地理学評論
Online ISSN : 2185-1719
Print ISSN : 0016-7444
51 巻 , 2 号
選択された号の論文の9件中1~9を表示しています
  • 中田 高, 高橋 達郎, 木庭 元晴
    1978 年 51 巻 2 号 p. 87-108
    発行日: 1978/02/01
    公開日: 2008/12/24
    ジャーナル フリー
    琉球列島の完新世離水サンゴ礁の地形とその年代から,地震性地殻変動地域におけるサンゴ礁形成過程と完新世後半の海水準変動曲線の復元を試みた.このため,離水サンゴ礁の地形断面を簡易測量によって作成し,異なった層準面から得られた58個のサンゴ化石試料の14C年代からサンゴの礁発達過程を明らかにしようとした.小宝島,宝島および喜界島において復元された相対的海水準変動曲線から,間歇的地震性隆起によってサンゴ礁の離水段化が進んだことがわかった.地殻変動は長期的には等速的であり,間歇的地震性隆起により段化は進むが,地震間の地殻変動が比較的静穏な時期には海水準変動は氷河性海水準変動そのものであるという考えから,喜界島の相対的海水準変動曲線から間歓的隆起量を除去し,海水準変動曲線を復元した.この海水準変動曲線は,日本で一般的に受け入れられているFairbridge curveにみられる,いわゆる後氷期の高位海水準は認められず, Shepard curveに代表されるゆるやかに上昇し現海水準に達する海水準変動曲線に近い.
  • 太田 陽子, 町田 洋, 堀 信行, 小西 健二, 大村 明雄
    1978 年 51 巻 2 号 p. 109-130
    発行日: 1978/02/01
    公開日: 2008/12/24
    ジャーナル フリー
    古海面を記録する地形・堆積物の高度・年代資料から,完新世における海面の推移を考察するために,琉球列島の喜界島で調査を行なった.本島の完新世段丘はI~IVの4段丘面に細分され,4回の相対的な海面停滞期があったことを示す.I面は,その一部のみが,またII面以下はすべてがサンゴ礁からなる.とくにII面は幅が広く,典型的な裾礁として形成された.各段丘面を構成するサンゴの14C年代と旧汀線高度は,I面で6,000~6,800 y. B. P., 9~13m,II面で3,500~5,200 y. B. P., 5~7m,III面で3,000~3,500 y. B. P., 2.5~5m,IV面で1,500~2,500 y. B. P., 1.5~2mである.これらは,新しいものほど低位置の海岸側にあり,サンゴ礁が水平方向に拡張してきたことを示す.1.5m/1,000年という等速な隆起を仮定して相対的海面変化曲線からユースタティックな海面変化曲線をえがくと, 6,500 y. B. P. と4,000 y. B. P.を中心とする2回の高海面停滞期と, 5,500 y. B. P.と2,000 y. B. P.を中心とする2回の海面低下期が現われる.両期の間の海面変化の量はせいぜい±2~3m程度と思われる.2回目の高海面停滞期は長期にわたり,II面の広いサンゴ礁の形成をうながした.サンゴの成長が,いわゆるクライマティックオプティマム期よりおくれて5,000 y. B. P.ごろからさかんになったことは,酸素同位体比の分析結果による融氷状況とも一致している.
  • 岡田 篤正
    1978 年 51 巻 2 号 p. 131-146
    発行日: 1978/02/01
    公開日: 2008/12/24
    ジャーナル フリー
    リアス海岸域では,段丘やその堆積物,とくに沖積谷底を構成する地層の状態やその年代などの資料が従来乏しく,段丘形成期以降の海水準変動や地形発達などに関する実証的研究はあまりなされてこなかった.最近,若狭湾岸で主として原子力発電所建設に伴う調査や大規模工事が行なわれ,沖積谷底の層序や14C年代が糊してきた.それらの資料から考察すると,当地域でも最終氷期以後の海水準変動の様子が璽らかとなり,2.5~3万年前の亜間氷期に対応する高海面,1.8~2万年前の最終氷期中の大海退,5~8千年前の縄文海進(最高頂期,約6千年前),1.5~4千年前の縄文後期~古墳時代中期の小海退などの現象が認められる.これらのほかにも,小海進や小海退の可能性が地形・地質上認められるが,具体的な年代資料は得られなかった.こうした海水準変動はリアス海岸域においても地形(とくに平地)や地層形成上かなり大きく関与していることが判った.
