Lithostratigraphy of the Neogene Goto Group and finding of plant megafossils in Wakamatsu-jima and Nakadori-jima, central part of Goto Islands, Nagasaki Prefecture

The Taishu Group, a marine formation with a thickness of >5400 m, crops out on Tsushima Island, located in the southwestern Japan Sea. The group, which is generally regarded as early Eocene to early Miocene in age, provides important information about the tectonic setting of the Japan Sea. In this study, we present new SHRIMP U-Pb dates for igneous zircons from the Kunehama Tuff, which is in the basal part of the Taishu Group, and the Oobaura Tuff, which is in the uppermost part of the group. Results show that the Taishu Group was deposited rapidly, during the short interval of 17.9-15.9 Ma (earlymiddle Miocene), and is equivalent to other early-middle Miocene strata found in the Japan Sea region. Our results provide new constraints on the geological history of the Japan Sea and its islands.

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“…(), G oto = Y asunaga et al . (), S himane = T akayasu et al . (), H okutan = M atsumoto (), F ukui = F ujii et al .…”

Section: Discussionmentioning

confidence: 99%

Age of the Taishu Group, southwestern Japan, and implications for the origin and evolution of the Japan Sea

et al. 2014

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“…The upper subunit of the middle unit contains willow ( Salix ) remains, but it does not contain the evergreen Lauraceae or oaks characteristic of the Daijima‐type flora (Yasunaga et al, 2007). The occurrences of these fossils show that the upper subunit of the middle unit of the Goto Group was deposited under relatively cool climate conditions (i.e., in the temperate zone) as compared with the Daijima‐type environment recorded by the upper unit (Yasunaga et al, 2007).…”

Section: Resultsmentioning

confidence: 99%

“…The sequence coarsens and thickens upwards. NK‐2 block (Atotsugi; Figure S1): In southern Aokata (Figure S1), alternating layers of sandstone and black shale crop out. Plant fossils have been identified at Atotsugi (Yasunaga et al, 2007). NK‐3 block (Ohota to Cape Shioyazaki; Figure S1): A well‐bedded sandstone–shale sequence occurs along the south coast of Cape Shioyazaki.…”

Section: Stratigraphymentioning

confidence: 99%

Stratigraphic reconstruction of the lower–middle Miocene Goto Group, Nagasaki Prefecture, Japan

Kiyokawa

Yasunaga²,

Hasegawa

et al. 2022

Island Arc

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The Goto Islands are located at the westernmost tip of the Japan archipelago, and preserve a lower–middle Miocene sedimentary sequence deposited during rifting of the continental margin and opening of the Sea of Japan. The stratigraphy of the Goto Group and new K–Ar, fission‐track, and U–Pb age data were used to determine the initial conditions of rifting in southwest Japan. The thickness of the Goto Group is 2000–3000 m. The lower unit (ca. 22–17.6 Ma) consists of thick, greenish, volcaniclastic rocks with basaltic volcanic material, representing the initial stages of continental rifting. The middle unit (ca. −17.6 Ma) consists of alternating sandstones and shales deposited in lacustrine and meandering fluvial environments in a syn‐rift sedimentary basin during a period of volcanic activity. The upper unit (ca. 17.6–16.8 Ma) consists of thick sandstones of fluvial–deltaic facies that were deposited during rapid subsidence at the continental margin. This unit was deposited by a large fluvial system that flowed into the Sea of Japan. These sequences contain relatively cooler to warmer flora (Daijima‐type) and record the warm period of the Miocene Climatic Optimum. The Goto felsic volcanic rocks (16.8 ~ 15.4 Ma) unconformably overlie the Goto Group, and granitic magmatism (ca. 16–14.5 Ma) occurred after sedimentation of the Goto Group. The widespread lacustrine, meandering–braided fluvial, and vast deltaic systems of the Goto Group, and felsic volcanism, were formed due to rapid subsidence that produced a horst‐and‐graben basin during the early stages of rifting of a volcanic arc along the eastern margin of Eurasia. These events occurred from 22.0 to 16.8 Ma before and during the formation of the Sea of Japan.

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“…FIGURE 10 Correlation of the early to middle Miocene chronostratigraphy of the southwestern Japan Sea. Data from previous studies are sourced for Yangnum (Yoon, 1992), Pohang (Akimoto et al, 1999), Goto (Yasunaga, Kiyokawa, & Uemura, 2007), Shimane (Takayasu et al, 1992), Sasebo (Komatsubara et al, 2005), Tsushima (Ninomiya et al, 2014), Iki (Chijiwa, 2010;Huang & Okamoto, 1980;Sakai & Nishi, 1990), and Yuya-wan (Ozaki, 1999) 1. The Okinoshima Formation was altered at temperatures > 200 C in a neutral alteration zone.…”

Section: Discussionmentioning

confidence: 99%

U–Pb and fission‐track dating of a submarine pyroclastic rock from southwest Japan

Ninomiya

Taniguchi²,

Shimoyama

et al. 2017

Island Arc

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The Okinoshima Formation crops out on Okinoshima Island and comprises a thick sequence (> 200 m) of pyroclastic rocks and alternating beds of sandstone and mudstone. Because Okinoshima Island is located between Honshu and Tsushima Island, the Okinoshima Formation potentially provides an important record of volcanism during the opening of the Japan Sea in northwest Kyushu, as well as a record of the formation of the present Genkai Sea region. In consideration of the lack of previous geochronological work, dating (fission‐track and U–Pb) of igneous zircons extracted from the Okinoshima Formation were undertaken and studied the clay mineral alteration in the pyroclastic material in order to reveal its thermal history. These data are used to constrain the age of the Okinoshima Formation and the present Genkai Sea region. Our results show that no thermal event has reset the fission‐track age after deposition of the pyroclastic rocks, and that the Okinoshima Formation was deposited at 16.2 Ma. The present Genkai Sea region is a deep‐sea basin, and its formation at 16.2 Ma was accompanied by submarine volcanism and rapid subsidence that marked the climactic stage of Japan Sea formation. After 16 Ma, the tectonic setting of the present Genkai Sea region changed from one of extension (related to the formation of the Japan Sea) to one of compression, with uplift occurring under the influence of the clockwise rotation of southwest Japan. Consequently, after 16 Ma the present Genkai Sea region became isolated from the forming processes of the Japan Sea.

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Lithostratigraphy of the Neogene Goto Group and finding of plant megafossils in Wakamatsu-jima and Nakadori-jima, central part of Goto Islands, Nagasaki Prefecture

Cited by 4 publications

References 2 publications

Age of the Taishu Group, southwestern Japan, and implications for the origin and evolution of the Japan Sea

Age of the Taishu Group, southwestern Japan, and implications for the origin and evolution of the Japan Sea

Stratigraphic reconstruction of the lower–middle Miocene Goto Group, Nagasaki Prefecture, Japan

U–Pb and fission‐track dating of a submarine pyroclastic rock from southwest Japan

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