<p> Magnetization associated with the emplacement or a rock body may be thermo-remanent magnetization (TRM) in an igneous body or detrital-remanent magnetization (ORM) in a sedimentary deposit. At the time or Formation the acquired remanence will tend to lie in the ambient field direction. This primary remanence may not remain unchanged through geologic time. Viscous demagnetization may progressively destroy the remanence in the primary direction or it may be reset as VRM in a later different ambient field direction. The amount or acquired VRM will depend on the temperature the rock is heated to and the length or time the heating lasts as well as the magnetic properties or the remanence carriers.</p> <p> The remanence may also be changed by chemical reactions taking place in the magnetic minerals. The remanence acquired during these chemical changes (CRM) is round, by this work, to be a determining factor in the stability or and initial NRM during thermal remagnetization. </p> <p> Synthetic samples were stored for up to 32 days at 400 C it is possible to access geologic time. To simulate viscous changes over geologic time elevated temperatures applied for laboratory times are related to longer times at lower temperatures using the thermal activation curves. Changes in remanence during the storage were observed at various times throughout the experiment. The remanence in samples with an initial NRM was diminished, remanece in samples with a weak initial NRM increased in intensity but the remanence direction lay in the Field direction after as little as l/2 a day storage time. </p> <p> Thermal demagnetization allows separation of the magnetization on the basis of blocking temperature spectra. During the storage the initial magnetite was oxidized to cation deficent magnetite with significantly higher blocking temperatures than those found in the magnetite. Hysteresis measurements, and thermomagnetic mesurements indicate that this change results primarily From the shirt in Tc due to cation deficency. Apparently the change in T did not significantly affect the mechanisms responsible for blocking remanence but merely shifted the blocking temperatures by a similar amount. In samples with a weak initial NRM the chemical change completely reset the magnetization and in samples stored for times as short as only 8 days the initial remanence direction could not be recovered. </p> / Thesis / Bachelor of Science (BSc)

Made available in DSpace on 2015-03-26T13:53:14Z (GMT). No. of bitstreams: 1 texto completo.pdf: 5187172 bytes, checksum: 61b37fe6f98b554b3f89fd456eb5e011 (MD5) Previous issue date: 2010-03-22 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / This study aimed to characterize the anthroposols located under natural shelter of limestone rocks in the north of Minas Gerais, where pre-Columbian people lived for thousands of years, bringing and removing matters of different natures and origins. In these shelters, very unique anthropogenic soils were developed, and on which there is still no pedological studies. Therefore, we sought to physically, chemically, mineralogically and micromorphologically characterize these soils collected from five archaeological sites, four in limestone shelters and one in a non-sheltered environment, present in two protected areas in the north of Minas Gerais: Parque Nacional (PARNA) Cavernas do Peruaçu and Parque Estadual da Lapa Grande. The samples were subjected to physical and chemical routine analysis, full attack, total organic carbon (TOC) and fractionation of humic substances, mineralogical and micromorphological analysis, besides fractionation of inorganic forms of phosphorus and extraction of oxides. According to the results, the soils have polycyclic genesis, marked by an evident climate alternation associated with distinct periods of human occupation. This polycyclic nature gives them very different characteristics of soils developed under natural pedogenic processes. In general, the soils have very different color tints, varying from 2.5YR to 10YR in the same profile. Texturally, there is no predominance of any significant fraction, being loam the dominant textural class. In the sand fraction, the amount of shells, bones, and especially coal, particles originating from the cumulative process of human occupation is considerable. Chemically, the soils under shelters have high pH values, around 8.5 to 9.0. The cationic exchange complex is almost entirely populated by exchangeable bases, especially Ca and Mg, reaching values of V (%) equal to 100% in all layers, as in the Lapa do Boquete and Malhador. The levels of P-extractable (Mehlich-1) were high in all sheltered soils, reaching 103-649 mg/dm 3. However, in the site outside of these shelters they were much lower, yet suggesting an even improvement of this element associated with anthropic activity. In mineralogy, the presence of kaolinite, illite, calcite and apatite, and iron oxide (hematite, goethite and maghemite) was detected in the clay fraction. The silt and sand fractions revealed the presence of quartz, mica, calcite, magnetite and apatite. In the sand fraction the same minerals were also identified from the silt fraction. The presence of oxides with magnetic attraction in all fractions is remarkable, especially in the sand fraction, mainly associated with charred layers. The TOC levels showed a considerable extent, expressed by values from 0.12 to 5.25 g kg-1. The Humin fraction is predominant over the others (humic and fulvic acids) in all layers. The micromorphological analysis revealed an abundance of material in distinct levels of physical-chemical change, showing the polygenetic nature of soils. The results of this study allow us to infer that the occupation of these shelters was episodic and cumulative over the millennia, since there is a degree of uniformity of the