This thesis provides a detailed study of environmental magnetism in a speleothem. It focuses on a stalagmite from Pau DAlho cave (15°1220S, 56°4841W) located in Rosário dOeste, Mato Grosso State, Brazil. This speleothem grew during the past 1355 years, with average growth rate of ~168 mm/ka and encompasses two key events in the South American Summer Monsoon (SASM), the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA), major dry and wet, respectively. The rock magnetic experiments conducted, include isothermal remanent magnetization (IRM) and anhysteretic remanent magnetization (ARM) acquisition curves, thermal demagnetization of three-axis IRM acquisition, hysteresis loops, first order reversal curves (FORC) and low-temperature SQUID magnetometry experiments. The main magnetic remanence carriers in the stalagmite are magnetite and goethite, with a nearly constant relative proportion. Magnetite has remanent coercivities between 14-17 mT, and its magnetic properties are similar to those produced by pedogenic processes. Magnetic remanence is broadly correlated with carbon and oxygen isotope data throughout most of the speleothem, suggesting that precipitation and soil dynamics above the cave exert a strong control on the input of magnetic minerals into the Pau dAlho cave system. Dry periods like the MCA are associated with less stable soils that result in higher mineral fluxes carried into karst systems via groundwater, while conversely, colder and wetter periods like the LIA are associated with soils topped by denser vegetation that are more capable of retaining micrometer-scale pedogenic minerals, and thus reduce mineral fluxes into karst environments. / Esta tese fornece um estudo detalhado do magnetismo ambiental de espeleotemas. Este estudo é feito em uma estalagmite da caverna Pau D\'Alho (15 ° 12\'20 \"S, 56 ° 48\'41\" W), localizado em Rosário d\'Oeste, Mato Grosso, Brasil. Este espeleotema cresceu durante os últimos 1355 anos, com taxa média de crescimento de ~ 168 mm/ka e engloba dois eventos climáticos do Sistema de Monção Sul-americano (SMSA), a Anomalia Climática do Medieval (ACM) e a Pequena Idade do Gelo (PIG), eventos secos e molhados, respectivamente. Os experimentos de magnetismo de rocha incluem: magnetização remanecte isotermal (MRI), ciclos de histerese, magnetização remanente anisterética (MRA), desmagnetização térmica em três eixos, first order reversal curves (FORC) e experimentos de baixa temperatura. Os principais portadore magnéticos na estalagmite são magnetita e goethita, com uma proporção relativa quase constante. A magnetita tem coercividades entre 14-17 mT, e as suas propriedades magnéticas são semelhantes às produzidas por processos pedogênicos. As remanências magnéticas são amplamente correlacionadas com dados de isótopos de carbono e oxigênio durante o registro, sugerindo que a precipitação e a dinâmica do solo acima da caverna exerce um forte controle na entrada de minerais magnéticos no sistema de cavernas Pau d\'Alho. Períodos secos como o ACM estão associados a solos menos estáveis, que resultam em maiores fluxos de minerais detríticos carreados para o sistema de cavernas, ao passo que, inversamente, os períodos frios e chuvosos como a LIA estão associados a solos cobertos pela vegetação mais densa que são mais capazes de reter minerais pedogênicos de escala micrométrica, e, assim, diminuir os fluxos de minerais detríticos para o sistema de cavernas.

