The Journal of the Geological Society of Japan

The Miyamori ultrabasic mass in Iwate Prefecture is metamorphosed, at its western side, by intrusion of granodioritic rocks., The zone of metamorphism (maximum width about 4km) developed in the serpentine and serpentinized dunite may be divided, geologically as well as petrographically, into the following subzones from west to east; 1st zone: enstatite-cummingtonite-spinel zone and spinel-hornblende zone., 2st zone: tremolite-(actinolite)-anthophylite-chlorite zone., 3rd zone: tremolite-antigorite zone., 4th zone: antigorite zone., The rocks which characterize the 1st to 3rd subzones were probably formed simultaneously according to the differece in physice-chemical conditions depending on their distances from the granodiorite mass., This was immediately followed by retrogressive metamorphism during which the rocks of each of the three subzones were successively replased by minerels characteristic of the subzone directly on its east (lower grade one) and finally by antigorite., This mineral first appears as veins through the rocks of the 1st to 3rd subzones, but is finally collected togerther to form large masses which are designated as the 4th zone., There is no evidence to show that the rocks of these subzones were formed progressively from lower grade one.,

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This paper deals with the Pleistocene and Pliocene formations of the northern part of Miura Peninsula., We have selected at first 3 standard cross section lines, along which the stratigraphical relations are observable clearly., These are as follows: I) Totsuka-Enoshima line, II) Hino-Kamakura line, III) Tomioka-Zushi line., In the vicinity of Yokohama, 4 section lines closely located are added mainly for the purpose of tracing there the supposed anticlinolium., The formations of this area are divided into two groups, the upper, the upper the Narita and the lower the Miura., Here we refer to the Miura group only., The foraminiferal fauna of the Miura group is divided into the following 8-10 faunal units in the are surveryed., I., (Totsuka-Enoshima line): 1) Nodosaria-Nodogenerina, 2) Cibicides, 3) Elphidium-Cibicides, 4) Bulimina-Cassidulina, 5) Bulimina-Rotalia, 6) Cassidulina, 7) Pseudononion-Lagenonodosaria, 8) Pseudononion., II., (Hino-Kamakura lilne): 1) Nodosaria-Nodogenerina, 2) Cibicides-Uvigerina, 3) Elphidium-Cibicides, 4) Cibicides-Bulimina, 5) Bulimina, 6) Cassidulilna, 7) Elphidium-Cibicides, 8) Rotalia-Lagenonodosaria, 9) Pseudononion., III., (Tomioka-Zushi line): 1) Nodosaria-Nodogenerina, 2) Cassidulina-Cibicides, 3) Elphidium-Cassidulina, 4) Elphidium-Cibicides, 5) Cassidulina-Bulimina, 6) Cassidulilna-Rotalia, 7) Elphidium-Cibicides, 8) Elphidium-Planulina, 9) Pseudononion-Lagenonodosaria, 10) Pseudononion., IV., (Tomioka-Horinouchi line): 1) Bulimina, 2) Cassidulina, 3) Pseudononion., V., (Nakazato-Nishitobe line): 1) Rotalia, 2) Bulimina, 3) Pseudononion., VI., (Western side of the Yokohama Station): 1) Bulimina., VII., (Shimokashio-Kamihoshikawa line): 1) Rotalia, 2) Bulimina, 3) Pseudononion., From these faunal units we distinguished the following 6 faunal groups: 1) Nodosaria-Nodogenerina group which represents the Zushi member of the Kamakura formation 2) Cibicides-Cassidulilna-Uvigerina group which represents the Ikego member of the Kanazawa formation., 3) Elphidium-Cassidulina-Cibicides group which represents The Nojima member of the Kanazawa formation., 4) Gassidulina-Bulimina-Rotalia group which represents the Ofuna member of the Sugita formation., 5) Cassidulina-Eiphidium-Planulina group which represents the Koshiba member of the Sugita formation and the lower Nakazato member of the Sugita formation in the vicinity of Yokohama., 6) Pseudononion group which represents the typical Nakazato member of the Sugita formation., The Koshiba member has a very variable rock facies in its distribution, losing gradually its characteristics towards Ofuna, and being hardly distinguished from the Nakazato member in the vicinity of Yokohama., Elphidium-Planulina group, the typical Koshiba fauna, has changed into Cassidulina group corresponding to the variation of the rock facies., Cassidulina-Elphidium-Planulina group means both of the Cassidulina group and the Elphidium-Planulilna group, of which the former distributes widely in the are, while the latter only locally., Then the presence of an anticlinolium is ascertained in the vicinity of Yokohama, instead of the monoclinal structure as hitherto been considered.,

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