Satoru Kojima

MESOZOIC TERRANE ACCRETION IN NORTHEAST CHINA, SIKHOTE-ALIN AND JAPAN REGIONS

Abstract The Nadanhada Range in Northeast China is composed of upper Paleozoic limestone, greenstone, middle to late Triassic bedded chert, and middle Jurassic siliceous shale; these rocks are enclosed in post-middle Jurassic clastic rocks. The lithologic association, ages, radiolarian assemblages and geologic structure of the Nadanhada Range are very similar to those of the Tamba-Mino-Ashio terrane in Southwest Japan. This indicates that the Nadanhada Range is the northern extension of the Tamba-Mino-Ashio terrane. Mesozoic tectonostratigraphic terranes identified in Northeast China, Sikhote-Alin and Southwest Japan are: the Khanka terrane (a micro-continent composed of Precambrian metamorhic rocks and Paleozoic to Mesozoic sedimentary and volcanic covers), the Nadanhada-Western Sikhote-Alin terrane (a disrupted terrane composed of upper Paleozoic to Jurassic sedimentary rocks), the Eastern Sikhote-Alin terrane (a terrane composed mainly of early Cretaceous clastics), the Tetyukhe terrane (a disrupted terrane composed of upper Paleozoic to early Cretaceous sedimentary rocks), the Hida terrane (a continent-type stratigraphic terrane composed of Precambrian and upper Paleozoic basement covered with Jurassic to Cretaceous coarse clastics), and the Tamba-Mino-Ashio terrane (a disrupted terrane composed of upper Paleozoic to earliest Cretaceous sedimentary rocks). Accretionary history of these terranes is discussed on the basis of paleomagnetic and paleobiogeographic data.

Low-latitude and Southern Hemisphere origin of Anisian (Triassic) bedded chert in the Inuyama area, Mino terrane, central Japan

Paleomagnetic and paleontologic studies of Middle Triassic to earliest Jurassic radiolarian bedded chert in the Inuyama area, southern Mino terrane of central Japan, have shown that the chert was deposited in an equatorial region with a paleolatitude between 10°N and 10°S, and in particular, the lower to middle Anisian chert depositional basin was situated in the Southern Hemisphere. The chert has four characteristic components of remanent magnetization. The highest blocking temperature component, carried by hematite, shows positive fold and reversal tests and is regarded as the primary remanent magnetization acquired just after deposition. The other three components are interpreted as a present field overprint and two postfolding remagnetizations. The absolute, tilt-corrected inclinations of the primary component are less than 20° for all the samples of Middle Triassic to earliest Jurassic age, with the mean inclination of the lower to middle Anisian chert being 11.0°±4.3°. Paleomagnetic polarity reversals observed for the lower to middle Anisian chert are well correlated with those of the European Triassic sections, under paleontologic age constraints using radiolarians and conodonts, provided that the Anisian chert in Inuyama was deposited in the Southern Hemisphere. This conclusion illuminates the paleogeographic evolution of the chert-bearing accretionary complexes not only in Japan but along the eastern margin of Asia as well.

A correlation of accretionary complexes of southern Sikhote-Alin of Russia and the Inner Zone of Southwest Japan

This paper briefly describes the geology of southern Sikhote-Alin of Russia and the Inner zone of Southwest Japan, and presents a new correlation model in which the Samarka terrane (sensu stricto), Udeka Formation, Sebuchar Formation and Kalinovka ophiolite in Sikhote-Alin are considered as northern extensions of the Mino-Tamba terrane, Hikami Formation, Kozuki Formation, and Yakuno ophiolite in Southwest Japan, respectively. This correlation is based on the similarities in lithology, age, faunal assemblage, and structural relationship between them. The Samarka and Mino-Tamba terranes consists of Jurassic accretionary complexes including Permian greenstone-limestone complex, Permian to Lower Jurassic radiolarian bedded chert, Jurassic clastic rocks, and Jurassic melanges. The Udeka and Hikami formations are composed mainly of greenish gray sandstone with minor shale intercalations yielding Permian radiolarians. The Sebuchar and Kozuki formations are characterized by basalts accompanied with shale, limestone and chert. The limestone includes Carboniferous fusulinaceans, while Permian radiolarians occur in the chert. The Kalinovka and Yakuno ophiolites consist of a series of ultramafic to mafic igneous rocks with an ophiolitic succession. Since the ages of these ophiolites have not been clearly established, we correlate them on the basis of their lithology and tectonic positions. These units form a stack of nappes from the lower to upper horizons in the following order: Mino-Tamba terrane, Hikami Formation, Kozuki Formation, and Yakuno ophiolite in Japan, and Samarka terrane (sensu stricto), Udeka Formation, Sebuchar Formation, and Kalinovka ophiolite in Russia. This correlation supports the reconstruction model of Japan before the opening of the Sea of Japan proposed by Yamakita and Otoh (1999).

