Departmental Bulletin Paper Cenozoic biostratigraphy, chronostratigraphy and paleoceanography in the Boso Peninsula and Bandai Volcano in the Aizu region, East Japan

Motoyama, Isao  ,  Itaki, Takuya  ,  Kamikuri, Shin'ichi  ,  Taketani, Yojiro  ,  Okada, Makoto

32(Supplement)pp.1 - 27 , 2017-10 , 新潟大学理学部
InterRed XV in Niigata 2017 Niigata University (JAPAN) Oct/22-Oct/27, 2017
The Boso Peninsula is a geologically active region where Cenozoic marine sediments formed in a wide variety of depositional and tectonic environments, including ocean basins, trench, trench-slope basins, forearc basins, and shelf to coastal zones. Radiolarians are key to dating most of these sedimentary rocks. In the northern part of the peninsula, Quaternary sedimentary sequences consisting mainly of siltstone and sandstone crop out along canyons of the Yoro and other rivers. There is no better place in the world than the Yoro canyon to correlate the Pleistocene geomagnetic polarity records to marine micro-biostratigraphy, oxygen isotope records, and radiometric ages from volcanic ash layers. This feature is of great benefit to establishing the boundary stratotype of the lower and middle parts of the Pleistocene Stage. In the more mountainous area to the south, visitors can trace the geological history back to middle Miocene through continuous sedimentary sequences. The earliest fossils imprinted in the rock of the peninsula are of early Cretaceous radiolarians from the Mineoka ophiolite complex. Since the Early Miocene the southern part of the peninsula was covered by seas and close to the trench where the Philippine Sea Plate subducts under the North American Plate. Continual subduction of the oceanic plate resulted in a pile of accreted Miocene sedimentary rocks in the southern part of the peninsula. Cover sediments unconformably resting on those accretionary prisms are thought to represent trench-slope basin deposits. Well-developed uplifted marine terraces in the southern portion of the peninsula represent the Holocene-continuing seismic activity associated with the earthquake cycle. Mount Bandai is a cone-shaped active stratovolcano. Past eruptions and collapses of mountain body formed a dammed lake, Lake Inawashiro, the fourth largest lake in Japan, to the south and created the numerous beautiful lakes in the forest land to the north. Bandai Volcano and its surrounding area was registered as a Japanese Geopark in 2011.

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