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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Sistema pedológico Planosolo-Plintossolo no Pantanal de Barão de Melgaço-MT / Pedological system Solonetz-Plinthosol in the Pantanal of Barão de Melgaço-MT

Beirigo, Raphael Moreira 18 December 2008 (has links)
O Pantanal é a maior planície continental inundável do mundo, englobando um mosaico de diferentes habitats, sustentando grande diversidade vegetal, animal e de solos. É constituído por onze sub-regiões, sendo uma delas a do Pantanal de Barão de Melgaço, que está localizado ao nordeste dessa bacia sedimentar quaternária. Apresenta uma heterogeneidade espacial de solos que está relacionada com a diversidade de feições geomórficas. Estas, adicionadas aos tipos de inundação, geram uma grande diversidade de microhabitats: Cordilheiras, Paleodiques, Murunduns, constituem as formas de relevo raramente inundáveis, enquanto que as Planícies fluviais, Campos, Baías, Corixos e Vazantes apresentam inundações anuais ou permanentes. No Pantanal de Barão de Melgaço, as altitudes variam de 100 a 150m e a declividade é inexpressiva. O material de origem dos solos é formado por sedimentos arenosos, síltico-arenosos, argilo-arenosos e arenoconglomeráticos semiconsolidados a consolidados a Formação Pantanal. Contém uma diversidade única de solos, freqüentemente com mineralogia 2:1, cuja morfologia reflete as condições de regime hídrico de cada microambiente: Planossolos, Plintossolos, Planossolos Nátricos, Vertissolos e Neossolos Flúvicos se distribuem de acordo com as feições geomórficas encontradas, sendo na grande maioria afetados por processos redoximórficos. O objetivo desta dissertação foi caracterizar e conhecer os processos pedogenéticos dos solos de um sistema pedológico Planossolo-Plintossolo em duas das principais feições geomórficas do Pantanal de Barão de Melgaço. O estudo foi realizado na RPPN (Reserva Particular do Patrimônio Natural) SESC Pantanal, no município de Barão de Melgaço, Estado de Mato Grosso. No sistema pedológico estudado foram identificados quatro solos da classe dos Plintossolos Argilúvicos e Háplico e dois Planossolos Nátricos. A transição dos Planossolos Nátricos para os Plintossolos é evidencia a pela perda gradual do caráter sódico e aumento do processo de plintização. À medida que ocorre a redução da saturação por Na+, a CTC dos solos torna-se saturada por Al3+. A presença de solos com caráter sódico ou nátrico nas partes altas da paisagem, pode ser uma evidência das mudanças climáticas que ocorreram no Pantanal, neste caso tratando-se de solos reliquiais. As principais causas da manutenção dos altos teores de Na nos Planossolos Nátricos, são a porosidade muito fechada dos horizontes subsuperficiais e as elevadas taxas de evapotranspiração no Pantanal, mesmo ocorrendo em posição mais elevada na paisagem local. Os Nódulos de Fe e Mn que ocorrem nesses solos não são pedorelíquias. Foram formados e continuam se formando em condições climáticas atuais. / The Pantanal is the largest continental flood plains, comprising a mosaic of different habitats, maintaining plant diversity, animal and soil. It consists of eleven sub-regions, one of which the of the Pantanal of Barão de Melgaço, which is located north of the Quaternary sedimentary basin. It presents a spatial heterogeneity that is related to the diversity of geomorphic features. This, added to the types of flooding and soil, generate a wide variety of microhabitats: Cordileira paleoriverbanks, termite hills, the forms of relief are rarely flooded, while the Plains river, Grasslands, Bays, Corixo and present ebb Annual floods or permanent. In the Pantanal of Barão de Melgaço, the above sea level ranging from 100 to 150m and the slope is negligible. The parent material of the soil is composed of sandy sediment, síltico-sand, clay-sandy and sandyconglomerate semiconsolidados the consolidated Training Pantanal. It contains a unique diversity of soils, often with 2:1 mineralogy, whose morphology reflects the conditions of water regime of each microenvironment: Planosols, Plinthosols, Solonetz, Vertisols and Fluvisols are distributed according to the geomorphic features found, and the great most affected by processes redoximorphic. The goal of this dissertation was to characterize and identify the processes pedogenetic soil of a system pedological Solonetz-Plinthosol in two of the main geomorphic features of the Pantanal of Barão de Melgaço. The study was conducted in RPPN (Private Reserve of Natural Heritage) SESC Pantanal, in the Barão de Melgaço county, State of Mato Grosso from Brazil. The transition of Solonetz for Plinthosol is given by the gradual loss of sodium and increase character of the plintização. As is the reduction of the saturation of Na+, the CEC soil becomes saturated by Al3+. The presence of soil character natric in the hillslope is an evidence of climate changes that occurred in the Pantanal, where the soils relic. The main causes of maintenance of high levels of Na in Solonetz are very closed the porosity of subsurface horizons and high rates of evapotranspiration in the Pantanal. The nodules of Fe and Mn that occur in these soils are not relic and were formed and are still forming in weather conditions to actually.
12

