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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.
71

Late Pliocene–Early Pleistocene North Atlantic Circulation: Integrating Dinocyst Assemblages and Foraminiferal Geochemistry

Hennissen, Jan 07 August 2013 (has links)
During the Late Pliocene, between 3.3 Ma and 2.6 Ma, tectonic events changed ocean basin interactions against a background of shifting orbital forcing mechanisms and a global cooling trend. A climate system that had been locked in a stable, warm state gradually transformed into one typified by the high-amplitude glacial–interglacial fluctuations characteristic of the later Quaternary. The onset of Northern Hemisphere glaciations in the Late Pliocene marks an important step in this transition, due to the role of feedback mechanisms including ice albedo. A crucial factor in this Northern Hemisphere ice sheet expansion is the North Atlantic surface ocean circulation. To evaluate how they are linked, a ca. 200-kyr time slab spanning 2782-2520 ka (Late Pliocene–Early Pleistocene) was analyzed at millennial scale resolution from eastern North Atlantic Deep Sea Drilling Project (DSDP) Site 610 and Integrated Ocean Drilling Program (IODP) Site U1313. The causes of the Plio-Pleistocene climatic turnover are compared to that of the well-documented Marine Isotope Stage (MIS) M2 occurring in the Late Pliocene (3.3 Ma). MIS M2, a severe glacial event seen as a precursor to later Quaternary-style glaciations, was investigated from western North Atlantic DSDP Site 603. Utilizing a same-sample methodology, two paleoceanographic proxies were used: (1) dinocyst assemblages, and (2) foraminiferal geochemistry (δ18O and Mg/Ca). Dinocysts are proven tracers of sea-surface temperature (SST), salinity, nutrient supply, and sea ice cover, and are analyzed here to characterize the overlying water masses at the studied sites. Strong dinocyst assemblage fluctuations attest to variations in the influence of the North Atlantic Current (NAC). Using Mg/Ca ratios for the planktonic foraminifer Globigerina bulloides to determine absolute SSTs allows salinity changes to be reconstructed when combined with stable oxygen isotopes. This study shows a persistent Gulf Stream–NAC in the western North Atlantic during MIS M2, favoring a southern shift of the NAC over a shutdown of the thermohaline circulation. At the newly established Plio-Pleistocene boundary, a profound turnover in dinoflagellate cyst assemblages reveals a shift in ocean mode during MIS 104 (2.6 Ma). Three distinct dinocyst ecozones demonstrate this fundamental reorganization of the North Atlantic circulation.
72

Vývoj pleistocénního zalednění české části Šumavy (Případová studie z okolí Černého a Čertova jezera) / Development of Pleistocene glaciation of the Czech part of the Šumava Mts. (Case study of the Černé and Čertovo Lakes)

Vočadlová, Klára January 2011 (has links)
This Ph.D. thesis presents new facts about a paleoenvironmental development of the northern part of the Bohemian Forest (area of Černé Lake and Čertovo Lake) in the Late Pleistocene and Early Holocene. The main goals of the research are: characterize the glacier landforms in the Bohemian Forest and define the variance of these landforms; determine factors influencing formation and development of the glaciation in the study area; describe environmental settings and its changes during deglaciation and in Early Holocene by using environmental proxies. This research proceeds from original data obtained by geomorphological mapping, morphometric analysis and proxy data analyses originated from a sediment sequence in a peat bog in the Černé Lake vicinity. The common attributes of the Bohemian Forest cirques and cirque variability was determined using morphometric and morphologic characteristics of the cirques on the Bavarian and Czech side of the mountain range. These characteristics were compared with other cirques of the Bohemian Massif and other chosen mountain ranges of the world. The cirque overdeepening was defined on the basis of headwall shapes and it emerged that overdeepening of the cirques in the Bavarian Forest and in the High Sudetes reflects a different extent of the Pleistocene glaciation....
73

Microbialitos e microfósseis da Formação Sete Lagoas, Neoproterozoico, Brasil: implicações geomicrobiológicas em um contexto de mudanças climáticas e evolutivas / not available

