Preliminary tephrochronological study of the Yezo Group (uppermost Albian–basal Campanian) in north Japan

• Published in: Cretaceous research 2019-11, Vol.103, p.104158, Article 104158
• Main Authors: Kuwabara, Sato, Takashima, Reishi, Orihashi, Yuji, Nishi, Hiroshi, Satoh, Takafumi, Hayashi, Keiichi
• Format: Article
• Language: English
• Subjects: Apatite trace element compositions; Cretaceous teprochronology; Northwest pacific; Tephrostratigraphy; Tuff; Yezo group
• ISSN: 0195-6671; 1095-998X
• DOI: 10.1016/j.cretres.2019.06.004

The Yezo Group, exposed in north Japan, is a Cretaceous siliciclastic marine sequence accumulated in the active Asian continental margin of the northwest Pacific. This group is regarded as an important Cretaceous reference sequence in Japan because the detailed age of the group has been determined by numerous studies of bio- and chemostratigraphies, in addition to the radiometric dating of tuffs. Here we preliminarily establish a tephrostratigraphy in the middle–upper parts of the Yezo Group (uppermost Albian–basal Campanian interval) based on the trace-element composition of apatite contained in tuffs to improve the regional stratigraphic correlation of the Cretaceous sequences in the northwest Pacific region. The results demonstrate that the Cl, Mg, Mn, Fe, Y and Ce contents of apatite are useful to discriminate and correlate individual tuffs in the Yezo Group. The correlation of tuffs among distant areas in Hokkaido, Japan revealed three widely traceable (within a distance of several hundreds of kilometers) tuffs intercalated in the lower Cenomanian, Turonian/Coniacian boundary and the Santonian/Campanian boundary. Correlation of the tuffs also solves the local biostratigraphic problem where the datum plane of age-diagnostic fossils is sometimes diachronous across areas, which is attributed to the sporadic occurrences of fossils and/or different depositional settings. •Trace element compositions of apatite are applicable to discriminate and correlate Cretaceous tuffs.•Cretaceous tephrostratigraphy is established based on apatite trace element compositions in the Yezo Group, northwest Pacific region.•Correlations of tuffs were successful among the sections for a distance of several hundred kilometers.•Correlation of tuffs solves the local diachronous biostratigraphic problem.