Sistema pedológico Planosolo-Plintossolo no Pantanal de Barão de Melgaço-MT / Pedological system Solonetz-Plinthosol in the Pantanal of Barão de Melgaço-MT

Raphael Moreira Beirigo 18 December 2008 (has links)
O Pantanal é a maior planície continental inundável do mundo, englobando um mosaico de diferentes habitats, sustentando grande diversidade vegetal, animal e de solos. É constituído por onze sub-regiões, sendo uma delas a do Pantanal de Barão de Melgaço, que está localizado ao nordeste dessa bacia sedimentar quaternária. Apresenta uma heterogeneidade espacial de solos que está relacionada com a diversidade de feições geomórficas. Estas, adicionadas aos tipos de inundação, geram uma grande diversidade de microhabitats: Cordilheiras, Paleodiques, Murunduns, constituem as formas de relevo raramente inundáveis, enquanto que as Planícies fluviais, Campos, Baías, Corixos e Vazantes apresentam inundações anuais ou permanentes. No Pantanal de Barão de Melgaço, as altitudes variam de 100 a 150m e a declividade é inexpressiva. O material de origem dos solos é formado por sedimentos arenosos, síltico-arenosos, argilo-arenosos e arenoconglomeráticos semiconsolidados a consolidados a Formação Pantanal. Contém uma diversidade única de solos, freqüentemente com mineralogia 2:1, cuja morfologia reflete as condições de regime hídrico de cada microambiente: Planossolos, Plintossolos, Planossolos Nátricos, Vertissolos e Neossolos Flúvicos se distribuem de acordo com as feições geomórficas encontradas, sendo na grande maioria afetados por processos redoximórficos. O objetivo desta dissertação foi caracterizar e conhecer os processos pedogenéticos dos solos de um sistema pedológico Planossolo-Plintossolo em duas das principais feições geomórficas do Pantanal de Barão de Melgaço. O estudo foi realizado na RPPN (Reserva Particular do Patrimônio Natural) SESC Pantanal, no município de Barão de Melgaço, Estado de Mato Grosso. No sistema pedológico estudado foram identificados quatro solos da classe dos Plintossolos Argilúvicos e Háplico e dois Planossolos Nátricos. A transição dos Planossolos Nátricos para os Plintossolos é evidencia a pela perda gradual do caráter sódico e aumento do processo de plintização. À medida que ocorre a redução da saturação por Na+, a CTC dos solos torna-se saturada por Al3+. A presença de solos com caráter sódico ou nátrico nas partes altas da paisagem, pode ser uma evidência das mudanças climáticas que ocorreram no Pantanal, neste caso tratando-se de solos reliquiais. As principais causas da manutenção dos altos teores de Na nos Planossolos Nátricos, são a porosidade muito fechada dos horizontes subsuperficiais e as elevadas taxas de evapotranspiração no Pantanal, mesmo ocorrendo em posição mais elevada na paisagem local. Os Nódulos de Fe e Mn que ocorrem nesses solos não são pedorelíquias. Foram formados e continuam se formando em condições climáticas atuais. / The Pantanal is the largest continental flood plains, comprising a mosaic of different habitats, maintaining plant diversity, animal and soil. It consists of eleven sub-regions, one of which the of the Pantanal of Barão de Melgaço, which is located north of the Quaternary sedimentary basin. It presents a spatial heterogeneity that is related to the diversity of geomorphic features. This, added to the types of flooding and soil, generate a wide variety of microhabitats: Cordileira paleoriverbanks, termite hills, the forms of relief are rarely flooded, while the Plains river, Grasslands, Bays, Corixo and present ebb Annual floods or permanent. In the Pantanal of Barão de Melgaço, the above sea level ranging from 100 to 150m and the slope is negligible. The parent material of the soil is composed of sandy sediment, síltico-sand, clay-sandy and sandyconglomerate semiconsolidados the consolidated Training Pantanal. It contains a unique diversity of soils, often with 2:1 mineralogy, whose morphology reflects the conditions of water regime of each microenvironment: Planosols, Plinthosols, Solonetz, Vertisols and Fluvisols are distributed according to the geomorphic features found, and the great most affected by processes redoximorphic. The goal of this dissertation was to characterize and identify the processes pedogenetic soil of a system pedological Solonetz-Plinthosol in two of the main geomorphic features of the Pantanal of Barão de Melgaço. The study was conducted in RPPN (Private Reserve of Natural Heritage) SESC Pantanal, in the Barão de Melgaço county, State of Mato Grosso from Brazil. The transition of Solonetz for Plinthosol is given by the gradual loss of sodium and increase character of the plintização. As is the reduction of the saturation of Na+, the CEC soil becomes saturated by Al3+. The presence of soil character natric in the hillslope is an evidence of climate changes that occurred in the Pantanal, where the soils relic. The main causes of maintenance of high levels of Na in Solonetz are very closed the porosity of subsurface horizons and high rates of evapotranspiration in the Pantanal. The nodules of Fe and Mn that occur in these soils are not relic and were formed and are still forming in weather conditions to actually.
13