If a rock is to retain a geologically meaningful magnetic record of its history, it is essential that it contains magnetic minerals which are capable of carrying stable magnetic remanence. Of the natural occurring magnetic minerals, magnetite is the most important because of its abundance and strong magnetic signature. The stability, i.e., the resistance to demagnetisation or reorientation, of magnetic remanence is related to grain size; in smaller grains the magnetic moments align to have single domain (SD) structures, in larger grains complex magnetic patterns are formed (multidomain (MD)). “Classical” domain theory predicts that SD remanence is stable, whilst MD remanence is not. However experimental evidence has shown that both SD and MD grains can have stable remanences. In this thesis the origin of stable MD remanence is examined. There are two opposing theories; one suggests that the stability is due to independent SD-like structures, the other postulates that the stability is due to metastable MD structure. A series of experiments were designed to examine the stability using a selection of characterised synthetic and natural samples. Low-stress hydrothermal recrystallised samples where grown for this study. For the first time, the stability of thermoremanence induced in hydrothermal crystals to cooling was examined. The results agree with previous observations for crushed and natural magnetites, and support kinematic models. The behaviour of SIRM and thermoremanences in MD magnetite to low-temperature cooling to below the crystallographic Verwey transition at 120-124 K (T_v) and the cubic magnetocrystalline anisotropy isotropic point (T_k) at 130 K was investigated. On cooling through T_v, SIRM was observed to decrease and demagnetise, however thermoremanence was found to display a large increase in the magnetisation at T_v, which was partially re- versible on warming. The size of the anomaly is shown to be dependent on the temperature at which the thermoremanence is acquired, internal stress and grain size. The anomaly is attributed to the large increase in the magnetocrystalline anisotropy which occurs on cooling through T_v . It is postulated that low-temperature cycling demagnetisation is due to kinematic processes which occur on cooling between room temperature and T_k. Characterisation of low-temperature treated remanence and partially alternating field demagnetised remanence, suggest that the stable remanence is multidomain. Low-temperature cooling of remanence in single sub-micron crystals was simulated using micromagnetic models. The models predict the observed anomaly for thermoremanence on cooling through T_v, and also the relative behaviour of SIRM and thermoremanence. The single domain threshold was calculated for the low-temperature phase of magnetite, and was found to be 0.14 microns, compared to 0.07 microns at room temperature.

The Stillwater Complex J-M reef, the only economic platinum deposit in the United States, consists of a 0.5 to 4 m-thick stratiform horizon of PGE-rich sulfides in an Archean layered mafic intrusion. The origin of this reef has been studied extensively using geochemical methods, yet remains highly debated. Dynamic magmatic processes have been virtually ignored in these geochemical studies. Magnetic methods provide a proven inexpensive approach to offer rapid, and reproducible results to deliver insight into these dynamic processes. I propose to investigate the variations of magnetic properties of layered rocks of the Stillwater Complex in the stratigraphic vicinity of the J-M reef. In this study, detailed magnetic methods were performed on a 115 ft core containing the J-M reef and adjacent rocks. A previously undiscovered cyclicity of magnetic susceptibility was found in the hanging wall and J-M reef section. Further tests were performed to determine the origin of the magnetic cycles. The footwall section lacked the magnetic properties seen in the J-M reef and hanging wall rocks. Both anisotropy of magnetic susceptibility, and high field magnetic data was collected at a high resolution interval along the core. It is possible that the results of this study can be used to constrain the origin of the ore body.

This thesis provides a detailed study of environmental magnetism in a speleothem. It focuses on a stalagmite from Pau DAlho cave (15°1220S, 56°4841W) located in Rosário dOeste, Mato Grosso State, Brazil. This speleothem grew during the past 1355 years, with average growth rate of ~168 mm/ka and encompasses two key events in the South American Summer Monsoon (SASM), the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA), major dry and wet, respectively. The rock magnetic experiments conducted, include isothermal remanent magnetization (IRM) and anhysteretic remanent magnetization (ARM) acquisition curves, thermal demagnetization of three-axis IRM acquisition, hysteresis loops, first order reversal curves (FORC) and low-temperature SQUID magnetometry experiments. The main magnetic remanence carriers in the stalagmite are magnetite and goethite, with a nearly constant relative proportion. Magnetite has remanent coercivities between 14-17 mT, and its magnetic properties are similar to those produced by pedogenic processes. Magnetic remanence is broadly correlated with carbon and oxygen isotope data throughout most of the speleothem, suggesting that precipitation and soil dynamics above the cave exert a strong control on the input of magnetic minerals