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Temporal and spatial characteristics of the paleomagnetic field


This project aims to improve the knowledge on the characteristics of the long-term geomagnetic variations in the past. Two main aspects will be investigated: the secular variation during the Permo-Carboniferous Reversed Superchron (PCRS) and the variations in paleointensity during Early Cretaceous.The secular variation will be treated through the dispersion it causes on the paleomagnetic directions. The dispersion Sb parameter is calculated for a data set, and compared to the so called secular variation curves as a function of latitude. For low latitudes smaller than expected Sb values have already been found. Data will be obtained from sequences of rithmites from the Permo-Carboniferous Itararé Group, Paraná Basin, Brazil magnetized at mid-paleolatitudes. The advantage of working with these cyclic deposited rocks is that they are suitable for cyclostratigraphic analyses, which may provide a good estimate of the elapsed time for the whole sedimentation. This is important as a better evaluation of the Sb parameter may be achieved if various secular variations are adequately sampled.The paleointensity determinations will be performed on the sample Paraná Magmatic Province (Lower Cretaceous Ar/Ar ages of ~134-133 Ma) sample collection already available at IAG/USP. The samples will be selected based on the behavior of the magnetic remanence during demagnetization: a stable single component of magnetization is desirable. The magnetic minerals carrying the remanence must show single domain structure and high coercivity. Samples will represent two distinct areas of the province with ages differing about 1 Ma. We expect to improve the very meager paleointensity data set for the Lower Cretaceous in southern latitudes. (AU)

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