Palaeoenvironments of the Earliest (Middle Devonian) Tetrapod Trackways from the Holy Cross Mountains, Poland; Locomotion in a Terrestrial Setting? / De tidigaste tetrapod-spåren från mellersta devon − liv i en död efemär sjö?

Qvarnström, Martin January 2015 (has links)
The palaeoenvironment from which early tetrapods emerged is crucial to comprehend in order to understand the mechanisms that drove and allowed the terrestrialization of vertebrates; one of the most important evolutionary ‘events’ in the history of animals. Nevertheless, much of the terrestrialization is shrouded in obscurity, inter alia, due to scarcity of early tetrapods in the fossil record. Each new discovery of anything linked to vertebrate terrestrialization is therefore of great importance. Here, I present new detailed analyses of the palaeoenvironmental conditions at the time of formation of the earliest (early Middle Devonian) tetrapod trackways found in the Zachełmie Quarry in the Holy Cross Mountains of southern Poland. The trackways are found in three horizons in a clay-rich dolomitic succession represented by the Lower Complex of the Wojciechowice Formation. This Lower Complex is composed of short shallowing upward sequences that often terminate with desiccation cracks and/or paleosols. Vertically fluctuating δ18O values in the complex suggest multiple episodes of closed hydrological systems. A model of ephemeral to perennial lakes in a terrestrial setting is therefore proposed. Such environment is in concordance with evidence of scarce bioturbation and a flourish of microbial communities that, in contrast to a normal marine setting, most likely represent an ecologically stressed ecosystem. Furthermore: non-marine rare earth element (REE) signals, desiccation events, fossils of green algae (charophytes), paleosol development, low energy cyclic deposits and general lack of marine taxa in the body and trace fossil records in this complex firmly establishes the interpretation of palustrine carbonates formed in a lacustrine-like setting. However, in the lower part of the complex, some highly fractioned marine fossils occur. These are suggested to have been transported during wash-up events which temporally places the setting in marine proximity. Seasons of monsoonal rainfall resulted in erosion and influx of detrital grains which is evidenced by fine planar lamination (of seasonal cyclicity) in most of the sediments and occasional occurrence of blackened clasts (and rain-drop imprints). Thus, none of the pre-existing palaeoenvironmental hypotheses of tetrapod emergence are in full concordance with the data from the Zachełmie Quarry. Instead, a new palaeoenvironment is proposed for the earliest tetrapods: schizohaline ephermal to perennial lakes with periodic desiccation. This infers that already in the early Middle Devonian, tetrapods had conquered the terrestrial realm and were perhaps already capable of terrestrial locomotion over quite substantial distances. / Däggdjur, reptiler, fåglar och amfibier utgör tillsammans en besläktad djurgrupp som kallas för tetrapoder (fyrfotingar). Deras gemensamma förfader härstammade från de lobfenade fiskarna men skiljde sig från dem genom att inneha utvecklade ben med tår istället för de ”köttiga” fenor som de lobfeniga fiskarna karaktäriseras av. Denna evolutionära nyhet tillät, tillsammans med en rad andra egenskaper (lungor, skydd för uttorkning av dermis etc.), att vertebrater helt och hållet kunde koloni-sera land. I och med att vår egen existens är en direkt följd av denna evolutionära händelse är detta ett hett forskningsämne inom evolutionsbiologin. Ändå är mycket fortfarande höljt i dunkel beträffande hur koloniseringen av land gick till och vad det var som drev denna utveckling eftersom övergången skedde under en, i geologisk mått, snabb tidsrymd. Dock har de sista årtiondena resulterat i flertalet nya fossilfynd av primitiva tetrapoder. Ett fynd som är speciellt spektakulärt eftersom det är den hittills äldsta efterlämningen av tetrapoder, är fotspår som uppenbart är gjorda av ett djur som hade ben och tår istället för fenor. Detta förvånade hela det vetenskapliga samfundet eftersom det innebar att vi (tetrapoderna) utvecklades tidigare än vad som var dittills trott och att vertebrat-koloniseringen av land förmodligen skedde flertalet miljoner år tidigare. Vad som också skiljer ett spårfossil från andra fossil är att de är spår av djuren från när och där de levde till skillnad från bara deras skelettdelar som oftast transporterats från där de dog och bara preserveras i speciella miljöer. Detta har jag utnyttjat i detta arbete för att försöka avgöra i vilken miljö de är avsatta i. Jag har analyserat de sedimentära bergarterna i stenbrottet i södra Polen med skärningen som innehåller de lagren i vilka fotspåren finns. Analyser av sällsynta jordartsmetaller från de tre lager där fotspår är tydliga, antyder en speciell avsättningsmiljö som inte liknar en typisk havsmiljö. I den undre delen av lagerföljden där de spårbärande lagren påträffats finns återkristalliserade saltkristaller, torkningssprickor och fossila jordar som indikerar korta respektive långvariga perioder av uttorkning. Andra fossil som i en normal marin miljö borde bevaras i en dolomitisk kalksten lyser med sin frånvaro och istället påfinns massiv koloni-sering av cyanobakterier. Detta brukar ske i speciella miljöer som avviker från vanlig marin komposi-tion, så som äldre sötvattensmiljöer eller laguner med hög salthalt, som därmed är ”svårbebodd” för djur som annars livnär sig på de fotosyntiserande bakterierna. Implikationen av mitt arbete är att tetrapoderna redan i tidig mellan Devon (ca 390 miljoner år sedan) inte bara hade utvecklat ben utan också att de kunde använda dem över landsträckor för att ta sig till, och mellan, kontinentala vatten. Detta är ännu en viktig pusselbit i pusslet som ämnar rekonstruera tetrapodernas (och vår egen) uppkomst.
14

