A PRELIMINARY MAGNETOSTRATIGRAPHIC STUDY OF THE BEIHANZHAI LOESS SECTION
Liu Dongsheng An Zhisheng
The stratigraphic sequence of the Beihanzhai loess section at Luochuan is similar to that of the typical Heimugou loess section of Pleistocene age. Loess samples were collected from the major output of the Beihanzhai section for determining the B/M boundary.The NRM of specimens was measured on a cryogenic fluxgate magnetometer in the Pa-leomagnetic Lab. of A.N.U. The stepwise TH and AF demagnetization of the specimens were carried out, respectively. The analysis of orthogonal diagrams constructed on the basis of demagnetization data indicates that TH demagnetization is better than AF demagnetization to obtain the characteristic NRM components. The data on inclination, declination and latitude of V.G.P. show that the B/M boundary approximately lies between loess bed L8 and palaeosol bed S7, and the Jalamillo subchron is at least recorded at the portion from S10 to L10.By comparing the magnetic data from the Beihanzhai loess section with those from the Heimugou loess section reported in 1977, it is obvious that the Olduvia subchron is recorded at the second palaeosol complex in the middle part of Early Pleistocene loess at Wu-cheng. Evidence shows that the Luochuan loess began depositing in Early Matuyama at about 2.3-2.4 m.y. ago.