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Acesso aberto (Open Access)
Contribuição dos sedimentos e ictiólitos para a identificação do ambiente de formação do Sambaqui do Moa (Saquarema-RJ)
(Universidade Federal do Pará, 2014-08-28) MACHADO, Sauri Moreira; SILVA, José Francisco Berrêdo Reis da; http://lattes.cnpq.br/1338038101910673; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302
The Moa’s shellmound is an archaeological site located in Itaúna, Saquarema coastline from the State of Rio de Janeiro. Three moments of occupation were recognized this site: stratum 3 corresponding to the beginning of the occupation of this site basis; 2, intermediate, points to a more intense occupation with great concentration of mollusks, fish bones and human burials; and 1, the most superficial, related to the last occupation. To identify the environmental conditions of development from Moa’s shellmound, sediment samples and zooarchaeological material were collected in these three strata. The zooarchaeological material is represented by microscopic fish remains (ichthyoliths), composed by microteeth with different morphologies: canines, incisors and molars. The sediments according to XRD analyzes are composed by quartz and kaolinite, calcite, aragonite and fluorapatite. The latter is the main mineral of zooarchaeological material, while calcite and aragonite reflect the remains of shells contained there, abundant in this site. The mineralogical analyses were confirmed by chemical analysis, in which high levels of P2O5, CaO and FB (H2O, CO2), account for the fluorapatite, calcite and aragonite. Chemical modifications variations of the C and P in microteeth suggest that these experienced mineralization, an initial fossilization process, post-deposition. The data of stable isotopes 13C and 15N allowed defining the source of organic matter from Moa’s shellmound as marine/brackish, where the vegetation is represented, predominantly, for C3 plants by type of rainforest. The 87Sr/86Sr ratios in ichthyoliths confirm that the environment surrounding the shellmound as estuary. The tooth morphology allowed us to recognize five families previously not recorded for the site, as Labridae, Serranidae, Ariidae, Erythrinidae and Characidae, which confirm the estuarine environment. The age of the Moa’s shellmound by radiocarbon from the sediments showed disruption of stratum 2, causing a reversal of aged strata which can be explained by processes of formation and/or changes in the rivers changed the geological and geomorphological settings area. Another explanation could be human interference, due to the large number of burials (over 30), has upset the order of the moments of occupation from Moa’s shellmound, and possible erosion. The Moa’s shellmound is therefore installed in an area of marine-estuarine transition.
Acesso aberto (Open Access)
Detecção de mudanças paleoambientais no litoral do Rio Grande do Norte (RN) durante o Holoceno médio e superior
(Universidade Federal do Pará, 2017-08-16) BATISTA, Edson José Louzada; FRANÇA, Marlon Carlos; http://lattes.cnpq.br/8225311897488790
The vegetation dynamics during the Holocene on the coastal region of Rio Grande do Norte (RN) was characterized by mangrove establishment, expansion and contraction. The dynamics of this vegetation is mainly related to the sedimentary dynamics and to the relative sea level change (RSL) recorded for this period. During the last millennium, sedimentary process controlled the vegetation dynamics along stratigraphic profiles formed by sequences of active tidal channels, followed by abandonment. Therefore, based on grain size, sedimentary structures, pollen data, isotopic data (δ13C and δ15N), C/N ratio and 14C dating of the sedimentary organic matter of two cores (NAT 6 and NAT 8) sampled in the tidal plain, shows a paleoenvironmental model since mid- to late-Holocene (~7 k yr BP to modern), described by four facies associations: (A) estuary/channel, represented by massive sandy deposits (facies Sm) and mud deposition; (B) abandoned channel, represented by the wavy heterolithic bedding (facies Hw), lenticular heterolytic bedding (facies H1) and small intervals with massive sand (facies Sm); (C) active channel, corresponding to massive sandy deposits (facies Sm); and (D) low marsh (mangroves/herbaceous plain and palms), represented by clay deposits with lenticular heterolithic bedding (facies Hl). In this context, short-time (millennium/century) changes between mangroves and other associated vegetation in this region are not necessarily related to RSL or to the climatic changes (allocyclic process), but to the sedimentary dynamics (autocyclic process) must have controlled mainly the pollen assembly along the stratigraphic profiles studied.
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)
A resposta dos manguezais de um estuário do sul da Bahia sob influência das mudanças do clima, flutuações do nível do mar e dinâmica dos canais durante o Holoceno
(Universidade Federal do Pará, 2017-06-09) OLIVEIRA, Nêdra Nunes; COHEN, Marcelo Cancela Lisboa; http://lattes.cnpq.br/8809787145146228
This work integrates palynology, sedimentology, geomorphology and radiocarbon dating, as well as δ13C, δ15N, and C/N from sedimentary organic matter obtained by the description of a core (5,20 m deep) sampled ~8 km from current coastline, 2m above sealevel at Jucuruçu River valley, near the city of Prado, south coast Bahia-Brazil. Based on this core and previously published works, the effects of climate and Relative Sea-level (RSL) changes on Jucuruçu’s mangroves during the Holocene were detailed. Along the studied core two phases were identified and correlated with others sediment cores. The first phase occurred in part of the middle Holocene (7200 - <6950 cal yr BP), developed on a tidal flat colonized by mangrove. It presents a transition from C3 terrestrial plants to marine organic matter upward this phase. On second phase, a fluvial plain developed followed by a mangrove shrinkage and, herbaceous and ferns expansion. At this phase, the biogeochemical data revealed an increased trend to organic matter sourced from freshwater. The integration of palaeoenvironmental data reveals an important RSL rise, which caused a marine incursion inside this river valley and allowed mangroves establishment under a strong estuarine influence, this incursion reached ~23 km upstream during the middle Holocene. The RSL fall at the middle and late Holocene caused a gradual mangrove replacement by mainly herbaceous vegetation associated to freshwater plankton predominance up river, while mangroves and marine algae migrated to the Jucuruçu river mouth. A decrease fluvial discharge during early and middle Holocene most likely favored this mangrove migration pattern and estuarine/marine organic matter spreading upstream. In contrast, probably the mangrove establishment at river mouth up present days was favored by an increase fluvial discharge at late Holocene. Noteworthy is the fact that tidal channels dynamics have controlled mangrove distribution last thousand years. Therefore, this study allowed to identify and to describe the effects of allogenic (caused by climate and RSL change) and autogenic processes (conducted, for example, by channels dynamic).