Mesozoic radiolarian biostratigraphy of Japan and collage tectonics along the eastern continental margin of Asia

Abstract Jurassic accretionary complexes mainly composed of Carboniferous to Permian limestone associated with greenstone, Triassic bedded chert, Jurassic siliceous shale and clastic rocks form the basement rocks of Japan. The stratigraphy of these complexes has recently been analysed utilizing radiolarian fossils, resulting in the discovery that Japan comprises a collage of disrupted terranes. International co-operative works reveal that lithologically and biostratigraphically similar terranes are distributed in northeast China (Nadanhada terrane) and Sikhote-Alin, USSR (Khabarovsk terrane). Paleomagnetic studies demonstrate that prior to opening of the Sea of Japan the Japanese Islands were located much closer to the eastern margin of the Asian continent where the Nadanhada and Khaborovsk terranes are now exposed. Features of the Mino terrane in central Japan are characteristic of these terranes which originally formed along the continental margin of East Asia. Seamounts covered by fossiliferous limestone formed during the Carboniferous to Permian at low latitudes. The seamounts drifted towards a continental margin together with upper Paleozoic sediments, Triassic bedded chert and Lower Jurassic siliceous shale which accumulated around them. Upper Paleozoic, Triassic and Lower Jurassic formations were accreted to the eastern continental margin, which was a large tectonic collage developed as the Chinese mainland during the Late Triassic. Enormous amounts of clastic detritus were deposited in sedimentary basins where jumbling and telescoping of pelagic sediments took place in a complicated fashion producing a melange. The provenance of clastic detritus within the Mino terrane is interpreted as a platform on which Permian and Carboniferous calcareous sediments containing diagenetic lutecite and orthoquartzite formations were widespread. These formations covered a Precambrian metamorphic and granodioritic basement similar to that seen in the South China region. Accretion culminated in the earliest Cretaceous and the large disrupted terrane which had developed was transpressed northwards along the eastern margin of the continent. During this period of dispersal the original terrane was sheared, fragmented and separated into many smaller terranes some of which were transported to the Sikhote-Alin region by the Late Cretaceous. The most recent dispersal occurred during the opening of the Sea of Japan, which is closely related to the latest movement of the Pacific plate. Studies of radiolarian micropaleontology and the significance of these fossils to the resolution of the biostratigraphy and the tectonic history of Japan are reviewed. The results of biostratigraphic analyses are discussed in relation to the Mesozoic tectonics of East Asia.

Growth-ring analysis of Early Tertiary conifer woods from the Canadian High Arctic and its paleoclimatic interpretation

Abstract Fossil forests, where petrified stumps were preserved in growth position, have been found within Early Tertiary sediments near Strathcona Fiord, Ellesmere Island, Canadian Arctic Archipelago. These fossil forests are obvious evidence for Early Tertiary climate much warmer than that of today. We analyzed the growth rings of petrified woods from two fossil forest sites (one in middle Paleocene, and the other in late Early Eocene) to extract information on climate change. The woods consist most abundantly of Metasequoia and cf. Glyptostrobus, suggesting that these forests grew in similar environments of warm to cool temperate climates. Mean ring width, mean sensitivity and power spectrum were calculated for ring-width sequences. Although significant difference in the mean ring width between the two forests was found, a comparison with living trees suggests that the difference can be attributed to the specific difference between the forests, so that a significant climate change may not necessarily be invoked. We found little significant difference in the mean sensitivity and power spectrum between the forests, neither did we find any strong indication of periodicities. Consideration of all features suggests that there was no significant difference in climate of middle Paleocene and late Early Eocene time in the High Arctic. However, the mean ring-widths of these forests were significantly smaller than that reported for mid-Cretaceous High Arctic fossil forest.

PERMIAN RADIOLARIAN FAUNAS FROM CHERT IN THE KHABAROVSK COMPLEX, FAR EAST RUSSIA, AND THE AGE OF EACH LITHOLOGIC UNIT OF THE KHABAROVSK COMPLEX

Abstract The Khabarovsk Complex, a Jurassic accretionary complex distributed in and around the Khabarovsk city area, Far East Russia, comprises mélange and schist facies. From the review of previous studies including Russian papers, the lithology and age of the constituent rocks of the mélange facies can be summarized as follows: Upper Paleozoic basic volcanic rocks, mainly pillow lava, and altered gabbro, Upper Carboniferous to Upper Permian fusulinoidean-bearing limestone associated with tuff, Lower and Middle Jurassic siliceous mudstone, Upper Jurassic tuffaceous mudstone, uppermost Jurassic carbonate concretions embedded in mudstone, and age-unknown sandstone. Newly found sequences of limestone-chert and of basalt-chert in the mélange facies crop out along the Amur River in the Khabarovsk city area. A chert sample of the limestone-chert sequence contains Albaillella aff. asymmetrica and Pseudoalbaillella aff. lomentaria, and a chert sample of the basalt-chert sequence includes Follicucullus monacanthus, Follicucullus porrectus, and Pseudoalbaillella cf. yanaharaensis. The radiolarian assemblages from the limestone-chert and basalt-chert sequences have a maximum age of middle Early Permian and late Middle Permian, respectively, overlapping the time of deposition of the fusulinoidean-bearing limestone. The co-occurrence of chert and limestone indicates that the fusulinoidean-bearing limestone was formed on a basaltic topographic high in a pelagic ocean whereas the radiolarians accumulated in a deeper part. Limestone debris occasionally flowed into the depositional site of the radiolarian chert. Although the Khabarovsk Complex was simply considered as a northern extension of the Mino–Tamba Belt of the Inner Zone of southwest Japan, we propose a new correlation based on the lithologic associations. The mélange facies of the Khabarovsk Complex is correlative with one of the Kasugano, Funabuseyama, Nabi, and Yabuhara Formations in the Mino–Tamba Belt, whereas the schist facies is correlative with the Hikami Formation of the Ultra–Tamba Belt.

