Bulletin of the Mizunami Fossil Museum

Bulletin of the Mizunami Fossil Museum No. 3

Plant microfossils such as dinoflagelate cyst, pollen grains and others were obtained from the Saho and the Saidaiji Formations exposed on northern and northwestern parts of Nara City. The dinoflagellate cyst assemblage is composed of following two assemblages, the assemblage A characterized by a dominant occurrence of Hemicystodinium zoharyi and the assemblage B mainly consisting of Operculodinium and Spi1iferites. The pollen assemblage is made up of Pimts, Fagus, evergreen type Quercus and Ulmus-Zelkova, and includes commonly warm temperate to subtropical genera Lagerstroemia, Liquidambar and Sapium. Also, freshwater green algae, Pediastrum is obtained.

The marine to brackish sediments in the Saho and the Saidaiji Formations seemed to be deposited in a lagoonal to inner bay area affected by a warm current and rivers based on a dominance of Hemicystodinium zolzatyi and an occurrence of Tuberculodinium vancampoae and Pediastrum. The presence of warm temperate to subtropical genera such as Liquidambar and others supports the above mentioned assumption.

The occurrence of Hyst1ichokolpoma rigaudae and the resemblance of the pollen diagram between the present samples and Ma 1 of the Osaka Group at Senriyama reported by Tai (1970) support that the Saho and the Saidaiji Formations belong to the lower part of the Osaka Group and that the marine to brackish bed in these formations corresponds with Ma 1. Finally, nine species of dinoflagellate cysts are described.