Navegando por CNPq "CNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA::SEDIMENTOLOGIA"

Agora exibindo 1 - 20 de 37

Acesso aberto (Open Access)
Acúmulo e fracionamento de fósforo nos sedimentos do estuário do rio Coreaú (Ceará) para avaliação do impacto da carcinicultura
(Universidade Federal do Pará, 2014-11-17) AQUINO, Rafael Fernando Oliveira; KAWAKAMI, Silvia Keiko; http://lattes.cnpq.br/5306256489815710; CORRÊA, José Augusto Martins; http://lattes.cnpq.br/6527800269860568
The shrimp culture (shrimp farms) is one of the activities of aquaculture widely employed in Brazilian estuaries and mangroves. The shrimps are fed with phosphate enriched compounds. Thus, the effluent produced by farms can accelerate the eutrophication process. An increase of shrimp farming has been seen in Coreaú River Estuary, state of Ceará, but data about environmental quality are scarce to allow monitoring of the region. The aim of the present research was to assess the contribution of the shrimp farms on phosphorus input to the Coreaú River Estuary. The main forms of phosphorus: bioavailable (P-Exch); bound to iron oxy-hydroxides (P-Fe), on the biogenic, autigênica carbonates and apatite (P-CFAP), on the detrital apatite (P-FAP) and organic phosphorus (P-Org) and as well as total organic carbon (%TOC) and chlorophyll-a were determined in samples of surface sediments and cores from the margins of the Coreaú River Estuary. The high concentrations of P-Total in surface sediments indicated the need for monitoring studies. The larger fraction was P-Fe, composing 30% of P-Total, approximately. These results indicate the ability of the iron oxy-hydroxides to immobilize or release phosphorus. The contribution of the farm’s effluents was evidenced by higher concentrations of P-Org in points adjacent to discharge areas. In sediment cores, the highest P-Total concentrations were found predominantly in fine sediments (silt and clay), with the P-Fe, P-CFAP and P-FAP fractions being the main contributors. The sedimentation rates and concentration increases of P-Total indicate the possible period of deforestation and starting or maximum activity of shrimp farms in the end of the 1980 and mid 1990, respectively. High phosphorus concentrations as well as %TOC and chlorophyll-a levels suggested a significant anthropogenic contribution, associated with a high potential for eutrophication.
Acesso aberto (Open Access)
Análise da dinâmica morfo-sedimentar da praia da Marieta – Ilha do Marco-Maracanã (NE do Pará)
(Universidade Federal do Pará, 2010-04-19) GUERREIRO, Juliana de Sá; EL-ROBRINI, Maâmar; http://lattes.cnpq.br/5707365981163429
This study aims the investigation of the morphological and sedimentological variations occurred in Marieta’s Beach- Marco Island (NE of Pará) during the rainy season (March) and rainyless season (November) of 2007, seeking to identify the main factors responsible by these variations. The Marieta’s beach has 3 km long, with NW-SE direction, and is supported by the sediments of the Barreiras Group, Post-Barreiras and the recent sediments that provide much of the sediment at the mouth of the estuary Urindeua. Topographic profiles were conducted in June in the following subdivisions Beach Marieta: Sector sandy spit - profiles I and II (tgβ = 0.0015); central section - profiles III, IV (tgβ = 0.0017) and NW sector - and V profiles VI (tgβ = 0.005). We applied the following morphological beach models: Inmam & Guza (1975), Sandy Spur -        in the rainy season         in the rainyless period, Sector Central -      12 in the rainy season        during rainyless. These results show a strong reflection with some dissipation, characterized as Intermediate Bar and Longitudinal with the NW sector, which indicated a Dissipative behavior during the two periods studied, According to Wright & Short (1984) had a whole beach Dissipative behavior during the two periods studied -       in the rainy season         in the less rainy period; And following Masselink & Short (1993) showed the profiles to be modified by tides, with dissipative bars RTR = 4 in the rainy season and RTR= 3.6 in the rainyless period. The beaches are predominantly covered by very fine sand, very well selected and moderately selected, with mesocurtic and platicurtic kurtosis and negative asymmetry at the supratidal zones during the rainy season and in areas of infratidal in the rainyless season in other areas of the beach Marieta were approximately symmetrical and positive asymmetries. The Marieta’s beach has been profiled morpho-sedimentary influenced by the displacement of the Convergence Zone Inter-Tropical (ITCZ) in the rainy season (1736.6 mm) and at rainless (2.4 mm). The speed of the wind was weaker during the rainy season with an average of 6.7 nodes while in the less rainy period the average speed was 11.3 knots with preferential direction NE, and therefore, buckled with higher energy (Hb = 1 , 5 m in the rainy season in March). Coupled with an amplitude of 5.5 m tide reaching the innermost areas of the beach. In the less rainy period, the waves were smaller, compared to the rainy season, which reached 1.2 m combined with an amplitude of 4.8 m tide. Through these parameters showed that the major changes in the beach profile were associated mainly to the interaction of the effects of winds, waves and tides, showing the strong relationship between the shape and orientation of the beach and the incidence of these agents.
