Navegando por Assunto "Paleoecologia"

Agora exibindo 1 - 5 de 5

Acesso aberto (Open Access)
A comunidade de tubarões (Chondrichthyes : selachii : Galea) da formação pirabas, Neógeno da Amazônia Oriental
(Universidade Federal do Pará, 2005-03-10) COSTA, Sue Anne Regina Ferreira da; RICHTER, Martha; http://lattes.cnpq.br/9381228195500524; TOLEDO, Peter Mann de; http://lattes.cnpq.br/3990234183124986
The shark community (Selachii:Galea) from the Pirabas Formation in one of the most representative of the Neogene in South America due to its high diversity of taxa and range of ecological components. The presence of eight known genera enabled to establish hypothesis about the trophic chain of the vertebrate palaeocommunity, as well as to corroborate previous reconstructions about the paleoenvironmental parameters of this geologic unit. This study dealt with the taxonomic revision of the shark community on both generic and species leveis, allowing the following composition: Carcharhinus spl, Carcharhinus sp2, Carcharhinus sp3, Carcharhinus priscus, Sphyrna magna, Hemipristis serra, Carcharodon megalodon, Isurus sp, Ginglymostoma serra, Ginglymostoma obliquum. The analyses of newly collected specimens and microscopic material allowed a considerable expansion of identified individuals up to 231 teeth. This work is a contribution to refine the knowledge about the regional patterns of shark paleobiogeography.
Acesso aberto (Open Access)
Environmental changes during the last millennium based on multi-proxy palaeoecological records in a savanna-forest mosaic from the northernmost Brazilian Amazon region
(Universidade Federal do Pará, 2015-09) MENESES, Maria Ecilene Nunes da Silva; COSTA, Marcondes Lima da; ENTERS, Dirk; BEHLING, Hermann
The environmental changes and the dynamics of the savanna-forest mosaic, over the last 1050 years, have been reconstructed by pollen, charcoal, radiocarbon dating mineralogical and geochemical analyses of sediment cores taken from three different Mauritia flexuosapalm swamps in the northernmost part of the Brazilian Amazon region (northern state of Roraima). Studies on the relationship between the modern pollen rain and the regional vegetation provide additional information for the interpretation of the fossil pollen records. The fossil pollen assemblages and geochemical results indicate relatively wet climatic conditions throughout the recorded period. Despite these moist conditions, fires were frequent and are one of the reasons for the dominance of a grassy savanna instead of forest expansion in the study area. Considering the generally wet climatic conditions, these fires were most likely caused by human activities. Even today, fires hinder forest expansion into savanna areas. Sandy hydromorphic soils may also act as an edaphic control to maintain the current sharp boundary between forest and savanna ecosystems.
Acesso aberto (Open Access)
Ictiólitos da Formação Pirabas, mioceno do Pará, Brasil, e suas implicações paleoecológicas
(Universidade Federal do Pará, 2011-06-01) COSTA, Sue Anne Regina Ferreira da; RICHTER, Martha; http://lattes.cnpq.br/9381228195500524; ROSSETTI, Dilce de Fátima; http://lattes.cnpq.br/0307721738107549
The Pirabas Formation (Oligo-miocine), which is represented by carbonates deposits through the Brazilian Coastal Area between the States of Pará and Piauí, is recognized for its fossil richness. Among the many fossils paleoichthyofauna stands out for its abundance in outcrops, but the absence of stratigraphic and facies control of these fossil restricted their potential use in paleoenvironmental interpretations. The joint use of the technique of wet sieving for the recovery of ichthyoliths and microfacies and facies analysis of sediments taken from Pirabas Formation deposits, which were exposed in the B17 mine (Capanema-PA), allowed for the first time the use of vertebrate fossil for the elaboration of an interdisciplinary paleoenvironmental reconstruction model. The 3594 recovered ichthyoliths, along with the 5 facies associations and the 4 carbonate microfacies, led to the conclusion that these deposits of Pirabas Formation were formed in marine-marginal depositional system, with different environments genetically associated as shore face (surf zone), beach, lagoon, tidal channel and tidal delta, which would be part of an estuarine system with the influence of wave, marked by four different depositional cycles related to possible transgressiveregressive episodes. The estuarine environment was confirmed by the assembly of ichthyoliths, observing that this assembly is formed by both freshwater specimens, represented by the Characidae family, an unheard occurrence for the unit until then, as for marine specimens, for example, the sharks. Several dental types, possibly attributed to representatives of brackish waters, such as the genera Dasyatis and Sarpa, both equally registered for the first time, also strengthens the proposed environment. The distribution of the ichthyological community evidences palaeoenvironmental control, having registered their highest abundance in deposits of tidal channel. However, the influence of relative sea level resulted in the development of transgressive-regressive depositional cycles, which also exerted strong control on the stratigraphic distribution of the B17 Mine registered ichthyoliths, reinforcing the importance of interdisciplinary studies in refining palaeoecological reconstruction of this unit.
