Late Jurassic radiolarians from mudstone near the U–Pb-dated sandstone ofthe North Kitakami Belt in the northeastern Shimokita Peninsula, Tohoku, Japan

Uchino, Takayuki; Suzuki, Noritoshi

doi:10.9795/bullgsj.71.313

Cited by 9 publications

(5 citation statements)

References 32 publications

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“…Recently, as a result of surveys mainly in the Rikuchu-Seki District located north of our study area, Nakae et al (2021) proposed that the Seki Unit should be divided into two tectonostratigraphic units; the upper Kassenba Complex (coherent facies; chert, mudstone and sandstone) and the lower Seki Complex (coherent facies; chert and mudstone) Region (modified from Geological Survey of Japan, AIST, 2020). Age data of the accretionary complex are based on the compilation by Uchino and Suzuki (2020). Rads: radiolarian fossils.…”

Section: Geological Outlinementioning

confidence: 99%

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Geology and accretionary age of the Otori Unit, North Kitakami Belt

Muto

Ito

2023

Bull. Geol. Surv. Japan

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The North Kitakami Belt in Northeast Japan mainly comprises accretionary complexes formed during the Jurassic to earliest Cretaceous. The accretionary complex of the North Kitakami Belt is less studied compared to the age-equivalent accretionary complexes in Southwest Japan. Here, we provide additional data on the accretionary complex formerly classified as the Otori Unit, distributed in the northeastern part of the North Kitakami Belt in the upper reaches of the Akka River in Iwate Prefecture. Based on detailed field mapping, we clarified that the Otori Unit is composed of the structurally lower coherent facies of chert and siliceous mudstone (Okoshizawa Subunit) and the structurally upper mixed facies of mudstone, sandstone, chert and minor basaltic rocks (Osakamoto Subunit). Manganese nodules from siliceous mudstone within the Okoshizawa Subunit yielded radiolarians indicating the Bathonian (upper Middle Jurassic). Detrital zircon grains from sandstone in the Osakamoto Subunit has a youngest age of ~170 Ma (YC1σ: 171.8 ± 2.4 Ma; YSG: 170.9 ± 3.8 Ma). Based on the radiolarian and detrital zircon ages, the accretionary age of the Otori Unit is estimated as the Bathonian. Our new data were also considered to discuss the correlation between the North Kitakami Belt and the Southern Chichibu Belt in Southwest Japan. The Otori Unit corresponds to the Ohirayama Unit of the Southern Chichibu Belt in structural position, and the two units are similar in being a mixed facies and have overlapping accretionary age. However, the Otori Unit lacks limestone and has a considerably younger age for siliceous mudstone, suggesting that the two units may not be strictly correlative.

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Section: Geological Outlinementioning

confidence: 99%

“…Fig.1 Geology of the basement rocks of northern TohokuRegion (modified from Geological Survey of Japan, AIST, 2020). Age data of the accretionary complex are based on the compilation byUchino and Suzuki (2020). Rads: radiolarian fossils.…”

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confidence: 99%

Geology and accretionary age of the Otori Unit, North Kitakami Belt

Muto

Ito

2023

Bull. Geol. Surv. Japan

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“…We studied pelagic deep-sea sedimentary rocks (mostly bedded chert) that belong to the Jurassic accretionary complex of the North Kitakami Belt (Ehiro et al, 2008). These sedimentary rocks were deposited in the Superocean Panthalassa (Figure 1A) then transported and accreted at the subduction zone along its western margin by plate motion during the Jurassic to earliest Cretaceous (Isozaki et al, 1990;Wakita and Metcalfe, 2005;Ehiro et al, 2008;Uchino and Suzuki, 2020).…”

Section: Geological Settingmentioning

confidence: 99%

Conodont biostratigraphy of a Carboniferous–Permian boundary section in siliceous successions of pelagic Panthalassa revealed by X-ray computed microtomography

Muto

Takahashi

2023

Front. Earth Sci.

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Pelagic deep-sea siliceous successions in accretionary complexes preserve precious records of a vast deep seafloor that is now lost due to plate subduction. Microfossils are the key means of age assignment of these successions, but poor preservation due to tectonic deformation and metamorphism at the subduction zone hamper biostratigraphic records. X-ray computed microtomography, while not widely used in biostratigraphic studies until now, allows us to visualize fossils that are impossible or difficult to extract from host rocks due to poor preservation. In this study, we applied this method on conodonts from a pelagic chert–claystone succession in Okoshizawa, Iwaizumi Town, Northeast Japan, using a laboratory-based X-ray microscope. This work is a first close look at conodont biostratigraphy across the Carboniferous–Permian boundary in pelagic deep Panthalassa. We identified conodonts including ten species that are used as zonal markers in intensely studied areas such as around the East European Platform and Midcontinent United States. Based on the occurrence of conodonts, the studied section in Okoshizawa was correlated to the lower Moscovian to middle Artinskian. Confirmation of Moscovian to Artinskian age diagnostic conodonts from pelagic Panthalassa strengthens their role as global biostratigraphic indicators. By identifying more numerous specimens compared to the conventional hydrofluoric acid dissolution method, we were able to obtain information about conodont faunal characteristics around the Carboniferous–Permian boundary in pelagic deep areas of Panthalassa. The dominant taxa changed from Streptognathodus to Mesogondolella in the middle Asselian, probably reflecting an ecological takeover by the latter in the deep waters.