Sanchez, Evelyn Aparecida Mecenero 11 February 2015 (has links)
A Formação Sete Lagoas, base do Grupo Bambuí, tem sido alvo de constantes discussões sobre o contexto temporal e ambiental sob a qual esta unidade foi depositada. Sua idade tem sido atribuída a dois momentos distintos do Neoproterozoico, e ambas têm implicações evolutivas significativas. A primeira proposta, baseadas em dados geoquímicos e litoestratigráficos,relaciona a deposição da Formação Sete Lagoas após o fim da glaciação Marinoana (do modelo paleoclimático Snowball Earth), há cerca de 635 Ma, quando mudanças paleogeográficas e geoquímicas levaram a mudanças climáticas de escala global, o quepode ter impactado significativamente na bioprodutividade do Edicarano. O segundo modelo deposicional baseia-se na ocorrência de Cloudina sp., um fóssil-guia do Ediacarano final, em níveis estratigráficos próximos à base da Formação Sete Lagoas, apontando, portanto, para uma idade mais nova que a primeira hipótese. No entanto, ambos os modelos preveem um cenário de mudanças, ocorridas no Neoproterozoico tardio, enquanto a Formação Sete Lagoas estava sendo depositada. Tais mudanças foram de natureza climática, paleogeográfica e geoquímica, que influenciaram a composição da atmosfera e da hidrosfera, e culminaram em profundas mudanças na biosfera. Propôs-se aqui uma análise pormenorizada de microbialitos e microfósseis da Formação Sete Lagoas, visando compreender como os produtores, base dos ecossistemas, teriam respondido a tantas transformações ambientais e ecológicas, além de estabelecer a abrangência estratigráfica dos microbialitos e microfósseis desta unidade. Foram analisadas tramas de microbialitos carbonáticos e precocemente silicificados, amostras de mão para comparação e dados de afloramentos. Uma avaliação de materiais reportados em meados e na segunda metade do século passado também foi necessária, tendo em vista os avanços recentes no campo da Paleobiologia do Pré-Cambriano. Os dados demonstraram que a Formação Sete Lagoas conta com uma riqueza treze formasmicrobialíticas, sendo onze detalhadas neste trabalho e encontradas ao longo de toda a formação, tanto sobre o Cráton do São Francisco, quanto sobre a Faixa Brasília, porém em baixa quantidade. Estas formas são compostas por onze tipos de tramas, cujo conteúdo biogênico em última análise, remete, mesmo que de forma reliquiar, à formas cianobacterianas recentes reconhecidas como formadoras de estromatólitos. Por outro lado, microfósseis silicificados não são comuns, e foram observados apenas em três localidades, onde já tinham sido reportados. Porém, a re-análise deste material permitiu refinar os dados e identificar cinco táxons, quatro cianobacterianos - os gêneros Siphonophycus, Oscillatoriopsis e Eosynechococcus- e um Incertae sedis - o gêneroArchaeotrichion. A baixa diversidade de microfósseis, ou seja, baixa riqueza e baixa abundância, somada à baixa abundância e densidade de microbialitos nos afloramentos analisados foi interpretada como resultados de eventos diagenéticos e tectônicos que resultaram na perda de material. Outra vertente do  presente trabalho foi a re-avaliação de estruturas reportadas como fósseis há cerca de 50 anos, cuja interpretação à luz dos conhecimentos atuais, permitiram a identificação de alguns como pseudofósseis, a reclassificação deuma espécie de acritarco esferomórfico (Leiosphaeridia jacutica[Timofeev 1966]) e de outro espécime como provável Nemiana simplexPalij 1976. De um modo geral, pode-se perceber que, embora poucos espécimes tenham sido preservados, o registro fóssil da Formação Sete Lagoas é variado e inclui microbialitos, microfósseisbentônicos e planctônicos, identificados neste trabalho, além de icnofósseis, biomarcadores e metazoários reportados em trabalhos anteriores, mas que ainda demandam novas considerações. A ocorrência vertical de microbialitos ao longo de toda a unidade e a diversidade de tramas que os compõem demonstram que a bioprodutividade não sofreu declínio com as mudanças paleoambientais, seja por conta de mudanças climáticas, se considerarmos a Formação Sete Lagoas como capa carbonática, seja pelo estabelecimento de metazoários nos ecossistemas, se a considerarmos uma unidade depositada a partir do Ediacarano tardio. / The Sete Lagoas Formation, base of BambuíGroup, has been under constant discussion about the temporal and environmental context under it was deposited. Its age has been attributed to two different moments ofNeoproterozoic, each one comprising significative evolutionay changes. The first one, based on geochemical and lithostratigraphic data, related the deposition of Sete Lagoas Formation to the end of Marinoan glacial episode (the Snowball Earthpaleoclimatic model), ca. 635 Ma, when pelogeographic and geochemical changes resulted in global climatic changes, that could result in significative impacts over the Ediacaran bioprodutivity. The second age model is based on the occurrence of Cloudinasp., an index fossil of Terminal Neoproterozoic, in stratigraphic levels near the base ofthe formation, pointing for a younger age that previously proposed. However, both modelspredict a scenario of environmental changes, occurred during the Late Ediacaran, while the Sete Lagoas Formation deposited. Such changes include climatic, paleogeographic and geochemical, that influenced the composition of atmosphere and hydrosphere, what resulted in profound changes in the biosphere. Here it was proposed a detailed study of microbialites and silicified microfossils of Sete Lagoas Formation, aiming to understand the responses of producers, the framework of any ecosystem, would reacted to suchpaleoenvironmental and ecological changes, as well also establish the stratigraphic occurrence of Sete Lagoas Formatiom microbialites and microfossils. Fabrics of carbonate and early silicified microbialites were analyzed, aswell hand samples for comparison and data acquired in the outcrops. Previous reported material, collect in the past half century was also re-evaluated due to new knowledge concerning the Paleobiology of Precambrian. The data showed that the Sete Lagoas Formation has a richness of thirteen microbialite forms, which eleven were detailed in this paper and found throughout the unit, on the São Francisco Craton, as well on the Brasília Fold Belt, but in low abundance. These forms are composed of eleven types of fabrics, which biogenic content ultimately refers, even if reliquiar preservation, to Recent cyanobacteria recognized as mat formers. Moreover, silicified microfossils are not common, and were only observed in three localities, where they had already been reported. However, re-analysis of this material allowed to refine the data and identify five taxa, four cyanobacteria - Siphonophycus, Oscillatoriopsis, Eosynechococcus- and one Incertae sedis - Archaeotrichion. The low diversity of microfossils, including low richness and low abundance, coupled with the low abundance and density of microbialites in outcrops were interpreted as a result of diagenetic and tectonic events that resulted in the loss of material. Another aspect of this work was the re-evaluation of structures reported as fossils for about 50 years, whose interpretation in the light of updated knowledge, allowed the identification of some pseudofossils as the reclassification ofa species of sphaeromorphic acritarch (Leiosphaeridia jacutica [Timofeev 1966]) and putative Nemiana simplexPalij 1976. In general, it can be seen that, although a few specimens have been preserved, the fossil record of the Sete Lagoas Formation is varied and includes microbialites, benthic and planktonic microfossils, identified in this work, as well as trace fossils, biomarkers and metazoan reported in previous works, which require new considerations. The vertical occurrence of microbialites throughout the unit and the variety of frames that make up demonstrate that bioproductivity did not declined due to paleoenvironmental changes, either due to climate change, considering the formation Sete Lagoas Formation as cap carbonate, or by establishment ofmetazoan ecosystems, if we consider a unit deposited during the Late Ediacaran.
74

