Quaternary stratigraphy of the Osaka sedimentary basin, central Japan

Quaternary sediments in the Osaka sedimentary basin are composed mainly of nonindurated sand, gravel, silt, and clay intercalated with a number of volcanic ash layers. These sediments consist of two sedimentary units. The lower unit contains only freshwater facies, while the freshwater facies in the upper unit are frequently intercalated with marine clay beds, labeled Ma-1, Ma0, ……Ma13 in ascending order. Twenty-one sedimentary cycles in the upper unit, which represent alternating flu-violacustrine sediments and marine clay beds, indicate successive climatic changes from glacial to interglacial periods. The Quaternary sequences in the Osaka Basin can be correlated to oxygen isotope records obtained from deep sea cores, based on a combination of litho-, bio-, magneto-, and tephro-stratigraphy. The twenty-one marine clay beds, each of which represents a marine transgression, were deposited during interglacial high sea-level periods from Marine Isotope Stage 37 to Stage 1. The Ma 3, Ma 6, and Ma 9 marine clay beds, which are characterized by a warm-temperate paleoclimate and high sea levels, can be regarded as the most useful marker horizons for Mid-Pleistocene stratigraphy.