Akiyoshi Limestone Research Articles

Beyond the Akiyoshi Orogeny: unravelling overturned structures and tectonic processes in the Permian accretionary complex of the Mine-Akiyoshidai area, Yamaguchi, western Japan

The concept of the Akiyoshi Orogeny emerged from geological studies of the overturned Akiyoshi Limestone. However, our understanding of the stratigraphy and geological structure of the siliceous–clastic rocks surrounding the Akiyoshi Limestone remains incomplete. We therefore conducted a geological survey within the Beppu unit, which is distributed north of the Akiyoshi Limestone. We found substantial overturning of the strata, even within the siliceous–clastic rocks that form the upper section of the ocean plate stratigraphy within the accretionary complex. The Tsunemori Formation, representing sediments of the forearc or trench slope basin, has also undergone overturning. Extensive overturned structures therefore exist throughout the entire accretionary complex of the Mine-Akiyoshidai area. To understand the mechanism behind these overturned structures within the accretionary complex, we focused on the collision and deformation resulting from the interaction between the accretionary wedge and a massive seamount, along with the back-stop. The overturning of the forearc or slope basin sediments suggests that post-accretion deformation along a large lateral fault may have occurred during the collision between the South and North China blocks. These tectonic events during and after accretion may represent the true nature of the Akiyoshi Orogeny. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists

Late Carboniferous (Kasimovian and Gzhelian) Fusulines of the Ichinotani and Mizuyagadani Formations in the Fukuji Area, Hida Marginal Terrane, Central Japan

Fusuline biostratigraphy and faunal composition of the upper part the Ichinotani Formation and lower part of the Mizuyagadani Formation in the Fukuji area, central Japan are reexamined and compared to those of previous works. The upper part of the Upper Member of the Ichinotani Formation is composed mainly of the upper Kasimovian and lower Gzhelian strata, and is characterized by the partial reappearance of Moscovian strata dominant in the lower part of the Upper Member, suggesting a more complicated geological structure of the formation than previously assumed. Fusulines apparently correlatable to the middle part of the Kasimovian have not been found in the Fukuji area. The species Carbonoschwagerina morikawai is restricted to the lower part of the Mizuyagadani Formation. Faunal composition and correlation of age-diagnostic fusuline species are reviewed paleobiogeographically between the Fukuji and other areas especially of the Akiyoshi Limestone. Described herein are two species of non-fusuline foraminifers and nine species of fusulines including Montiparus japonicus sp. nov.

Carboniferous foraminifers and biostratigraphy of lower Akiyoshi Limestone (Japan)

Carboniferous foraminifers and biostratigraphy of lower Akiyoshi Limestone (Japan)

Early Permian (Sakmarian, Artinskian, Kungurian) foraminifers and Biostratigraphy of the Akiyoshi Limestone (Japan)

Early Permian (Sakmarian, Artinskian, Kungurian) foraminifers and Biostratigraphy of the Akiyoshi Limestone (Japan)

Sedimentation and karstification of the Carboniferous‒Permian Akiyoshi Limestone in the Akiyoshi accretionary complex, southwest Japan

Sedimentation and karstification of the Carboniferous‒Permian Akiyoshi Limestone in the Akiyoshi accretionary complex, southwest Japan

Tectonic setting for Tsunemori Formation in the Permian accretionary complex of the Akiyoshi Belt, Southwest Japan

