DEGEO - Departamento de Geologia
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/8
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Resultados da Pesquisa
Item Estimated degradation of the Caatinga based on modern pollen rain deposited in reservoirs.(2022) Ledru, Marie-Pierre; Cassino, Raquel Franco; Gomes, Vaneicia dos Santos; Sfair, Julia Caram; Araújo, Francisca Soares deThe vegetation cover is the result of many biological and abiotic interactions. To identify the different factors that cause changes is crucial when defining future sustainable development and protection of natural resources. In the Brazilian semiarid region, the vegetation cover has been subjected to drastic deforestation and land use at centennial-scale that has led to desertification. Pollen analysis is an efficient tool to reconstruct the different processes of degradation of the vegetation cover over time. We built a referential data set for the vegetation cover using 48 pollen surface samples collected in the reservoirs of the Ceará. We used satellite images for comparison with the pollen signatures and defined an alteration score to express the correlation between terrestrial pollen and anthropic cover. Our results showed our surface samples to be generally representative of the vegetation cover and of the general degradation of the landscape. Our study areas can be considered as degraded as the initial categories “preserved” or “intermediary” are not reflected in the pollen assemblages, in agreement with results of botanical surveys and the historical background. The on-going process of desertification is climate-independent and was initiated many decades or centuries ago by intensive land use for agriculture and grazing.Item An Upper Pleistocene macroflora indicates warm and dry climate during an interglacial in central Brazil.(2021) Follador, Gabriela Luiza Pereira Pires; Cassino, Raquel Franco; Varajão, Angélica Fortes Drummond Chicarino; Rodrigues, Jonathas de Souza BittencourtThis study is the first report of the fossil macroflora of the Paleolagoa Seca, an Upper Quaternary fossil locality of lacustrine origin in central Brazil. Here we present an analysis of well-preserved fossil leaves collected from an argillite level dated at ca. 43,000 cal yr BP and discuss the paleoclimatic implications of this record. We reconstructed paleotemperature and paleoprecipitation using Leaf Margin Analysis (LMA) and Leaf Area Analysis (LAA), respectively, and used mineralogical (XRD and IR) and palynological analyses of the fossiliferous level to assess a complete picture of the past landscape. To test the ability of LMA and LAA models available for Southern Hemisphere to correctly predict Mean Annual Temperature (MAT) and Mean Annual Precipitation (MAP) for the Paleolagoa Seca, we applied several calibration models to the leaf dataset of a modern Cerrado forest and then compared predictions with modern climate data. Six LMA calibration models presented consistent MAT results and all four LAA calibration models provided satisfactory estimations of the modern MAP. The botanical iden- tification of the fossil leaves and the pollen record indicated a mosaic of open savanna, dry forests and gallery forest around the Paleolagoa Seca. The reconstructed MAP for the Paleolagoa Seca ranged between 647 and 948 mm depending on the LAA equation, which is at least 500 mm lower than the current MAP. The recon- structed Mean Annual Temperature (MAT) ranged between 22.6 and 26.3 ◦C, indicating a higher-than-present MAT, which we relate to a combination of high summer insolation and low humidity. Comparison with other local fossil macrofloras, including from nearby localities, and with other paleoclimatic records suggests that the observed dry conditions at Paleolagoa Seca were related to interhemispheric climate forcing and to a weakening of the South American Summer Monsoon (SASM).Item Quantitative reconstruction of vegetation cover from modern pollen rain in the Cerrado biome of Brazil.(2021) Cassino, Raquel Franco; Ledru, Marie-PierreFossil pollen assemblages are an important tool to reconstruct vegetation variability at centennial and millennial- scales. However, in the Cerrado biome of Brazil, the influence of the local vegetation, the heterogeneity of the landscape and the accuracy of pollen identification leads to a wide margin of error in interpretation. In this study, we present a method of quantitative reconstruction of past vegetation cover (forest, savanna, and grassland) that accounts for these different aspects. Our method is based on analysis of 47 surface samples collected in the southern Cerrado biome (east-central Brazil). First, we defined criteria that can be used to identify the local ecosystem (lake, marsh, palm swamp, or gallery forest) represented by the pollen assemblages. The pollen as- semblages were then compared to data extracted from vegetation maps, resulting in the assessment of three pollen score equations related to each of the vegetation types (forest, savanna, and grassland). Based on these scores, we developed linear regression models that can be used to reconstruct the proportion of each type of land cover from pollen assemblages. We compared the results obtained for three different areas (respectively with 300 m, 500 m, and 1 km radius) to evaluate the size of the pollen source area for the Cerrado sites. We apply our models to two fossil pollen records to illustrate their use and application. Our method for the quantitative reconstruction of past land cover in the Cerrado biome is a new tool to investigate climate drivers and the long- term effects of fire in this Neotropical savanna.Item Vegetation and fire variability in the central Cerrados (Brazil) during the Pleistocene-Holocene transition was influenced by oscillations in the SASM boundary belt.