Paleomagnetism and Paleoenvironmental Magnetism Studied on BDP-98 Sedimentary Cores from Lake Baikal

Summary

Paleomagnetic and rock-magnetic studies were conducted on two sedimentary cores, BDP-98-1 (200 m in length) and BDP-98-2 (ca. 410 m in length from 191 m to 600 m deep), drilled at the Academician Ridge of Lake Baikal. The magnetic inclination records assigned to the geomagnetic polarity time scale (GPTS) indicate that BDP-98-1 attained an age of 5 Ma. For BDP-98-2, owing to the long reversed interval between 290 m and 350 m, it became difficult to find a correlation to GPTS. A correlation tested in this study suggests that the basal age is over 11 Ma at 600 m deep. The average sedimentation rate for BDP-98-1 and the upper 50 m of BDP-98-2 is estimated as 4.1cm/kyr. The sedimentation over the long reversed interval is as high as 29.3cm/kyr, and below this depth, to 600 m, the rate is about 4.5cm/kyr.

The magnetic properties of the BDP-98-1 sediment were also studied. The rock-magnetic parameter of anhysteretic remanent magnetization (ARM) susceptibility/susceptibility decreases after about 3 Ma, while the susceptibihty increases. Spectral analyses on the susceptibility show that the shift in spectral character from a 100-kyr eccentricity cycle to a 41-kyr obliquity cycle occurred at ca. 3 Ma. These characteristic changes may be correlated with the change in the paleoenvironment in the Baikal region caused by the intensification of northern hemisphere glaciation. After 1.2 Ma, the susceptibihty variation increases in amplitude, which may be correlated with the elevation of the Himalayas and Tibetan Plateau, which reached above the snow line at 1.2 Ma.