Tsugaru Peninsula Research Articles

Geological record of 18th and 19th century tsunamis along the Japan Sea coast of Tsugaru Peninsula, northwestern Japan

Our stratigraphic and paleontological investigations revealed three sandy event deposits (E1, E2, and E3) within peaty clay at the Sotomeyachi site on the Japan Sea coast of Honshu (mainland of Japan), northwestern Japan. Visual examination and X-ray computed tomographic images of samples of the deposits provided evidence of strong currents characterized by rip-up mud clasts, load casts, and erosional lower stratigraphic contacts. Marine, brackish, and freshwater diatom species in the deposits indicate they were derived from various coastal sources. Radiocarbon dating constrained the ages of event deposit E2 to 1764–1902 CE and E3 to 1558–1845 CE, 1699–1918 CE, and 1704–1781 CE. According to historical records, the E2 deposits likely correspond to the tsunami generated by the 1833 Shonai-oki earthquake, and the E3 deposits correspond to a tsunami associated with either a submarine landslide associated with the 1741 Oshima-Oshima eruption or the 1793 Nishi-Tsugaru earthquake. Because our numerical simulation of the 1741 tsunami showed no significant inundation at the study site, it is more likely that the 1793 earthquake was responsible for tsunami deposit E3. The E1 deposit is discontinuous and showed different characteristics (absence of load structures, rip-up mud clasts and mixed diatom assemblages) to those of events E2 and E3, so it is unlikely to be a tsunami deposit.

Satellite Tracking of Migration Routes of the Eastern Buzzard (Buteo japonicus) in Japan through Sakhalin.

We satellite-tracked the eastern buzzard (Buteo japonicus) wintering in Japan to delineate both northward and southward migration routes, destinations, and stopover behavior. Twenty-two buzzards were captured and fitted with functional platform transmitter terminals. For these buzzards that departed from the capture sites, we observed a total of 65 northward migrations during 2008-2016 and a total of 55 southward migrations during 2008-2015. In spring, the eastern buzzards migrated eastward along the Seto Inland Sea in the Chugoku region or further inland. In eastern Honshu, they followed two different routes. One was to Hokkaido via the Tsugaru Peninsula from central or northern central Honshu northward along the side of the Sea of Japan in northern Honshu. The other was to Hokkaido via the Shimokita Peninsula, mainly from the Pacific Ocean side of northern Honshu, moving eastward through central Honshu. Of the 17 birds tracked, 10 summered in Sakhalin, three in Hokkaido, three in northern Honshu, and one unknown. In autumn, the buzzards retraced their northward migration routes. Of the 14 birds that were tracked the entire southward migration, 13 (92%) returned to their respective capture sites. One juvenile wintered in an area different from the capture site. Our study contributes to a deeper understanding of the distribution of breeding and wintering grounds and the migration routes of B. japonicus. In addition, the information on migration obtained in this study can contribute toward appropriate environmental impact assessment for wind power facilities in Japan.

Age of the Isomatsu Formation in the Tsugaru Peninsula, northeastern Japan: zircon U-Pb dating of a Miocene green tuff bed

磯松層は中新世のグリーンタフからなり，その既報ジルコンフィッショントラック（FT）年代は層序学的に推定される年代よりも有意に若い．今回筆者らは，若いFT年代が決定されたのと同じジルコンに対してLA-ICP-MS法によるU-Pb年代測定を行った．磯松層下部の火砕岩から約17.7Maの238U-206Pb年代が得られ，これは磯松層下部の堆積年代を近似する，またはその下限を制限する年代と見なされる．磯松層の年代は約17.7Maから約16Maまでの間と考えられ，それを踏まえて筆者らは津軽半島北部の下部中新統の年代層序モデルを改訂した．今回の測定結果は，調査地域またはその近傍でのマグマ活動，磯松層の堆積に示される調査地域における海進，および磯松層堆積時に起こったと考えられるハーフグラーベンの活動に対して，新たな年代制約を与えるものである．

東北日本, 津軽半島北部に分布する磯松層のフィッション・トラック年代

東北日本, 津軽半島北部に分布する磯松層のフィッション・トラック年代

津軽半島における新第三紀以降のテクトニクス

津軽半島における新第三紀以降のテクトニクス

5 青森県津軽半島十三湖周辺における蚊相の調査(第59回日本衛生動物学会東日本支部大会講演要旨)

5 青森県津軽半島十三湖周辺における蚊相の調査(第59回日本衛生動物学会東日本支部大会講演要旨)

Pliocene to lower Pleistocene foraminiferal assemblages from the southeastern Tsugaru Peninsula, Northeast Japan

Pliocene to lower Pleistocene foraminiferal assemblages from the southeastern Tsugaru Peninsula, Northeast Japan

The floristic composition and distribution pattern of Quercus mongolica var. grosseserrata forest on the Tsugaru Peninsula, Aomori Prefecture.

The floristic composition and distribution pattern of Quercus mongolica var. grosseserrata forest on the Tsugaru Peninsula, Aomori Prefecture.

The geographical distribution of Polycelis (Polycelis) sapporo and Seidlia schmidti in the Far East

Polycelis (Polycelis) sapporo (Ijima et Kaburaki, 1916) is a non-stenothermal species, common in Hokkaido (including all of the adjacent islands), Northern Japan, except in the alpine region. It is also distributed in Aomori Prefecture in the northernmost part of Honshu. To the south, its range is bounded by a line from the base of the Tsugaru Peninsula, over Mt. Iwaki, Mt. Shirakami, Mt. Tashiro, Lake Towada, Mt. Hakkoda, the Natsudomari Peninsula, to the west of Mutsu and Ohata in the Shimokita Peninsula. In Russia, the species is recorded only from the southern part of Sakhalin. Seidlia schmidti (Zabusov, 1916) is a stenothermal species found in cold-water biotops. It occurs in the North and East of Hokkaido including the Shiretoko Peninsula and Rishiri Island. In Russia, the species is recorded from the southern part of Sakhalin, Primorskiy, Habarovsk including the base of the Chukotskiy Peninsula, and the Kamchatka Peninsula (and Bering Island).

Integrated radiolarian and diatom biostratigraphy of the Neogene strata in the Tsugaru Peninsula, Aomori Prefecture, northern Honshu, Japan

Integrated radiolarian and diatom biostratigraphy of the Neogene strata in the Tsugaru Peninsula, Aomori Prefecture, northern Honshu, Japan

Late Neogene Radiolarian Biostratigraphy in the Subarctic Northwest Pacific

Late Neogene Radiolarian Biostratigraphy in the Subarctic Northwest Pacific

Petroleum Source Rocks from the Neogene Tsugaru Basin, Northern Honshu, Japan

The purpose of this study is to evaluate possible petroleum source rocks in the Neogene Tsugaru basin. Evaluation is based on three criteria: organic richness, organic maturity, and organic type. One hundred forty-one samples of mudstones from seven transects were analyzed. Samples from the middle Miocene Kodomari Formation and younger sections generally contain more than 0.5% total organic carbon and amorphous organic matter, but are thermally immature. Samples of the lower Miocene Odose and Isomatsu formations obtain maturities equivalent to the threshold of intense oil generation, but do not contain sufficient type or quality of organic matter to be considered an oil source. Although this study failed to identify an effective source rock, it does suggest that a possible effective source may exist off the west coast of Honshu and in the eastern part of the Tsugaru Peninsula. In these areas, organic maturation of the possibly organic-rich Neogene sediments may have proceeded further than in regions investigated in this study as a consequence of a Neogene sedimentary package that is more than 2000 m thick.

津軽盆地における石油根源岩評価

The purpose of this study is evaluation of possible petroleum source rocks in the Neogene Tsugaru Basin. Evaluation is based on three criteria, namely organic richness as expressed by organic carbon content, organic maturity as determined by Thermal Alteration Index, and organic type as expressed by visual kerogen composition. One hundred forty-one samples of mudstone from 7 surface routes on land were analysed regarding the three criteria. The results show two characteristic points as follows; (1) Samples from the Middle Miocene Kodomari Formation upward generally include more than 0.5% organic carbon and amorphous type organic matter. But in maturation, they do not exceed the threshold of intense oil generation. (2) Samples of the Lower Miocene Odose and Isomatsu Formations reach the threshold of intense oil generation. But they fail to meet both the organic richness criterion and the organic type criterion.Although it is determined that no source rock was found, this study suggests that possible source rock may be found in two areas, off the west coast and in the east part of the Tsugaru Peninsula. In these areas organic maturation of the Neogene sediments may have proceeded further than in routes investigated in this study, due to the fact that at over 2, 000 meters thick, the Neogene sediments in these areas are much thicker than in those in this study. Therefore there is a possibility that petroleum has been produced in deep Middle Miocene mudstone in these areas.

Vertical Distribution and Standing Crop of Seaweeds, Seagrasses, Sea Urchins and the Spiny Top Shell Along the Coasts from Tappi to Fujishima, Tsugaru Peninsula, Aomori Prefecture.

Standing crops of 9 species of macroalgae (Phaeophyta), 2 species of seagrasses, 4 species of sea urchins, and the spiny top shell was investigated at depths of 2, 5, 10, 15, and 20m along 23 transects on the coasts from west of Tappi to Fujishima, Tsugaru Peninsula, Aomori Prefecture on August 2-6, 1985. Characteristic differences were observed in their vertical distributions be-tween the Japan Sea coast and the Tsugaru Channel coast with Tappi Point as the border. The vertical distribution of standing crops of the spiny top shell and the sea urchin Strongylocentrotus nudus was quite similar to that of Ecklonia stolonifera and Laminaria japonica, respectively. These results suggest that the two species of seaweed, whether for food or habitat, are favored by sea animals.

Breeding of Little Tern on the West Coast of Aomori Prefecture

Little Tern Sterna albifrons is a common summer visitor north to the Kanto plain in Honshu. Akita Pref. has been regarded as the most northern breeding place in Japan. However, its breeding in Hachinohe City in Aomori Pref. was reported recently. The author discovered another colony of about 30 birds on the beach of Shiura, Tsugaru Peninsula in 1982. There were 10 nests, with 6 nests containing 2 eggs and 4 nests 3 eggs. Most eggs were laid on June 13-15 and hatching took place on July 5-10. Wingbeat of juveniles was first observed on July 20 and flapping on July 24.

On the development of the geological structure in the southern part of the Tsugaru peninsula, Aomori Prefecture

On the development of the geological structure in the southern part of the Tsugaru peninsula, Aomori Prefecture

On the so-called Palaeozoic deposits in the Tsugaru peninsula, Aomori Prefecture

On the so-called Palaeozoic deposits in the Tsugaru peninsula, Aomori Prefecture

正誤表(第15巻 第4号)

正誤表(第15巻 第4号)

Marine Terraces of the Tsugaru Peninsula, Aomori Prefecture

The Tsugaru Peninsula, in the northernmost of Tohoku region is characterized by the development of several marine terraces. The author has studied this area since 1959, and in this paper, he discussed on these terraces and the earth movements of this district.The followings are the conclusion : a) these marine terraces are classified into 8, and are correlated with those of the Shimokita peninsula (Table 1), b) it is recognized that the peninsula once had undergone a tilting movement from south to north (Fig. 5), and in the Tsugaru alluvial plain, there is an NNW-SSE down-warping movement (Fig. 7), c) location and development of marine terraces in this terrain have a close connection with geological structure.

The Forest Resources in Northeastern Japan and their Exploitation

The forests in Northeastern Japan occupy 13.8% of the national acreage of wooded land, but in accumulation they show as high a percentage as 17.8%. In spite of such abundant holdings, their exploitation is not advanced, the amount of timber production being only 12.5% of the nation. Main reasons are (1) their inaccessibility, (2) in-convenient transportation, (3) remoteness from markets and (4) lack of local capital to exploit. Another and the major reason, however, is the fact that the forests are mainly of broad-leaved trees of low economic value. Therefore it has been encouraged to increase the forestation of coniferous trees of higher economic value. Present writer wants to add another reason to explain undevelopment of forestry in Northeastern Japan. In the feudal age, some of the more important forest areas such as that of Cryptomeria japouica in the northern part of Akita Pref., and that of Chamaecyparis obtusa in Tsugaru Peninsula had been carefully saved from the view point of resource maintenance, and the same policy has been adopted since they were annexed to the national forest in the Meiji era. As the result, cutting has been limited to an amount low enough to maintain them. In Northeastern Japan, national forests cover half of the total acreage of the region. The percentage is higher than that in any other region and this fact contributes greatly to maintain the forest resources. Viewed from economic exploitation, however, far more rational management is expected. The forests of broad-leaved trees are distributed in almost every part, but more important ones are the national forests in the interior such as Tadami and Kurikoma wood-lands. However, these resources have been regarded as valueless because most of them are superannuated. After World War II, however, they regained their economic importance as Japan lost her coniferous forest resources in her former territories, and at the same time manufacturing technique was greatly improved for the utilization of hardwoods. There is an inceasing demand for them as materials for the pulp and fiber board manufacturing industries. One cannot forget, however, that the forests in the interior are of much value not only as the sources of raw materials, but also as protection for the prevention of soil erosion and floods, and at the same time they are indispensable as the protector of water resources for hydroelectricity. Therefore, it is desirable to consider the exploitation of forest resources from many angles. Tadami and Kurikoma areas are included in the Government's multipurpose development areas, and much is expected from their exploitation.