INTERPRETATION OF THE DEPOSITIONAL ENVIRONMENT AND PALEOCLIMATE OF DINOSAUR SITES, BRUSHY BASIN MEMBER OF THE JURASSIC MORRISON FORMATION, EAST-CENTRAL UTAH

VanDeVelde, David M. 10 August 2006 (has links)
No description available.
15

Response of Soils and Soil Ecosystems to the Pennsylvanian-Permian Climate Transitionin the Upper Fluvial Plain of the Dunkard Basin, Southeastern Ohio, USA

Carnes, Jennifer L. 14 September 2017 (has links)
No description available.
16

Testing the causes of middle Miocene Neotropical provinciality in South America

Catena, Angeline M., Catena 31 May 2018 (has links)
No description available.
17

A Sequence Stratigraphic Analysis of the Allegheny Group (Middle Pennsylvanian),Southeast Ohio

Stubbs, Dreadnaught G. 13 July 2018 (has links)
No description available.
18

Paleopedology and fluvial sedimentology of the Upper Devonian Catskill Formation, Central Pennsylvania: A test of the distributive fluvial system

Oest, Christopher January 2015 (has links)
The Upper Devonian Catskill Formation represents marginal marine and alluvial sediments which prograded into the Appalachian Basin during the Acadian Orogeny. Distributive fluvial systems (DFS) are prevalent in modern actively aggrading basins in all tectonic and climatic regimes and may be common in the rock record. In this study, I reinterpret the Catskill Formation as a prograding distributive fluvial system (DFS) on the basis of up-section variability in paleosols, channel sandstone textural trends, and alluvial architecture. At least three distinct pedotypes representative of prevailing soil forming conditions are identified during deposition of the Irish Valley, Sherman Creek, and Duncannon Members of the Catskill Formation. Increased paleosol drainage is inferred from an up-section transition from hydromorphic aqualfs within the Irish Valley Member to non-calcareous, uderts within the Duncannon Member. Qualitative field observations of channel sandstone morphology show an increase in channel size up-section. Channels occur as small isolated bodies at the base of the section, transitioning to relatively larger, amalgamated channels, and finally, large isolated channel bodies up-section. Sandstones are litharenites and coarsen-upward throughout the Catskill Formation overall. This coarsening upward trend results from increasing paleo-flow competency in larger channels up-section. These results are consistent with deposition of the Catskill Formation by DFS processes and demonstrate the utility of paleopedological analysis in interpreting alluvial depositional processes. Identifying DFS in the rock record has implications for paleosol-based paleoclimatic studies, as paleosols forming on prograding DFS have increased paleosol drainage up-section, which could potentially be misinterpreted as a shift from prevailing humid to arid paleoclimatic conditions. Recognition of DFS in the rock record also has implications for basin analysis and exploration of fluvial aquifers and hydrocarbon reservoirs, as the stratigraphic architecture of DFS are fundamentally different from tributary systems at the basin scale. / Geology
19

Pedogênese e morfogênese na superfície de São José dos Ausentes (RS) no quartenário tardio: evidências em paleofundo de vale na bacia hidrográfica do rio dos Touros / Pedogenesis and morphogenesis on the surface of São José dos Ausentes (South of Brazil) at the latequartenary: evidence on the valley Paleodepth at the rio dos Touros hydrographic basin

