Microfacies and depositional setting of the Upper Triassic mid-oceanic atoll-type carbonates of the Sambosan Accretionary Complex (southern Kyushu, Japan)

The Upper Triassic shallow-water limestones of the Sambosan Accretionary Complex are reconstructed as a remnant of a mid-oceanic atoll-type build-up upon a seamount in the Panthalassan Ocean. The Sambosan atoll-type carbonates and its pedestal were accreted along with deep-water ribbon-chert and related siliceous rocks to the eastern margin of Asia during the Late Jurassic to Early Cretaceous. Studied limestones crop out in southern Kyushu Island, southwest Japan. Although the prevailing and intense deformation during the accretionary process prevents measurement of sections in stratigraphic successions, and sedimentary structures are poorly preserved, microfacies description and foraminifers analysis allow us to speculate the depositional setting of the Sambosan limestones. Seventeen microfacies are distinguished and several foraminifers of Tethyan affinity are identified. Foraminifers indicate a Late Carnian to Rhaetian age. The Tethyan affinity of the macro- and microfaunas suggests that the Sambosan seamount was located presumably in a low- to middle-latitudinal zone of the southern hemisphere during the Late Triassi

Evolutionary Process from Mockina bidentata to Parvigondolella andrusovi: Evidence from the Pizzo Mondello Section, Sicily, Italy

During their last phase of evolution, the pectiniform conodont elements manifested an evident trend of simplification and miniaturization. This phase started from the late Norian (Sevatian) in the Late Triassic and the evolutionary process of genus Mockina to Parvigondolella, in particular between Mockina bidentata and Parvigondolella andrusovi, is one of the most significant examples. Parvigondolella has been reported worldwide since it was first described in the early 1970s. However, it has recently been suggested that genus Parvigondolella is an ecostratigraphic morphotype of genus Mockina, and thus a phenotype controlled by the environmental conditions, and not an independent taxon. In the Pizzo Mondello Section (Sicily, Italy), transitional forms between M. bidentata and P. andrusovi have been found at different evolutionary stages. We have investigated the oceanic conditions at the time by using redox-sensitive elements (Mn, Fe, V, Cr, and Ni) and seawater temperatures from biogenetic δ O to understand the possible environmental influences on the phylogenetic evolution between Mockina and Parvigondolella. The geochemical and isotope analyses indicate that the redox condition and temperature were stable during the evolution of genus Parvigondolella in Pizzo Mondello, confirming that genus Parvigondolella is a real taxon and not a phenotype. A new conodont species named Parvigondolella ciarapicae n. sp. is described here for the first time.This study was supported by the grants PRIN to Manuel Rigo (No. 2017W2MARE); and the China Scholarship Council to Yixing Du (No. 201708510096). Development of conodont oxygen isotopic analysis by SHRIMP was supported by Australian Research Council Discovery to Ian S. Williams (No. DP1096252). Open Access funding provided by Università degli Studi di Padova. The final publication is available at Springer via https://doi.org/10.1007/s12583-020-1362-2

Groundwater helium anomaly reflects strain change during the 2016 Kumamoto earthquake in Southwest Japan

Geochemical monitoring of groundwater and soil gas emission pointed out precursor and/or coseismic anomalies of noble gases associated with earthquakes, but there was lack of plausible physico-chemical basis. A laboratory experiment of rock fracturing and noble gas emission was conducted, but there is no quantitative connection between the laboratory results and observation in field. We report here deep groundwater helium anomalies related to the 2016 Kumamoto earthquake, which is an inland crustal earthquake with a strike-slip fault and a shallow hypocenter (10 km depth) close to highly populated areas in Southwest Japan. The observed helium isotope changes, soon after the earthquake, are quantitatively coupled with volumetric strain changes estimated from a fault model, which can be explained by experimental studies of helium degassing during compressional loading of rock samples. Groundwater helium is considered as an effective strain gauge. This suggests the first quantitative linkage between geochemical and seismological observations and may open the possibility to develop a new monitoring system to detect a possible strain change prior to a hazardous earthquake in regions where conventional borehole strain meter is not available.UTokyo Research掲載「地下水のヘリウム量は大地震の前触れを告げる指標になりうるか」 URI: http://www.u-tokyo.ac.jp/ja/utokyo-research/research-news/groundwater-helium-level-could-signal-potential-risk-of-earthquake.htmlUTokyo Research "Groundwater helium level could signal potential risk of earthquake" URI: http://www.u-tokyo.ac.jp/en/utokyo-research/research-news/groundwater-helium-level-could-signal-potential-risk-of-earthquake.htm

The Jurassic of the Northern Calcareous Alps and its Global Boundary Stratotype Section and Point (GSSP)

