Minuma Lowland is an erosional valley that lies in the Oomiya Upland, Saitama Prefecture. The author has investigated the stratigraphy of the Holocene deposit filling the erosional valley. The surface deposit is about 6.5 meters thick and is composed of peat and gray clay. This is underlain by a sand bed over 6-15 meters thick. Moreover, the author has investigated the Holocene Paleoenvironments and the highest sea level based on the diatom assemblages contained in their deposits in the Minuma Lowland. Diatom assemblages from this area showed that the highest level of the sea attained was at least +3.9-+4.1 meters above sea level. The highest stage of the sea level is probably younger than about 5950-5540y.B.P.

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自然環境の荒廃著しい丹沢山塊における人間活動影響を評価するため降水と沢水の化学動態に基づいて各集水地の地質特性を検討し,個々の水系のキャラクタリゼーションを試みた。山塊主稜線によって分水される東北斜面の中津川,西斜面の玄倉川,南西斜面の水無川,および山塊東端の大山南東斜面の大山川の4水系における沢水,および標高立地の異なる5地点での降水を採取し, ICP発光分析,イオンクロマト,炭素分析によって主要無機化学種を定量した。水系間の比較により,沢水の化学性はそれぞれの水系に固有の性質であることが示唆されたが,降水の寄与による季節変動が認められた。沢水の化学性における降水の寄与を除くため降水中の塩化物イオンに対する各化学種の組成比に基づいて風化起源の濃度を求め,風化起源化学種の組成比の組み合わせによる水系間の比較を行った。その結果,各水系の水質は風化起源化学種間の組成比の組み合わせによる7種類の水質指標によって分類され,それぞれの分布が丹沢山塊の地質区分と良好な対応関係を示すことが分かった。本研究は水系の化学性によって集水地の地質と化学風化の態様に関わる特性を把握する可能性を示し,対象水系における環境影響を評価するために必要な基礎的知見を提供する。

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The Arakawa Lowland is situated in the western part of the Kanto Plain. Diatom analyses of a large number of boring core samples obtained from the Lowland have been performed, and marine clay deposits on the US (Holocene upper sand bed) have been found in the Arakawa Lowland. Holocene sediments of the Arakawa Lowland can be divided into five diatom zones, of which the fourth is subdivided into subzone A, B, and C. The marine clay deposits roughly correspond to subzone A of the fourth diatom zone. This subzone is characterized by euhalobous species, dominant among them Actinocyclus normanii and Melosira sulcata. The marine clay deposits lie horizontally from Akabane in the Tokyo Lowland to the JR Kawagoe Line in the Arakawa Lowland, and spread vertically from 0m to 3.0m above sea level.
The author has investigated the problems of the marine clay deposits using data obtained through diatom analyses and ¹⁴C dating. In consequence, the geomorphological history of this area in the Holocene period is inferred as follows. (1) Between about 7, 970y.B.P. and 4, 860 to 3, 130y.B.P., fluvial valleys were drowned by Jomon transgression and were filled with marine sediments. (2) From about 5, 270 to 4, 570y.B.P., the US (Holocene upper sand bed) was formed in this area. (3) Around 3, 990y.B.P., marine clay deposits accoumulated on the upper sand bed. (4) After the period 4, 450 to 3, 130y.B.P., the uppermost alluvial deposits were formed.

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