• Journal of the Korean earth science society
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• v.27 no.1
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• pp.95-117
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• 2006

From the Tertiary Yeonil Group distributed in Songra and Cheongha areas, the northern part of the Pohang Basin, nine archaeomonad species belonging to two genera, and other three types of chryophycean cysts considered as stomatocysts, five endoskeletal dinoflagellate species belonging to three genera and eighteen ebridian species belonging to eleven genera were identified. Based on above siliceous microfossil assemblages, the Yeonil Group is corresponded to Middle Miocene age. The group is correlated with the Calvert Formation (Maryland in USA) and the Hojuji Formation (in Central Japan) by its archaeomonad cysts. And, the group is correlated with the intervals of Actiniscus elongatus to Middle Hermesinella conata zones in Southwest Pacific region and of Spongebria miocenica to Middle Hermesineila schulzii zones in $V{\o}ring$ Plateau, Norwegian Sea, based on the ebridian assemblages of the group. From the chrysophycean cyst including archaeomonad, endoskeletal dinoflagellate and ebridian assemblages in the Yeonil Group of the study area, it is inferred that cold water masses dominated during the deposition oi the group with occasional warm water. The upper part of the group might be somewhat colder than the lower one of the group in depositional condition. In addition, minute chrysopycean cysts considered as stomatocysts suggest the influence of fresh or brackish water during the deposition of the group.