Magnetic polarity ages of the fossil-bearing strata at the Sihetun section, West Liaoning: A preliminary result

Rock-magnetic and palaeomagnetic studies have been carried out on the inter val of famous fossil-bearing sedimentary rocks and its overlying basalts an d underlying basalts at the Sihetun section, West Liaoning Province. Normal polarity was obtained for the sedimentary Interval and the underlying basa lts, while reversed polarity was found In the overlying basalts. Taking acc ount of the new Ar-40/Ar-39 ages (Swisher et al., 1999), we classified the fossil-bearing sedimentary Interval into the Barremian M3n zone (Early Cret aceous age). Several abnormal horizons on magnetic properties, probably cor responding to the tuffs, were observed In the fossil-bearing sedimentary in terval. This implies that the massive bio-extinction may link to dramatic e nvironmental changes that were caused by volcanic eruptions.