淡路島最南部の和泉層群
1952 年 61 巻 2 号 p. 67-72
詳細
1952 年 61 巻 2 号 p. 67-72
The Island of Awaji in Hyogo Prefecture is occupied in its southern part by the upper Cretaceous Izumi group and is famous for the occurrence of the interesting fossils. The hitherto described fossils, however, were mainly derived from the lower half of the group. The writers recently surveyed through the Cretaceous area and especially made, a detailed work on the southern steep slopes of the island, with the results that a fossiliferous member was discovered near the uppermost part of the group and that the stratigraphy of the upper half was considerably revised. The emended stratigraphic sequence of the Izumi group in this island is as follows in ascending order :
1. Tsui basal conglomerate, 200 meters thick.
2. Minato shale, very fossiliferous, 500 m.
3. Yoroizaki sandstone, with subordinately interbedded shale, 1, 400 m.
4. Shichi shah, fossiliferous, 400 m.
5. Kitaama sandstone and shale (emended) : Thick series of alternating sandstone and shale, 3, 300 m. The sandstone is predominant in the lower part, whereas the shale is predominant in the upper part. Layers of liparitic tuff are intercalated at horizons and especially remarkable in the lower part. Fossils occur sporadically from the sandstone of the quarries.
6. Nada sandstone and conglomerate (emended) : Sandstone with interbedded shale and conglomerate, 1, 100 m.
7. Shimonada fine-sandy siltstone, containing nodules and fossils abundantly. 370 m (+).
8. Shimonada white sandstone, with sporadic fossils, 250 m (+).
Layers of tuff are intercalated in members (7) and (8).
The identified fossils derived from the upper half (i. e. 58) are listed in the table of the Japanese text. From these fossils the upper half of the group is safely correlated to the upper Hetonaian in Hokkaido, the approximate equivalent of the uppermost Senonian of Europe, and is a representative of the uppermost Cretaceous in Southwest Japan.
Together with the stratigraphy some interesting features of the geologic structure in the southernmost part of the island are described. (See the annexed geologic map.)