Acesso aberto (Open Access)
Inferências paleoambientais para o Nordeste da Amazônia Oriental a partir do estudo de registros fósseis e composição isotópica de carbono (d13C) e oxigênio (d18O) em rocha total de carbonatos da Formação Pirabas (PA), Mioceno Inferior
(Universidade Federal do Pará, 2015-11-03) FERREIRA, Denys José Xavier; RUIVO, Maria de Lourdes Pinheiro; http://lattes.cnpq.br/9419564604488031
The Lower Miocene (~23¿16 Ma.) from the Northeastern Eastern Amazon has aroused interest in the scientific community during many decades. It belongs to a geological Epoch characterized by a transition period to the modern world, and marked by many climatic and geological changes, that allowed the establishment of a rich fauna and flora. Within this context, Pirabas Formation is discussed. It is an Lower Miocene unit characterized by great carbonate and silicate sediment deposition, considered one of the most significant paleontological units from Brazilian Cenozoic. Many researches were developed on Pirabas Formation, which allowed the accuracy of reconstruction interpretation of its possible Miocene landscape. Even though there were efforts related to the recuperation of paleoenvironment information from Northeastern Eastern Amazon trough the integration among fossil and sediment data, as well as stratigraphic and facies information, there’s still a lack in researches related to the recuperation of integrated and refined information in paleoenvironment between paleocomunity and geochemical studies. This gap of studies illustrates Pirabas Formation as an important elucidative unit for past scenarios and regional environment evolution, as well as being of great relevance for the comprehension of impacts from global Miocene events in Brazilian territory, specially in northern Atlantic coast. The main objective of this work, of multidisciplinary approach, is to refine the paleoenvironment interferences in Pirabas Formation, related to space disposition of paleoenvironment and the dynamic of sea level in Northern Pará State. For the study, three areas were chosen due to its importance and logistic: Ponta do Castelo (Fortaleza Island), Atalaia Beach (Salinopólis City) and B-17 Mine (Capanema City). The methods used in this research were diversity analysis, dominance and similarity of paleofauna, as well as Correspondence Analysis (CA), from fossil data from Pirabas Formation in order to characterize the paleoenvironment; and the composition of stable carbon isotopes (δ13C) and oxygen (δ18O), in carbonate whole rocks from the studied unit, to comprehend the paleoenvironment dynamics. The results indicated: 1) the diversity of the registered paleofauna for the areas in Formação Pirabas is apparently related to the type of depositional environment, in which Capanema and Salinópolis are similar for presenting restricted depositional environment, such as lagoon and estuary, and Fortaleza Island indicated better association to the coastal shelf during marine regression; 2) there are predominancy relations between the paleoenvironment according to the temporal representativeness of some facies from the respective depositional cycles in each studied area, as the coast line approaches during marine regression. ; 3) Ponta do Castelo is related to a paleoenvironment of marine/coastal predominance; Atalaia Beach to lagoon with estuary influences; and B-17 Mine to estuary and fluvial; 4) there was a tendency to carbon isotopes (δ13C) impoverishment, indicating the continental influence in the coast during marine regression; 5) and propensity to oxygen isotopes (δ18O) enrichment, reveling influences of the latitude and continent formation effects in the areas during sea retrieve. Trough the results of this research it was possible to understand the space distribution of the paleoenvironment of predominancy (suggested term this work) in Northeastern Eastern Amazon, as well as refine the paleoenvironment interference methods to Pirabas Formation.
Acesso aberto (Open Access)
Padrões na estruturação de comunidades de mamíferos terrestres na América do Sul
(Universidade Federal do Pará, 2001-12-19) DINIZ, Felipe Monteiro; TOLEDO, Peter Mann de; http://lattes.cnpq.br/3990234183124986
In the analysis of the causes that lead to the convergence of patterns in the structure of terrestrial mammalian faunas in South America, there have always been a challenge to obtain an exact portrayal of observable evolutionary processes in larger scales. In this paper, we aimed at the analysis of the distributional patterns for South American terrestrial mastofauna, trying to correlate the different communities with distinct graphs through the use of a refined coenogram method. It takes into account ecological variables that influence the distribution and size of species (feeding, locomotion, and weight), and examines the possibilities of application of this methodology in the analysis of extinct South American terrestrial mammalian faunas. The results show some consistency in using such methodology for extant assemblages, and also a good possibility of its application for extinct ones. However, some considerations should be made on gaps in the knowledge over distributional patterns of current mammalian faunas, such as the evolutionary and ecological relationship between mammals and the South American continent.