The Chinese loess in Xifeng, II. A study of anisotropy of magnetic susceptibility of loess from Xifeng

Abstract

Measurements of specimens from the loess profile of Xifeng, Gansu province, China, all show original magnetic fabric for sediments, i.e. nearly horizontal foliation and the commonly oblate magnitude ellipsoid. The degree of anisotropy always shows a strong correlation with the foliation F rather than with the lineation L. Specimens from wind-blown loess, redeposited water-lain loess and red clay show their own distribution areas respectively in a diagram of L versus F. Magnetic fabric provides evidence for the suggestion that the red clay, like the overlying wind-blown loess, is aeolian in origin, the data points from the red clay all falling within the distribution area of the wind-blown loess data points. The magnetic fabric measured from present-day palaeosols may still represent the features of the parent loess although the orientation of fabric has been slightly weakened through pedogenesis, as shown in the present study.

Early and middle Matuyama geomagnetic excursions recorded in the Chinese loess-paleosol sediments

“…Figure 9(i) shows the depth plots of the degree of anisotropy (P ≡ K1/K3). Liu et al (1988b) found that re-deposited loess has a higher degree of anisotropy (1.032 ≤ P ≡ K max /K min ≤ 1.064) than original wind-blown deposits (1.002 ≤ P ≤ 1.034). Our results reveal that all specimens have P values significantly less than 1.032, showing original deposits.…”

Aeolian origin and palaeoclimatic implications of the ?red clay? (north China) as evidenced by grain-size distribution

“…This deposit has been investigated for over 70 yr (Anderson, 1923), with most attention being given to stratigraphy, fossil fauna and petrology. However, the origin of the 'Red Clay' remains controversial (Zhao, 1987;Kukla, 1987;Liu et al, 1988;Cao et al, 1994;Zhang and Xue, 1995;Sun et al, Figure 1 Sampling sites of the 'Red Clay', loess -palaeosol, lacustrine and fluvial sediments in north China. Black squares are sampling sites.…”

Rock Magnetic Properties and Palaeoclimate of Chinese Loess.

“…The degrees of alignment of magnetic dust grains deposited in different mediums are different, and such alignment differences can be investigated by anisotropy of magnetic susceptibility (AMS) or magnetic fabric measurement (Liu et al, 1988b(Liu et al, , 1990b. The silty layers L9 and L 15 with almost no weathering characteristics, were chosen to be typical of loess; The 5th palaeosol S5, where susceptibility and the pedogenesis are both at a maximum in the profile, was chosen as a typical palaeosol.…”