Pre-Cretaceous accretionary complexes

Matsuoka

2018

Island Arc

Self Cite

Uppermost Permian–lowermost Triassic siliceous claystone is well‐known as being a possible décollement zone in accretionary processes of mid‐Mesozoic accretionary complexes in Southwest Japan; meanwhile, fewer studies have focused on other décollement zones in Permian pelagic sequences. The Ryokami‐yama Thrust in the Southern Chichibu terrane, eastern Mt. Ryokami, Kanto Mountains, has been considered an out‐of‐sequence thrust and might show a former décollement zone in the formation's Permian pelagic sequences. This study shows the Permian pelagic sequences (lithology and radiolarian age) of the Ryokami‐yama Chert Formation on the Ryokami‐yama Thrust. The basal part of the Ryokami‐yama Chert Formation consists of pale‐green basaltic tuff breccia and overlying red‐ocher thick‐bedded chert intercalating dolomites. The red‐ocher thick‐bedded chert yielded radiolarians of the Pseudoalbaillella lomentaria Range‐Zone of the Sakmarian (Cisuralian: lower Permian). Compilation of the Permian pelagic sequences of the mid‐Mesozoic accretionary complexes in previous studies indicates that the bases of the Permian chert of many geologic units are concentrated in the Pseudoalbaillella lomentaria Range‐Zone. The following hypothesis is suggested here: the basaltic rock underlying the Sakmarian chert acted as a décollement zone in the Permian pelagic sequences of some geologic units of the mid‐Mesozoic accretionary complexes.

Section: Introductionmentioning

confidence: 99%

Lithology and radiolarian age of the Ryokami‐yama Chert Formation in eastern Mt. Ryokami: Possible décollement zone in Permian pelagic sequence in mid‐Mesozoic accretionary complexes of Southwest Japan

Matsuoka

2018

Island Arc

Self Cite

“…Permian and Jurassic ACs other than the Tamba-Mino and Ashio terranes exist in the Japanese Islands such as the Akiyoshi terrane (Permian AC) of the Inner Zone of Southwest Japan, Chichibu composite terrane of the Outer Zone of Southwest Japan and the North Kitakami terrane of Northeast Japan (e.g. Kojima et al, 2016). Furthermore, the Jurassic ACs extend to adjacent regions of Japan, such as Northeast China, Far Eastern Russia and the Philippines (e.g.…”

Section: Permian and Jurassic Acs In Other Areasmentioning

confidence: 99%

Radiolarian age of Triassic striped chert within the Jurassic accretionary complex of the Ashio terrane in the Ashikaga area, Tochigi Prefecture, central Japan

Bull. Geol. Surv. Japan

2020

A striped structure within a single chert bed has been observed in the Tamba-Mino and Ashio terranes, Jurassic accretionary complexes of the Inner Zone of Southwest Japan. This study reports striped chert beds in four sections of the Ashio terrane in Ashikaga and Sano cities of Tochigi Prefecture, namely, Hikoma, Oiwa, Tsukiya and Orihime sections, and their radiolarian ages, except for the Hikoma section. The striped chert comprises streaks and spacing. The streak indicates a thin part of a pin-striped structure within a chert bed and consists mainly of clay minerals. The spacings indicate a thick part between the streaks and is composed mainly of cryptocrystalline quartz. The Oiwa section, which contains numerous striped chert beds, partially corresponds to the middle Carnian-middle Norian (Upper Triassic). The Tsukiya and Orihime sections, which include a few striped chert beds, partially correspond to the middleupper Anisian (Middle Triassic) and upper Norian-lower Rhaetian (Upper Triassic), respectively.

“…Mid-Mesozoic accretionary complexes are widely exposed in the Japanese Islands and generally contain Permian, Triassic and Jurassic radiolarians (e.g. Kojima et al, 2016). Because of their importance for age determination to draw the geological maps, their occurrences have been reported by several maps in most areas (Fig.…”

Section: − 408 −mentioning

confidence: 99%

Radiolarian research by the Geological Survey of Japan, AIST, with bibliographic lists from 1950 to 2019

Bull. Geol. Surv. Japan

Nakae

Itaki

2020

The Geological Survey of Japan (GSJ), established in 1882, marked its 135th anniversary in 2017 and has issued numerous publications, such as geologic maps, research articles and newsletters, during its history. This article compiles previous GSJ publications related to radiolarian research for future reference. In the GSJ publications from 1950 to 2019, the term of RADIOLARIA in Japanese appears in 252 Geological Maps of the Quadrangle Series (1:50,000), in 21 Geological Maps of the Quadrangle Series (1:200,000), in 75 articles of the Bulletin of the Geological Survey of Japan, in 14 items in Chishitsu News, in 21 items in GSJ Chishitsu News and in seven articles in the Cruise Report. The GSJ publications related to radiolarian research increased during the 1980s, which is consistent with the commonly called Radiolarian Revolution.