日本油田層位學の基礎資料としての男鹿半島鮮新世化石有孔虫群

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It was previously reported that the Wakimoto and Shibikawa formations of Oga Peninnania Akita Prefecture, afford the most saitable conditions for the establishment of a standard subdivision of the Jopanese Pliocene of the borderland of the Japan Sea, This extensive region is one of the two large palaeo-zoological provinces distinguished in the Japanese Pliocene deposits., (Jour., Geol., Soc., Japan, Vol., 46(547 & 551), 1939)., Continued research has shown (refer to table) that the massive, bluish gray sandy shale of the Wakimoto formation can be subdivided into zones by means of foraminiferal guide species., The three xones E, D and C are now recognized from the older to the younger, in the Wakimoto formation., The Shibikawa formation, by the same procedure, can be subdivided into the two zones B and A, the former being separated from the latter by a ligniteibed in the lower part of the formation., The E-zone, which is characterized by Globobulimina cf., pacifica CHSHMAN, Uvigerina cf., bifurcata d' ORWIGNY and Cassidulina yabei ASANO & NAKAMURA, is a neritic deposit., In this zone planktonic Globigerinidae are abundant while shallow water foraminifers are seldom found., Bluish gray sandy shale which characterizes this zone is litologically distinguished from the D-zone, which mainly consists of sandstone., D-zone is characterized by abundant Miliolidae and Nonionidae, but no Globigerinidae., The characteristic species is Uvigerina yabei ASANO., This zone was deposited in a sea shallower than that of E-zone., C-zone consists of materials similar to the E-zone, and from the abundant occurrence of Globigerinidae it is evidently a neritic deposit., Although the material and conditions of deposition of this zone is much similar to that of E-zone, the guide species readily serve to distinguish one from the other., Thus, the zones E, D and C were distinguished in the Wakimoto formation at Oibana-zaki, Wakimoto-mura, where the foraminifers are distributed from the lower to upper part of the formation., There appears to be no remarkable change in the lithological character of the sediments in which the zones were distinguished., Among the five zones distinguished with in the Wakimoto and Shibikawa formations, B-zone is most outstanding., It is characterized by such guide species as Gaudryina yabei ASANO, Gaudryna oga ASANO, Polystomellina discorbinoides YAEE & HANZAWA, and Eiphidium yabei ASANO., The majority of these species are evidently restracted to this zone thus rendering easily the disinction of this zone from the others., The sandy shale underlying the lignite bed exposed in the sea-cliff at Anden and hitherto refered to the Shibikawa formation by many authors, corresponds to this zone., The lithological characters of this zone is similar to the sediments of the Wakimoto formation., The sediments above the aforementioned lignite bed consists of loose sandstone., Typical exposures of this loose sandstone of the Shibikawa formation are the sea-criff at Anden, Iriai-mura, and the road cutting at ayazawa and Tominaga both in Wakimoto-mura., This loose andstone which builds up the greater part of the Shibikawa formation is A-zone., A-zone is characterized by Elphidium hanzawai ASANO, a guide species which is very seldom found in any of the other zones., Although A-zone includes the greater part of the Shibikawa formation, further subdivision by means of foraminifers is at present difficult owinug to overwhelming number of living species., The abundant occurrence of Miliolidae, Nonionidae and Polymorphinidae in this zone and indicates that deposition took place in a shallow sea., The five zones A to E, as previously reported can be recognized extensively in the oil-fields of the borderland of the Japan Sea and also in southwestern Hokkaido., However of particular importance is the occurrence of Polystomellina discorlinsides YABE & HANZAWA., The occurrence of this particular fossil from B zone suggests that its corre
1948-07-20

著者

淺野清
東北大學理學部地質學古生物學教室

日本油田層位學の基礎資料としての男鹿半島鮮新世化石有孔虫群

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