into the Pau dAlho cave system. Dry periods like the MCA are associated with less stable soils that result in higher mineral fluxes carried into karst systems via groundwater, while conversely, colder and wetter periods like the LIA are associated with soils topped by denser vegetation that are more capable of retaining micrometer-scale pedogenic minerals, and thus reduce mineral fluxes into karst environments. / Esta tese fornece um estudo detalhado do magnetismo ambiental de espeleotemas. Este estudo é feito em uma estalagmite da caverna Pau D\'Alho (15 ° 12\'20 \"S, 56 ° 48\'41\" W), localizado em Rosário d\'Oeste, Mato Grosso, Brasil. Este espeleotema cresceu durante os últimos 1355 anos, com taxa média de crescimento de ~ 168 mm/ka e engloba dois eventos climáticos do Sistema de Monção Sul-americano (SMSA), a Anomalia Climática do Medieval (ACM) e a Pequena Idade do Gelo (PIG), eventos secos e molhados, respectivamente. Os experimentos de magnetismo de rocha incluem: magnetização remanecte isotermal (MRI), ciclos de histerese, magnetização remanente anisterética (MRA), desmagnetização térmica em três eixos, first order reversal curves (FORC) e experimentos de baixa temperatura. Os principais portadore magnéticos na estalagmite são magnetita e goethita, com uma proporção relativa quase constante. A magnetita tem coercividades entre 14-17 mT, e as suas propriedades magnéticas são semelhantes às produzidas por processos pedogênicos. As remanências magnéticas são amplamente correlacionadas com dados de isótopos de carbono e oxigênio durante o registro, sugerindo que a precipitação e a dinâmica do solo acima da caverna exerce um forte controle na entrada de minerais magnéticos no sistema de cavernas Pau d\'Alho. Períodos secos como o ACM estão associados a solos menos estáveis, que resultam em maiores fluxos de minerais detríticos carreados para o sistema de cavernas, ao passo que, inversamente, os períodos frios e chuvosos como a LIA estão associados a solos cobertos pela vegetação mais densa que são mais capazes de reter minerais pedogênicos de escala micrométrica, e, assim, diminuir os fluxos de minerais detríticos para o sistema de cavernas.

Il est établi que la Lune a eu par le passé un champ généré par une dynamo interne. Cependant, les mécanismes à l’origine et permettant le maintien de la dynamo sont encore mal connus. La durée de ce champ magnétique est encore débattue. Mon travail de thèse a consisté tout d’abord à une caractérisation magnétique (aimantation naturelle et susceptibilité magnétique) d’une grande partie de la collection Apollo avec l’étude de 161 roches. J'ai utilisé le rapport aimantation naturelle sur susceptibilité comme indicateur grossier de la paléointensité. Ces résultats, cohérents avec les deux grandes époques du champ magnétique lunaire (époque de fort champ avant ~3.5 Ga et champ faible ensuite), ont permis de sélectionner des échantillons pour des analyses paléomagnétiques détaillées en laboratoire qui ont constitué la suite de mon travail. J’ai ainsi étudié l’aimantation naturelle de 25 échantillons Apollo et 2 météorites lunaires. Différentes techniques ont permis d’obtenir 8 valeurs de paléointensités (1-47 µT) et 7 limites supérieures de paléointensité (< 30 µT). Ces données, couplées aux âges radiométriques (existants et nouvellement acquis), retracent l’évolution du champ de surface lunaire au cours du temps. Les résultats corroborent l’existence d’une période de champ fort (4-3.5 Ga) et prolongent cette période jusqu’à environ 3 Ga. Les paléointensités > 1 µT que nous obtenons jusqu’à 0.1 Ga indiquent un arrêt très tardif de la dynamo. De plus, de faibles paléointensités sont obtenues dans l’époque de champ fort, suggérant une valeur de champ moyen plus faible que proposé dans la littérature. Cette étude permet de mieux contraindre l'évolution de ce champ lunaire. / It is admitted that the Moon used to have a magnetic field, generated by an internal dynamo. However, the mechanisms responsible for the dynamo and its preservation are still poorly known today. The lifetime of the magnetic field is also debated. My thesis was focused first on the magnetic characterization (natural magnetization and magnetic susceptibility) of a large part of the Apollo collection, with the study of 161 Apollo rocks. I used the ratio of the natural magnetization to the magnetic susceptibility to obtain an approximate indicator of paleointensity. Results of this ratio were coherent with the two major epochs determined in the lunar magnetic field (high field epoch before ~3.5 Ga and a weak field epoch after) and allowed me to select samples for detailed paleomagnetic analyses in another part of my thesis. Then, I studied in laboratory the natural magnetization of 25 Apollo samples and 2 lunar meteorites. Different methods were used to obtain 8 paleointensities values (between 1 and 47 µT) and 7 upper limits of paleointensity (< 30 µT).These data were coupled with radiometric ages to trace the evolution of the lunar surface field over time. These results corroborate the existence of a strong field epoch (4-3.5 Ga) and extend this epoch until ~3 Ga. Paleointensities of values > 1 µT obtained until 0.1 Ga indicates a very late interruption of the dynamo. Weak paleointensities were obtained in the high field epoch, suggesting a value of average field lower than previously proposed in literature. This study allows to better constrain the temporal evolution of the lunar magnetic field.

