High-resolution chronology of the lower Pleistocene Otadai and Umegase Formations of the Kazusa Group, Boso Peninsula, central Japan -Chronostratigraphy of the JNOC TR-3 cores based on oxygen isotope, magnetostratigraphy and calcareous nannofossil-

Tsuji Takashi, Miyata Yuichiro, Okada Makoto, Mita Isao, Nakagawa Hiroshi, Sato Yuri, Nakamizu Masaru

doi:10.5575/geosoc.111.1

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房総半島に分布する下部更新統上総層群大田代層と梅ヶ瀬層の高精度堆積年代―石油公団研究井TR-3コアの酸素同位体比・古地磁気・石灰質ナンノ化石に基づく年代層序―
ボウソウハントウニブンプスルカブコウシントウカズサソウグンオオタダイソウトウメガセソウノコウセイドタイセキネンダイセキユコウダンケンキュウイ TR 3 コアノサンソドウイタイヒコチジキセッカイシツナンノカセキニモトヅクネンダイソウジョ
High-resolution chronology of the lower Pleistocene Otadai and Umegase formations of the Kazusa group, Boso Peninsula, central Japan—Chronostratigraphy of the JNOC TR-3 cores based on oxygen isotope, magnetostratigraphy and calcareous nanofossil

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Detailed oxygen isotope stratigraphy using benthic foraminifers (Bolivina robusta, Bulimina aculeata and Melonis pompilioides) from cored hemipelagic mudstones enables the lower Pleistocene Otadai and Umegase Formations of the Kazusa Group in the Boso Peninsula, central Japan, a turbidite sequence with high depositional rate (average depositional rate of hemipelagic mudstone: 0.9m/k.y.), to be correlated with astronomically tuned pelagic sequences. Remarkable correlation between this isotope curve and those from DSDP Site607 from the North Atlantic, and ODP Site 677 and Site 849 from the tropical Pacific is well demonstrated magnetostratigraphically based on the Jaramillo normal Subchronozone. Numerical age model can be addressed to each oxygen isotope event in the studied sequence applying the age for correlative event in the deep sea sequence. <br> As a result of this study, the ages of events are determined as follows; 1) the first occurrence of Gephyrocapsa parallela: 1038-1041 ka, 2) the marker tephra layers O7, O11, O12 and O16: 1050-1056 ka, 1067-1070 ka, 1073-1078 ka and 1101-1105 ka, respectively, 3) the base of the Jaramillo normal Subchronozone: 1068-1084 ka, and 4) the boundary between the Otadai and Umegase Formations: 1011-1017 ka. The maximum error of the age determination is about 6 k.y.. Average sedimentary rates of turbidite sandstones, hemipelagic mudstones and total sediments are 1.9 m/k.y., 0.9 m/k.y. and 2.8 m/k.y., respectively.<br>

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The Journal of the Geological Society of Japan

The Journal of the Geological Society of Japan 111 (1), 1-20, 2005

The Geological Society of Japan

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