Pereira, Josielle Samara 16 March 2017 (has links)
Submitted by Fabielle Cheuczuk (fabielle.cheuczuk@unioeste.br) on 2017-09-01T14:13:36Z No. of bitstreams: 2 Josielle_Pereira_2017.pdf: 8525010 bytes, checksum: 1de2e1b7a0dd91b489e9259aa59dfd88 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-09-01T14:13:36Z (GMT). No. of bitstreams: 2 Josielle_Pereira_2017.pdf: 8525010 bytes, checksum: 1de2e1b7a0dd91b489e9259aa59dfd88 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-03-16 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / A significant number of studies has investigated the surface of Palmas (Paraná state)/Água Doce (Santa Catarina state), in the south of Brazil, aiming at understanding the evolution of its geomorphologic landscape in relation to the phenomena of pedogenesis and morphogenesis and, therefore, contributing with studies of the quaternary. It remains unclear, however, if the recognized phenomena are present on a local or a regional scale. Additionally, few studies have considered the continental quaternary in the Southern state of Rio Grande do Sul. Within this context, the present work attempts to identify the abovementioned scale as well as to contribute to the continental paleoenvironmental reconstruction of the South of Brazil. More specifically, the objective of this study is to recognize the occurrence of pedogenesis and morphogenesis phenomena on the surface of São José dos Ausentes (Rio Grande do Sul state) at the Late Quaternary, based on evidence from stratigraphic records of valley paleodepth of second-order hierarchy, in and attempt to understand the evolutionary picture of the second-order hierarchy valley. The methodological approach involved the use of a set of litho-, pedo-, allo- and chronostratigraphic criteria to characterize the materials from the pedostratigraphic section, as well as fieldwork and laboratory analyses. Thirty (30) stratigraphic horizons were recognized in the studied stratigraphic section, and they were distributed in three colluvial sequences – upper pedogenized; middle; and basal colluvial – and one pedogenetic hydromorphic sequence located at the base of the section. The integration of the results revealed that during the Late Interstadial (> 25,000 years BP), at the valley paleodepth, there were hydromorphic soil and hypodermic water flows on its drainage axis, similar to those found of the surface of Palmas/Água Doce, corresponding to the pedogenesis predominance phase. Afterwards, there was continuous action of the morphogenesis, generated by the alternation between processes of subtle mass-movement and surface runoff. The first morphogenesis events were punctual and responsible, and occurred between the end of the Last Interstadial and the Last Glacial Maximum. During the Last Glacial Maximum, the morphogenesis began to be governed by surface runoff. From >25.000 to >19.150 years BP, the sedimentation of colluvial units generated the pedostratigraphic levels equivalent to the basal colluvial sequence. From 19.150 years BP onwards, the sedimentation lost intensity and erosion predominated, promoting the installation of linear erosive incisions (paleogully) that truncated the basal colluvial sequence and part of the hydromorphic level. Soon after that, the morphogenesis again registers sedimentation governed by surface runoff. As a consequence, the colluvial units related to the intermediate colluvial sequence were generated. This phase lasted from <7.940 to >4.860 years BP, corresponding to the mid-Holocene. After 4.860 years BP, the morphogenesis continued to act, originating the upper colluvial sequence, however it lost vigor by