Diatom biostratigraphy of the middle Miocene marine sequence of the Ayukawa section in the Fujioka area, Gunma Prefecture, central Japan, with special reference to the correlation between the diatom biohorizon D55 and an 40Ar-39Ar age

Author(s): Suto, Itsuki; Takahashi, Masaki; Yanagisawa, Yukio
Author Affiliation(s): Primary:
University of Tsukuba, Institute of Geoscience, Ibaraki, Japan
Geological Survey of Japan, Japan
Volume Title: Chishitsugaku Zasshi Journal of the Geological Society of Japan
Source: Chishitsugaku Zasshi = Journal of the Geological Society of Japan, 108(11), p.746-760. Publisher: Nippon Chishitsugaku Gakkai, Tokyo, Japan. ISSN: 0016-7630 CODEN: CHTZA5
Note: In Japanese with English summary. 55 refs.; illus., incl. sects., 1 table, geol. sketch maps
Summary: Marine diatoms were examined for the 245 meter-thick Middle Miocene sequence (the Haraichi and Itahana Formations) exposed along the Ayukawa River in the Fujioka area. Gunma Prefecture, central Japan. The sequence is correlative with the Denticulopsis praedimorpha Zone (NPD 5B) and the Thalassiosira yabei Zone (NPD 5C) of Yanagisawa and Akiba (1998). The last common occurrence (LCO) of D. praedimorpha (D55), a biohorizon which defines the NPD 5B/5C boundary, is recognized between 1 and 3 meters above the Baba Tuff Bed in the upper Haraichi Formation. The numerical age of the biohorizon D55 can be regarded as same as the 40Ar-39Ar age of the Baba Tuff Bed (11.28±0.08 Ma), because of a high accumulation rate (ca. 35-39 cm/1,000 yr.). This age is about 0.2 Ma younger than the magnetostratigraphically estimated age for D55 at ODP Site 887 and 884 in the high latitude North Pacific. The direct relationship between the D55 biohorizon with high-resolution radiometric age should give important constraints on refining a global geologic time scale for the Miocene interval.
Year of Publication: 2002
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Algae; Ar/Ar; Asia; Ayukawa Japan; Baba Tuff; Cenozoic; Central Japan; Correlation; Denticulopsis; Diatoms; Far East; Fujioka Japan; Gumma Japan; Haraichi Formation; Honshu; Japan; Koizumia; Leg 145; Microfossils; Middle Miocene; Miocene; Neogene; Nitzschia; ODP Site 887; Ocean Drilling Program; Plantae; Sequence stratigraphy; Tertiary; Thalassiosira; Tomioka Group
Coordinates: N350000 N351000 E1390300 E1390200
Record ID: 2004047317
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