Chronologie et impact géomorphologique des glaciations quaternaires dans l'est des Pyrénées

Delmas, Magali 24 November 2009 (has links) (PDF)
L'objectif de cette étude est d'évaluer la part de l'empreinte glaciaire dans les paysages de la haute montagne aux latitudes moyennes. Peut-on transposer au Quaternaire la très grande efficacité de l'érosion glaciaire mesurée actuellement dans certaines montagnes et faire de cet agent le principal acteur de la morphogenèse ? Doit-on au contraire constater une forte résilience des paléoformes tertiaires et donc la faiblesse relative de l'érosion glaciaire ? Le domaine est-pyrénéen offre un terrain privilégié en raison du fort contraste nord-sud qui caractérise l'emprise spatiale et l'impact géomorphologique des paléoenglacements quaternaires. Deux axes de recherche complémentaires structurent ce travail. Le premier concerne la chronologie et la paléogéographie des glaciations quaternaires. Une cartographie géomorphologique détaillée permet de reconstituer les paléoemprises glaciaires. La production et l'exploitation de 81 datations 10Be fournissent une nouvelle vision du cycle würmien et contribuent au débat sur le caractère synchrone ou asynchrone des paléoenglacements de montagne, donc de la réponse continentale aux changements globaux. Sur ces bases chronologiques et cartographiques, le deuxième axe de ce travail vise à mesurer la variabilité spatio-temporelle de l'empreinte géomorphologique des glaciations. Il est possible (i) d'apprécier, pour le cycle würmien, la tranche érodée globale (~ 5 m) et la variabilité temporelle de l'érosion glaciaire grâce à la quantification du volume sédimentaire mobilisé sur le Sud Carlit, (ii) de mesurer et tenter d'expliquer la variabilité spatiale de l'empreinte glaciaire quaternaire à travers une analyse morphométrique de l'ensemble des cirques du domaine d'étude.
75

Quaternary glaciation of central Banks Island, NT, Canada

Lakeman, Thomas Ryan Unknown Date
No description available.
76

Morphological and behavioural responses of threespine stickleback (Gasterosteus aculeatus) to abrupt alterations in their selective landscape

Leaver, Stephen 03 November 2011 (has links)
Graduate
77

Vegetation and climate history of the Fraser Glaciation on southeastern Vancouver Island, British Columbia, Canada