Les structures de combustion constituent un témoin de la fréquentation humaine et leur étude permet d’appréhender un aspect du mode d’occupation d’un lieu donné. Ainsi, pour compléter les approches classiques qui s’intéressent à la typologie des foyers, à la fréquence des feux, à la nature des combustibles, etc., une caractérisation thermique de ces structures a été proposée. Elle s’appuie sur les impacts thermiques enregistrés par les sédiments soumis aux feux et plus précisément sur les modifications des propriétés de thermoluminescence (TL) et de magnétisme avec la chauffe.Le site-laboratoire est celui de la grotte de Fraux (Dordogne), occupée à l’Âge du bronze, dont le statut et le mode d’occupation pose question puisqu’elle présente tant des vestiges domestiques (sols de circulation, foyers, mobiliers) que des vestiges symboliques (manifestations pariétales, dépôts de mobilier). La place importante des foyers parmi ces vestiges a induit une étude spécifique de ces structures. En effet, ce site recèle plus d’une soixantaine de structures de combustion et, aspect important pour notre approche archéométrique, présente un état de conservation exceptionnel puisque la grotte est restée fermée depuis l’occupation de l’Âge du bronze.L’étude de certains foyers de la grotte des Fraux a permis de tester le potentiel de paléothermomètres fondés sur ces deux propriétés indépendantes à savoir la TL des grains de quartz et le magnétisme des oxydes de fer contenus dans les sédiments. Le paléothermomètre TL a été élaboré en comparant les signaux TL d’échantillons provenant de foyers archéologiques à ceux de références thermiques chauffées en laboratoire. Pour le magnétisme deux pistes ont été exploitées : les températures de déblocage de l’aimantation rémanente et l’évolution de la signature magnétique -minéralogie et taille de grain) avec la chauffe. La détermination des paléotempératures atteintes par les sédiments substrats des structures de combustion apporte une première indication sur leur intensité de chauffe. Afin d’étalonner ces informations paléothermométriques en termes d’énergie mise en jeu, des feux expérimentaux ont été réalisés. Ils ont permis de comparer les impacts thermiques entre feux archéologiques et feux expérimentaux, de construire un échantillonnage d’histoire thermique connue, mais aussi d’estimer les températures atteintes, les épaisseurs de sédiments affectés, les quantités de combustibles consommés pendant un temps donné, la quantité d’énergie dégagée par la combustion… Ces expérimentations ont aussi servi de base à une modélisation de la propagation de la chaleur dans les sédiments. Les simulations effectuées dans ce modèle numérique permettent alors d’estimer un temps minimal de fonctionnement des structures de combustion.Nous disposons ainsi d’un nouvel outil pour la caractérisation thermique de foyers archéologiques. / The study of the combustion structures, which are a remaining evidence of the human occupation, can give information about the way of occupation of a site. In this research we decided to complete the classical approaches of combustion structures generally based on typological description of hearths, frequency of fires, nature of fuel, etc. by a a thermal characterisation. This study deals with the thermal impacts recorded by the fired sediment. More precisely, the modifications of both thermoluminescence (TL) and magnetism properties with heating were investigated.The laboratory-site is the cave of Les Fraux (Dordogne, France) which was occupied in the Bronze Age. The archaeologists were wandering about the function and the way of occupation of this cave because of the existence of both domestic vestiges (archaeological occupation grounds, hearths, and ceramics) and symbolic evidences (rock art and votive ceramic deposition). A specific study of the combustion structures had started considering the significant number of hearths, more than sixty, and their importance in the human occupation. In addition, as the cave remained closed since the Bronze Age, the hearths are in an excellent state of conservation and that is an important point for our archaeometric study. The thermal characterisation of some hearths from the cave of Les Fraux firstly consisted in studying the paleothermometer potential of two properties: the thermoluminescence of quartz grains and the magnetism of iron oxides taken from the sediments. The TL paleothermometer was established by comparing TL signals of samples from archaeological hearths and those of thermal references heated in laboratory. Two properties were explored for the magnetic paleothermometer: the unblocking temperatures of the remanent magnetization and the evolution of magnetic signature (mineralogy and grain size) with heating. The paleotemperatures determined for the sediment of the hearths give a first information about the heating intensity of fires.Then experimental fires were carried out to calibrate paleothermometric data in quantity of energy and wood consumption, to check the suitability of laboratory thermal references, and to characterise the process of heat transfer inside the sediment. Finally, a numerical modeling of heat propagation within the sediment was implemented from temperatures recorded during fire experimentations. Numerical simulations performed in this model allowed us to estimate a minimal duration of functioning of the combustion structures.A novel tool for the thermal characterisation of combustion structures is then available.