the action of the pedogenesis, thus favoring melanization of the sequence. At this phase, the second order valley paleodepth became completely collimated and remobilized, constituting a morphology similar to the slope slightly inclined to the modern low-order hierarchy axis. / Muitos trabalhos foram realizados na superfície de Palmas(PR)/Água Doce(SC) buscando entender a evolução da paisagem geomorfológica dessa área relacionada aos fenômenos de pedogênese e morfogênese, contribuindo assim, aos estudos quaternários. Entretanto, algumas dúvidas ainda persistem para o entendimento no quadro evolutivo da dita área e uma delas é em identificar se os fenômenos reconhecidos se apresentam em uma escala local ou regional. Por outro lado, há poucos trabalhos referentes ao estudo do Quaternário Continental no Estado do Rio Grande do Sul. É nesse contexto que o presente trabalho está inserido, bem como visa responder à dúvida elencada e também contribuir para a reconstrução paleoambiental continental do sul do Brasil. Assim sendo, a presente pesquisa tem como objetivo reconhecer a ocorrência de fenômenos de pedogênese e morfogênese na Superfície de São José dos Ausentes (RS) no Quaternário Tardio, através de evidências em registros estratigráficos de paleofundo de vale de segunda ordem hierárquica e busca, desse modo, entender o quadro evolutivo do vale de segunda ordem hierárquica. A abordagem metodológica utilizada envolveu o uso conjunto de critérios lito-, pedo-, alo- e cronoestratigráficos na caracterização dos materiais da seção pedoestratigráfica, sendo realizado trabalho de campo e análises laboratoriais. Na seção estratigráfica estudada, foram reconhecidos 30 horizontes estratigráficos, distribuídos em três sequências coluviais, sendo elas: superior pedogeneizada; intermediária; e basal, e uma sequência pedogenética hidromórfica localizada na base da seção. A integração dos resultados mostrou que durante o Último Interestadial (> 25.000 anos AP), no paleofundo de vale havia solo hidromórfico e fluxos de água hipodérmicos em seu eixo de drenagem, similares àquelas encontradas na Superfície de Palmas/Água Doce, correspondendo à fase de predomínio da pedogênese. Posteriormente, houve a atuação contínua da morfogênese, gerada pela intercalação entre os processos de movimento de massa sutis e escoamento superficial. Os primeiros eventos da morfogênese foram pontuais e responsáveis, e ocorreram entre o final do Último Interestadial e o Último Máximo Glacial. Durante o Último Máximo Glacial a morfogênese passou a ser comandada pelo escoamento superficial. Entre >25.000 a >19.150 anos AP a sedimentação de unidades coluviais gerou os níveis pedoestratigráficos correspondentes à sequência coluvial basal. A partir de 19.150 anos AP a sedimentação perdeu intensidade e passou a predominar a erosão, promovendo estabelecimento de incisão erosiva linear (paleovoçoroca) que truncou a sequência coluvial basal e parte do nível hidromórfico. Logo após, a morfogênese retorna a registrar sedimentação comandada pelo escoamento superficial. Em decorrência foram geradas as unidades coluviais referentes à sequência coluvial intermediária. Tal fase durou entre <7.940 a >4.860 anos AP equivalendo ao Holoceno Médio. Após 4.860 anos AP a morfogênese continuou atuando dando origem à sequência coluvial superior, porém esta perdeu vigor através da atuação da pedogênese, favorecendo assim, a melanização da referida sequência. Nessa fase o paleofundo de vale de segunda ordem passou a ser plenamente colmatado e reafeiçoado, constituindo uma morfologia similar à encosta suavemente inclinada para o eixo de baixa ordem hierárquica moderna.
20