Miskelly, Kristen Rhea 12 December 2012 (has links)
Pollen records from southeastern Vancouver Island, British Columbia, show changes in vegetation and climate from the late Olympia Interstade through the Fraser Glaciation. This study provides important insights into phytogeographic patterns of Pacific Northwest flora, leads to an enhanced understanding of processes affecting present-day ranges of several plant taxa, and provides a historical perspective on the origin of coastal alpine ecosystems. Evidence for a previously unrecognized glacial advance in the region at ~21,000 14C yr BP, herein called the Saanich glacier, is provided. The results reveal widespread habitat and food sources suitable for the mega fauna that lived on southern Vancouver Island during the last glaciation. Vegetation during the Fraser Glaciation represented a mosaic of plant communities across a heterogeneous and productive landscape. Pollen spectra indicate that plant assemblages, dominated by Poaceae and Cyperaceae, were widespread. Similarities to tundra in northern Alaska and high elevation sites in British Columbia were detected. Vegetation varied geographically in the late Olympia (ca. 33,500-29,000 14C yr BP). Grassy uplands with scattered trees and local moist meadows occurred at Qualicum Beach under mesic and cool conditions, while cold and dry grass tundra prevailed at Skutz Falls. Increased non-arboreal pollen percentages at Qualicum Beach, 29,000 14C yr BP, reflect expansion of grassy meadows with diverse herbs under a cool and dry climate at the onset of the Fraser Glaciation. At Qualicum Beach between 25,160-24,190 14C yr BP, sedge wetlands were surrounded by open, dry uplands. Concurrently at Osborne Bay, Pinus-Picea-Abies-Poaceae parkland occurred. Dry and cold climate intensified as the Fraser Glaciation progressed after 24,000 14C yr BP and non-arboreal communities expanded. At Cordova Bay, cold and dry tundra or parkland in upland sites, and sedge wetlands on an aggrading floodplain are recorded. Sparse tree cover and grass-tundra surrounded a floodplain at Skutz Falls around 21,000 14C yr BP under cool and dry climate. Subalpine-like Picea-Abies-Pinus parkland and moist, species-rich grassland meadows occurred at McKenzie Bight at the same time. A sedge wetland occupied the site of deposition, and was periodically inundated as lake levels fluctuated. Upland grasslands at Cordova Bay are recorded between 21,600–19,400 14C yr BP, while local ponded areas developed on an aggrading floodplain at sea level. From 19,400-19,300 14C yr BP, parkland at Cordova Bay developed as climate moistened and warmed at the time of the Port Moody Interstade known from the Fraser Lowland. Abundant marine dinoflagellate cysts between 21,600–19,400 14C yr BP, reveal a high sea level stand and strong marine influence at Cordova Bay. Glacioisostatic depression of the crust on the east side of Vancouver Island is the most probable explanation. The presence of pollen-bearing glacio-lacustrine sediments at McKenzie Bight around 21,000 14C yr BP at ~93 m and contemporaneous isostatic crustal depression at Cordova Bay strongly suggest a major glacial body in the region at the same time as the Coquitlam advance in the Lower Mainland. Ice-free landscapes may have occurred on southern Vancouver Island through the Fraser glaciation beyond the Saanich glacier ice limits. / Graduate
78

Late Pliocene–Early Pleistocene North Atlantic Circulation: Integrating Dinocyst Assemblages and Foraminiferal Geochemistry

Hennissen, Jan 07 August 2013 (has links)
During the Late Pliocene, between 3.3 Ma and 2.6 Ma, tectonic events changed ocean basin interactions against a background of shifting orbital forcing mechanisms and a global cooling trend. A climate system that had been locked in a stable, warm state gradually transformed into one typified by the high-amplitude glacial–interglacial fluctuations characteristic of the later Quaternary. The onset of Northern Hemisphere glaciations in the Late Pliocene marks an important step in this transition, due to the role of feedback mechanisms including ice albedo. A crucial factor in this Northern Hemisphere ice sheet expansion is the North Atlantic surface ocean circulation. To evaluate how they are linked, a ca. 200-kyr time slab spanning 2782-2520 ka (Late Pliocene–Early Pleistocene) was analyzed at millennial scale resolution from eastern North Atlantic Deep Sea Drilling Project (DSDP) Site 610 and Integrated Ocean Drilling Program (IODP) Site U1313. The causes of the Plio-Pleistocene climatic turnover are compared to that of the well-documented Marine Isotope Stage (MIS) M2 occurring in the Late Pliocene (3.3 Ma). MIS M2, a severe glacial event seen as a precursor to later Quaternary-style glaciations, was investigated from western North Atlantic DSDP Site 603. Utilizing a same-sample methodology, two paleoceanographic proxies were used: (1) dinocyst assemblages, and (2) foraminiferal geochemistry (δ18O and Mg/Ca). Dinocysts are proven tracers of sea-surface temperature (SST), salinity, nutrient supply, and sea ice cover, and are analyzed here to characterize the overlying water masses at the studied sites. Strong dinocyst assemblage fluctuations attest to variations in the influence of the North Atlantic Current (NAC). Using Mg/Ca ratios for the planktonic foraminifer Globigerina bulloides to determine absolute SSTs allows salinity changes to be reconstructed when combined with stable oxygen isotopes. This study shows a persistent Gulf Stream–NAC in the western North Atlantic during MIS M2, favoring a southern shift of the NAC over a shutdown of the thermohaline circulation. At the newly established Plio-Pleistocene boundary, a profound turnover in dinoflagellate cyst assemblages reveals a shift in ocean mode during MIS 104 (2.6 Ma). Three distinct dinocyst ecozones demonstrate this fundamental reorganization of the North Atlantic circulation.
79