Este trabalho teve por objetivo investigar a escala temporal envolvida na deposição de ritmitos permocarboníferos da Bacia do Paraná (Subgrupo Itararé), expostos no Parque do Varvito (Itu, SP) e pedreira Itaú (Trombudo Central, SC), através de dados paleomagnéticos e de anisotropia de suscetibilidade magnética. Os estudos paleomagnéticos revelaram componentes de magnetização estável para ambas as coleções, com indicações de que a magnetização remanente é devida a portadores magnéticos (principalmente magnetita e hematita) de origem detrítica. A componente de magnetização característica, em ambos os casos, é de polaridade reversa, e foi identificada nos dois portadores magnéticos principais. A investigação da mineralogia magnética foi feita através de várias técnicas, incluindo espectroscopia Mossbauer, curvas termomagnéticas, curvas de histerese e ZFC/FC, além de microscopia ótica e eletrônica. Os dados paleomagnéticos e de anisotropia de susceptibilidade magnética permitiram a composição de séries temporais, que foram submetidas a análise espectral por transformada de Fourier de Lomb-Scargle para séries desigualmente espaçadas. Os espectros de potência resultantes foram posteriormente comparados com os espectros de séries de espessura individual das unidades litológicas, o que possibilitou a investigação de sinais harmônicos, sobre a qual foram propostas inferências a respeito das escalas temporais de sedimentação. Esta etapa do trabalho revelou escalas milenares para o domínio do tempo nos espectros de potência, indicando o registro dos ciclos orbitais de Milankovitch, bem como quase-periodicidades associadas à variabilidade solar e feedback do sistema oceânico-atmosférico, para todas as análises. Este conjunto de dados sugere o caráter não-anual de deposição dos ritmitos, ao contrário do proposto por alguns autores. O pólo paleomagnético calculado para a seção de Rio do Sul é compatível com o pólo do Permocarbonífero para a Bacia Sanfranciscana (MG), indicando que o intervalo de tempo envolvido na deposição dos sedimentos é suficientemente longo para eliminar os efeitos da variação secular do campo geomagnético. Alguns resultados adicionais desta tese proveram informações especiais: (i) Foram observados ciclos de indução solar (ciclos de Hallstattzein e de Suess) e a sugestão de ciclo compatível com o ciclo glacial-interglacial de Bond, recentemente sugerido como de origem solar, o que apontaria para uma possível feição harmônica, dominante sobre o sistema oceânico-atmosférico, e que poderia operar sobre períodos geológicos mais antigos; (ii) registro da remanência magnética possivelmente controlado por fatores mecânicos na sucessão de Itu, provavelmente relacionados a correntes de turbidez; (iii) indícios da presença de magnetossomas possivelmente rompidas e/ou oxidadas, em especial para a sucessão de Itu. / This work aims to investigate the timescale of the sedimentation of Permocarboniferous rhythmites from Paraná Basin (Itararé Subgroup) cropping out at the Parque do Varvito, (Itu, SP), and at the Itaú quarry, (Trombudo Central, SC) by means of paleomagnetic and anisotropy of magnetic susceptibility (ASM). The paleomagnetic study revealed stable magnetization components for both sections, which are carried by magnetic carriers (mainly magnetite and hematite) of detritic origin. The characteristic magnetization direction for each section is of reverse polarity and is found in both magnetite and hematite. Several techniques were used in the investigation the magnetic mineralogy including Mossbauer spectrometry, thermomagnetic curves, hysteresis and ZFC/FC curves, optical and electronic microscopy. Although not confirmed, some data pointed to the possibility of magnetic biomineralization with disrupted or oxidized mineral chains. The paleomagnetic and ASM data allowed the construction of time series that were submitted to spectral analysis by the Lomb-Scargle Fourier transform for unevenly spaced series. The resulting power spectra were then compared with the thickness spectrum. Based on the harmonic signals identified in all time series it was possible to infer deposition rates for