The purpose of this study is to reexamine the age, depositional environment, and tectonic setting of the Tsunemori Formation. This study provides a new tectonic model on the formation of Tsunemori Formation, which is a key formation to understand the Late Permian subduction and accretionary processes in Japan. The sedimentation age of the Tsunemori Formation is late Middle Permian to early Late Permian, based on radiolarians, such as Follicucullus cf. scholasticus Ormiston and Babcock reported in this study. This paper disproves the previous theory of atoll carbonates collapse at the trench for the Akiyoshi Limestone. Most of sedimentary rocks of the Tsunemori Formation is not pervasively sheared, are less deformed compared with sedimentary rocks of the typical accretionary complexes. There is no layer parallel or sub-parallel thrusting in the turbidite sequences of the Tsunemori Formation. Mudstone of turbidite and pebbly mudstone is lack of fissility and scaly cleavages. The styles of deformation, occurrence of reworked fossils, presence of calcarenite and limestone breccia suggest that the Tsunemori Formation was not a part of accretionary wedges, but possibly was fore arc or slope basin deposits. Presence of reworked fossils, calcarenite, limestone breccia suggest that a part of the provenance of Tsunemori Formation are limestone exposed at the arc trench gap, which was moved upward to reach the arc trench gap where the Akiyoshi Limestone provides its fragments and blocks into forearc and/or slope basins. Therefore, Tsunemori Formation is a deposit in the forearc basin and/or slope basin rather than trench deposits.

O-248 日本産の石炭紀魚類化石,とくに山口県美祢市の秋吉石灰岩層群産の軟骨魚類化石について(24. 脊椎動物化石,口頭発表,一般発表)

O-248 日本産の石炭紀魚類化石,とくに山口県美祢市の秋吉石灰岩層群産の軟骨魚類化石について(24. 脊椎動物化石,口頭発表,一般発表)

Geological research on building stones from Akiyoshi Limestone, Mine City, Yamaguchi Prefecture

Geological research on building stones from Akiyoshi Limestone, Mine City, Yamaguchi Prefecture

The Cretaceous Ofuku Pluton and Its Relation to Mineralization in the Western Akiyoshi Plateau, Yamaguchi Prefecture, Japan

AbstractThe relationship between the magmatism of the Cretaceous Ofuku pluton and mineralization in and around the Akiyoshi Plateau, Yamaguchi Prefecture, Japan was investigated using a combination of field observation, petrographic and geochemical analyses, K–Ar geochronology, and fluid inclusion data. The Ofuku pluton has a surface area of 1.5 × 1.0 km, and was intruded into the Paleozoic accretionary complexes of the Akiyoshi Limestone, Ota Group and Tsunemori Formation in the western part of the Akiyoshi Plateau. The pluton belongs to the ilmenite‐series and is zoned, consisting mainly of early tonalite and granodiorite that share a gradational contact, and later granite and aplite that intruded the tonalite and granodiorite. Harker diagrams show that the Ofuku pluton has intermediate to silicic compositions ranging from 60.4 to 77.9 wt.% SiO2, but a compositional gap exists between 70.5 to 73.4 wt.% SiO2 (anhydrous basis). Modal and chemical variations indicate that the assumed parental magma is tonalitic. Quantitative models of fractional crystallization based on mass balance calculations and the Rayleigh fractionation model using major and trace element data for all crystalline phases indicate that magmatic fractionation was controlled mainly by crystal fractionation of plagioclase, hornblende, clinopyroxene and orthopyroxene at the early stage, and quartz, plagioclase, biotite, hornblende, apatite, ilmenite and zircon at the later stage. The residual melt extracted from the granodiorite mush was subsequently intruded into the northern and western parts of the Ofuku pluton as melt lens to form the granite and aplite. The age of the pluton was estimated at 99–97 Ma and 101–98 Ma based on K–Ar dating of hornblende and biotite, respectively. Both ages are consistent within analytical error, indicating that the Ofuku pluton and the associated Yamato mine belong to the Tungsten Province of the San‐yo Belt, which is genetically related to the ilmenite‐series granitoids of the Kanmon to Shunan stages.The aplite contains Cl‐rich apatite and REE‐rich monazite‐(Ce), allanite‐(Ce), xenotime and bastnäsite‐(Ce), indicating that the residual melt was rich in halogens and REEs. The tonalite–granodiorite of the Ofuku pluton contains many three‐phase fluid inclusions, along with daughter minerals such as NaCl and KCl, and vapor/liquid (V/L) volume ratios range from 0.2 to 0.9, suggesting that the fluid was boiling. In contrast, the granite and aplite contain low salinity two‐phase inclusions with low V/L ratios. The granodiorite occupies a large part of the pluton, and the inclusions with various V/L ratios with chloride daughter minerals suggest the boiling fluids might be related to the mineralization. This fluid could have carried base metals such as Cu and Zn, forming Cu ore deposits in and around the Ofuku pluton. The occurrence and composition of fluid inclusions in the igneous rocks from the Akiyoshi Plateau are directly linked to Cu mineralization in the area, demonstrating that fluid inclusions are useful indicators of mineralization.