(2020) Cassino, Raquel Franco; Ledru, Marie-Pierre; Santos, Rudney de Almeida; Favier, CharlyThis study investigates historical fire regimes and arboreal cover variability in the Brazilian Cerrados, a large Neotropical savanna ecosystem, during the Pleistocene-Holocene transition and early Holocene, and then tests whether the observed variation is linked to South American Summer Monsoon (SASM) variability. We present high-resolution pollen, XRF and charcoal records from Lagoa Feia, located in central Cerrados, and assess how they compare with other pollen records from the surrounding region to investigate regional trends of vegetation and fire regime variability. Our results show that the Pleistocene-Holocene transition was marked by a wet episode, which included moist forest expansion and rising lake levels, that correlates well with increased monsoon activity in a large area of central South America during the same period. This wet episode chronologically coincides with the Younger Dryas cold episode in the northern hemisphere. Our data revealed moisture declines in central Cerrados after 11.2 kyr BP, along with centennial-scale fluctuations from dry to wet conditions throughout the early Holocene period until around 6 kyr BP. These dry/wet oscillations are associated with weakened SASM activity and repeated shifts of its belt position during this time range. Fire activity increased in central Cerrados just after the onset of drier conditions during the early Holocene, and likely contributed to decreased arboreal cover at that time. A trend of increasing moisture in the region was observed after 6 kyr BP. Our study reveals how centennial and millennial-scale changes in monsoon activity influenced arboreal cover, diversity and fire regimes in the central Cerrados.Item A methodological proposal for the analysis of Cladocera (Crustacea, Branchiopoda) subfossils from sediments of temporary aquatic ecosystems.(2019) Silva, Edissa Emi Cortez; Cassino, Raquel Franco; Leibowitz, Zachary William; Sant'Anna, Eneida Maria EskinaziThe main objective of the present study was to promote some adaptations to the standard methodology used in the analysis of Cladocera subfossils. The samples used in this study were collected at Lagoa dos Coutos, a temporary lake located on an outcrop with iron-rich duricrust in the Serra do Gandarela (Minas Gerais, Brazil). The sediment from this pond, typical of temporary ecosystems in the region, is characterized by rigid concretions that are difficult to dissolve in aqueous media, making it difficult to visualize and analyze subfossils taxa. Sediment samples were prepared according to the standard methodology used in paleolimological studies and the methodological adaptations proposed in the present study, which included the addition of 1 mg of Kochia scoparia, a palynological marker used to estimate subfossil density, as well as the addition of hydrofluoric acid (HF) to oxidize silicate materials. The samples prepared according to the new methodological procedure improved Cladocera subfossil visualization, facilitating the taxonomic analysis of the species. The samples submitted to the standard methodological procedure had a significantly higher mean of sediment particles (mean of 84.2 sediment particles) and 70% more residues compared to the samples prepared with the newly proposed methodology (mean of 22.1 sediment particles). Absolute data on the temporal variation of the density of Cladocera subfossils was obtained by using the palinological marker K. scoparia, which showed higher densities of subfossils in more recent, humid periods (112,000 subfossils/cm3 at 5 cm, equivalent to 3,500 years BP). The results indicate that the new methodology can contribute to advances in paleolimnological studies of temporary aquatic ecosystems, whose lake histories are rarely investigated, despite their ecological relevance as ecosystems that indicate environmental and climatic changes.Item A Late Quaternary palynological record of a palm swamp in the Cerrado of central Brazil interpreted using modern analog data.(2018) Cassino, Raquel Franco; Martinho, Caroline Thaís; Caminha, Silane Aparecida Ferreira da SilvaThe fossil pollen record from a Late Quaternary peat core collected in the São José palm swamp, in the northwest region of Minas Gerais state (Central Brazil), is interpreted using a dataset of modern pollen spectra as modern analogs. Principal component analysis and dissimilarity coefficients were used to compare fossil and modern samples, supporting the interpretation of past environmental dynamics. The results suggest that at ca. 15,700 and ca. 15,400 cal years BP, the buriti (Mauritia flexuosa) palm (that characterizes the palm swamps today) was absent and the climate was colder. Around 15,200 cal years BP, the increasing occurrence of buriti and the development of the Cerrado stricto sensu, a savanna woodland, indicate a warmer climate. At the end of the Late Pleistocene and during the Pleistocene-Holocene transition, the palm swamp central zone expanded and a dense Cerrado stricto sensu developed, suggesting a warm and humid climate. By the end of the Early Holocene, a much drier climate is suggested by the shrinkage of the palm swamp and a more open regional vegetation. Subsequently, and until ca. 4400 cal years BP, a wetter climate is indicated by the extended central zone of the São José palm swamp that reached a maximum expansion at ca. 6500 cal years BP. After 3500 cal years BP, the predominance of the Campo Sujo, a herbaceous-shrubby vegetation, indicates the return of relatively dry conditions. In the last two millennia, a decrease in the extent of the humid zone of the palm swamp suggests an intensification of drier conditions. Lower precipitation inferred at the end of the Holocene, and the predominantly humid conditions in the Middle Holocene, is different from the general pattern observed in southern and western Cerrado sites, but is in agreement with paleoclimate data from Northeastern Brazil.Item Diversidade de grãos de pólen das principais fitofisionomias do cerrado e implicações paleoambientais.