Environmental Magnetism Research on the Magnetic Effects by Different Drying Processes to Tidal Flat Sediments

Key words: 
• environmentai magnetism /
• oven-drying /
• air-drying /
• iyophiiization /
• magnetic effects

Abstract: Magnetic effects in sediment of Yangtze River estuary tidal flat is studied in laboratory by different drying treatments. Three treatments, including oven-drying, air-drying and lyophilization are applied in the core（total length：21 cm, sampled from high tidal-flat）and tidal flat surface（0 ~ 5 cm）sediment samples（high, middle and low tidal flat）, and then the magnetic properties, water and total organic matter contents has been measured systematically. Results show that oven-drying, air-drying and lyophilization treatment processes de affect the most of magnetic minerals . The SIRM—χ crossplot of the core samples shows linearly significant correlation, the upper part sub-samples of the core have high value of SIRM andχ , the bottom part have low value of SIRM andχ. According to F_300mT, "S_{- 20mT} and"S_{- 100mT}, ferrimagnetic minerals dominate the magnetic properties in the Yangtze River estuary tidal flat sediments. The particlesize of whole core become finer from bottom to upper sub-samples. The differences of the three samples treatments are insignificant, according to type of magnetic minerals, consistence of dominated magnetic minerals, concentration of magnetic minerals and particle size, in the whole core sub-samples and its variations. The oven-drying is still effective sample treatment, and the lyophilization is the best sample drying method of the three. Under the general condition, the effect of oven-drying and air-drying samples to magnetic change, compare with lyophilization, is so little that it does not result in magnetic parameters wrong interpretation. However, for clay samples, airdrying samples will cause much difference in the value of magnetic parameters, thus its air-drying water contents after magnetic measurement should be avoided or calibrated. Another result shows that organic matter contents are positively correlated with main magnetic parameters. This study has some limits because of only test for the tidal flat sediment samples, so if do some further deduction on this topic, more studies on various sediments and soiis sampies are necessary.