CORRELATION OF WIDESPREAD TEPHRA DEPOSITS BASED ON PALEOMAGNETIC DIRECTIONS - LINK BETWEEN A VOLCANIC FIELD AND SEDIMENTARY SEQUENCES IN JAPAN

Magnetic measurements were made of the Yabakei and the Imaichi pyrocla stic-flow deposits of the late Matuyama Chron in central Kyushu and th eir correlative co-ignimbrite ashes: the Pink and the Azuki tephra dep osits in the Kinki district, and the Ku6C and the O7 tephra deposits i n Bose Peninsula. Site mean magnetic directions of the Imaichi deposit are all of reversed polarity with declinations deflected slightly to the east. These directions are consistent with those of the Azuki and the Ku6C ashes. Magnetizations of the Yabakei, the Pink. and the O7 as hes are also consistent with one another. All are characterized by sha llow inclinations (about 30 degrees) of normal polarity with slightly westerly declinations. The identical paleomagnetic directions of these widespread tephra confirm correlations that have been proposed mainly on the basis of glass and mineral chemistry, and provide a tephrochro nological linkage between the source volcanic area and the lacustrine or marine sequences over distances of at least 1000 km. This linkage a llows us to correlate the oxygen isotope record of the Kazusa Group in Bose Peninsula with the alternating marine/non-marine lithology of th e Osaka Group in the Kinki district. Radiometric dates from the Yabake i and the Imaichi pyroclastic-flow deposits are concordant with the as tronomically-calibrated geomagnetic polarity time scale. Copyright (C) 1996 INQUA/Elsevier Science Ltd