Influence of Akiyoshi limestone bedrock on elemental concentrations and Sr isotopic ratio in stream sediments

Influence of Akiyoshi limestone bedrock on elemental concentrations and Sr isotopic ratio in stream sediments

Middle Permian sponge–microencruster reefal facies in the mid-Panthalassan Akiyoshi atoll carbonates: observations on a limestone slab

A Murgabian (Middle Permian) reef-core facies in the Akiyoshi Limestone, southwest Japan, which is of mid-Panthalassan atoll origin, is here described from a limestone slab. The reef-core facies is composed mainly of boundstone with submarine cement and matrix. The reef-building community is characterized by a high-diversity biota, including sponges (sphinctozoans, inozoans, and chaetetids), bryozoans (fistuliporids and cryptostomates), crinoids and various microencrusters (Tubiphytes, Archaeolithoporella, reticular and laminar microbialites, encrusting foraminifers and problematic laminar red algae). Among them, sphinctozoan sponges and microencrusters such as Tubiphytes and microbialites are the most abundant. This community is similar to a time-equivalent lagoonal mound (patch-reef) biota on the Akiyoshi atoll in terms of the dominant sponges, Tubiphytes and microbialites, but differs in the additional occurrence of bryozoans, Archaeolithoporella and encrusting foraminifers, which probably preferred higher-energy conditions in the reef-core environment. Among temporally changing reef-building communities on the Carboniferous–Permian Akiyoshi atolls, the sponge-dominated reefal community described here flourished on mid-Panthalassan atolls in a relatively stable warm-water environment during a Middle Permian post-deglacial period.

Middle Permian sponge–microencruster community in building stones from the Akiyoshi Limestone

Middle Permian sponge–microencruster community in building stones from the Akiyoshi Limestone

Late Paleozoic Foraminifers from Limestone Blocks and Fragments of the Permian Tsunemori Formation and Their Connection to the Akiyoshi Limestone Group, Southwest Japan

Abstract. Late Early Carboniferous (late Visean) to late Middle Permian (Capitanian) foraminifers have been recovered from limestone blocks and fragments contained in the Tsunemori Formation in Yamaguchi Prefecture, Southwest Japan, which is unconformably overlain by the Upper Triassic Mine Group. An analysis of the Tsunemori fauna shows an almost identical composition with that of the Akiyoshi Limestone Group. The ages of the limestone clasts of the Tsunemori Formation nearly completely coincide with those of the strata of the Akiyoshi Limestone Group. The Akiyoshi Limestone Group is subdivided into 28 foraminiferal zones, and faunal elements corresponding to 24 of these 28 zones are recognized in limestone blocks and fragments of the Tsunemori Formation. Species from the remaining four zones (late Visean Endothyra sp. Zone, the late Moscovian Fusulinella bocki Zone, early Asselian Sphaeroschwagerina fusiformis Zone, and Bolorian Misellina dyhrenfurthi Zone) in the Akiyoshi Limestone Group have not been ...

