Rock composition and provenance of gravels in the Middle- and Late Pleistocene Nagahama- and Hasirimizu Members in the Boso- and Miura Peninsulas, central Japan

概要

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For the purpose of demonstrating the origin of gravels, rock composition of gravels was analyzed for gravelly strata of the Middle Pleistocene Nagahama Sand and Gravel Member distributed in the western area of the central Boso Peninsula, and Late Pleistocene Hasirimizu Gravel Member distributed in the eastern part of the central Miura Peninsula. Gravels of the Nagahama Member are mainly composed of Mesozoic and Paleozoic sedimentary rocks (62.3%), Miocene green tuffs and igneous rocks (34.8%), and Tertiary sedimentary rocks (2.8%). Gravels of the Hasirimizu Member consist of Mesozoic and Paleozoic sedimentary rocks (86.3%), Miocene green tuffs and igneous rocks (13.6%).Judging from the geological distribution and paleogeography during the Middle to Late Pleistocene in the Kanto region, the gravels of the Mesozoic and Paleozoic rocks were derived mainly from the Kanto Mountainland, the Miocene green tuffs and igneous rocks were from the Tanzawa Mountainland, and the Tertiary sedimentary rocks might be from the Mineoka Mountainland. These results mean that the Kanto- and Tanzawa Mountainlands uplifted also in the Middle to Late Pleistocene. Relatively abundant occurrence of the gravels of the Tertiary sedimentary rocks may suggest uplift of the Mineoka Mountainland at the time of deposition of middle part of the Nagahama Member.
日本堆積学会の論文