Reconstruction of tidal delta and barrier islands in Paleo-Tokyo Bay

古东京湾潮汐三角洲和障壁岛的重建

基本信息

批准号：
63540620
负责人：
MASUDA Fujio
金额：
$ 1.02万
依托单位：
Tsukuba University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1988
资助国家：
日本
起止时间：
1988 至 1989
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-63540620/
关键词：
Paleo-Tokyo Bay tidal delta barrier islands Washover deposits Facies analysis Pleistocene Shimosueyoshi Period バリアー島下未吉期

项目摘要

During this project, I clarify the existence of the barrier islands in the late Pleistocene Paleo-Tokyo Bay, and also proposed new sedimentary facies model of barrier islands. The barner islands were formed at the eastern mouth of Paleo-Tokyo Bay. A flood-tidal delta landward of barrier islands developed where now in Tamatukuri, Ibaraki. The sediments of sand wedge tapering into lagoonal mud, are composed of flood-tidal delta and washover sands. The tidal delta sediments are classified into three major facies of bottomset, delta-front and topset. The bottomset sediment shows a small-scale alternation of very fine- to fine-grained sand and mud, some of which show mud drapes or tidal bundles. The delta-front sediment is characterized by inclined cross-strata produced by migration of dunes or sand waves moved by currents flowing down the slopes. The topset sediments is deposited on the delta plane under shallow water condition. They show a upward-coasening sequence generated by the lagoonward progradation of delta. Overlying the flood-tidal delta sand body, the washover sands distribute directly on the lagoonal mud. The washover sands are composed of two major facies. The proximal facies of washover sand is characterized by parallel lamination and distinct convoluted structures. The distal facies is characterized by large-scale cross-strata and syndepositional open-cracks. These indicate rapid deposition of large quantities of washover sand. Some units of washover sands contain the evidence for earthquake activity during deposition. Some of the powerful waves responsible for the overwash may have been earthquake-generated tsunami waves.

在这个项目中，我阐明了晚更新世古东京湾中障壁岛的存在，并提出了新的障壁岛沉积相模型。巴纳群岛形成于古东京湾的东口。在现在的茨城县玉造市，堰洲岛向陆地发展了洪水潮汐三角洲。沉积物为楔形砂，逐渐变细为泻湖泥，由潮汐三角洲和冲刷砂组成。潮汐三角洲沉积可分为底积、三角洲前缘和顶积三大相。底部沉积物显示出极细粒到细粒的沙和泥的小规模交替，其中一些显示出泥幔或潮汐束。三角洲前缘沉积物的特点是由沙丘迁移或顺坡流下的水流移动的沙波产生的倾斜交叉地层。顶沉积物沉积在浅水条件下的三角洲平面上。它们显示了由三角洲向泻湖进积产生的向上科斯化序列。冲刷砂覆盖在洪水潮汐三角洲砂体上，直接分布在泻湖泥浆上。冲刷砂由两大相组成。冲刷砂近相具有平行层理和明显的旋回结构等特征。远端相以大范围的跨地层和同沉积开放裂缝为特征。这些表明大量冲刷砂的快速沉积。一些冲刷砂单元包含沉积期间地震活动的证据。造成过度冲刷的一些强大波浪可能是地震产生的海啸波。