Microbialitos e microfósseis da Formação Sete Lagoas, Neoproterozoico, Brasil: implicações geomicrobiológicas em um contexto de mudanças climáticas e evolutivas / not available

Evelyn Aparecida Mecenero Sanchez 11 February 2015 (has links)
A Formação Sete Lagoas, base do Grupo Bambuí, tem sido alvo de constantes discussões sobre o contexto temporal e ambiental sob a qual esta unidade foi depositada. Sua idade tem sido atribuída a dois momentos distintos do Neoproterozoico, e ambas têm implicações evolutivas significativas. A primeira proposta, baseadas em dados geoquímicos e litoestratigráficos,relaciona a deposição da Formação Sete Lagoas após o fim da glaciação Marinoana (do modelo paleoclimático Snowball Earth), há cerca de 635 Ma, quando mudanças paleogeográficas e geoquímicas levaram a mudanças climáticas de escala global, o quepode ter impactado significativamente na bioprodutividade do Edicarano. O segundo modelo deposicional baseia-se na ocorrência de Cloudina sp., um fóssil-guia do Ediacarano final, em níveis estratigráficos próximos à base da Formação Sete Lagoas, apontando, portanto, para uma idade mais nova que a primeira hipótese. No entanto, ambos os modelos preveem um cenário de mudanças, ocorridas no Neoproterozoico tardio, enquanto a Formação Sete Lagoas estava sendo depositada. Tais mudanças foram de natureza climática, paleogeográfica e geoquímica, que influenciaram a composição da atmosfera e da hidrosfera, e culminaram em profundas mudanças na biosfera. Propôs-se aqui uma análise pormenorizada de microbialitos e microfósseis da Formação Sete Lagoas, visando compreender como os produtores, base dos ecossistemas, teriam respondido a tantas transformações ambientais e ecológicas, além de estabelecer a abrangência estratigráfica dos microbialitos e microfósseis desta unidade. Foram analisadas tramas de microbialitos carbonáticos e precocemente silicificados, amostras de mão para comparação e dados de afloramentos. Uma avaliação de materiais reportados em meados e na segunda metade do século passado também foi necessária, tendo em vista os avanços recentes no campo da Paleobiologia do Pré-Cambriano. Os dados demonstraram que a Formação Sete Lagoas conta com uma riqueza treze formasmicrobialíticas, sendo onze detalhadas neste trabalho e encontradas ao longo de toda a formação, tanto sobre o Cráton do São Francisco, quanto sobre a Faixa Brasília, porém em baixa quantidade. Estas formas são compostas por onze tipos de tramas, cujo conteúdo biogênico em última análise, remete, mesmo que de forma reliquiar, à formas cianobacterianas recentes reconhecidas como formadoras de estromatólitos. Por outro lado, microfósseis silicificados não são comuns, e foram observados apenas em três localidades, onde já tinham sido reportados. Porém, a re-análise deste material permitiu refinar os dados e identificar cinco táxons, quatro cianobacterianos - os gêneros Siphonophycus, Oscillatoriopsis e Eosynechococcus- e um Incertae sedis - o gêneroArchaeotrichion. A baixa diversidade de microfósseis, ou seja, baixa riqueza e baixa abundância, somada à baixa abundância e densidade de microbialitos nos afloramentos analisados foi interpretada como resultados de eventos diagenéticos e tectônicos que resultaram na perda de material. Outra vertente do  presente trabalho foi a re-avaliação de estruturas reportadas como fósseis há cerca de 50 anos, cuja interpretação à luz dos conhecimentos atuais, permitiram a identificação de alguns como pseudofósseis, a reclassificação deuma espécie de acritarco esferomórfico (Leiosphaeridia jacutica[Timofeev 1966]) e de outro espécime como provável Nemiana simplexPalij 1976. De um modo geral, pode-se perceber que, embora poucos espécimes tenham sido preservados, o registro fóssil da Formação Sete Lagoas é variado e inclui microbialitos, microfósseisbentônicos e planctônicos, identificados neste trabalho, além de icnofósseis, biomarcadores e metazoários reportados em trabalhos anteriores, mas que ainda demandam novas considerações. A ocorrência vertical de microbialitos ao longo de toda a unidade e a diversidade de tramas que os compõem demonstram que a bioprodutividade não sofreu declínio com as mudanças paleoambientais, seja por conta de mudanças climáticas, se considerarmos a Formação Sete Lagoas como capa carbonática, seja