  • 豊島 吉則
    1978 年 51 巻 2 号 p. 147-157
    発行日: 1978/02/01
    公開日: 2008/12/24
    ジャーナル フリー
    山陰沿岸の広い範囲にわたり,波食棚・ノッチなどの海食微地形と,離水浜・浜堤などの海成堆積地形の測量を行なった.また海岸平野の内部から発掘された多くの考古学的遺物・遣跡とその包含地層の観察を行なった.このようなデータを海抜高度の面から整理して,およそ8つのグループにまとめることができた.これらの各グループの形成時代を判定して,海面変化曲線を画いた.この作業過程で海岸砂丘の形成史から知られる資料や古記録などをも検討し,総合的に判定をするよう努力した.その結果,山陰海岸では,縄文前期の海進の他,縄文後期と平安期にも強弱の差はあれ,海進が認められ,その間,縄文中期の西灘海退,弥生・土師期海退等が認められた.
  • 小元久 仁夫, 大内 定
    1978 年 51 巻 2 号 p. 158-175
    発行日: 1978/02/01
    公開日: 2008/12/24
    ジャーナル フリー
    完新世の海水準変化を解明するため,筆者らは日本列島の臨海沖積平野の中でも比較的地盤運動の緩慢な地域と考えられる仙台平野を取りあげ,主に現地調査によって採取した試料の14C年代測定,花粉分析,珪藻分析の結果と,空中写真の判読およびボーリングデータの解析に基づいて研究を進めてきた.その結果,仙台平野においては,海水準は7,500年前の-8mから最大振幅2m以下,周期1,000~1,590年でリズミカルな振動を繰り返しつつ,今日の海水準に到達したと推定される.完新世における仙台平野の地盤運動量が筆者らの見積りのように小さければ,仙台平野では縄文時代を通じ現海面を上回る高海水準は存在しなかった.
  • 森脇 広
    1978 年 51 巻 2 号 p. 176-187
    発行日: 1978/02/01
    公開日: 2008/12/24
    ジャーナル フリー
    Dent numerous Holocene sea-level curves have hitherto been published for various parts of the world. In this paper, about twenty such curves were selected and discussed. It is considered that the following two opinions discussed by Shepard (1964), Guilcher (1969), Fairbridge (1971) and others are the subject of the greatest controversy, although there are several clear disagreements among these curves as shown in Figs. 1_??_4. 1. When had the eustatic sea-level reached at the highest level? 2. Has the sea-level risen with minor fluctuations or without? Based on these two different standpoints, the curves can be classified into the following three types: (a) that in which the eustatic sea-level had risen above the present level with fluctuation (provisional name: high sea-level with fluctuation gro up, e.g. Fairbridge, 1961; Mörner, 1969; etc.); (b) that in which the present is the highest level and the sea-level has fluctuated (low sea-level with fluctuation group, e.g. Ters, 1973; Greensmith & Tucker, 1973; etc.); and (c) that which recognizes neither a high sea-level nor fluctuations (smooth group, e.g. Shepard, 1964; Scholl et al., 1969; etc.) (a) and (c) correspond to the curves known as the “Fairbridge Curve” and “Shepard Curve” respectively.
    Concerning about the standpoint 1, since Daly (1920) recognized previous shorelines a few feet above the present sea-level for various parts of the world and claimed that such shorelines were the result of ecstasy, many scientists have recognized this so-called “Daly's level”. However, various scientists, mainly those in the United States and Europe, have opposed this idea using the data obtained from North America and Europe, and have claimed that the present sea-level represents the highest level in the Holocene. The controversy on high sea-level during the Holocene period thus constitutes the most interesting problem.
