Diatom zonal key species and geologic ages of the Miocene Morozaki, Iwamura and Tomikusa Groups in the First Setouchi Province, central Japan.

知佳, 伊藤; 俊明, 入月; 雅夫, 岩井

doi:10.5575/geosoc.105.152

Cited by 27 publications

(6 citation statements)

References 6 publications

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“…The marine mammal Paleoparadoxia was described from the upper Kujiri facies near site M1 (Ijiri and Kamei 1961;Inuzuka 1984). BKSA95: Magnetostratigraphy of Berggren et al (1995), PFZ: Planktonic Foraminiferal Zones of Blow (1969), DZ: Diatom Zones of Barron and Gladenkov (1995) Ito et al (1999) and Ujihara et al (1999). able from site M5 to site M10. At the boundary of the two members, the lithofacies changes rapidly from tuffaceous sandstone to tuffaceous siltstone.…”

Section: Methodsmentioning

confidence: 99%

“…Gladenkov (1998) reported that the Yamanouchi Member of the Akeyo Formation is correlative with the Crucidenticula sawamurae Diatom Zone of Barron and Gladenkov (1995) (18.4 to 16.9 Ma; Yanagisawa and Akiba 1998). Ito et al (1999) investigated diatom floras from the Toyama Formation in the Iwamura Basin and other contemporary deposits in eastern Setouchi Province. They discovered key zonal diatom species assigned to the same diatom zone as represented in the Yamanouchi Member of the Akeyo Formation (Mizunami Group).…”

Section: Depositional Age Of Study Areasmentioning

confidence: 99%

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Paleoecology and taxonomy of Early Miocene Ostracoda and paleoenvironments of the eastern Setouchi Province, central Japan

Irizuki

2004

Micropaleontology

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Seventy-nine fossil ostracode species were identified in 40 of 80 samples from 15 sites of the Lower Miocene Mizunami and Iwamura Groups (ca. 18 Ma), eastern Setouchi Province, central Japan. Six ostracode associations and seven biofacies were discriminated, mainly on the basis of R-mode and Q-mode cluster analyses, respectively. Species that lived in the innermost part of enclosed brackish bay habitats became extinct and their Recent related species are absent. Most Miocene species of the genera Schizocythere, Cornucoquimba and Loxoconcha inhabited similar environments to related living species. They lived in nearshore sand and silty sand bottoms with Zostera beds under the influence of subtropical-water currents as inferred from fossil molluscan assemblages. Pseudoaurila species, which are extinct, are estimated to have been dominant on seagrass or algae during the late Early to early Middle Miocene, but after that, they were replaced by diverse Aurila and Loxoconcha species. Species of the genera Palmenella, Kotoracythere, Acanthocythereis, Robertsonites, Celtia, Elofsonella and Laperousecythere are nearly identical morphologically to cryophilic or circumpolar species living in cold water masses of northern high-latitude seas or lower sublittoral to bathyal zones in the Sea of Japan. They occur in Miocene sediments, however, in association with subtropical to mild-temperate, upper to middle sublittoral molluscan species. Ancestors of Recent cold-water species have thus inhabited Japan since at least the Early Miocene. They expanded their habitats southward according with global cooling in chron C5Dr interval (late Early Miocene) correlated with the the oxygen isotope maximum period (the base of the Zone Mi 1b; ca. 18 Ma). Eleven new species are described. This study presents the earliest Miocene record of ostracodes in and around Japan and contributes to inferences on the origin, phylogeny and speciation of Recent ostracodes living in high-latitude seas in the Northern Hemisphere. Toshiaki Irizuki et al.: Early Miocene Ostracoda and paleoenvironments of the eastern Setouchi Province, central Japan TEXT-FIGURE 1 Map showing the study areas. Shaded areas show the distribution of late Early to early Middle Miocene deposits. Black areas show the regions studied.

