INCONSISTENT PALEOMAGNETIC RECORDING OF THE BLAKE EVENT IN CHINESE LOESS RELATED TO SEDIMENTARY ENVIRONMENT

Three loess sequences located east of the Liupan mountain region, Chin a, were studied to obtain records of the Blake polarity event. Palaeom agnetic records from the appropriate stratigraphic interval of these t hree sequences, however, record the Blake event poorly in one case and not at all in the other two cases. It is important to understand why these loess sequences miss the Blake event, whereas others record it q uite well. We conclude that regional variations in the sedimentary env ironment over the Chinese loess plateau are responsible for the incons istent recording of the Blake event. The palaeomagnetic records sugges t a threefold subdivision of the Chinese loess plateau into (1) the ce ntral and southern portions of the part of the plateau that lies east of the Liupan Mountains, where the primary record of the Blake event h as been severely smoothed or wiped out by pedogenic processes during p alaeosol (Sl)formation; (2) the northern margin of the loess plateau t o the east of the Liupan Mountains, where frequent, severe dust storms have resulted in discontinuous records with a high probability of mis sing the Blake event; and (3) the region west of the Liupan Mountains, where loess sequences are deposited rapidly and nearly continuously w ith only minor pedogenesis, and are thus capable of recording short ev ents like the Blake.