Doctorate Thesis Defense
Student: Janine Araujo do Carmo
Programme: Geophysics
Title: “The Levantine Geomagnetic Anomaly: insights from paleomagnetic records of stalagmites from Morocco”
Advisor: Prof. Dr. Ricardo Ivan Ferreira da Trindade – IAG/USP
Examining Committee
- Prof. Dr. Ricardo Ivan Ferreira da Trindade – Orientador – IAG/USP
- Profa. Dra. Daniele Cornellio de Paiva Caldeira Brandt - IAG/USP
- Dra. Anita Di Chiara – INGV/Itália - (remote)
- Prof. Dr. Valdir Felipe Novello - University of Tübingen/Alemanha - (remote)
- Prof. Dr. Wilbor Poletti Silva - UFVJM - (remote)
Abstract
The Levant geomagnetic anomaly (LIAA)is an unusual geomagnetic phenomenon that occurred from the beginning of the first millennium BCE. This anomaly was identified through the record of exceptionally high intensities of the geomagnetic field in archaeological artefacts in the Levant region, reaching almost double the current intensity of the Earth's geomagnetic field. Therefore, it has received great attention due to its unique characteristics and implications for our understanding of the Earth's magnetic field. This anomalous regional field seems to extend beyond the Levant region, including the Canary Islands and the Iberian Peninsula, but the spatial extent and possible westward shift of the LIAA are still debated. In this study, we provide a continuous paleomagnetic and paleointensity record of 6,000 years from stalagmites in the Wintimdouine caves in Morocco, covering the time interval of the LIAA. Two main magnetic carriers were identified through alternating field and thermal demagnetization. The low coercivity mineral is partially oxidized magnetite, confirmed by low-temperature experiments. The high coercivity carrier is hematite, defined by the thermal demagnetization protocol. Both magnetic phases record the same direction of the magnetic field. This peculiar mineralogy allowed us to discuss the mechanisms of magnetization acquisition in speleothems using numerical models. Additionally, through magnetic mapping techniques, we found that magnetic stability is related to the quantity and size of magnetic grains present in the samples. The directional paleomagnetic data obtained from the stalagmites remained stable throughout the record. These directions were compared with global and regional magnetic models, showing overlap with the GEOMAGIA50 v3.4 data for the Mediterranean region and other geomagnetic models. Paleointensity estimates were obtained with the pseudo-Thellier method, and the results were calibrated using the Pfm9k.2 model. The intensity variation throughout the record showed no correlation with changes in the mineralogy of the stalagmites. The maximum intensity recorded during the LIAA was 111 ZAm2, below the established anomaly threshold (155 ZAm2). These results indicate that the magnetic anomaly of the LIAA is limited to Eastern Europe, suggesting a more complex structure of the geomagnetic field in that region during this period. Magnetic field models at the core-mantle boundary show different configurations of normal and reverse flux patches during the LIAA, indicating complex dynamics in this region.
Keywords: Geomagnetic anomaly, Levant, LIAA, Paleomagnetism, Speleothems