底生有孔虫にもとづく日本の後期新生代古水深指標  [in Japanese] Late Cenozoic paleobathymetric indices based on benthic foraminifers in Japan  [in Japanese]

Benthic foraminifers are regarded as the most useful tool for paleobathymetric reconstruction of the Upper Cenozoic. Their propriety as a paleobathymetric indicator, however, tends to decrease toward the past because the proportion of extinct species becomes larger in fossil assemblages and because the habitats for any species have changed with age. In this paper, reliability of benthic foraminifers as an index is discussed, and index species of several paleobathymetric zones are proposed for the Upper Cenozoic faunas. To recognize the difference among faunal components in similar environment of different age and in different region of the same age, we analysed the foraminiferal data from the three stratigraphic intervals each of two provinces separately. They are lower Middle Miocene, upper Middle Miocene to Lower Pliocene, and Upper Pliocene to Lower Pleistocene in Northeast Japan, and lower Middle Miocene, Upper Miocene, and Pliocene in Southwest Japan (Pacific coast-region including Kanto district). On the fossil species which is identical with the Recent one, their shallow bathymetric zone (SBZ) are estimated by analogy of SBZ of the Recent species at respective unit. On the other fossil species, the estimation of SBZ are based on the frequent co-occurrence with the SBZ known species in fossil assemblages. Successively, we apply those SBZ to fossil assemblages of the well-studied regions in Northeast Japan, for the evaluation of their reliability as paleobathymetric indices.