Tertiary Diatom Flora of Oga Peninsula, Akita Prefecture, Northeast Japan

機関リポジトリ

この論文をさがす

抄録

Ninety-one samples of diatomaceous rocks collected from seven separate sections of the Miocene and Pliocene strata of Oga Peninsula. Akita Prefecture, were studied. The samples are from, in ascending order, the upper part of the Onnagawa Formation, the Funakawa Formation, the Kitaura Formation, the Wakimoto Formation and the Shibikawa Formation. A total of 212 diatom taxa were identified through an examination of the strewn slides made for the samples. Their relative frequencies were estimated by a random count of 200 diatom valves from a strewn slide representing each sample. The analysis of the general features of the paleoecological interpretation of the diatom thanatccoenoses revealed, among other things, the following. The marine diatoms constitute almost entirely of the diatom thanatocoenoses throughout the Onnagawa and Funakawa formations. An appreciable increase of fresh-water and brackish-water species in the floral make-up is noticed in the samples representing the Kitaura. Wakimoto and Shibikawa formations, among which the most noticeable increase is in the Kitaura Formation. This is taken as sugjgesting that, starting from the upper part of the Funakawa Formation the marine sedimentary basin received more influx of fresh-water during the accumulation of fine clastic sediments than during the accumulation of the Onnagawa and Funakawa formations. The representations of brackish-water diatoms are very weak in these fossil assemblages. The general trend of increase in the benthonic : planktonic ratio in the marine diatom valves coincides well with that of the increase of the fresh-water elements. The present study is directed toward subdividing the Neogene sequence by the marine planktonic elements of the thanatocoenoses, to avoid from the biostratigraphic zoning, as much as possible, the influences of the drainage into the sedimentary environments. The stratigraphic distribution of the marine planktonic species (56 taxa) was analysed. Their relative frequencies in the marine planktonic populations were estimatcd on the basis of a random count of 200 marine planktonic diatoms for each sample. Seven diatom zones (Oga diatom zone 1 to 7) were distinguished on the basis of four categories comprising 18 speoies, of which 13 are extinot. Their occurrences are considered to be most important in subdividing the Neogene sequence of Oga Peninsula, as well as for correlation of the subdivisions with other areas. Taxonomic references were made for all diatom taxa Inentioned in the present paper. All of the marine planktonic diatoms are illustrated.

収録刊行物

詳細情報 詳細情報について

問題の指摘

ページトップへ