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Section: Methodsmentioning

confidence: 99%

Section: Depositional Age Of Study Areasmentioning

confidence: 99%

Paleoecology and taxonomy of Early Miocene Ostracoda and paleoenvironments of the eastern Setouchi Province, central Japan

Irizuki

2004

Micropaleontology

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“…This leads us to infer that the Japan Sea was connected with the Pacific by deep-sea pathways at least in the latest early-earliest middle Miocene. Moreover, diatom study has revealed that the age of the Morozaki Group on the Pacific side can be assigned to NPD2B of Akiba (1986) (Gladenkov, 1998;Ito et al, 1999). Thus, the deep-water species migrated from the Pacific side into the Japan Sea borderland just after the formation of a deep-sea basin in the latest early-earliest middle Miocene.…”

Section: Biogeographical Significancementioning

confidence: 99%

Latest early-earliest middle Miocene deep-sea molluscs in the Japan Sea borderland – the warm-water Higashibessho fauna in Toyama Prefecture, central Japan

Amano

Hamuro²,

Hamuro³

2004

Paleontological Research

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“…In the review by Otofuji et al (1985a), some of the Miocene sedimentary formations showing an eastward-deflected direction were estimated to be of middle Miocene age (16-15 Ma). However, recent radiometric, biostratigraphic, and magnetostratigraphic studies indicate that the actual age is 18-17 Ma (Ito et al 1999;Watanabe et al 1999;Hoshi et al 2000aHoshi et al , 2006Hoshi and Saida 2009;Sako and Hoshi 2014). In addition, Hoshi (2002) and raised the possibility that the eastward-deflected direction of middle Miocene volcanic rocks dated at 15-14 Ma records an extraordinary paleofield, such as may have occurred during a geomagnetic excursion or polarity transition and does not therefore represent a time-averaged direction.…”

Section: Paleomagnetic Directions and Tectonic Implicationsmentioning

confidence: 99%

Timing of clockwise rotation of Southwest Japan: constraints from new middle Miocene paleomagnetic results

et al. 2015

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Southwest Japan rotated clockwise during the late stage of the opening of the Japan Sea, although the exact timing of the rotation is controversial. A recent biostratigraphic study has revealed that the Miocene Oidawara Formation in eastern Southwest Japan was deposited just before 15 Ma; consequently, its paleomagnetic direction may help constrain the timing of rotation. For this purpose, we collected fine felsic tuffs and siltstones at 71 stratigraphic sites (horizons) in the Oidawara Formation. An analysis of alternating field and thermal demagnetization results yielded characteristic remanent magnetization (ChRM) directions for 177 samples. Approximately 80 % (142) of the samples exhibit reverse polarity ChRM directions that are thought to be paleofield directions of reverse polarity Chron C5Br. Normal polarity ChRM directions in 35 samples include primary paleofield records as well as records of secondary magnetization. The data suggest that a short normal polarity interval (microchron or cryptochron) at~15.8 Ma is present within the dominantly reverse polarity interval of Chron C5Br. Reliable site-mean directions for 19 sites yield a tilt-corrected formation-mean direction of D = 10.5°, I = 41.1°, α 95 = 7.0°, and k = 23.9, indicating virtually no rotation with respect to a reference paleomagnetic direction for the Asian continent. A rotation versus age plot for Southwest Japan indicates that the clockwise rotation started after 17.5 Ma and ceased largely before 15.8 Ma, yielding a rotation rate of~23°/Myr.

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Diatom zonal key species and geologic ages of the Miocene Morozaki, Iwamura and Tomikusa Groups in the First Setouchi Province, central Japan.

Cited by 27 publications

References 6 publications

Paleoecology and taxonomy of Early Miocene Ostracoda and paleoenvironments of the eastern Setouchi Province, central Japan

Paleoecology and taxonomy of Early Miocene Ostracoda and paleoenvironments of the eastern Setouchi Province, central Japan

Latest early-earliest middle Miocene deep-sea molluscs in the Japan Sea borderland – the warm-water Higashibessho fauna in Toyama Prefecture, central Japan

Timing of clockwise rotation of Southwest Japan: constraints from new middle Miocene paleomagnetic results

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