大阪堆積盆地第四系の層序学的研究

摘要

大阪周辺の丘陵地や台地に分布する大阪層群や段丘堆積層・大阪湾や平野地下に発達する都rn島・田中累層の層序学的研究の歴史を述べ，大阪堆積盆地第四系の岩相・火山灰・化石・古地磁rn気層序を説明した．また，大阪で組み立てられた第四系総合層序と海洋酸素同位体比層序との対rn比をもとに，中期更新世に関連する3つの重要層準，Ma3層，Ma6層,Ma9層の層準について，rn植物・動物化石などの層序学的資料を整理し，海洋の酸素同位体比などの層序的資料との関連をrn検討した．%Quaternary sediments in the Osaka sedimentary basin are composed mainly of nonindu-rated 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 paleo-climate and high sea levels, can be regarded as the most useful marker horizons for Mid-Pleistocene stratigraphy.