Faunal analysis of Early to Middle Jurassic radiolarians

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Radiolarian faunal composition was analyzed for five samples of Early to Middle Jurassic manganese carbonate nodule (M NJ-12, 9 Hi-145, GH-1, 0 IN-7 and S IN-1) from Mesozoic sedimentary complex of the Mino tertane, central Japan. The results are summarized as follows :(1) Specific number of each sample is 200 300, and these number are larger than those from chert and clastic samples.(2) Characteristic species of each sample have been assigned their geologic age to that (1) late Pliensbachian - Early Toarcian (185 Ma), (2) Aalenian (176 Ma), (3) early Bajician (172 Ma), (4) Bajocian (168 Ma) and (5) Bathonian (165 Ma). The estimation of the age order is supported by their quotient of similarity [QS] among faunas. QS were caluculated with a formula, QS = 2c / (a+b) [a, b : specific number of fauna, c : common specific number between a and b faunas].(3) It is inferred that style of faunal change was controled by a combination of both short ranged specific group (several million years) and long ranged specific group (more than ten million years).(4) Rate of origination and extinction of species also played an important role in control of the style of faunal change. The rate was calculated with a formula, R = a or b / t[a, b : number of originated species or extinct species, t : age interval between each sample ; my. l.