This paper summarises the recent progress and current status of research undertaken on the Jurassic strata of the Northern Calcareous Alps. The Jurassic GSSP (Global Boundary Stratotype Section and Point) at the Kuhjoch section of the Northern Calcareous Alps is also explained in detail. The base of the Jurassic strata is defined at this location by the occurrence of the oldest known Jurassic ammonite, Psiloceras spelae tirolicum Hillebrandt & Krystyn. The Upper Triassic to Lower Jurassic successions of the Northern Calcareous Alps were developed along the passive continental margin of the Neotethys Ocean. In Middle Jurassic time, a change in the plate tectonic setting influenced the sedimentary facies, which suggest northwest-verging nappe stacking in association with the partial closure of the Neotethys Ocean. Deep-water radiolarite basins developed in the area in front of the advancing nappes and were the sites of mass flow deposits that produced olistoliths of various sizes. These olistoliths were included in the radiolarite matrices. Therefore, the use of radiolarian fossils as a dating method plays an important role in understanding the formations of the Northern Calcareous Alps.ジュラ系の国際境界模式層序・位置がオーストリア国チロル州のクーヨッホ層序断面に置かれることが2010年に正式に決まった．それはジュラ紀最古のアンモナイトPsiloceras spelae tirolicumが初産出する層準で，ケンドゥルバッハ層の基底から5.8m上位に位置する．筆者らは2012年に行われた国際堆積学会の巡検でクーヨッホ層序断面を訪れたので，その概要を紹介する． ジュラ系の国際模式境界が置かれた北部石灰アルプスでは，近年の研究でオリストリスの基質をなす珪質堆積岩からジュラ紀の放散虫化石が数多く報告され，年代決定に有効なことが示された．本稿では特に研究が進んでいるザルツカンマーグート地方の代表的なジュラ紀層を紹介し，北部石灰アルプスの地質構造発達史を概観する

THE CASE FOR THE GLOBAL STRATOTYPE SECTION AND POINT(GSSP) FOR THE BASE OF THE NORIAN STAGE

The Norian Stage is the longest stage in the Phanerozoic, and some members of the boundary working group have been evaluating suitable Carnian-Norian boundary sections for roughly two decades. This has identified two possible candidate boundary sections, at Black Bear Ridge (British Columbia, Canada) and Pizzo Mondello (Sicily, Italy). After a formal voting procedure within the working group, ending on the 26th July, 2021, the Pizzo Mondello section was selected as the global stratotype section and point for the base of the Norian. We evaluated the global correlation potential of the two proposed primary markers, the conodont Metapolygnathus parvus and the ‘flat-clam’ Halobia austriaca. Secondary markers were also evaluated around these boundary datums for correlation potential, and the veracity of the proposed sections for GSSP status. Data and arguments for the proposed sections and datums are presented here. Through a two-stage process of option elimination in voting, conforming with ICS guidelines, the working group decided by 60% majority to propose that the first occurrence datum of Halobia austriaca in the Pizzo Mondello section at the base of bed FNP135A should become the ‘golden spike’ for the base of the Norian. A secondary biotic marker for this boundary is the first occurrence of Primatella (Carnepigondolella) gulloae, in sample NA43, ca. 0 m below FNP135A, and the FA of Dimorphites noricus (sample NA42.1) ca. 3.5 m above bed FNP135 (indicating the first subzone of the Jandianus Zone). The best physical secondary marker is the magnetozone PM5n with the proposed boundary ca.40% through the thickness of PM5n. Strengths of the chosen datum are: 1) it also maintains historical priority for ammonoid zonations, which had placed the base Norian near to this level in Europe, North America and probably NE Asia; 2) Halobia austriaca is widely distributed in all paleolatitudes and is a long-established taxon

Aulotortus friedli from the Upper Triassic gravitational flow deposits of the Kumagawa River (Kyushu, Southwest Japan)

The benthic foraminifer Aulotortus friedli is reported from the Upper Triassic carbonates (capped seamount) of the Sambosan Accretionary Complex in Kyushu, Southwest Japan. Specimens were collected from shallow-water limestone clasts in a debris flow sequence near the Ose locality along the Kumagawa River. The limestone clasts mainly represent shoal facies where the benthic foraminifer is extremely abundant. Because of the remarkable preservation of the Japanese specimens, they allow further description of the involutinid A. friedli. In addition, a detailed sedimentary and environmental analysis of the gravitational deposits where A. friedli occurs is given. Using microfacies analysis together with the biostratigraphic range of A. friedli and associated foraminifers, a new interpretation is proposed of a seamount collapse process that occurred during the Norian-Rhaetian and preceded the major collapse event of the Sambosan seamount, which has been placed in the Middle to Late Jurassic

Upper Triassic reef-limestone blocks of southwestern Japan: New data from a Panthalassan seamount

Norian–Rhaetian reef-limestone outcrops belonging to the Sambosan Accretionary Complex located near and within Inaba Cave, western Shikoku Island (Japan), are described in detail for the first time. This patch-reef complex is inferred to have formed within an atoll-type carbonate system accumulated over a mid-oceanic seamount surrounded by deep-water radiolarian cherts in the Panthalassic Ocean during the Late Triassic. Because most Upper Triassic reef studies are from the former Tethys Ocean, counterparts from the Panthalassic Ocean, such as this study, are fundamental in resolving sedimentological, palaeontological and palaeobiogeographical issues related to Late Triassic reefs. The microfacies, palaeontology and palaeoecology of the Inaba reef limestones were investigated. The reef-boundstone facies is characterised by abundant coralline sponges that, in association with microbial crusts, constitute the main framebuilders. Some phaceloid and/or dendroid corals occur, but these groups are poorly represented, as are algae. Microproblematica and foraminifers exhibit rich associations, acting as secondary reef builders and/or reef dwellers. The surrounding setting comprises biodetrital sponge–coral rudstone and well-preserved megalodont rudstone-floatstone. The sedimentary contact between reef and lagoon facies is observed for the first time within Inaba Cave. Important similarities with the coeval Upper Triassic reefs of the southern classic Peri-Tethys area and especially with the Omani seamounts are recognised, suggesting a more southern-Hemisphere origin for Upper Triassic Japanese reefs than predicted by previous reef studies