both Itú and Itaú rhythmites. This procedure pointed to millennial timescale, and periodical signal compatible to Milankovitch orbital forcing, as well quasi-periodicities related to solar variability and feedback of ocean-atmospheric system, were identified in both sections. Such evidences strongly point to the non-annual sedimentation character, in opposition to previous hypothesis. The paleomagnetic data from the Rio do Sul rocks allowed the calculation of a paleomagnetic pole which is in agreement to the one recently obtained for the Santa Fé Group, Sanfranciscana Basin (MG), indicating that the time interval comprised by the Rio do Sul rhythmites is long enough for eliminating the secular variation effects. Results from this work provide also indications for the record of (i) solar forcing cycles (Hallstattzein and Suess cycles); (ii) spectral peak values of 1,5-ky and 6,0 - 8,0 ky cycle, which is compatible to the glacial-interglacial Bond cycle observed in Quaternary geological records. Such result would extend to ancient times the atmosphere-ocean interaction pattern.

Este trabalho teve por objetivo investigar a escala temporal envolvida na deposição de ritmitos permocarboníferos da Bacia do Paraná (Subgrupo Itararé), expostos no Parque do Varvito (Itu, SP) e pedreira Itaú (Trombudo Central, SC), através de dados paleomagnéticos e de anisotropia de suscetibilidade magnética. Os estudos paleomagnéticos revelaram componentes de magnetização estável para ambas as coleções, com indicações de que a magnetização remanente é devida a portadores magnéticos (principalmente magnetita e hematita) de origem detrítica. A componente de magnetização característica, em ambos os casos, é de polaridade reversa, e foi identificada nos dois portadores magnéticos principais. A investigação da mineralogia magnética foi feita através de várias técnicas, incluindo espectroscopia Mossbauer, curvas termomagnéticas, curvas de histerese e ZFC/FC, além de microscopia ótica e eletrônica. Os dados paleomagnéticos e de anisotropia de susceptibilidade magnética permitiram a composição de séries temporais, que foram submetidas a análise espectral por transformada de Fourier de Lomb-Scargle para séries desigualmente espaçadas. Os espectros de potência resultantes foram posteriormente comparados com os espectros de séries de espessura individual das unidades litológicas, o que possibilitou a investigação de sinais harmônicos, sobre a qual foram propostas inferências a respeito das escalas temporais de sedimentação. Esta etapa do trabalho revelou escalas milenares para o domínio do tempo nos espectros de potência, indicando o registro dos ciclos orbitais de Milankovitch, bem como quase-periodicidades associadas à variabilidade solar e feedback do sistema oceânico-atmosférico, para todas as análises. Este conjunto de dados sugere o caráter não-anual de deposição dos ritmitos, ao contrário do proposto por alguns autores. O pólo paleomagnético calculado para a seção de Rio do Sul é compatível com o pólo do Permocarbonífero para a Bacia Sanfranciscana (MG), indicando que o intervalo de tempo envolvido na deposição dos sedimentos é suficientemente longo para eliminar os efeitos da variação secular do campo geomagnético. Alguns resultados adicionais desta tese proveram informações especiais: (i) Foram observados ciclos de indução solar (ciclos de Hallstattzein e de Suess) e a sugestão de ciclo compatível com o ciclo glacial-interglacial de Bond, recentemente sugerido como de origem solar, o que apontaria para uma possível feição harmônica, dominante sobre o sistema oceânico-atmosférico, e que poderia operar sobre períodos geológicos mais antigos; (ii) registro da remanência magnética possivelmente controlado por fatores mecânicos na sucessão de Itu, provavelmente relacionados a correntes de turbidez; (iii) indícios da presença de magnetossomas possivelmente rompidas e/ou oxidadas, em especial para a sucessão de Itu. / This work aims to investigate the timescale of the sedimentation of Permocarboniferous rhythmites from Paraná Basin (Itararé Subgroup) cropping out at the Parque do Varvito, (Itu, SP), and at the Itaú quarry, (Trombudo