HR: 1340h
AN: GP53B-1225 [Abstracts]
TI: Environmental Magnetic Record of the past 220 kyr from Timor Sea
AU: * Oda, H
EM: hirokuni-oda@aist.go.jp
AF: Geologicl Survey of Japan, AIST, Centrl 7, 1-1-1 Higashi, Tsukuba, 305-8567, Japan
AU: Yokoyama, Y
EM: yokoyama@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Sciences, University of Tokyo, SciBldg#1, 7-3-1 Hongo,
Tokyo, 113-0033, Japan
AU: Satoshi, H
EM: satoshi.h@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Sciences, University of Tokyo, SciBldg#1, 7-3-1 Hongo,
Tokyo, 113-0033, Japan
AB:
Environmental magnetic study was conducted on long piston core MD05-2970 from Timor Sea off northwest of
Australia during IMAGES cruise. The site is located at Lat. 9°25f00S and Lon. 130°60f00E with a
water depth of 437 m and the total length of the core is 29.82 m. Sediment consists of calcarious silt to clay with
abundant foraminifera. 14C and oxygen isotope measurements revealed that the core preserved 220 kyr
long record and that the sedimentation rates range from 18 cm/kyr at the top to 10 cm/kyr at the bottom. Intensity
of natural remanent magnetization is reduced two orders of magnitude by diagenetic dissolution of magnetic
minerals below 0.3 mbsf, which resulted in a poor paleomagnetic record. There are some horizons which show
reversed or intermediate polarity directions with higher magnetization intensity and higher coercivity compared
with the adjacent samples. This can be interpreted as CRM acquired in the direction different from the Earthfs
magnetic field. Low temperature magnetometry and thermal demagnetization of composite IRM revealed that
dominant magnetic mineral is magnetite with trace amount of hematite. Zone of dissolution is characterized by
downward decrease in Sratio to 0.7 mbsf and subsequent increase to 2 mbsf. This can be interpreted as an
initial dissolution of fine grained (possibly biogenic) magnetite and subsequent dissolution of hematite below 0.7
mbsf. Median destructive field of ARM is lower (~15 mT) during marine oxygen isotope stage (MIS) 7 compared
with the values above. Grain size parameters also show relatively higher values (finer grained) and
paleomagnetic directions are defined better (smaller MAD values) for MIS 7. These indicate that finer grained
magnetic minerals deposited or remained during MIS 7, which might have been resulted from environmental
change between MIS 7 and later stages.
DE: 1512 Environmental magnetism
DE: 3002 Continental shelf and slope processes (4219)
DE: 3005 Marine magnetics and paleomagnetics (1550)
DE: 4273 Physical and biogeochemical interactions
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting