Abstract
The paleoenvironment during the Miocene time in the Pohang basin is reconstructed on the basis of benthic foraminiferal assemblages. Q-mode principal components analysis of Miocene benthic foraminiferal assemblages reveals five important paleoenvironmental factors, namely CaCO3 contents, the deep and surface water masses and effects of coastal and cold water mass. Distributional patterns of fossil benthic foraminiferal species in the Pohang basin are deduced by integrating the result of this analysis, and assessing both the distribution of modern counterparts and water properties in the Northwest Pacific Ocean.In the northern area of the Pohang basin, the Heunghae Formation was deposited in the lower middle bathyal zone (800 to 2000 m water depth). In the central area of the basin, the paleodepth of the middle part of the Cheongogosa Formation and the Hagjeon Formation is estimated to be between the upper bathyal zone and the lower middle bathyal zone ranging from 200 to 800 m in water depth. The lower part of the Duho Formation was deposited in the lower middle bathyal zone. In the southern area of this basin, the Hagjeon Formation was deposited in the upper bathyal zone to upper middle bathyal zone. The paleodepth of the several horizons of this formation became as deep as the lower middle bathyal zone.The influence of the cold water mass is recognized in benthic foraminiferal assemblages in the middle to upper part of the Cheongogosa Formation, the Hagjeon and Duho Formations in the central area of this basin. This cold water mass flowed in this basin during the Zone N 8 to N 9.