Analyses of Common Elements and Oxides in the Paleosols of the Bahamas and of the Northern Mariana Islands

Ersek, Vasile 07 August 2004 (has links)
Paleosols from the Bahamas and the Northern Mariana Islands (CNMI) are closely related to past atmospheric circulation and dust load. In the Bahamas the sources of insoluble residue (IR) must be allogenic because the islands consist of almost pure carbonates. The Al2O3:TiO2 ratio was used to establish the provenance of the IR of the paleosols. Comparisons of this ratio from Bahamian paleosols, North African dust, Lesser Antilles ash and North American loess reveal that the African dust is the major contributor to the IR, with a potential minor volcanic input from the Lesser Antilles. The contribution of the North American loess to the IR was not determined because of geochemical similarities with the North African dust. The study of two outcrops in Eleuthera indicate that paleosols can act as aquicludes. The Bahamian samples were collected on a roughly north-south transect in order to establish the climatic influence on paleosol properties. Even though there is a marked climatic gradient in the Bahamas, the paleosol geochemistry shows no trend that could be related to paleoclimate. While previous studies indicated that the source of insoluble residues in the soils of CNMI is carbonate dissolution, the present study shows that atmospheric deposition of ash from the Mariana arc and dust from the Asian continent may play a significant role in paleosol formation.

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