第四紀研究

妙高火山・第IV期の活動とその噴出物

妙高火山群の地質記載・その1

早津賢二

1975 年 14 巻 1 号 p. 1-13
発行日: 1975/04/30
公開日: 2009/08/21

DOIhttps://doi.org/10.4116/jaqua.14.1

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The Myoko volcano, one of the stratovolcanoes in the northern part of the Fossa Magna, Central Japan, has the complicated history (Table 1).
The last activity of the Myoko volcano is called the IV stage, and is divided into precaldera, caldera, and central cone substages. The strata formed during this stage are collectively called the Myokosan group which consists of lavas, pyroclastic flow deposits, pyroclastic fall deposits, volcanic mud flow deposits, and lake deposits. They are described in detail and their stratigraphic relations are tabulated in Table 2 and Fig. 4.
The rocks of the essential eruptives are basalt, pyroxene andesite and hornblende andesite. They change from basalt to pyroxene andesite and hornblende andesite keeping step with the eruptive order. Quantitatively, the hornblende andesite is predominant.

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千葉県佐倉市上別所から産出したナウマンゾウについて

犬塚則久, 真野勝友, 大森昌衛

1975 年 14 巻 1 号 p. 15-20
発行日: 1975/04/30
公開日: 2009/08/21

DOIhttps://doi.org/10.4116/jaqua.14.15

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In 1973, fossil elephant bones were yielded from the sandy formation, at Kamibessho, Sakura-shi, Chiba Prefecture, Kwanto Regeon of Central Japan.
The formation, belonging to the lower part of Narita Formation also yielded many other molluscan fossils characterized by Glycymeris yessoensis, Diplodonta usta etc. The molluscan assemblage is closely related to that of Kamiiwahashi fossil beds of Narita Formation in other area except for a few remarkable characteristics, that is; containing less number of the genera than the other Kamiiwahashi beds and being found in thin fossil beds.
The fossil materials of the elephant include a lower jaw with the left second molar in situ, and a right tusk separated into three pieces. The mandible is rather large as P. naumanni of M2 stage and the shape of it generally resembles to the holotype of P. naumanni. The features observed on the grinded tooth indicate that the materials belong to the molar of P. naumanni, which is steno-crown type with distinct loxodont plica. The incisor is more thick and stout, suggesting that it belongs to male individual.

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奥尻島の海成段丘と第四紀地殻変動

宮浦正

1975 年 14 巻 1 号 p. 23-32
発行日: 1975/04/30
公開日: 2009/08/21

DOIhttps://doi.org/10.4116/jaqua.14.23

ジャーナルフリー

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For the purpose of testifying a generally accepted hypothesis in Japan, that is, crustal movements have continued in the Quaternary Period with the same mode and the same rate, marine terraces of Okushiri Island, which is located on the west of the Oshima Peninsula, Hokkaido (Fig. 1), were surveyed precisely, because it had been said that the Quaternary crustal movements of this island had changed in a mode by some researchers. The means of this investigation were to classify marine terraces, to measure altitudes of former shorelines of the terraces by an altimeter, and to infer the mode of crustal movements on the distribution of the altitudes obtained. The results are as follows.
(1) There are three higher denudation surfaces of marine origin and six marine terraces, the 1st to 6th terraces in descending order (Fig. 3).
(2) The altitudes of each former shoreline of the 3rd to 6th terraces are higher in the northwestern part of the island than in the southeast. The general strike of tilting is nearly ENE-WSW (Fig. 4, 5). The inclinations of tilting increase progressively from the younger terrace to the older one (Fig. 6).
(3) The equations of interrelation between the altitudes of the 3rd and 4th terraces and those of the 4th and 5th terraces are:
T₃=1.40T₄+1.65 (1)
T₄=1.04T₅+34.4 (2)
where T is the altitude of shoreline in meter.
(4) Therefore, the hypothsis of“same mode”in crustal movement seems to be accepted in this island, at least since the time of formation of the 3rd terrace. The terraces, however, have been not dated, the hypothesis of“same rate”is not checked.
(5) The constants of equation (1) take the same values approximately to those of equations which have been obtained from two terraces in some other part of the Uetsu Fold Zone, a Neogene-Quaternary fold zone, which may be correlated to the 3rd and 4th terraces in Okushiri Island.
(6) The mode of tilting inferred from the marine terraces is in accordance with the geologic structure of Neogene sedimentary strata in the northern part of Okushiri. Thus it is probable that such a tilting has continued since Neogene.

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石狩湾岸地域におけるボーリングコアの花粉分析

五十嵐八枝子

1975 年 14 巻 1 号 p. 33-55
発行日: 1975/04/30
公開日: 2009/08/21

DOIhttps://doi.org/10.4116/jaqua.14.33

ジャーナルフリー

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石狩湾岸の石狩町樽川, 同町花畔, 並びに札幌市屯田における4地点より得られたボーリングコアの花粉分析の結果, 新たに, 7花粉帯が識別された. 分析に用いた試料は, 深度130～200mに達するほぼ連続したコアから得た. 各花粉帯とも, 亜寒帯性の針葉樹花粉が非常に多く検出され, 現在よりも, 寒冷な気候を示している.
最も古い Zone Iでは, Picea, Larix, Abies などの亜寒帯性の針葉樹が優勢である. 特に, 北海道では絶滅種である Larix が, この Zone の上部に多く検出された. この時代は現在と比べ, 年平均気温で約8℃低かったと考えられる. 全層中最も寒冷な時代である.
Zone IIでは, Picea, Abies のほか, Zone Iの Larix に代り, やはり北海道では, 現在天然分布しない Tsuga が優勢となる. 前層に比べ幾分温暖化し, かつ, 冬期に乾燥する気候に移行した. 時代は, I, IIともに, 31,000年より古く, 主ウルム氷期以前の堆積物と考えられる.
Zone IIIは, ¹⁴C値 (30,000y. B. P.) からみて, 主ウルム氷期の初期に対比される. その植生は, Picea, Abies, Betula が主で, これに僅かに Larix, Tsuga を伴う. 現在より約6℃低温であった.
Zone IVは, 2つの¹⁴C値 (26,000y. B. P., 29,000y. B. P.) に挾まれる時代である. Zone I, II, IIIに比べての Picea の減少と, Corylus, Ulmus, Juglans といった温帯性広葉樹の増加から, 一時的に温暖化したと考えられる. Zone VIIの最上部を除き, 全層中, 最も温暖な時代である. 気温は, 年平均で現在より約4℃低かった.
Zone Vでは, 再び Picea が増加し, 広葉樹は減少する. その樹種構成は, Zone IIIとよく似ており, Zone IVの時代より再び寒冷化した.
Zone VIでは, Larix が再び増加し, その植生は, Zone Iに似ている. 現在の石狩に比べ, 年平均気温で, 6～7℃低温であった. Zone Vの下底が約26,000年前であり, 従って, Zone V,

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