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International Ocean Discovery Program (IODP) Expedition 382 in the Scotia Sea’s Iceberg Alley recovered among the most continuous and highest resolution stratigraphic records in the Southern Ocean near Antarctica spanning the last 3.3 Myr. Sites drilled in Dove Basin (U1536/U1537) have well-resolved magnetostratigraphy and a strong imprint of orbital forcing in their lithostratigraphy. All magnetic reversals of the last 3.3 Myr are identified, providing a robust age model independent of orbital tuning. During the Pleistocene, alternation of terrigenous versus diatomaceous facies shows power in the eccentricity and obliquity frequencies comparable to the amplitude modulation of benthic δ18O records. This suggests that variations in Dove Basin lithostratigraphy during the Pleistocene reflect a similar history as globally integrated ice volume at these frequencies. However, power in the precession frequencies over the entire ∼3.3 Myr record does not match the amplitude modulation of benthic δ18O records, suggesting Dove Basin contains a unique record at these frequencies. Comparing the position of magnetic reversals relative to local facies changes in Dove Basin and the same magnetic reversals relative to benthic δ18O at North Atlantic IODP Site U1308, we demonstrate Dove Basin facies change at different times than benthic δ18O during intervals between ∼3 and 1 Ma. These differences are consistent with precession phase shifts and suggest climate signals with a Southern Hemisphere summer insolation phase were recorded around Antarctica. If Dove Basin lithology reflects local Antarctic ice volume changes, these signals could represent ice sheet precession-paced variations not captured in benthic δ18O during the 41-kyr world.

So we, in a first part, studied the evolution of the magnetic signal through a section of a, complete and continuous, oceanic crust, from basalts to gabbros. In order to understand how the magnetic properties of rocks can tell us about the conditions of alteration in the oceanic lithosphere, we established a set of magnetic data (Curie temperature, hysteresis parameters, low temperature magnetic measurements) through the entire section of the oceanic crust, drilled at IODP Site 1256D, in the Equatorial Pacific Ocean. These magnetic data are compared to alteration temperatures, determined by thermobarometry (Alt et al., 2010) and show a close relationship between the alteration of the magnetic phases and the alteration temperatures, including the identification of an interval of strong alteration of the titanomagnetites (between 670 and 1028 mbsf (meters below sea floor). In addition, semi quantitative chemical analysis and microscopic observations (optical, SEM and TEM), performed on titanomagnetites, show a change in crystalline structure and a loss of titanium element (Ti4 +) in titanomagnetites to form a secondary phase rich in titanium, in this same interval of strong alteration. In a second part, the acquisition of numerous sea-surface magnetic profiles and a high resolution magnetic profile ("deep tow") through the Cretaceous Normal Superchron (83-120 Ma), allowed us to test the stability of the geomagnetic polarity of the superchron and to highlight the presence of numerous magnetic anomalies: anomalies of short wavelength or "tiny-wiggles” through the entire period and magnetic anomalies of greater length wave, similar to short intervals of reverse polarity. Our measurements show that the behavior of the magnetic field during the superchron is no different from previous periods (chrons M0-M1-M2) and the following magnetic period (chrons 33n and 33R) and the definition of ‘superchron’, long geomagnetic event without inversions, must be questioned; Cette thèse concerne l’étude du message magnétique de la lithosphère océanique. Nous nous sommes, dans un premier temps, intéressés à l’évolution du signal magnétique à travers une section de croûte océanique complète et continue des basaltes jusqu’aux gabbros. Le but était de comprendre comment les propriétés magnétiques des roches peuvent nous renseigner sur les conditions d’altération dans la croûte océanique. Nous avons donc établi un jeu de données magnétiques (température de Curie, paramètres d’hystérésis, mesures magnétiques basse température) sur l’ensemble de la section de croûte océanique forée au site IODP 1256D, dans l’océan Pacifique. Ces données sont confrontées aux températures d’altération, établies par thermo barométrie et mettent en évidence une étroite relation entre l’altération des phases magnétiques et les températures d’altération. De plus, des analyses semi-quantitatives et des observations microscopiques (optique, MEB et MET) mettent en évidence un changement de structure cristalline, associée à une perte de titane, permettant la formation d’une phase secondaire, l’hydroschorlomite, dans un intervalle de forte altération des phases magnétiques (entre 670 et 1028 mbsf (meters below sea floor)). Dans un second temps, l’acquisition de profils d’anomalies magnétiques marines de surface et d’un profil d’anomalies de fond « deep tow » à travers le superchron du Crétacé (entre 83 et 120 Ma) nous a permis de tester la stabilité de polarité du champ géomagnétique durant cette période. Nous mettons en évidence la présence d’anomalies magnétiques : des anomalies de courtes longueurs d’onde ou « tiny-wiggles » à travers l’ensemble du superchron et des anomalies magnétiques de plus grande longueur d’onde, assimilables à de courts intervalles de polarité inverse. Nos mesures montrent que le comportement du champ magnétique durant le superchron n’est pas différent des périodes qui le précèdent (chrons M0-M1-M2) et le suivent (chrons 33n et 33r). La définition de superchron doit être remise en question.