(2016) Cassino, Raquel Franco; Martinho, Caroline Thaís; Caminha, Silane Aparecida Ferreira da SilvaO Cerrado é um dos biomas com maior biodiversidade florística do Brasil e encerra uma grande diversidade de formações vegetais. A história do Cerrado e suas modificações ao longo dos últimos milênios, influenciadas, entre outros fatores, por mudanças climáticas, foram determinantes no estabelecimento das características atuais da paisagem nas regiões dominadas por essa vegetação. O conhecimento da flora polínica característica dos diferentes ambientes que fazem parte desse bioma tem importantes aplicações. Por exemplo, estudos palinológicos de sedimentos depositados no Quaternário tardio constituem uma importante fonte de dados sobre a história recente do Cerrado e sobre a paleoecologia do Brasil Central. O estudo desses registros deve se basear no conhecimento de conjuntos polínicos atuais e na relação observada entre esses conjuntos e a vegetação atual. Com essa finalidade, neste catálogo, são apresentados sessenta tipos polínicos identificados em amostras superficiais coletadas em três parques nacionais, áreas de preservação da vegetação do Cerrado. Estão assinaladas a ocorrência e a abundância de cada tipo polínico nos diversos ambientes amostrados e foram caracterizados os táxons polínicos que podem ser considerados indicadores desses ambientes em estudos paleoecológicos.Item Reconstituição paleoambiental do Chapadão dos Gerais (Quaternário Tardio) a partir da análise palinológica da vereda Laçador, Minas Gerais, Brasil.(2013) Cassino, Raquel Franco; Meyer, Karin Elise BohnsA análise palinológica de um testemunho sedimentar coletado em uma vereda, denominada Vereda Laçador, em Buritizeiro, Minas Gerais, resultou na elaboração de um modelo de evolução paleoambiental para o Quaternário tardio da região do Chapadão dos Gerais, no Bioma Cerrado. Duas fases de clima mais frio que o atual foram registradas, uma delas no fi nal do Pleistoceno (ca. 13.250 anos cal. AP) e a outra, entre aproximadamente 11.500 e 10.500 anos cal. AP. Intercalados a estas fases mais frias ocorreram dois períodos de expansão da vereda sob um clima quente e semi-úmido semelhante ao atual. No Holoceno tardio, após cerca de 7.000 anos cal. AP, a presença de um clima quente e mais seco que o atual foi registrado pela retração da vereda, aumento de elementos herbáceos e presença de elementos arbóreos adaptados ao clima semi-árido. A comparação com dados palinológicos de estudos prévios permitiu verifi car a infl uência de mudanças climáticas regionais na região do Chapadão dos Gerais.Item Modern pollen spectra of the Cerrado vegetation in two national parks of Central Brazil, and implications for interpreting fossil pollen records.(2015) Cassino, Raquel Franco; Martinho, Caroline Thaís; Caminha, Silane Aparecida Ferreira da SilvaTwenty four surface sampleswere collected for palynological analysis fromdifferent environments in the Cerrado biome, which extends over a vast area in Central Brazil. These samples were used to investigate the relationship between vegetation and pollen spectra in the Cerrado and, thereby, contribute to amore precise interpretation of fossil pollen records from this region, particularly those collected on palm swamps. Pollen grains from the phytophysiognomy that surrounds the palm swamp generally occur in low percentages in surface samples, whereas local plants are very abundant in the pollen spectra. Although local taxa tend to predominate, two aspects of the landscapemay be reconstructed fromthe pollen spectra using numericalmethods: the local environment of the deposition site and the surrounding regional vegetation. Using PCA and dissimilarity coefficient analysis, a group of seventeen taxa and a group of fourteen arboreal taxa are proposed as those that provide improved results when investigating the local environment and regional vegetation, respectively. Because herbaceous taxa are very abundant in the palm swamps, an analysis of the content of arboreal taxa in the pollen spectra is more appropriate for reconstructing the openness of the regional vegetation.Item Morfologia de grãos de pólen e esporos de níveis holocênicos de uma vereda do Chapadão dos Gerais (Buritizeiro, Minas Gerais), Brasil.(2011) Cassino, Raquel Franco; Meyer, Karin Elise BohnsEsporos de briófitas e pteridófitas e grãos de pólen de gimnospermas e angiospermas foram obtidos em quinze amostras de um testemunho de sedimentos holocênicos, de 150 cm de profundidade, coletado em uma vereda no Chapadão dos Gerais, em Buritizeiro (Minas Gerais, Brasil). As idades radiocarbônicas variaram entre 11.370+70 anos AP na base do testemunho e 1440+25 anos AP no nível do topo. Os 92 taxons identificados foram descritos em suas características morfológicas e abordados em seu habito e habitat, a partir das informações existentes para as plantas modernas relacionadas. As formas identificadas e ilustradas contribuem para o conhecimento da flora polínica do Cerrado e constituem material de referencia na identificação de palinomorfos em trabalhos de reconstituição do paleoambiente em áreas hoje cobertas ou relacionadas a este bioma.