Reconstruction of ”Tsugaru Strait” during Early Pleistocene

Abstract

The position of paleo-Tsugaru Strait is reexamined using foraminiferal fossils from the lower Pleistocene marine sediments in the Oshima Peninsula, Southwest Hokkaido and Aomori Prefecture, northernmost Honshu. According to the previous research by this author around the Tsugaru Strait, during early Pleistocene, paleo-Tsugaru Current flowed along same route of present Tsugaru Current. Lower Pleistocene foraminiferal fossils from the central part of Tsugaru Peninsula indicate the influence of warm current, supporting the above estimation on the route of paleo-Tsugaru Current. The lower Pleistocene strata in the central part of Oshima Peninsula deposited on upper bathyal zone. However, these strata contain no warm water foraminiferal fossils. This means that this area was not the exit of paleo-Tsushima Current, even if this area connected the Pacific Ocean and Sea of Japan.