The relatively small attainable depth max m represents the major limit of the AF SYSTEM methodology and it may restrict the interval of investigation. Nevertheless, we stress the fact that deeper cores obtained by all the other methods for instance the Livingston piston corer are discontinuous, since only cm of sediments are extracted in each coring operation. Therefore, the cores obtained are the sums of these short segments and are severely affected by both presence of re-worked material and duplication of the stratigraphic sequence, due to the absence of a liner protecting the open hole.
These objects can yield the magnetic declination from the last time they were fired or used. In order to perform archaeomagnetic analyses, a number of samples are removed from the feature by encasement in non-magnetic plaster within non-magnetic molds. These samples are marked for true north at the time of collection. Each of the samples is measured in a large cell induction magnetometer, to determine its thermal remanent magnetization. The results are statistically processed and a vector is generated that shows orientation that will yield a location for the North Pole at the time of the last thermal event of the feature.
Data from this feature is compared to the regional secular variation curve in order to determine the best-fit date range for the feature's last firing event. Damiele Giordano Associated Researcher Ph. Marina Devidze Associated Researcher. Application of this methodology for dating of young volcanic products and archaeological samples, its advantages, and limitations are given in a huge literature e. Tanguy et al. The sampling method involves the collection of several big samples, each weighing 0.
In the case of lavas, each block is first detached and then replaced in its original position. Plaster of appropriate fluidity is poured on the block, to support a plate carrying a spherical spirit level, thus making a horizontal surface 6—7 cm in diameter on which the sun shadow is marked for calculation of the geographical north.
In the laboratory, the samples are re-plastered in square molds 12 cm in size. Measurements are performed by means of a large rotating induction magnetometer and an AF demagnetization device for big samples Le Goff, The advantages of this method with respect to traditional core-drilling are the extremely precise orientation of the sample in the field and the possibility of obtaining high-precision data on lavas, welded scoriae, and high temperature-emplaced, non-welded, pyroclastic deposits Hoblitt et al.
