資料公開

資料公開

タイトル A late Middle Jurassic boreal belemnite Cylindroteuthis from central Japan and its paleobiogeographic implications
カテゴリ 研究論文
概要 A late Middle Jurassic boreal belemnite Cylindroteuthis from central Japan and its paleobiogeographic implications. Memoir of the Fukui Prefectural Dinosaur Museum 9, 1–7.

Abstract: A single rostrum of Cylindroteuthis (Cylindroteuthis) cf. theofilaktovi Nikitin recovered from the Late Bathonian- Early Callovian Kaizara Formation of the Tetori Group in Shimoyama, Kuzuryu area, Central Japan, is described for the first time in East Asia. This belemnite species has been previously known only from the Early Callovian of Central Ukraine in Eastern Europe. Since the family Cylindroteuthididae has been considered as the typical Boreal or northern element in the Jurassic belemnite paleobiogeographic studies, its occurrence in the Inner Zone (Japan Sea side) of Southwest Japan clearly indicates that Cylindroteuthis expanded its distribution to the mid-latitudes of the Northwest Pacific at that time. This expansion possibly corresponds to the Early Callovian spread of boreal cylindroteuthids toward south into Europe in the Boreal-Atlantic seas. The occurrence of Cylindroteuthis from the Kaizara Formation strongly suggests that a cooler current possibly from the Arctic reached the Tetori Basin in the Late Bathonian-Early Callovian time.
タイトル Deposition of serpentine-bearing conglomerate and its implications for Early Cretaceous tectonics in northern Japan
カテゴリ 研究論文
概要 Yoshida, K., Iba, Y., Taki, S., Sugawara, M., Tsugane, T., Hikida, Y., 2010.
Deposition of serpentine-bearing conglomerate and its implications for Early Cretaceous tectonics in northern Japan. Sedimentary Geology 232, 1-14.

Abstract
The discovery of serpentinite-bearing conglomerate including detrital blue amphibole grains in Cretaceous forearc basin sediments in the northern part of Japan supports large tectonic movement in the forearc basin during the Early Cretaceous. Conglomerate and sandstone are intercalated in the Lower Cretaceous offshore mudstone sequence and contain serpentinite clasts, chromian spinels, blue amphiboles, and oolitic grains with chromian spinel nuclei. The conglomerate and sandstones were deposited as a debris flow consisting of an admixture of siliciclastic terrigenous sediments and calcareous biogenic material with serpentinite-derived sediments. The sandstones consist of feldspathic–lithic arenites and wackes, and their composition suggests that most of the terrigenous material was derived from the Cretaceous volcanic terrane and the Jurassic accretionary complex located to the west of the depositional basin. However, the serpentinite body correlated with the provenance of the sediments is not distributed in these terranes. Because the oolitic grains in the matrix of the conglomerate include only angular chromian spinels and serpentine clasts without quartz and feldspar grains, most of the serpentinite-derived sediments are considered to have been supplied primarily from a serpentinite body exposed along the shallow marine environments near the sedimentary basin. Therefore, the serpentine- derived sediments and feldspathic and lithic materials have essentially different sources. Thus, we may infer that the examined sediments are due to large slope failure affecting a relatively wide area of shallow coast involving the place where the serpentine body was emplaced and the place where river-fed terrigenous siliciclastic sediments accumulated.
The stratigraphic range of the serpentinite-derived sediments, which are sporadically distributed in the Cretaceous forearc basin of northern Japan, suggests that the serpentinite-derived material was actively supplied to the forearc basin in Albian times. Recent tectono-stratigraphy of the Late Mesozoic accretionary complex in Japan reveals a strike–slip movement in the subduction zone around northeastern Asia. Large earthquakes affected by active strike–slip motion of the oceanic plate are inferred to be the trigger of tectonic movement, such as large slope failure following serpentine intrusion in the forearc region. Another possibility is that subduction of a large number of seamount on the oceanic plate might also cause a large change in basin morphology, bringing about large slope failure.
タイトル Early Albian Mytiloides (Inoceramidae, Bivalvia) from the Northwest Pacific: a pioneering species for Late Cretaceous inoceramid diversification
カテゴリ 研究論文
概要 Takahashi, A., Iba. Y., 2009.
Early Albian Mytiloides (Inoceramidae, Bivalvia) from the Northwest Pacific: a pioneering species for Late Cretaceous inoceramid diversification.Paleontological Research 13, 199-205.