Central, SC) by means of paleomagnetic and anisotropy of magnetic susceptibility (ASM). The paleomagnetic study revealed stable magnetization components for both sections, which are carried by magnetic carriers (mainly magnetite and hematite) of detritic origin. The characteristic magnetization direction for each section is of reverse polarity and is found in both magnetite and hematite. Several techniques were used in the investigation the magnetic mineralogy including Mossbauer spectrometry, thermomagnetic curves, hysteresis and ZFC/FC curves, optical and electronic microscopy. Although not confirmed, some data pointed to the possibility of magnetic biomineralization with disrupted or oxidized mineral chains. The paleomagnetic and ASM data allowed the construction of time series that were submitted to spectral analysis by the Lomb-Scargle Fourier transform for unevenly spaced series. The resulting power spectra were then compared with the thickness spectrum. Based on the harmonic signals identified in all time series it was possible to infer deposition rates for both Itú and Itaú rhythmites. This procedure pointed to millennial timescale, and periodical signal compatible to Milankovitch orbital forcing, as well quasi-periodicities related to solar variability and feedback of ocean-atmospheric system, were identified in both sections. Such evidences strongly point to the non-annual sedimentation character, in opposition to previous hypothesis. The paleomagnetic data from the Rio do Sul rocks allowed the calculation of a paleomagnetic pole which is in agreement to the one recently obtained for the Santa Fé Group, Sanfranciscana Basin (MG), indicating that the time interval comprised by the Rio do Sul rhythmites is long enough for eliminating the secular variation effects. Results from this work provide also indications for the record of (i) solar forcing cycles (Hallstattzein and Suess cycles); (ii) spectral peak values of 1,5-ky and 6,0 - 8,0 ky cycle, which is compatible to the glacial-interglacial Bond cycle observed in Quaternary geological records. Such result would extend to ancient times the atmosphere-ocean interaction pattern.

<p>Детаљним теренским и лабораторијским истраживањима четири најважнија лесно-палеоземљишна профила у нашој земљи: Батајница &ndash; Дунав, Стари Сланкамен &ndash; Чот, Рума &ndash; циглана и три профила на Тителском лесном платоу, обухваћено је преко 160 mпрофила, а прикупљено је и лабораторијски обрађено преко 3.500 узорака, што до сада представља најобимније и најдетаљније истраживање лесно-палеоземљишних секвенци (ЛПС) у нашој земљи. Дат је детаљан литолошки и педолошки опис ЛПС, које су формиране у различитим палеогеографским условима. На основу резултата палеомагнетских истраживања која су обављена у две независне лабораторије и на два сета спесимена, прецизно је дефинисан положај последње пуне геомагнетне реверзије (бринес/матујама) која се одиграла пре 778 хиљада година. У исто време она представља званични границу између доњег и средњег плеистоцена. На основу позиције ове границе у доњем делу лесног хоризонта V-L9, формирана је нова интерпретација постојећег хроностратиграфског модела. Истраживањима особина стенског магнетизма, коришћењем параметара магнетне сусцептибилности и магнетне сусцептибилности зависне од фреквенце, формирана је јасна слика о палеоклиматским условима који су постојали током формирања слојева леса и образовања серије фосилних земљишта. Транзиција од екосистема суптропског појаса завршног дела доњег плеистоцена и почетног дела средњег плеистоцена, преко шума умереног појаса током средњег дела средњег плеистоцена, ка степским палеоземљиштима у каснијим периодима плеистоцена, јасно је осликана у типовима фосилних земљишта.