A preliminary study of thermally enhanced magnetic fabric in the Tertiary sediments from the Qaidam basin, NW China

Abstract

A preliminary observation has been made of the magnetic fabric in 14 specimens of undeformed sediment which exhibit repeatable principal orientation in undemagnetized state as well as after some steps of thermal demagnetization. They were chosen from 2000 specimens of the Tertiary formations of inland fluvio-lacustrine facies in the Qaidam basin, NW China. It was found that no large changes in magnetic fabric occur after stepwise thermal demagnetization up to 300°C, but some significant changes take place after treatment at higher temperature (500° up to 750°C). It is shown that the orientations of the 3 principal axes remain unchanged after each demagnetization step, whereas the differences between the principal values (L′=K1−K2 and F′=K2−K3) are greatly enhanced after high temperatures have been applied. The enhancement of L′ and F′ with no change in principal orientations facilitates the determination of the principal orientations. In our case one may easily measure the thermally enhanced magnetic lineation to estimate the palaeocurrent direction.