pelo estabelecimento de metazoários nos ecossistemas, se a considerarmos uma unidade depositada a partir do Ediacarano tardio. / The Sete Lagoas Formation, base of BambuíGroup, has been under constant discussion about the temporal and environmental context under it was deposited. Its age has been attributed to two different moments ofNeoproterozoic, each one comprising significative evolutionay changes. The first one, based on geochemical and lithostratigraphic data, related the deposition of Sete Lagoas Formation to the end of Marinoan glacial episode (the Snowball Earthpaleoclimatic model), ca. 635 Ma, when pelogeographic and geochemical changes resulted in global climatic changes, that could result in significative impacts over the Ediacaran bioprodutivity. The second age model is based on the occurrence of Cloudinasp., an index fossil of Terminal Neoproterozoic, in stratigraphic levels near the base ofthe formation, pointing for a younger age that previously proposed. However, both modelspredict a scenario of environmental changes, occurred during the Late Ediacaran, while the Sete Lagoas Formation deposited. Such changes include climatic, paleogeographic and geochemical, that influenced the composition of atmosphere and hydrosphere, what resulted in profound changes in the biosphere. Here it was proposed a detailed study of microbialites and silicified microfossils of Sete Lagoas Formation, aiming to understand the responses of producers, the framework of any ecosystem, would reacted to suchpaleoenvironmental and ecological changes, as well also establish the stratigraphic occurrence of Sete Lagoas Formatiom microbialites and microfossils. Fabrics of carbonate and early silicified microbialites were analyzed, aswell hand samples for comparison and data acquired in the outcrops. Previous reported material, collect in the past half century was also re-evaluated due to new knowledge concerning the Paleobiology of Precambrian. The data showed that the Sete Lagoas Formation has a richness of thirteen microbialite forms, which eleven were detailed in this paper and found throughout the unit, on the São Francisco Craton, as well on the Brasília Fold Belt, but in low abundance. These forms are composed of eleven types of fabrics, which biogenic content ultimately refers, even if reliquiar preservation, to Recent cyanobacteria recognized as mat formers. Moreover, silicified microfossils are not common, and were only observed in three localities, where they had already been reported. However, re-analysis of this material allowed to refine the data and identify five taxa, four cyanobacteria - Siphonophycus, Oscillatoriopsis, Eosynechococcus- and one Incertae sedis - Archaeotrichion. The low diversity of microfossils, including low richness and low abundance, coupled with the low abundance and density of microbialites in outcrops were interpreted as a result of diagenetic and tectonic events that resulted in the loss of material. Another aspect of this work was the re-evaluation of structures reported as fossils for about 50 years, whose interpretation in the light of updated knowledge, allowed the identification of some pseudofossils as the reclassification ofa species of sphaeromorphic acritarch (Leiosphaeridia jacutica [Timofeev 1966]) and putative Nemiana simplexPalij 1976. In general, it can be seen that, although a few specimens have been preserved, the fossil record of the Sete Lagoas Formation is varied and includes microbialites, benthic and planktonic microfossils, identified in this work, as well as trace fossils, biomarkers and metazoan reported in previous works, which require new considerations. The vertical occurrence of microbialites throughout the unit and the variety of frames that make up demonstrate that bioproductivity did not declined due to paleoenvironmental changes, either due to climate change, considering the formation Sete Lagoas Formation as cap carbonate, or by establishment ofmetazoan ecosystems, if we consider a unit deposited during the Late Ediacaran.
80

Утицај глацијалног процеса на засипање Лукавичко-луковског краса (Црна Гора) / Uticaj glacijalnog procesa na zasipanje Lukavičko-lukovskog krasa (Crna Gora) / The Impact of glacial process on sedimentary filling of the Lukavičko-lukovski karst (Montenegro)

