Magnetostratigraphy of the uppermost part of the Pliocene Kuwae Formation (Natsui Section) along the Tainai River,Kitakanbara area,Niigata Prefecture,central Japan

摘要

The magnetostratigraphy for the uppermost part of the Pliocene Kuwae Formation was established along the Tainai River (Natsui Section) in the Niigata Prefecture,Japan.Characteristic components were identified from fourteen sites out of 60 collected sites through the progressive thermal demagnetization (PThD) test,but no stable component was recognized for all pilot specimens through the progressive alternating field demagnetization (PAFD) test.After the tilt-correction for inclined sites,the normally and overlying reversely magnetized sequence was recognized.Combining with biostratigraphic-age constraints,the normal and following reversed polarity sequence can be correlated to the uppermost part of the Gauss (C2An.1n) and the lowest Matuyama (C2r.2r) Chrons.Thus the Matuyama/Gauss boundary (2.581 Ma) is located at the uppermost part of the Natsui Section,which gives an upper limit for the underlying marine sequence of the Pliocene Kuwae Formation.