We study a simple magnetohydrodynamical approach in which hydrodynamics and MHD turbulence are coupled in a shell model, with given dynamo constraints in the large scales. We consider the case of a low Prandtl number fluid for which the inertial range of the velocity field is much wider than that of the magnetic field. Random reversals of the magnetic field are observed and it shown that the magnetic field has a nontrivial evolution--linked to the nature of the hydrodynamics turbulence.

Palaeomagnetic studies are e.g. important for demonstrating and quantifying horizontal movement and rotation of pieces of the Earth's crust. The constant movement and recycling of plates, in other words plate tectonics, is an important mechanism for the Earth to lose its heat. It is generally accepted that plate tectonics is the dominant mechanism since 2 billion years ago, but for older periods in the Earth's history, this is still a topic of debate. Plate tectonics cause large-scale horizontal movement, while other mechanisms mainly cause vertical movement. My PhD research has focused on 2.8 to 2.7 billion year old rocks of the Pilbara Craton, Western Australia, and 2.9 to 2.7 billion year old rocks from the Kaapvaal Craton, South Africa. Over 3000 oriented rock cores were taken from geological formations that have formed within ca. 60 million years. Palaeomagnetic tests demonstrate that the magnetization preserved in the rocks is still that from the time of rock formation. This means that the recorded magnetic directions can be translated to a (palaeo)latitude, which is the latitude at which the rocks have formed. The research demonstrates that the latitude of formation of the rocks has changed through time. At ca. 2720 million years ago, the Pilbara Craton changed latitudinal position with a rate of ca. 50 cm per year and shifted some 1600 km in total. This demonstrates that significant horizontal movements occurred as early as 2.7 billion years ago, which supports the arguments of the advocates of the occurrence of plate tectonics in Earth's early history. Additionally, my research has demonstrated that the Earth's magnetic field has been stable since at least 2.8 billion years ago. The character of the ancient field appears to be much like the current field, including the occurrence of geomagnetic reversals, the magnetic intensity, and the amount of secular variation. Some researchers ascribe a stable geomagnetic field to the presence of a solid inner core. If this were true, based on my findings, the Earth's solid inner core would have to be at least 2.8 million years old

Palaeomagnetic studies are e.g. important for demonstrating and quantifying horizontal movement and rotation of pieces of the Earth's crust. The constant movement and recycling of plates, in other words plate tectonics, is an important mechanism for the Earth to lose its heat. It is generally accepted that plate tectonics is the dominant mechanism since 2 billion years ago, but for older periods in the Earth's history, this is still a topic of debate. Plate tectonics cause large-scale horizontal movement, while other mechanisms mainly cause vertical movement. My PhD research has focused on 2.8 to 2.7 billion year old rocks of the Pilbara Craton, Western Australia, and 2.9 to 2.7 billion year old rocks from the Kaapvaal Craton, South Africa. Over 3000 oriented rock cores were taken from geological formations that have formed within ca. 60 million years. Palaeomagnetic tests demonstrate that the magnetization preserved in the rocks is still that from the time of rock formation. This means that the recorded magnetic directions can be translated to a (palaeo)latitude, which is the latitude at which the rocks have formed. The research demonstrates that the latitude of formation of the rocks has changed through time. At ca. 2720 million years ago, the Pilbara Craton changed latitudinal position with a rate of ca. 50 cm per year and shifted some 1600 km in total. This demonstrates that significant horizontal movements occurred as early as 2.7 billion years ago, which supports the arguments of the advocates of the occurrence of plate tectonics in Earth's early history. Additionally, my research has demonstrated that the Earth's magnetic field has been stable since at least 2.8 billion years ago. The character of the ancient field appears to be much like the current field, including the occurrence of geomagnetic reversals, the magnetic intensity, and the amount of secular variation. Some researchers ascribe a stable geomagnetic field to the presence of a solid inner core. If this were true, based on my findings, the Earth's solid inner core would have to be at least 2.8 million years old.

