日本産Miogypsinaのnepionic accelerationと時空分布

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Seven populations of Miogypsina from localities all over Japan are statistically analyzed on the basis of the neplonic acceleration theory, which was suggested first by TAN SIN HOK (1936) and revealed through the numeral measurement of nepionic characters of many miogypsinid populations from various parts of the world by a series of DROOGER's works (summarized in 1963). Using DROOGER's measurements on the nepionic characters of the Miocene miogypsinids from the Aquitaine Basin, France (1955), the senior author (UJIIE and OSHIMA, 1960; UJIIE, 1966) calculated the "Evolutionary Line", to which the strict course of their nepionic acceleration is attributed, in a three-dimension coordinate system with three parameters representing nepionic characters as their axes. Therefore, the comparison between positions of two feet of the respective perpendiculars from coordinates of two given populations to the line: estimates the difference of the acceleration between the two populations from the Aquitaine Basin as well as in the Japanese miogypsinids. As a result, Japanese miogypsinids can be divided into two different species, i.e., Miogypsina kotoi of the older type, comparable to Miogypsina intermedia in their grade of the acceleration, and Miogypsina japonica, n. sp. of the younger one, to Miogypsina cushmani. This classification will be supported by the other morphologic characters. It is very frequent that the former accompanies Lepidocyclina (Nephroiepidina) and the latter Operculina complanata japonica. The stratigraphic distributions of the two species of Miogypsina also coincide with their steps of the nepionic acceleration; namely, M. kotoi occurs only in the Globigerinatella insueta/Globigerinoides bisphericus Subzone of SAITO (1963) (=N. 8 of BLOW's zonation, 1969), while M. japonica is restricted in the Globorotalia fohsi barisanensis Zone (SAITO, 1963) (=N. 9). Besides, the paleogeographic distributions shown in two separate maps indicate an interesting fact that marine sediments of N. 8 occur only along the Pacific Ocean side and in its branching sea through the central zone of northeastern Honshu, whereas Miogypsina japonica-bearing sediments are found along the Japan Sea side and in its branchings. This tendency suggests a large scale shifting of the main region of sedimentation towards the Japan Sea from N. 8 to N. 9, and implies some correlation with the appearance of the Japan Sea as an open sea since N. 9. More detailed description in English will be given in the Bulletin of the National Science Museum, Tokyo, vol. 16, where Miogypsina japonica, n. sp. is also described.
日本地質学会の論文
1973-03-31

日本産Miogypsinaのnepionic accelerationと時空分布

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