关键词: 长江中游, 风成砂, 亚黏土层, 磁组构, 古气候

Abstract:

In order to establish the magnetic fabric identification marks of aeolian sands in the middle reaches of the Yangtze River and discuss the relationship between the magnetic fabric parameters，paleoclimate and paleoenvironment，the authors carried out the field investigations and found Xingang sanddune section in Jiujiang City，Jiangxi Province，then collected and measured the magnetic susceptibility oriented samples of the section.The results indicate that (1)The magnetic fabric parameter values of the aeolian sands and clayey layer in the Xingang aeolian sands section are quite different.The magnetic susceptibility 〖WTBX〗(κ)〖WTBZ〗 of clayey layer in this section is at peak and its average is 14327(10-6 SI)，while the anisotropy degree of susceptibility 〖WTBX〗(P)〖WTBZ〗 is in valley.However，aeolian sands are contrary to the clayey layer.〖WTBX〗κ〖WTBZ〗 value is in valley and its average is 21.81(10-6 SI) while 〖WTBX〗P〖WTBZ〗 value is at peak as a whole but with quite large fluctuations.(2)The magnetic foliation〖WTBX〗(F)〖WTBZ〗 of most clayey layer samples are bigger than the magnetic lineation 〖WTBX〗(L)〖WTBZ〗 while only some 〖WTBX〗F〖WTBZ〗 of samples in aeolian sands are bigger than 〖WTBX〗L〖WTBZ〗，which indicates that the magnetic foliation development degree of clayey layer is better than the aeolian sands′.(3) Compared to the fluvial and lake sediments (the inclination of long axis of river sediments is generally smaller than 10°，the inclination of short axis is larger than 80°)，the inclination of long axis of aeolian sands′ magnetic susceptibility ellipsoid in Xingang section is larger (22°～24°) and the short axis′s is smaller (45°～51°).(4)The average value (0668 8) of aeolian sands′ magnetic matrix particle size 〖WTBX〗(q)〖WTBZ〗 is bigger than the 〖WTBX〗q〖WTBZ〗 value (024) of the fluvial sediments in the middle reaches of the Yangtze River，which reveals that the sorting of aeolian sands is worse than fluvial sediments.These characteristics can act as the magnetic fabric identification marks of alluvial and aeolian deposits in the middle reaches of the Yangtze River.(5)There are 9 clayey layers that have different development degree in the 3.25～26.2 m strata section，which points out that the climate in this period not only transferred 9 times from drycold to warmwet but also had different intensities.〖

Key words: the middle reaches of the Yangtze River, aeolian sand, clayey layer, magnetic fabric, paleoclimate