A Carboniferous spiriferid brachiopod Purdonella tschernyschewiformis (Ozaki, 1931) was collected from a piece of limestone float, derived from the Upper Carboniferous (Bashkirian) limestone of the Ichinotani Formation in the Mizuboradani Valley, Fukuji area, Hida Gaien Belt, central Japan. Purdonella has mainly been reported from the Upper Carboniferous and Lower Permian of the Boreal region, and P. tschernyschewiformis has been described from the Upper Carboniferous (Bashikirian-Moscovian) of Northeast China (Liaoning) and Northwest China (Xinjiang). Therefore, the occurrence of P. tschernyschewiformis from the Upper Carboniferous limestone of Fukuji indicates that the Hida Gaien region, including the Fukuji area, was part of the continental shelf along the eastern margin of North China (Sino-Korea) during the Late Carboniferous.
Miocene subaqueous volcaniclastic rocks that represent an oceanic island arc belonging to the paleo-Izu-Bonin arc are widely distributed in the Tanzawa area, South Fossa Magna. We identified multiple peperites that formed in a setting of arc volcanism. These peperites developed where intrusive and extrusive mafic magma mingled with unconsolidated subaqueous volcaniclastic and non-volcanic sediments. Peperite is an indicator of in situ subaqueous volcanism within unconsolidated to poorly consolidated sediments. In this paper, we describe four types of peperite (facies A-D) and their locations in paleo-subaqueous volcanoes, and investigate their genesis. Peperite has been commonly classified into blocky and fluidal/globular types. Facies A and B contain both fluidal and blocky juvenile clasts that are not widely dispersed in the host sediments. The host sediments of both types are pumiceous lapilli tuff and volcanic mudstone. Facies C is composed of fluidal juvenile clasts that mingled with tuff breccia. Again, juvenile clasts are not widely dispersed in the host sediments. Facies D is blocky peperite, for which the host sediments are tuff breccia. Juvenile clasts are partly dispersed. It had been assumed that the morphology of peperite (i.e., fluidal vs. blocky) is controlled mainly by the grain size of host sediments; however, this is considered unlikely in the case of the juvenile clasts examined in the present study.
On 14 June 2008, the Iwate-Miyagi inland earthquake (MJ7.2) occurred along a NNE-SSW-trending reverse fault at the boundary between Iwate and Miyagi Prefectures, resulting in heavy damage and loss of human life. After the earthquake, the present author undertook a hearing investigation of pre- and coseismic changes in hot spring activity in and around the epicentral region. Coseismic changes in the discharge rate and color of hot spring water were more commonly observed in the hanging wall of the fault than in the footwall. A preseismic increase in water temperature (of up to 5°C) was recorded at the Matsurube, Shinyu, and Yuhama spas, located near the epicentral region. Increases in discharge rate were recorded at the Kawatabi spa and part of the Narugo spa, which are located at the southern end of the aftershock area. These preseismic changes were clearly observed, yet a tilt meter and GPS unit set very close to the epicenter did not detect any precursor events. These observations provide important information regarding preseismic deformation of the earth’s crust and strategies for earthquake prediction.
We report a new discovery of Lower Triassic (Spathian) chert and siliceous claystone at two localities within the Mino terrane in the Mt. Funabuseyama area, central Japan. The two localities were thought to be underlain by the Hashikadani Formation, which is characterized by upper Lower to uppermost Permian siliceous rocks, representing deep-water facies that formed on the lower slope of an oceanic seamount and the surrounding ocean floor in the Panthalassa Ocean. The Lower Triassic siliceous rocks occur close to upper Middle to upper Upper Permian chert and siliceous claystone. The neighboring Permian and Triassic siliceous rocks show identical facing directions. The close proximity of the exposures, lithologic affinities, and identical facing indicate that the Lower Triassic siliceous rocks rest upon the Upper Permian Hashikadani siliceous rocks and were primarily accumulated as part of a Permo-Triassic siliceous rock succession. The inferred Permo-Triassic siliceous rock succession comprises (1) upper Middle to upper Upper Permian grayish chert with minor black chert in the upper part (ca. 20 m thick; Follicucullus scholasticus-F. ventricosus Zone to Neoalbaillella ornithoformis Zone) ; (2) uppermost Permian gray chert, including alternating black chert, greenish gray siliceous claystone, and black claystone (ca. 6-7 m thick; Neoalbaillella optima Zone) ; and (3) upper Lower Triassic rocks characterized by an upward increase in the proportion of grayish chert along with gray siliceous claystone and black claystone (thickness unknown; Spathian). These new findings indicate that the stratigraphy and age of the Hashikadani Formation should be revised. Our data suggest that the accumulation of Permian siliceous sediments around a Panthalassic mid-oceanic seamount persisted until at least the late Early Triassic, across the Permo-Triassic boundary. The revised Hashikadani Formation has potential as an archive of long-term environmental changes in a mid-oceanic realm of the Panthalassa Ocean.
We re-examined the age and depositional environment of the Ebishima Limestone in the northernmost Tsushima Islands, which had previously been interpreted as Pliocene shallow-marine deposits. Limestone that overlies Miocene siliciclastics consists mainly of well-sorted marine bioclasts and calcite cement. The occurrence of high-angle planar cross-stratification and fossil land snails indicates deposition in a coastal sand-dune environment. The cement was meteoric, as indicated by the low values of carbon and oxygen isotopes (-5.7 and -4.5 per mil PDB, respectively) and the absence of sulfides. Radiocarbon analyses of bulk inorganic carbon yield an age of 41,497±574 cal. BP., which is possibly influenced by the meteoric calcite cement. Therefore, the carbonate dunes were deposited prior to 40 ka. Considering the environment of subsidence at the Tsushima Islands, the coastal dunes represented by the Ebishima Limestone were probably deposited during a period of high sea level in the Middle-Late Pleistocene.