The inoceramid bivalve Mytiloides ipuanus (Wellman, 1959) from the Lower Albian is reported for the first time in the Northwest Pacific and described in detail. This is the oldest record of a Cretaceous inoceramid in this region. It is possible that the present study documents the origin of the extreme diversification and abundance of inoceramid bivalves in the Late Cretaceous of the Northwest Pacific. The beginning of inoceramid diversification in the Late Cretaceous is seen during the latest Early Cretaceous, which suggests that M. ipuanus is an important species for inferring the causes of the Late Cretaceous flourishing of inoceramids.
タイトル First record of Late Albian canaliculate rudist from northern California and re-assessment of Durania? californica Anderson, 1958.
カテゴリ 研究論文
概要 Iba. Y., Sano, S., Skelton, P.W., Kagi, H., Tanabe, K., 2009,
First record of Late Albian canaliculate rudist from northern California and re-assessment of Durania? californica Anderson, 1958. Cretaceous Research 30, 540-546.

Rudist specimens of Late Albian age from the Upper Chickabally Mudstone Member of the Budden Canyon Formation, Great Valley Sequence, in northern California, are identified as a canaliculate rudist taxon based on shell morphology and mineralogy. Since they are incomplete right valves without cardinal and myophoral parts, their systematic placement is difficult, though their canal characters are similar to those of relatively derived caprinuloidinid rudists such as Texicaprina and Jalpania (Caprinidae) of the Caribbean/Gulf region. Re-assessement of the holotype specimen of Durania? californica from the Upper Albian of northern California reveals that it does not belong to the Radiolitidae, but is also a canaliculate rudist. The distribution of canaliculate rudists, probably caprinuloidinids, in the mid- latitudes of the Northeast Pacific suggest that this area belonged to the Tethyan Realm at that time, and a faunal connection existed between the Northeast Pacific and the Caribbean and/or the Central Pacific at least in the Late Albian.
タイトル An Early Albian Arctic-type ammonite Arcthoplites from Hokkaido, northern Japan, and its paleobiogeographic and paleoclimatological implications
カテゴリ 研究論文
概要 Iba, Y., 2009,
An Early Albian Arctic-type ammonite Arcthoplites from Hokkaido, northern Japan, and its paleobiogeographic and paleoclimatological implications.Journal of Asian Earth Sciences 34 46-50.

An Early Albian Arctic-type ammonite Arcthoplites was discovered from the Kamiji Formation of the Yezo Group in the Nakagawa area, northern Hokkaido, northern Japan. This is the first reliable record of a hoplitid ammonite from Japan and clearly indicates the distribution of an Arctic fauna in the middle lat- itudes of the North Pacific at that time. Synchronously with the appearance of this Arctic-type ammonite, the tropical Tethyan biota (Mesogean taxa) disappeared from Hokkaido and elsewhere in the Northwest Pacific. These biogeographic changes suggest the existence of a ‘‘cooling” episode in the Early Albian North Pacific.
タイトル Paleobiogeography of the pectinid bivalve Neithea, and its pattern of step-wise demise in the Albian Northwest Pacific.
カテゴリ 研究論文
概要 Iba, Y., Sano, S., 2008,
Paleobiogeography of the pectinid bivalve Neithea, and its pattern of step-wise demise in the Albian Northwest Pacific. Palaeogeography, Palaeoclimatology, Palaeoecology 267, 138-146.

