores. Therefore, those geologic structure maps of the Osaka Plain are available for not only the geo-technical utilization but also the estimation of the historical basin activity.