Stratigraphy and Subsurface Structure of Holocene Deposits around Uemachi Upland in the Central Osaka Plain

This.paper presents results of a recent geological study of the Holocene deposits in the Osaka Basin, especially at the central area around Uemachi Upland. The study was based upon the analysis of a large number of borehole data compiled in the computer database. 14C datings of fossils sampled by boring and excavation sites were carried out at several key sites and used to interpret the processes of deposition. The Holocene deposit, named the Umeda Formation, is subdivided into three layers by facies. In some marginal zones at Tenma around the Uemachi Upland, where the Holocene deposit fades out, dense sand and gravel layers were found and were considered Pleistocene deposits without any geological indication. The subground structures in the Osaka Plain were obtained in vertical sections along eight lines; they show not only Holocene but also Upper Pleistocene structures in the area. Based upon 14C dating, the marginal facies of sand and gravel layers around the Uemachi Upland were identified as Holocene deposits. They are interfingered with the main clay layer facies of the Umeda Formation. Other tectonic structures like flexures as well as geotechnical aspects are also discussed