Middle Permian sponge–microencruster bioherms in the Akiyoshi Limestone, SW Japan: implications for Late Palaeozoic reef evolution on mid‐Panthalassan atolls

Middle Permian lagoonal bioherms are described from mid‐Panthalassan atoll carbonates (Akiyoshi Limestone) in the Akiyoshi accretionary complex, SW Japan. The bioherms are composed of frame‐building sphinctozoan and inozoan sponges, together with encrusting organisms, including chaetetids, Shamovella, calcareous red algae, and other microbes. Of them, sphinctozoan sponges, Shamovella, and microbes (forming microbialites) are the most dominant. Chaetetids, which were predominant in the Early Pennsylvanian but rapidly decreased in the late Moscovian, are also common in these bioherms. Archaeolithoporella and bryozoans are rare, probably due to the low‐energy lagoonal environment.This sponge–microencruster community replaced the Gzhelian–Asselian Palaeoaplysina–microencruster community on the Akiyoshi atolls during the Sakmarian–Kubergandian interval. This drastic change in the reef‐building community type almost coincides with the rapid deglaciation of the Gondwanan ice sheet and superplume activity beneath the mid‐Panthalassan ocean. The prosperity of calcareous sponges was possibly controlled by environmental factors such as warming and eutrophication after the Gondwanan glaciation. Copyright © 2012 John Wiley & Sons, Ltd.

秋吉石灰岩中部ペルム系の海綿-被覆性微生物群集：パンサラッサ海洋島上での礁進化のなかでの位置づけ

秋吉石灰岩中部ペルム系の海綿-被覆性微生物群集：パンサラッサ海洋島上での礁進化のなかでの位置づけ

COMPARATIVE STUDY OF THE CAPITANIAN (LATE GUADALUPIAN) FORAMINIFERAL FAUNAS IN THE LEPIDOLINA SHIRAIWENSIS ZONE OF THE AKIYOSHI LIMESTONE GROUP, SW JAPAN

Middle Permian (Guadalupian) foraminiferal faunas in Japan are divided into the Akiyoshi, Chichibu, and Kurosegawa faunas based on the spatiotemporal distribution and phyletic evolution mainly of neoschwagerinid, verbeekinid, and schwagerinid fusulines. The Capitanian Akiyoshi Fauna of the Lepidolina shiraiwensis Zone in the Akiyoshi Limestone Group of the Akiyoshi Belt consists of 48 species assignable to 35 genera of foraminifers (17 species assignable to 13 genera of fusulines and 31 species to 22 genera of non-fusuline foraminifers). Fusulines in the fauna are represented by Lepidolina shiraiwensis, Sumatrina longissima, and Verbeekina douvillei . On the whole, the Capitanian Akiyoshi Fauna is as variable as the coeval Chichibu Fauna and somewhat less variable than the coeval Kurosegawa Fauna. The interrelation of variability and richness between the fusuline and non-fusuline foraminifers is locally controlled by ecological and depositional facies changes during the Capitanian. Taxonomic composition and richness of these three faunas throughout the Middle to Late Permian are related to environmental and faunal changes in the Panthalassan-originated seamounts and continental shelves in and around circum-Pacific regions. Twelve species assignable to nine genera including Parafusulina nagatoensis n. sp. are systematically described from the Lepidolina shiraiwensis Zone of the Akiyoshi Limestone Group.

Abundant occurrences of microbialites and tidal-flat deposits in the Artinskian (Lower Permian) part of the Akiyoshi Limestone, SW Japan

Abundant occurrences of microbialites and tidal-flat deposits in the Artinskian (Lower Permian) part of the Akiyoshi Limestone, SW Japan

An Early–Middle Guadalupian (Permian) isotopic record from a mid-oceanic carbonate buildup: Akiyoshi Limestone, Japan

