HR: 0800h
AN: V41F-1526 [Abstracts]
TI: Pb-Pb isochron age and Sr isotope study for the Middle-Upper Permian limestone in the Kamura area in
Kyushu, Japan.
AU: * Fukui, M
EM: mannief@maui.sci.kumamoto-u.ac.jp
AF: Kumamoto university, 2-39-1 Kurokami Kumamoto, Kumamoto, 860-8555
Japan
AU: Kani, T
EM: kani@sci.kumamoto-u.ac.jp
AF: Kumamoto university, 2-39-1 Kurokami Kumamoto, Kumamoto, 860-8555
Japan
AU: Nohda, S
EM: snohda@sci.kumamoto-u.ac.jp
AF: Kumamoto university, 2-39-1 Kurokami Kumamoto, Kumamoto, 860-8555
Japan
AU: Isozaki, Y
EM: isozaki@chianti.c.u-tokyo.ac.jp
AF: Tokyo University, 3-8-1 Komaba Meguro Tokyo, Tokyo, 153-9802
Japan
AB:
We have analyzed Pb and Sr isotopes of the Guadalupian to Lopingian (Permian) limestone in the Kamura area that derived from
paleo-atoll complex on ancient mid-oceanic seamount. The study section is composed of the Guadalupian Iwato Formation and
Lopingian Mitai Formation, spanning across the Guadalupian and Lopingian (G-L) boundary characterized by a major extinction
event immediately before the Permo-Triassic boundary. The present study aims to characterize geochemically the G-L boundary
event in terms of Pb and Sr isotopic systems. 87Sr/86Sr of the study section show a narrow variation within a range
from 0.7070 to 0.7075. According to Veizer et al. (1997), the Middle- Upper Permian limestones recorded a minimal
87Sr/86Sr around the G-L boundary, and a remarkable positive excursion in the Lopingian. The present Sr isotope
study confirmed the same positive excursion started synchronously at the G-L boundary also in mid-oceanic domain. A Pb-Pb
isochron age 243±24Ma (MSWD:12) was measured for the rocks at the G-L boundary in the study section. Because the
limestone in Kamura area primarily deposited on ancient mid-oceanic seamount, it does not contain any zircons or appropriate
minerals for isotopic dating. At present Pb-Pb isochron must be an important clue for numerical discussion of
biostratigraphic process. This age appears slightly younger than those referred in major published time scales, i.e.,
260.4±0.7Ma. (Gradstein et al., 2004).
DE: 1000 GEOCHEMISTRY
DE: 1100 GEOCHRONOLOGY
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005