Misaki A.,Kitakyushu Museum of Natural History and Human History |
Ohara M.,Wakayama Prefectural Museum of Natural History
Paleontological Research | Year: 2011
Late Cretaceous heteromorph ammonoids, Ainoceras kamuy and Ainoceras paucicostatum, were discovered for the first time from the Futakawa Formation in the Aridagawa area, Wakayama, southwestern Japan. Other molluscan fossils such as Eupachydiscus sp., Gaudryceras aff. striatum, "Gigantocapulus" transformis, Sphenoceramus nagaoi, Sphenoceramus orientalis and Inoceramus balticus also cooccur with Ainoceras, and together they indicate the lower Campanian Stage. Recently, the middle TuronianSantonian and upper lower CampanianMaastrichtian litho- and biostratigraphy in the Aridagawa area was established. Therefore, the lower Campanian strata in the study area fill the gap between them and supplement the Upper Cretaceous stratigraphy in the Aridagawa area. The results of this study advance the biostratigraphy and correlation of the marine Cretaceous strata in the northwestern Pacific region. © 2011 by the Palaeontological Society of Japan.
Shigeno M.,Kumamoto University |
Mori Y.,Kitakyushu Museum of Natural History and Human History |
Shimada K.,Kyushu University |
Nishiyama T.,Kumamoto University
European Journal of Mineralogy | Year: 2012
Petrography, isocon analysis and singular value decomposition analysis of jadeitites and metasomatic rocks surrounding them from the Nishisonogi metamorphic rocks revealed that the metasomatic rocks developed outside the stability field of jadeite + quartz after jadeitites had been included by a serpentinite mélange in a subduction channel possibly during exhumation. The jadeitites occur at two localities, Tone and Mie in Nagasaki City, from a serpentinite mélange in the Nishisonogi metamorphic rocks. The jadeitite mineral assemblage is jadeite/omphacite + paragonite + phlogopite + albite + clinozoisite/epidote ± muscovite ± analcime. Jadeite core with fine-grained quartz inclusions and the inclusion-free rim is partially replaced by albite. These jadeitites are surrounded by metasomatic zones of albitites and/or a muscovite rock. The mineral assemblage of the albitites is albite + clinozoisite/epidote ± muscovite ± omphacite ± phlogopite ± amphibole ± chlorite, and that of the muscovite rock is muscovite + clinozoisite + chlorite. Because these zones have no high-pressure minerals, they represent products in a P-T regime outside the stability field of jadeite + quartz. Isocon analyses between the jadeitites and the metasomatic zones reveal that K2O, H2O, Sr and Ba were added to jadeitite and SiO2, Na2O and Fe2O3 were removed. REE-rich veinlets emanate from clinozoisite grains, suggesting REE mobility during the fluid-jadeitite interactions. The metasomatic zones developed by interaction between jadeitites and serpentinite via K-, Sr- and Ba-rich fluid, during exhumation from the stability field of jadeite + quartz through that of albite to that of analcime. © 2012 E. Schweizerbart'sche Verlagsbuchhandlung.
Iba Y.,Ruhr University Bochum |
Mutterlose J.,Ruhr University Bochum |
Tanabe K.,University of Tokyo |
Sano S.-I.,Fukui Prefectural Dinosaur Museum |
And 2 more authors.
Geology | Year: 2011
Belemnites, a very successful group of Mesozoic cephalopods, flourished in Cretaceous oceans until the Cretaceous-Paleogene event, when they became globally extinct. Following this event the modern types of cephalopods (squids, cuttlefish, octopus) radiated in the Cenozoic in all oceans. In the North Pacific, however, a turnover from belemnites to the modern types of cephalopods about 35 m.y. before the Cretaceous-Paleogene event documents a more complex evolutionary history of cephalopods than previously thought. Here we show that the modern types of cephalopods originated and prospered throughout the Late Cretaceous in the North Pacific. The mid-Cretaceous cephalopod turnover was caused by cooling and the closure of the Bering Strait, which led to a subsequent faunal isolation of this area. In the Late Cretaceous the former niches of the fast-swimming belemnites were taken over by the modern types of cephalopods, which evolved endemically. The Cretaceous-Paleogene event only allowed the modern types of cephalopods to spread globally and to take over the niches previously held by belemnites. © 2011 Geological Society of America.
Misaki A.,Kitakyushu Museum of Natural History and Human History |
Maeda H.,Kyoto University
Island Arc | Year: 2010
The litho- and biostratigraphy of the mid- to upper-Cretaceous System around the Yagumaike Pond in the Aridagawa area, Wakayama, Southwest Japan, were investigated. Many Middle to Late Albian megafossils were found in the strata of a block bounded by faults. It was also revealed that the Upper Cretaceous System of other blocks ranges from the Middle Turonian to Santonian. The Albian megafossil assemblage contains few benthic organisms, in contrast with the abundance of nektons found (e.g. cephalopods). Sedimentological observations of the mudstone profiles also indicate that scarcely or weakly bioturbated, well-laminated mudstone is dominant among the Albian deposits. These results suggest deposition of the Albian mudstone under a dysaerobic to anoxic environment. It is comparable to the extended oceanic anoxia (OAEs) in mid-Cretaceous time. Albian deposits with similar characteristics are also known to exist in Shikoku, Southwest Japan. A wide sedimentary basin that was directly affected by global environmental events, such as OAEs, seemed to be formed on the Chichibu Belt in the Albian. The Upper Cretaceous strata in the study area are extremely thin, similar to the coeval deposits on the Chichibu Belt in Shikoku. It is suggested that the sedimentation rate in the sedimentary basin on the Chichibu Belt was extremely low during early Late Cretaceous time. © 2010 Blackwell Publishing Asia Pty Ltd.
Komoto N.,Japan National Institute of Agrobiological Science |
Yukuhiro K.,Japan National Institute of Agrobiological Science |
Ueda K.,Kitakyushu Museum of Natural History and Human History |
Tomita S.,Japan National Institute of Agrobiological Science
Molecular Phylogenetics and Evolution | Year: 2011
Phasmids are remarkable mimics of twigs, sticks, and leaves. This extreme adaptation for crypsis can easily lead to the convergent evolution of morphology, making it difficult to establish a taxonomic system of phasmids. Accordingly, there are multiple phylogenetic hypotheses that conflict with each other. Phylogenetic arrangements suggested by molecular data disagree with the morphology-based taxonomy in some instances. We collected 13 phasmatodean species, sequenced their mitochondrial genomes, and recovered their molecular phylogeny. Our analyses did not support the monophyly of Areolatae or Anareolatae, two major infraorders of Phasmatodea. The position of Neohirasea was also quite different from the conventional taxonomic systems, thus challenging the previously assumed monophyly of the subfamily Lonchodinae. The enigmatic taxon, Timema, was shown to be distantly related to other phasmatodeans. © 2010 Elsevier Inc.