Đurović Mirela 12 December 2020 (has links)
<p>Лукавичко-луковски&nbsp; крас&nbsp; припада&nbsp; Динарском&nbsp; красу.&nbsp; Налази&nbsp; се&nbsp; у&nbsp; средишњем&nbsp; делу Црне&nbsp; Горе,&nbsp; у&nbsp; области&nbsp; површи&nbsp; и&nbsp; брда.&nbsp; Представља&nbsp; западни&nbsp; део&nbsp;&nbsp; Mорачких&nbsp; планина,&nbsp; у висинској зони од 820 до 2050&nbsp; m&nbsp; н.в. Ову област изграђују различите мезозојске карбонатне стене&nbsp; прекривене&nbsp; седиментима&nbsp; квартарне&nbsp; старости.&nbsp; На&nbsp; овом&nbsp; простору&nbsp; формирани&nbsp; су различити&nbsp; генетски&nbsp; типови&nbsp; рељефа&nbsp; са&nbsp; доминацијом&nbsp; крашког&nbsp; рељефа.&nbsp; Просторним&nbsp; и временским&nbsp; преклапањем&nbsp; крашког&nbsp; процеса&nbsp; са&nbsp; глацијалним&nbsp; процесом&nbsp; формиран&nbsp; је&nbsp; сложен глациокрашки&nbsp; рељеф.&nbsp; Плеистоценска&nbsp; глацијација&nbsp; оставила&nbsp; је&nbsp; значајне&nbsp; последице,&nbsp; а&nbsp; као најважнија је засипање краса моренским и претранспортованим моренским материјалом.Применом&nbsp; Schmidt&nbsp; Hammer&nbsp; теста&nbsp; утврђена&nbsp; је&nbsp; релативна&nbsp; хронологија&nbsp; различитих типова&nbsp; квартарних&nbsp; седимената.&nbsp; Реконструкцијом&nbsp; ерозивних&nbsp; и&nbsp; акумулативних&nbsp; облика глацијалног&nbsp; рељефа&nbsp; анализиран&nbsp; је&nbsp; интезитет,&nbsp; обим&nbsp; и&nbsp; број&nbsp; глацијалних&nbsp; фаза.&nbsp; Утврђено&nbsp; је постојање три старије глацијалне фазе и једне млађе, у временском распону од MIS 12 преко MIS&nbsp; 6&nbsp; и&nbsp; MIS&nbsp; 5d&nbsp; &ndash;&nbsp; 2&nbsp; до&nbsp; млађег&nbsp; дријаса.&nbsp; Засипање&nbsp; Лукавичко-луковског&nbsp; краса&nbsp; извршено&nbsp; је моренским&nbsp; материјалом&nbsp; и&nbsp; његовим&nbsp; претранспортовањем&nbsp; од&nbsp; стране&nbsp; флувијланог, денудационог и гравитационог процеса. Засипање је било делимично и потпуно. Делимично засипање извршено је субподинским моренама, док је потпуно засипање везано за просторе<br />чеоних&nbsp; и&nbsp; ивичних&nbsp; морена.&nbsp; Акумулација&nbsp; претранспортованог&nbsp; моренског&nbsp; материјала&nbsp; је највиши степен потпуног засипања краса када су поља, као највећи крашки облици рељефа, у потпуности засута.</p> / <p>Lukavičko-lukovski&nbsp; kras&nbsp; pripada&nbsp; Dinarskom&nbsp; krasu.&nbsp; Nalazi&nbsp; se&nbsp; u&nbsp; središnjem&nbsp; delu Crne&nbsp; Gore,&nbsp; u&nbsp; oblasti&nbsp; površi&nbsp; i&nbsp; brda.&nbsp; Predstavlja&nbsp; zapadni&nbsp; deo&nbsp;&nbsp; Moračkih&nbsp; planina,&nbsp; u visinskoj zoni od 820 do 2050&nbsp; m&nbsp; n.v. Ovu oblast izgrađuju različite mezozojske karbonatne stene&nbsp; prekrivene&nbsp; sedimentima&nbsp; kvartarne&nbsp; starosti.&nbsp; Na&nbsp; ovom&nbsp; prostoru&nbsp; formirani&nbsp; su različiti&nbsp; genetski&nbsp; tipovi&nbsp; reljefa&nbsp; sa&nbsp; dominacijom&nbsp; kraškog&nbsp; reljefa.&nbsp; Prostornim&nbsp; i vremenskim&nbsp; preklapanjem&nbsp; kraškog&nbsp; procesa&nbsp; sa&nbsp; glacijalnim&nbsp; procesom&nbsp; formiran&nbsp; je&nbsp; složen glaciokraški&nbsp; reljef.&nbsp; Pleistocenska&nbsp; glacijacija&nbsp; ostavila&nbsp; je&nbsp; značajne&nbsp; posledice,&nbsp; a&nbsp; kao najvažnija je zasipanje krasa morenskim i pretransportovanim morenskim materijalom.Primenom&nbsp; Schmidt&nbsp; Hammer&nbsp; testa&nbsp; utvrđena&nbsp; je&nbsp; relativna&nbsp; hronologija&nbsp; različitih tipova&nbsp; kvartarnih&nbsp; sedimenata.