</p> / <p>Detaljnim terenskim i laboratorijskim istraživanjima četiri najvažnija lesno-paleozemljišna profila u našoj zemlji: Batajnica &ndash; Dunav, Stari Slankamen &ndash; Čot, Ruma &ndash; ciglana i tri profila na Titelskom lesnom platou, obuhvaćeno je preko 160 mprofila, a prikupljeno je i laboratorijski obrađeno preko 3.500 uzoraka, što do sada predstavlja najobimnije i najdetaljnije istraživanje lesno-paleozemljišnih sekvenci (LPS) u našoj zemlji. Dat je detaljan litološki i pedološki opis LPS, koje su formirane u različitim paleogeografskim uslovima. Na osnovu rezultata paleomagnetskih istraživanja koja su obavljena u dve nezavisne laboratorije i na dva seta spesimena, precizno je definisan položaj poslednje pune geomagnetne reverzije (brines/matujama) koja se odigrala pre 778 hiljada godina. U isto vreme ona predstavlja zvanični granicu između donjeg i srednjeg pleistocena. Na osnovu pozicije ove granice u donjem delu lesnog horizonta V-L9, formirana je nova interpretacija postojećeg hronostratigrafskog modela. Istraživanjima osobina stenskog magnetizma, korišćenjem parametara magnetne susceptibilnosti i magnetne susceptibilnosti zavisne od frekvence, formirana je jasna slika o paleoklimatskim uslovima koji su postojali tokom formiranja slojeva lesa i obrazovanja serije fosilnih zemljišta. Tranzicija od ekosistema suptropskog pojasa završnog dela donjeg pleistocena i početnog dela srednjeg pleistocena, preko šuma umerenog pojasa tokom srednjeg dela srednjeg pleistocena, ka stepskim paleozemljištima u kasnijim periodima pleistocena, jasno je oslikana u tipovima fosilnih zemljišta.</p> / <p>Detailed field and laboratory studies of four major loess-paleosol sequences in our country: Batajnica - Danube, Stari Slankamen - Čot, Ruma - brickyard and three sub-profiles on the Titel loess plateau, is covered by over 160 m of sections and collected and laboratory analyzed over 3,500 samples, which so far is the most comprehensive and most detailed research of loess-paleosol sequences (LPS) in our country. A detail description of the lithological and pedological LPS, which are formed in different paleogeographical conditions, was presented. Based on the results of palaeomagnetic experiments which ware performed in two independent laboratories and on the two sets of specimen, the position of Matuyama/Brunhes boundary whics took place 778 ka, was precisely defined. At the same time it is the official boundary between the Lower and Middle Pleistocene. Based on the position of this magnetic reversal in the lower part of loess horizons V-L9, a new interpretation of existing chronostratigraphic models was formed. Investigation of the rock magnetism properties, using the magnetic susceptibility and frequency dependent magnetic susceptibility, a clear picture of the palaeoclimate conditions that existed during the formation of layers of LPS was formed. The transition from the subtropical zone ecosystems of the final part of the Lower Pleistocene and the initial portion of the Middle Pleistocene, through forests of temperate belt during the middle part of the Middle Pleistocene, to the steppe paleosol in the later periods of the Pleistocene, is reconstructed according different soil types.</p>

Mgr. Petr Schnabl - Dissertation Paleomagnetism and magnetomineralogy of rocks from the Bohemian Massif and Tethyan Realm Abstract The thesis deals with paleomagnetic and rock magnetic properties of Silurian/Devonian and Jurassic/Cretaceous limestones, Paleogene/Neogene basaltic rocks and altered Silurian basalts. The main goal is to determine the history of the Earths' magnetic field from the Silurian to the present. Two lithostratigraphic formations are defined in the Jičín volcanic field on the basis of volcanology, paleomagnetism and radiometric dating. The Trosky Formation (24.6?/18.3 - 15.7 Ma) is composed of several Strombolian-type volcanoes, while the Kozákov Formation (5.2 - 4.6 Ma) is represented by effusive products with a crater vent of a single giant volcano. One Pliocene (4.3-3.3 Ma) and two Pleistocene phases (2.6 -2.1 Ma and 1.8 - 1.1 Ma) of volcanic activity Magnetostratigraphy is a very important tool for the definition of the J/K boundary. The boundary between the Crassicolaria and Calpionella zones is present within geopolarity zone M19n. The boundary between the ammonite zones Jacobi and Durangites also lies close to this point. Paleomagnetic directions of Silurian and Devonian rocks in the Bohemian Massif are very difficult to interpret and have been studied as a challenging problem...