The pectinid bivalve genus Neithea is one of the most important indicators for understanding the biogeographic relationships between the Tethyan Realm and North Pacific Province during the Cretaceous Period. Changes in temporal species diversity, endemic/widespread species composition, and origination and demise ratios of Neithea at each Cretaceous stage boundary in the Northwest Pacific were analyzed from a biogeographic perspective. Neithea is continuously present in the Northwest Pacific during the Berriasian to late Albian time interval. Species diversity reached its maximum in the late Aptian, being correlated with the global warming phase. Step-wise demise of Neithea in the Northwest Pacific during the Albian is subdivided into three stages: the late Aptian/early Albian, early Albian/middle-late Albian, and late Albian/ early Cenomanian. Thereafter, Neithea disappeared in the Northwest Pacific and never reappeared. This pattern is the reverse of the Albian diversification of Neithea in the Mediterranean, and also contrary to the Mid-Cretaceous global warming trend. Demise of Neithea in the Northwest Pacific occurred simultaneously with the step-wise demise of Mesogean taxa (e.g., rudists) which strongly supports the idea that the Northwest Pacific gradually became independent from the Tethyan Realm during the Albian. It also suggests a long-term deterioration of the faunal interchange between the North Pacific Province and Tethyan Realm throughout the Late Cretaceous. This biogeographic change was possibly caused by Albian “cooling” and changes in oceanic flow/heat transport in the Northwest Pacific.
タイトル The first Pacific record of the Late Aptian warming event
カテゴリ 研究論文
概要 Takashima, R., Sano, S., Iba, Y., Nishi, H., 2007,
The first Pacific record of the Late Aptian warming event. Journal of Geological Society, London, 164, 333-339.

Carbonate platforms consisting of hermatypic coral, rudists and larger foraminifers formed along the margin of the NE Japanese islands during the mid-Late Aptian. The geographical northern limit of the carbonate platforms extended to c. 368N at that time, which is the highest latitude for coral and/or rudist formation in the North Pacific region. This geographical extension of the carbonate platform in the NW Pacific indicates extreme climatic warmth in the mid-latitudes and strong poleward heat transport systems. Contemporaneous warming has been detected in European and Australian regions, as represented by the migration of Tethyan fauna toward the boreal realm and the positive excursion of ä13C and negative excursion of ä18O in deep-sea carbonates. Our new constraint on the northern limit of ‘reef’ growth reinforces the view that an interval of greenhouse-like warmth punctuated the Late Aptian climate.
タイトル Albian demise of the Tethyan biota in the Pacific: A possible causal link to the formation of the South Atlantic and Western Interior Seaway
カテゴリ 講演資料
概要 Iba, Y., Sano, S., 2007,
Albian demise of the Tethyan biota in the Pacific: A possible causal link to the formation of the South Atlantic and Western Interior Seaway.Geophysical Research Abstract, 9, 03250.
タイトル Mesorbitolina (Cretaceous larger foraminifera) from the Yezo Group in Hokkaido, Japan and its stratigraphic and paleobiogeographic significance
カテゴリ 研究論文
概要 Iba, Y., Sano, S., 2006,
Mesorbitolina (Cretaceous larger foraminifera) from the Yezo Group in Hokkaido, Japan and its stratigraphic and paleobiogeographic significance.Proceedings of the Japan Academy, Series B 82, 216-223.
タイトル Two coleoid jaws from the Upper Cretaceous of Hokkaido, Japan. Journal of Paleontology
カテゴリ 研究論文
概要 Tanabe, K., Hikida, Y., Iba, Y., 2006,
Two coleoid jaws from the Upper Cretaceous of Hokkaido, Japan. Journal of Paleontology, 80, 138-145.

Two isolated cephalopod jaws recovered from the middle Turonian of the Obira area and the Campanian of the Nakagawa area, Hokkaido, Japan, consist of short outer, and large and posteriorly elongated inner ‘‘chitinous’’ lamellae, with a sharply pointed rostrum in the outer lamella. These features are common with the upper jaws of Recent cephalopods. Comparison with the upper jaws of ammonoids and Recent cephalopods indicates that the two Cretaceous upper jaws are attributed to the Coleoidea other than the Octopodida. This assignment is also suggested by the cladistic analysis of the Nakagawa specimen compared with five upper jaw characters on 22 Recent cephalopod species. The Obira specimen differs from the Nakagawa specimen in having a much smaller jaw and a larger jaw angle, but its order-level assignment could not be determined because of imperfect preservation. The Nakagawa specimen shares several common features with the upper jaws of Recent Oegopsina; thus we assigned its higher systematic position to this suborder. Based on the extremely large upper jaw (97 mm maximum length), a new genus and species (Yezoteuthis giganteus) is proposed. This new taxon would have been as large as the modern giant squid Architeuthis, which commonly exceeds more than 5 m in body length. Our study postulates that studies of jaws are important to reconstruct the phylogeny of the Coleoidea.