&nbsp; Rekonstrukcijom&nbsp; erozivnih&nbsp; i&nbsp; akumulativnih&nbsp; oblika glacijalnog&nbsp; reljefa&nbsp; analiziran&nbsp; je&nbsp; intezitet,&nbsp; obim&nbsp; i&nbsp; broj&nbsp; glacijalnih&nbsp; faza.&nbsp; Utvrđeno&nbsp; je postojanje tri starije glacijalne faze i jedne mlađe, u vremenskom rasponu od MIS 12 preko MIS&nbsp; 6&nbsp; i&nbsp; MIS&nbsp; 5d&nbsp; &ndash;&nbsp; 2&nbsp; do&nbsp; mlađeg&nbsp; drijasa.&nbsp; Zasipanje&nbsp; Lukavičko-lukovskog&nbsp; krasa&nbsp; izvršeno&nbsp; je morenskim&nbsp; materijalom&nbsp; i&nbsp; njegovim&nbsp; pretransportovanjem&nbsp; od&nbsp; strane&nbsp; fluvijlanog, denudacionog i gravitacionog procesa. Zasipanje je bilo delimično i potpuno. Delimično zasipanje izvršeno je subpodinskim morenama, dok je potpuno zasipanje vezano za prostore<br />čeonih&nbsp; i&nbsp; ivičnih&nbsp; morena.&nbsp; Akumulacija&nbsp; pretransportovanog&nbsp; morenskog&nbsp; materijala&nbsp; je najviši stepen potpunog zasipanja krasa kada su polja, kao najveći kraški oblici reljefa, u potpunosti zasuta.</p> / <p>The&nbsp; Lukavičko-lukovski&nbsp; karst&nbsp; belongs&nbsp; to the&nbsp; Dinaric&nbsp; karst.&nbsp; It occupies&nbsp; the&nbsp; central&nbsp; part&nbsp; of Montenegro&nbsp; within&nbsp; the&nbsp; area&nbsp; of&nbsp; plains&nbsp; and&nbsp; hills.&nbsp; Representing&nbsp; the&nbsp; western&nbsp; part&nbsp; of&nbsp; the&nbsp; Morača Mountains&nbsp; it&nbsp; is&nbsp; placed&nbsp; between&nbsp; 820&nbsp; to&nbsp; 2050&nbsp; m&nbsp; a.s.l.&nbsp; The&nbsp; area&nbsp; is&nbsp; built&nbsp; by&nbsp; different&nbsp; Mesozoic carbonate rocks and the overlying Quaternary sediments. Among different genetic types of relief, the karst one&nbsp; is prevailing. The spatial and temporal overlap of karst and glacial processes&nbsp; led to complex&nbsp; glaciokarst&nbsp; relief.&nbsp; Pleistocene&nbsp; glaciation&nbsp; left&nbsp; behind&nbsp; considerable&nbsp; changes&nbsp; including&nbsp; the karst filled by moraine and re-transported moraine material as the most significant. Implementing&nbsp; the&nbsp; Schmidt&nbsp; Hammer&nbsp; test&nbsp; the&nbsp; relative&nbsp; chronology&nbsp; of&nbsp; different&nbsp; Quaternary sediments was determined.&nbsp; The intensity, extent, and a number of glacial phases were analyzed by reconstruction&nbsp; of&nbsp; erosive&nbsp; and&nbsp; accumulative&nbsp; forms&nbsp; in&nbsp; glacial&nbsp; relief.&nbsp; The&nbsp; existence&nbsp; of&nbsp; three&nbsp; older glacial phases and a younger once, within&nbsp; the temporal range from MIS 12 over MIS 6 and&nbsp; MIS 5d &ndash;&nbsp; 2 to the Younger Dryas has been resolved. Filling of the Lukavičko -lukovski karst by moraine and&nbsp; re- deposited&nbsp; moraine&nbsp; material&nbsp; under&nbsp; fluvial,&nbsp; denudation,&nbsp; and&nbsp; gravity&nbsp; processes&nbsp; was&nbsp; partial&nbsp; to complete. The former take place by piedmont moraines, while the later were caused by terminal and lateral moraines. Accumulation of re-deposited moraine material&nbsp; is the highest stage of karst filling when karst polje as the largest karst landform becomes completely inhumated.</p>

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