A new method to estimate accumulation rates of lignites in the Eocene Buchanan Lake Formation, Canadian Arctic

Abstract Exceptionally well-preserved Eocene plant fossils occurring in leafy litter mats from the Buchanan Lake Formation, Canadian Arctic, make it possible to estimate the accumulation rate of the lignite. This method is based on the assumption that the projected leaf-surface area of individual tree species per unit of ground-surface area (leaf-area index) is more or less constant. The calculated accumulation rate of 1.6 mm/year has been corrected to the minimum accumulation rate of 0.8 mm/year by considering the effects of organic decomposition. Since the compaction ratio of the leaf lignite is difficult to estimate, correct comparison with accumulation rates of modern and Quaternary peats that have been determined by using 14C ages is impossible. However, the accumulation rate calibrated in the peat stage of coalification by using the compaction ratio of woods embedded in the leaf lignite is within the range of accumulation rates determined for modern and Quaternary peats.

Large-scale landslides in Toyama Prefecture, central Japan, and their probable relationship with earthquakes

Large-scale landslides along the Kubusu and Besso rivers in Toyama Prefecture are developed in the Miocene Iwaine Formation, which is composed of andesitic lava, tuff, and tuff breccia. In the middle member of this formation, the tuff is easily altered to montmorillonite-bearing rock, and subsequently plays an important role in the development of landslides events, which tend to be large-scale events, as the massive lava of the upper member forms a cap rock over the tuff. The Kiritani and Koinami basins, which are flat intermontane basins located along the Kubusu and Besso rivers, respectively, are interpreted as landslide-dammed lakes, later filled with sediment. Accelerator mass spectrometry 14C ages show that the landslides forming each dam occurred simultaneously, at approximately 2500 BP. These ages were measured from wood fragments embedded in the landslide material of Kiritani, and from an in situ stump drowned during the impoundment of Koinami. If the trigger of these landslides was an earthquake, it is most likely to have been the penultimate event along the Atotsugawa fault zone.

Campanian (upper Cretaceous) radiolarians from a shale clast in the Paleogene of central Java, Indonesia

Abstract A Campanian (upper Cretaceous) radiolarian asemblage containing two new species is described from a reddish brown shale clast in a Paleogene breccia formation in the Karangsambung area, central Java, Indonesia. The occurrence of some species typically found in low paleolatitudes strongly suggest s that the radiolarians were deposited in a tropical ocean. On the other hand, coeval Campanian radiolarian assemblages from the blocks in the Luk-Ulo melanges, which unconformably underlies the Paleogene breccia formation, are lacking in the “tropical species” obtained from the clast in the Tertiary cover. The faunal difference indicates that the Campanian Radiolaria-bearing siliceous rocks in the Luk-Ulo melanges and Paleogene formation were deposited in different paleolatitudes and juxtaposed before the deposition of the Paleogene rocks.

Development History of Landslide-Related Sagging Geomorphology in Orogenic Belts: Examples in Central Japan

Small-scale geomorphic features of sagging have been known to occur in mountainous areas in Japan by the analyses of high resolution map images made from the LiDAR data. Development histories of the sagging landforms were analyzed by the GIS analyses, field mapping, machine and hand auger boring, AMS 14C dating, and tephra geochronology in the Mt. Kanmuriyama, Tsuenomine and Nogo-Hakusan areas. Sediments accumulated in the ridge-top depression in the Mt. Kanmuriyama area yield wood fragments with the ages of 1,234–1060, 6,191–5,996 and 7,931–7,731 cal BP, and also include the K-Ah tephra of ca 7.3 ka. These ages indicate that the depression started to form at the beginning of warm and humid climate after the last glacial period. On the other hand, the double ridges in the Mt. Tsuenomine area formed much earlier before the deposition of the Kikai-Tozurahara tephra about 95 ka. The GIS analyses of sagging in the Mt. Nogo-Hakusan area indicate that most of them are distributed on the flat or gentle surface just above the knick line (erosion front); it means that the knick lines retreat through the repetitive formation and destruction of the sagging landforms.