    Compiling the data on Holocene sea-level changes from areas which were considered locally stable, the author mapped areas where the present sea-level was reported as the highest level and those where the sea level was considered to have risen above its present level in the Holocene respectively (Fig. 5). As a result, regionality with continental scale were recognized: in North America and part of Europe, the present sea-level is the highest in the Holocene, whereas in South America, Africa, Asia, and Australia, a high sea-level is generally recognized. Such differences have been also recognized by Gill (1971), etc., who claimed that this problem should be discussed on a continental scale. However, no concrete explanation has yet been put forward. It is interesting to note that such differences over wide areas have been well explained on the basis of broad crustal movements effected by glacio- and hydro-isostasy as recently stated by Walcott (1972). As shown in Fig. 5, most part of North America and Europe, where the present sea-level is the highest, represents the peripheral zone of the former ice sheets and have submerged by glacio-isostasy, whereas the regions where the sea-level has risen above its present level in the Holocene out have been uplifted by hydro-isostasy. If this explanation of the problem relating to high sea-level by glacio-and hydro-isostasy is justified, it is thus not significant to discuss the problem further from the eustatic point of view.
    As for the standpoint 2, judging from the data in Table 1, it appears that the difference between a fluctuating curve and a smooth curve does not result from local conditions in the area (e.g. landform, local crustal movements, tidal range, etc.) or the methods employed for determination of the altitude and age of the past sea-level. It might be resulted from the fact that the indivisual researcher's appraisal of errors contained in the altitude and age of past sea-levels has played an important role.
  • 井関 弘太郎
    1978 年 51 巻 2 号 p. 188-196
    発行日: 1978/02/01
    公開日: 2008/12/24
    ジャーナル フリー
    In recent years, there have developed some studies on sea-level changes during the Late Holocene in Japan. When reviewed in detail, however, the results of those studies are found consisting of two cases; one case for a curve-drawing in favor of the Fairbridge curve, and the other for that in favor of the Shepard curve by making different assumptions about the process of crustal movements. This is also true even when the same area is chosen as an objective of those studies. This shows that in Japan where crustal movements have been great, studies about crustal movements themselves must be important in order to investigate ecstatic sea-level changes.
    Nevertheless, there are in them some common points concerning the height of the past sea-level changes. One is that the sea-level changs at the last glaciation maximum (about 18, 000 B. P.) are thought to have ben about 140 meters below the present sea-level, judging from the depth of the bottom in some buried valleys which can be found throughout Japan. Another is that, judging from the depth of th bottom in marine silt and clay beds that were accumulated in time of the Flandrian transgression, the sea level at the earliest period of the Holocene is supposed to have been about 40 meters below the present sea level.
    As studis about the recent alluvial formation proceed, there have lately emerged some researchers who insist on sea-level changes in favor of the Shepard curve, while most of the researchers in Japan have reported that the sea level was higher around 6, 000 B. P. than at the present. Although some studies have reported that the sea level fell temporarily and rose again later in some areas, there would be little possibility that the fluctuation was caused by glacial eustasy. It is because it would be almost impossible to assume that the expansion of an ice sheet made the sea level lower at a rate of over 0.1 meter per century. Apart from such fluctuations, traces can be found throughout Japan which indicate that the sea level was two to three meters lower around 2, 000 B. P. than now.
    It would seem to me that future studies in Japan about the sea level, first of all, should consist of finding out regional characteristics of curves for sea-level changes on the continental scale, by eliminating as much influence as possible caused by crustal movements or orogenic movements limited to a comparatively narrow area. It would not be possible, I assume, to investigate eustatic and absolute sea-level changes until we are through with those problems discussed above.
  • 1978 年 51 巻 2 号 p. 197-198,201
    発行日: 1978/02/01
    公開日: 2008/12/24
    ジャーナル フリー
  • 1978 年 51 巻 2 号 p. 200
    発行日: 1978年
    公開日: 2008/12/24
    ジャーナル フリー
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