Landform evolution and sedimentary environment of the riverine coastal plain around the Holocene/Pleistocene boundary.

本研究旨在厘清全新世/更新世界线附近河流沿岸平原的地貌和沉积环境，并对诺比平原的全新世/更新世界线进行了详细的分析。从沉积物中可以看出最新更新世沉积相的区域差异。这种差异被认为是由当时每个地点的地貌和沉积环境造成的。三角洲前缘可以看到厚厚的砂质沉积物，当时的潮滩上可以看到厚厚的牡蛎壳床的地方。此外，在洪泛平原地区，河流相泥质沉积物发育得很广。在全新世/更新世界线的接触处也可以看到浅层解剖的山谷和河道充填。这些沉积物的区域差异是当时三角洲缓慢海侵和位置不同的结果。在津格鲁和阿巴希里的小河沿岸平原，泥质全新世沉积覆盖了最新的更新世沉积，由砂或砂砾组成。泥炭层偶尔出现在泥质沉积物的最低部分。这表明，这些低洼地以泛滥平原为主，处于更新世/全新世界线的沉积环境中，有些地方可以看到向沼泽状态的突变。

This research aims to clarify the landforms and sedimentary environments of the riverine coastal plain in the period around the Holocene/Pleistocene boundary.Detail analysis of the Holocece/Pleistocene boundary of the sediments was done on the Nobi plain. Regional defferences of the facies in the latest Pleistocene can be seen in the sediments. The differences are considered to be caused by the elandforms and sedimentary environments of each location at that time. Thick sandy sediments can be seen in the delta front, and the places where the thick oyster shell bed can be seen in the tidal flat at that time. Furthermore, in the places of the flood plain, fluvial muddy sediments develop widery. Shallow dissected valleys and channel fills are also seen in the contact of the Holocene/Pleistocene boundary. These regional differences of the sediments are the result of the slow transgression and the difference of the location in the deltas at that time.In the small riverine coastal plains at the Tsugaru and the Abashiri, muddy Holocene sediments cover the latest Pleistocene sediments which are consisted of sand or sandy gravels. Peat layrs are occasionaly seen in the lowest part of the muddy sediments. This shows that the sedimentary environment of the Pleistocene/Holocene boundary in these lowlands in mainly flood plain, and the abrupt change to the marshy condition can be seen in some places.