Παλαιομαγνητικές και μαγνητικές ιδιότητες ιζημάτων και υπόβαθρου σε πυρήνες γεωτρήσεων απο τον βόρειο ελλαδικό χώρο : συμβολή στη διερεύνηση των συνθηκών διαγένεσης

Abstract

The scope of this thesis is the palaeomagnetic investigation and the study of the magnetic properties of core sediments. The study of the magnetic properties of minerals can provide useful information regarding the magnetization process of materials and the magnetic carriers. This knowledge is implemented in geological problems related with tectonic and diagenetic procedures. The first chapter introduces the principles of palaeomagnetism and the most important magnetic properties as, for example, the remanent magnetization, the magnetic susceptibility and the anisotropy of the susceptibility. The second chapter includes a general description of palaeomagnetic devices (magnetometers, demagnetization devices, magnetic susceptibility meter and magnetic anisotropy meter). It also refers to all methodologies which are used, and finally it includes the statistical method for the palaeomagnetic interpretation. Chapter three develops the palaeomagnetic investigation of cores through the international bibliography and a number of applications to the hydrocarbon exploration is discussed. The forth chapter describes the geology of the study area and the previous geological and geophysical studies performed in this area. Finally, a detailed lithostratigraphic description is given for each studied core. In fifth chapter results of the laboratory treatment of the samples are presented (AF and thermal demagnetizations, isothermal remanent magnetization, thermomagnetic analysis). Representative examples of demagnetization, isothermal and thermomagnetic curves are also given. Chapter six contains the interpretation of the obtained results. At the beginning, the various problems that we faced during the procedure are discussed (storage problems, check of the perpendicularity of cores) and a re-orientation of the samples is attempted. Tables of the final directions are presented as well as the results of the study of the rock magnetic properties and thin sections. Finally, the obtained results are compared with the published palaeomagnetic results of the broader area. In the end of the thesis, two appendixes are placed. The first contains tables of the laboratory measurements of the magnetic susceptibility and in the second, representative Zijderveld diagrams are presented. The final results of the thesis can be summarized as follows: ## The studied samples were not orientated because they were derived from cores. For that reason it was impossible to obtain any results about the palaeomagnetic declinations. ## A re-orientation of the magnetic declination is attempted by using the viscous component of the magnetization and the presence of goethite. After the isolation of the viscous component of the samples it is shown that this component is affected by a parasitic component of magnetization, which is created into the storage, where the samples have been placed for more than 20 years. This fact makes the viscous component useless. Goethite is fingered out in some cases and the reorientation of declination (for these specific samples) can take place. As a next step, is examined the accuracy of the inclination values by using the anisotropy method. Samples, which appeared to have inclination values of the Kmin axe of anisotropy less than 75o, are grouped and corrected for their inclination values. ## The magnetic cleaning reveals a different behavior of the samples according to the demagnetization process. During the thermal demagnetization, the majority of the samples show (after 450o-500oC) an anomalous increase of the intensity of magnetization. This increase is due to the formation of new parasitic minerals, which overlap the main component of the magnetization. During AF demagnetization, the behavior of the samples is more regular, thus, it is possible to obtain the primary component of the magnetization. ## Samples from Epanomi cores appeared to be very weakly magnetized so it is impossible to obtain any palaeomagnetic results. Additionally, the study of the thin sections confirms the absence of the magnetic minerals into their structure.