Radiocarbon age of a Holocene terrace of the Chikoi River at the Russia-Mongolia Border

A well-developed terrace was identified along the Chikoi River at the Russia-Mongolia border. The terrace deposits consist of massive fine sands of more than 8 m with numerous organic-rich paleosol horizons. Resulting radiocarbon ages for paleosol horizons suggest that floodplain emergence and terrace formation occurred in the early Holocene

チガクケイ センモンガッキョウカイ ニヨル イッパン シミン オ タイショウ ト シタ アウトリーチ ジュンケン ノ ジッセン ホウコク

日本第四紀学会では，徳島県で開催された2011年の研究大会にあわせて，「100万年の東四国を探る」というテーマで親子を含む一般市民を対象にした巡検を行った. それを「アウトリーチ巡検」と呼び，全部で52名の参加者があった. アンケート調査によれば，参加者はアウトリーチ巡検を肯定的にとらえており，今後もアウトリーチ巡検の実施を希望していた. 今後，日本地学教育学会と地学に関係する研究系の学協会とが連携して，このようなアウトリーチ巡検を学会の学術大会にあわせて実施することが期待される

Downstream variation in particle size, form, roundness, and lithology : a case study of the doki river, southwest japan

This study documents downstream variation in the maximum size, form roundness, and lithology of particles along the mainstream of the Doki River, northeastern Shikoku Island, southwest Japan. In order to reconstruct the pattern of ancient streams with a typical geomorphological scale in Japan, that formed existing gravel deposits, geometrical indices complemetary to clast fabric data and representative of the particle population are proposed. For the paleocurrent interpretation, these should be relatively simple and less time-consuming to use. The maximum particle size progressively decreases downstream, while roundness increases. The proportion of clasts of a specified lithology varies downstream in an organized manner, especially far from the source area. In contrast, no particle form parameter shows significant downstream variation. These facts suggest that maximum particle size and roundness are useful parameters, and that lithological composition provides complementary data, while particle form is an unreliable factor for paleocurrent interpretation

Plio-Pleistocene Behavior of the Itoigawa-Shizuoka Tectonic Line in Northern Nagano Prefecture, Central Japan: Paleomagnetism of the Omine-SK110 Tephra

This study aims to reveal Late Pliocene to Early Pleistocene geomorphic and structural evolution of the Omine Belt, North Fossa Magna, central Japan, associated with tectonic movement of the Itoigawa-Shizuoka tectonic line. A comparison of the paleomagnetic directions of a distinct wide-spread tephra, which is exposed in different areas, is useful to detect tectonic rotation because it gives instantaneous paleomagnetic directions from proximal to distal areas. The Omine-SK110 tephra with an estimated age of 1.65－1.60Ma is distributed in the Omine Belt as Omine Welded Tuff and in the west Tama Hills of the Kanto Plain as a co-ignimbrite of the Horinouchi 2 Tuff. Pro-gressive alternating field and thermal demagnetization experiments reveal that both tephras have reversed paleomagnetic directions that are almost identical to each other. As the west Tama Hills had been in a tectonically stable area since Late Pliocene, there might be no vertical-axis rotation in the Omine Belt. Thus, the Omine Belt would not be a pull-apart basin with left-lateral strike-slip faulting between the Otari-Nakayama fault and the active fault system of the Itoigawa-Shizuoka tectonic line