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“…This study revealed that the Takinosawa Unit distributed to the north of the Tsunatori Unit in the Nedamo Belt is an Early Triassic accretionary complex. Accretionary complexes in the North Kitakami Belt are considered to show a younging polarity of Early Jurassic to Early Cretaceous from southwest to northeast (Ehiro et al, 2008;Kojima et al, 2016;Suzuki et al, 2007;Uchino & Suzuki, 2020). Recently, a Late Triassic accretionary complex has been inferred on the basis of latest Triassic zircon-bearing and Middle-Late Triassic radiolarian-bearing tuffaceous mudstone (TfHi9 in Figure 2) in the south westernmost North Kitakami Belt, east of Morioka City (Uchino, 2017).…”

Section: Younging Polarity Of Accretionary Complexes In the Northern Kitakami Massifmentioning

confidence: 99%

“…High-P/T metamorphic rocks in both Southwest Japan and the Kitakami Massif might have formed in the same arc-trench system of the circum-Pacific orogenic belt (e.g., Tsujimori & Itaya, 1999). Based on lithological similarities, such as Megalodon-fossil-bearing Upper Triassic Suzuki et al (2007), Uchino and Suzuki (2020), and other studies referred to in these four papers limestone (Sano et al, 2009) and "Torinosu-type" Upper Jurassic limestone (e.g., Murata, 1962;Onuki, 1959), part of the Jurassic accretionary complexes in the Akka-Tanohata Subbelt of the North Kitakami Belt have been considered the Sanbosan Unit of the southern belt in the Chichibu Belt (e.g., Isozaki & Maruyama, 1991;Takahashi et al, 2016) (Figure 11). However, the Early Carboniferous Tsunatori Unit in the Nedamo Belt cannot be correlated with any geotectonic units in Southwest Japan.…”

Section: Correlation Of the Takinosawa Unitmentioning

confidence: 99%

Recognition of an Early Triassic accretionary complex in the Nedamo Belt of the Kitakami Massif, Northeast Japan: New evidence for correlation with Southwest Japan

Uchino

2021

Island Arc

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The Kitakami Massif of the Tohoku district, Northeast Japan, consists mainly of the South Kitakami Belt (Silurian-Cretaceous forearc shallow-marine sediments, granitoids, and forearc ophiolite) and the North Kitakami Belt (a Jurassic accretionary complex). The Nedamo Belt (a Carboniferous accretionary complex) occurs as a small unit between those two belts. An accretionary unit in the Nedamo Belt is lithologically divided into the Early Carboniferous Tsunatori Unit and the age-unknown Takinosawa Unit. In order to constrain the accretionary age of the Takinosawa Unit, detrital zircon U-Pb dating was conducted. The new data revealed that the youngest cluster ages from sandstone and tuffaceous rock are 257-248 Ma and 288-281 Ma, respectively. The Early Triassic depositional age of the sandstone may correspond to a period of intense magmatic activity in the eastern margin of the paleo-Asian continent. A 30-40 my interval between the youngest cluster ages of the sandstone and the tuffaceous rock can be explained by the absence of syn-sedimentary zircon in the tuffaceous rock. The new detrital zircon data suggest that the Takinosawa Unit can be distinguished as an Early Triassic accretionary complex distinct from the Early Carboniferous Tsunatori Unit. This recognition establishes a long-duration northeastward younging polarity of accretionary units, from the Carboniferous to Early Cretaceous, in the northern Kitakami Massif. Lithological features and detrital zircon spectra suggest that the Early Triassic Takinosawa Unit in the Nedamo Belt is comparable with the Hisone and Shingai units in the Kurosegawa Belt in Shikoku. The existence of this Early Triassic accretionary complex strongly supports a pre-Jurassic geotectonic correlation and similarity between Southwest and Northeast Japan.

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Late Jurassic radiolarians from mudstone near the U–Pb-dated sandstone ofthe North Kitakami Belt in the northeastern Shimokita Peninsula, Tohoku, Japan

Cited by 9 publications

References 32 publications

Geology and accretionary age of the Otori Unit, North Kitakami Belt

Geology and accretionary age of the Otori Unit, North Kitakami Belt

Conodont biostratigraphy of a Carboniferous–Permian boundary section in siliceous successions of pelagic Panthalassa revealed by X-ray computed microtomography

Recognition of an Early Triassic accretionary complex in the Nedamo Belt of the Kitakami Massif, Northeast Japan: New evidence for correlation with Southwest Japan

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