Formation of the Seabed is the History of the Earth

The undersea floor bed of Kansai International Airport is made up of layers of sand and clay. The thickness of the layers increases as the sea deepens.

At the top of the formation, the clay layer called the Holocene clay Layer is approximately 20 m in thickness. And below the holocene clay layer, the Pleistocene layer that consists of alternating layers of hard clay and gravel adds up to hundreds of meters. The Pleistocene layer can be divided into upper and lower parts. The hardness of the upper part is such that it gives a little when pressed hard, and the hardness of the lower part is that it never gives even when pressed hard.

The holocene clay layer is the layer that has accumulated in the fourth Alluvial epoch (Holocene) extending from the end of the last Ice Age, about 10,000 years ago, to the present day. The KIX site in those times as now has always been in the deep sea. The Alluvial clay layer has accumulated under the sea at KIX over the past 10,000 years.

The Pleistocene layer accumulated in the fourth Pleistocene epoch (Pleistocene times) from approximately 2 million years ago to 10,000 years ago. This is the time characterized by the Ice Ages when mammoths trod the earth and the intervening Interglacial Ages. During the Ice Ages, the temperature dropped and the water level decreased as the low temperatures trapped water in glaciers. Conversely, the temperature rose, ice began to melt, and the water level increased during the Interglacial Ages. The range of the water level change was so great that it exceeded 100 m. Osaka Bay has repeatedly transformed itself from sea to lake to land in cycles of tens of thousands to a hundred thousand years as the water level changed.

The Ground of the Seabed Comprises the Layers of Sand and of Clay

Clay accumulates on the seabed when the ground is under the sea. Sand accumulates on the ground when the water level decreases and the ground emerges from the water. In addition, the movement of the earth's crust slowly lowered the seabed additionally, deepening the depth of the Osaka Bay in Pleistocene times. As Osaka Bay deepens, clay and sand have accumulated on the floor of the seabed almost without exposure to strata erosion by rivers or rain. As the sample shows, the Pleistocene formation of the Osaka Bay comprises alternating layers of clay and sand. Only a few geologic formations of this type remain. In Japan , we can find this type of geologic formation under Osaka Bay and Beppu Bay .

The Details of Formation of the Seabed under Kansai International Airport