characteristics originated from human activity along the profiles. On the other hand, there are nuances that demonstrate that the occupation showed variations in relation to its type and intensity. Low values of Mehlich-P, relative to other anthropossols, reinforce the archaeological hypothesis that the shelters were not used as fixed settlement sites, of large numbers of people, but probably as traffic areas where they developed specific activities. Finally, it was found that the pedological attributes studied are proving useful and significant in the interpretation of archaeological information, complementing and reinforcing the need for greater interaction between pedology and archeology. The soils studied have many specific characteristics that differentiate them considerably from the other Brazilian anthropossols so far studied. In addition, the sheltered soils have a kind of heterogeneity originated from its depositional polycyclic nature, which makes it impossible for them to be classified in current systems. Therefore, it is necessary to undertake further studies on such soils in other regions of Brazil in order to know them better and obtain more similarities to group these soils, making them sortable. / O presente estudo teve como objetivo caracterizar os antropossolos localizados sob abrigos naturais de rochas calcárias, no norte do estado de Minas Gerais, onde populações pré-colombianas viveram por milhares de anos, aportando e removendo matérias de naturezas e procedências distintas. Nestes abrigos desenvolveram-se solos antropogênicos muito peculiares, e sobre os quais ainda não se tem estudos pedológicos. Portanto buscou-se caracterizar física, química, mineralógica e micromorfologicamente alguns solos coletados em cinco sítios arqueológicos, sendo quatro em abrigos calcários e um em ambiente não abrigado, presentes em duas unidades de conservação no norte de Minas: o Parque Nacional (PARNA) Cavernas do Peruaçu e o Parque Estadual da Lapa Grande. As amostras foram submetidas a análises físicas e químicas de rotina, ataque total, carbono orgânico total e fracionamento das substâncias húmicas, análises mineralógicas e micromorfológicas, além de fracionamento das formas inorgânicas de fósforo e extração de óxidos. De acordo com os resultados encontrados, os solos estudados apresentam gênese policíclica, marcada por uma pronunciada alternância climática associada a distintos períodos de ocupação antrópica. Essa natureza policíclica confere aos mesmos, características bem distintas de solos desenvolvidos sob processos pedogenéticos naturais. De maneira geral os solos apresentam cores com matizes bem distintas, chegndo a variar de 2,5YR a 10YR no mesmo perfil. Texturalmente não existe predomínio expressivo de nenhuma fração, sendo a classe textural franco a dominante. Na fração areia é considerável a quantidade de partículas de conchas, de ossos, e principalmente de carvão, originárias do processo cumulativo de ocupação antrópica. Quimicamente os solos sob os abrigos apresentam valores de pH elevados, em torno de 8,5 a 9,0. O complexo de troca catiônica é praticamente todo preenchido pelas bases trocáveis, principalmente Ca e Mg, alcançando valores de V(%) iguais a 100% em todas as camadas, como na Lapa do Boquete e do Malhador. Os teores de P-extraível (Mehlich-1) encontrados foram elevados em todos os solos dos abrigos, atingindo valores de 103 a 649 mg/dm3. Já no sítio fora dos abrigos estes foram bem menores, mesmo assim sugerindo um enrriquecimento deste elemento associado a atividade antrópica. Na mineralogia detectou-se na fração argila a presença de caulinita, illita, calcita e apatita, além de óxidos de ferro (hematita, goethita e aghemita). As frações silte e areia revelaram a presença de quartzo, micas, calcita, magnetita e apatita. Na fração areia também foram identificados os mesmos minerais da fração silte. É marcante a presença de óxidos com atração magnética em todas as frações, especialmente na fração areia, associada principalmente a camadas carbonizadas. Os teores de COT revelaram uma amplitude considerável, expressa pelos valores de 0,12 a 5,25 dag kg-1. A fração Humina é predominante sobre as demais (Ácidos Húmicos e Ácidos Fúlvicos) em todas as camadas. As análises micromorfológicas revelaram uma riqueza de materiais em níveis de alteração físico-química distintas, evidenciando a natureza poligenética dos solos. Os resultados obtidos neste estudo permitem inferir que a ocupação destes abrigos foi episódica e cumulativa ao longo dos milênios, visto que existe uma certa homogeneidade das características provenientes da atividade humana ao longo dos perfís. Por outro lado existem nuanças que demonstram que a ocupação mostrou variações no que tange ao tipo e a intensidade da mesma. Baixos valores de P-Mehlich, em relação a outros antropossolos, reforçam as hipóteses arqueológicas de que os abrigos não eram utilizados como locais de assentamento fixos, de grandes contingentes humanos, mas provavelmente como locais de passagem onde se desenvolviam atividades específicas. Por fim constatou-se que os atributos pedológicos estudados, se revelam uteis e significativos na interpretação das informações arqueológicas, complementando e reforçando a necessidade de uma maior interação entre a pedologia e a arqueologia. Os solos estudados apresentam muitas características particulares que os diferenciam consideravelmente dos demais antropossolos brasileiros até agora estudados. Além disso, os solos sobabrigos apresentam uma heterogeneidade, proveniente da sua natureza deposicional policíclica, que os impossibilita de serem classificados nos sistemas de atuais. Sendo assim torna-se necessário realizar mais estudos em solos dessa natureza em outras regiões do Brasil a fim de conhecê-los melhore obter similaridades que permitam agrupar estes solos tornando-os classificáveis.