Palaeomagnetic studies are e.g. important for demonstrating and quantifying horizontal movement and rotation of pieces of the Earth's crust. The constant movement and recycling of plates, in other words plate tectonics, is an important mechanism for the Earth to lose its heat. It is generally accepted that plate tectonics is the dominant mechanism since 2 billion years ago, but for older periods in the Earth's history, this is still a topic of debate. Plate tectonics cause large-scale horizontal movement, while other mechanisms mainly cause vertical movement. My PhD research has focused on 2.8 to 2.7 billion year old rocks of the Pilbara Craton, Western Australia, and 2.9 to 2.7 billion year old rocks from the Kaapvaal Craton, South Africa. Over 3000 oriented rock cores were taken from geological formations that have formed within ca. 60 million years. Palaeomagnetic tests demonstrate that the magnetization preserved in the rocks is still that from the time of rock formation. This means that the recorded magnetic directions can be translated to a (palaeo)latitude, which is the latitude at which the rocks have formed. The research demonstrates that the latitude of formation of the rocks has changed through time. At ca. 2720 million years ago, the Pilbara Craton changed latitudinal position with a rate of ca. 50 cm per year and shifted some 1600 km in total. This demonstrates that significant horizontal movements occurred as early as 2.7 billion years ago, which supports the arguments of the advocates of the occurrence of plate tectonics in Earth's early history. Additionally, my research has demonstrated that the Earth's magnetic field has been stable since at least 2.8 billion years ago. The character of the ancient field appears to be much like the current field, including the occurrence of geomagnetic reversals, the magnetic intensity, and the amount of secular variation. Some researchers ascribe a stable geomagnetic field to the presence of a solid inner core. If this were true, based on my findings, the Earth's solid inner core would have to be at least 2.8 million years old

Palaeomagnetic studies are e.g. important for demonstrating and quantifying horizontal movement and rotation of pieces of the Earth's crust. The constant movement and recycling of plates, in other words plate tectonics, is an important mechanism for the Earth to lose its heat. It is generally accepted that plate tectonics is the dominant mechanism since 2 billion years ago, but for older periods in the Earth's history, this is still a topic of debate. Plate tectonics cause large-scale horizontal movement, while other mechanisms mainly cause vertical movement. My PhD research has focused on 2.8 to 2.7 billion year old rocks of the Pilbara Craton, Western Australia, and 2.9 to 2.7 billion year old rocks from the Kaapvaal Craton, South Africa. Over 3000 oriented rock cores were taken from geological formations that have formed within ca. 60 million years. Palaeomagnetic tests demonstrate that the magnetization preserved in the rocks is still that from the time of rock formation. This means that the recorded magnetic directions can be translated to a (palaeo)latitude, which is the latitude at which the rocks have formed. The research demonstrates that the latitude of formation of the rocks has changed through time. At ca. 2720 million years ago, the Pilbara Craton changed latitudinal position with a rate of ca. 50 cm per year and shifted some 1600 km in total. This demonstrates that significant horizontal movements occurred as early as 2.7 billion years ago, which supports the arguments of the advocates of the occurrence of plate tectonics in Earth's early history. Additionally, my research has demonstrated that the Earth's magnetic field has been stable since at least 2.8 billion years ago. The character of the ancient field appears to be much like the current field, including the occurrence of geomagnetic reversals, the magnetic intensity, and the amount of secular variation. Some researchers ascribe a stable geomagnetic field to the presence of a solid inner core. If this were true, based on my findings, the Earth's solid inner core would have to be at least 2.8 million years old.