In order to understand the oceanographic changes before the Guadalupian–Lopingian (Permian) boundary mass extinction event, we investigated the isotopic compositions of the inorganic carbon and the oxygen ( δ 13C carb and δ 18O carb) of the Guadalupian (Middle Permian) shallow marine carbonates deposited on a seamount-top in the superocean Panthalassa. The drilled samples were obtained at Kaerimizu in the Akiyoshi area, SW Japan. We focused on the Roadian-Wordian (Middle Guadalupian) interval that spans over 7 fusuline zones; i.e. the Parafusulina kaerimizuensis Zone ( Pk Z.), Afghanella ozawai Zone ( Ao Z.), Neoschwagerina craticulifera robusta Zone ( Ncr Z.), Verbeekina verbeeki – Afghanella schenki Zone ( Vv – As Z.), Neoschwageina fusifor m is Zone ( Nf Z.), Verbeekina verbeeki Zone ( Vv Z.), and Colania douvillei Zone ( Cd Z.), in ascending order. Analytical results showed that the δ 13C carb values stayed almost constant around + 3.0‰ PDB in the Pk Z., Ao Z. and the lower half of the Ncr Z., and those in the upper-section gradually decreased down to −2.0‰, of which the lowest was found in the Cd Z. We statistically extracted the samples with presumably better preserved δ 13C carb values in the Kaerimizu section ranged between + 0.5 and + 4.0‰ with average values of δ 13C carb of + 2.7 ± 1.0‰, on the basis of δ 13C carb– δ 18O carb characterization. This interval shows a monotonous decrease in δ 13C carb values from ca + 4.0‰ to + 2.0‰. This indicates that the primary productivity might be generally high in the Wordian mid-oceanic domain but slightly declined in the Late Wordian. The studied Early-Middle Guadalupian interval is chemostratigraphically correlated with the other mid-Pansalassan paleo-atoll limestone e.g. Iwato Formation in Japan, suggesting that the relatively high δ 13C carb (over + 3.0‰) of seawater predominated in shallow mid-superocean during the middle Middle Permian.

Carboniferous-Permian long-term sea-level change inferred from Panthalassan oceanic atoll stratigraphy

This paper traces late Palaeozoic second-order sea-level change based on the stratigraphy of the Akiyoshi Limestone, an accreted Carboniferous-Permian Panthalassan atoll carbonate succession in SW Japan. The estimated subsidence of a volcanic edifice and the variable rate of carbonate accumulation reveal the long-term sea-level history of the late Palaeozoic. During Bashkirian time, just after the lowstand stage at the mid-Carboniferous boundary, a slow progressive long-term sea-level rise began. This sea-level rise then increased greatly during Moscovian time. The following Kasimovian to Asselian interval represents a stable highstand stage. Beginning in the Sakmarian, sea level fell slowly and became stable in the Yakhtashian (= Artinskian). This stable sea level was maintained into the Midian (= Capitanian), although a small-scale sea-level rise of approximately 55–70 m is recognized in the Murgabian (= Wordian). The most noteworthy aspect of this change of sea level is the rapid sea-level rise during the Moscovian that created a very large accommodation space and resulted in accumulation of a thick carbonate succession. The eustatic rise from the earliest Bashkirian lowstand to the latest Moscovian highstand had an amplitude of approximately 230–240 m. Such a large-scale eustatic rise in the long-term sea-level change would most likely be caused by greater uplift of the ocean floor along the mid-oceanic ridges, as a result of an increase in the production of oceanic crust during that time.

Carboniferous to Permian paleoenvironmental changes revealed in Akiyoshi Limestone – commemorating field excursion for the 50th anniversary of the foundation of Akiyoshi-dai Museum of Natural History, Mine –

山口県西部秋吉台には，秋吉帯のペルム紀付加体を特徴づける秋吉石灰岩（下部石炭系～中部ペルム系）が広く分布する．秋吉石灰岩はパンサラッサ海大洋域に位置していた海山の頂部で堆積した浅海成石灰岩からなり，約8000万年間の気候・海水準変動を記録している．本見学旅行では，サンゴ礁相，ウーライト質石灰岩で示される石炭紀古世中期の温暖・高海水準環境，大型生物礁の衰退と離水堆積物で示される石炭紀新世後期における寒冷化と離水・古カルスト形成，干潟相および離水砂浜相で特徴づけられる堆積サイクルが示すペルム紀中世の短周期海水準変動などについて現地討論を行う．また本年で創立50周年を迎える美祢市立秋吉台科学博物館を訪れ，学術研究，自然保護に対する同館の貢献をふり返る．