上部層は、砂岩と厚い赤色〜灰緑色泥岩が交互に堆積したカラフルな互層である。厚さ1000 mを越える地層には温暖であった白亜紀中頃の情報が記録されている。砂岩層は河川の流路に積もった砂や自然堤防を越えて運ばれてきた砂に由来し、その堆積構造から河川が蛇行していたことが示される。

泥岩層は炭質物やプラタナス類などの葉体化石を含み、河川の周辺の堆積物と解釈できる。そこには被子植物主体の植生が存在していたであろう。また、上部層に頻繁に挟まれる凝灰岩層は、周辺地域で火山活動が活発だったことを物語る。御船層群上部層には豊富な恐竜化石が含まれている。

The “upper formation” is composed of alternating layers of sandstone and thick red and greenish gray mudstone giving it a colorful aspect.

Formations exceeding a 1000 meters thickness often contain information concerning the warm-mid cretaceous. In fact, as sandstone layers are derived from an accumulation of sand in the river channel or from sand that has been carried beyond the natural levee, such sedimentary structure indicates a past meandering river.

By analyzing the mudstone layers, we were able to determine that it contains carbonaceous material like platanus leaf fossils, which lead us to consider that those material was deposited in the vicinity of a river where the vegetation was mainly composed of angiosperm. Besides the information mudstone layers bring us, the “upper layer” teaches us also a fair insight on the volcanic activities. Indeed the fact that the “upper layer” is frequently sandwiched by tuff layers teaches us how strong was the surrounding volcanic activity.

Mifune group formation’s “upper formation” is rich in dinosaurs that are about to be unraveled.