Acesso aberto (Open Access)
Análise faciológica da formação Codó (Aptiano superior) na Região de Codó (MA), leste da Bacia do Grajaú
(Universidade Federal do Pará, 2000-09-11) PAZ, Jackson Douglas Silva da; ROSSETTI, Dilce de Fátima; http://lattes.cnpq.br/0307721738107549
The Codó Formation, focused in this paper, is exposed in the adjacencies of Codó town, eastern Maranhão State, where it consists of intergraded shales, limestones and evaporites, laterally continuous, forming shoaling-upward successions averaging 2.5 m in thickness. Sedimentological features, the abundance of freshwater ostracodes and Charophyte algae, as well as the absence of any marine fauna, characterize this unit as a dominantly lacustrine unit, which can be described by three broad facies associations, attributed to: 1. central lake; 2. transitional lake; and 3, marginal lake. The central lake facies association represents the base of the shoaling upward successions and consists of two facies: a) black shale; and b) evaporite. The dominance of shale beds in this association indicates sedimentation in low energy depositional settings, typical of central lake areas, where the abundance of pyrite and the bituminous composition point to highly reducing conditions. The scarcity of infauna is indicated by the complete absence of bioturbation, which is consistent with anoxia. The evaporite facies point to a highly saline lake setting. The transitional facies association consists of: a)laminated argillite; hb)lime- mudstone; c)peloidal limestone (mudstone to packstone); and d)meso-crystalline limestone. These deposits, between central lake and marginal lake facies associations, own in the middle portion of the shoaling upward cycles, consistent with a transitional lacustrine setting. The marginal lake facies association represents the top of the shoaling upward successions and consists of a variety of intergrading lithofacies: ajmassive pelite; b)calcite-arenite; Cc) ostracodal limestone (wackestone to grainstone); d) pisoidal limestone (packstone) ; e)gipsite-arenite; £f) tuffa; and 9) rhythmite. These deposits show an abundance of sedimentary features (i.e., paleosoil, karstic surface, fenestrae) typical of subaerial and/or meteoric exposure, which is consistent with their interpretation as marginal lake deposits. A lacustrine facies model with ramp margin and low energy flow is proposed for the study area, taking into account the following characteristics: 1) low rates of sediment supply; 2) presence of areas with low relief around the lacustrine basin; 3) abundance of sedimentary features recording episodes of subaerial and/or meteoric exposure; and 4) prevalence of marginal facies. This interpretation is further suggested by: 1) the small thickness of the depositional cycles, which is attributed to decreased accommodation; 2) absence of turbiditic deposits, which are typical in lacustrine settings with pronounced slope break; and 3) absence of resedimented deposits, which are also common in bench margin lacustrine settings. The abundance of black shales and evaporites suggests a hydrologically closed lacustrine basin with stratified and saline water column for the study area. The depositonal cycles identified reveal a regressive character for this lacustrine succession. Three types of cycles were recognized: 1) complete shoaling-upward cycle; 2) incomplete shoaling-upward cycle; and 3) flooding-upward cycle. The origin of these cycles is attributed to tectonism, based on the assymetrical vertical stacking pattern. This interpretation is corroborated by the presence of sin- sedimentary deformational features related to sin- depositional sismic activity. The faciological, palaeontological and geochemical data presented in this work suggested on show that the Late Aptian marine transgression recorded in the northern portion of the São Luís-Grajaú Basin did not reach the Codó area.
Acesso aberto (Open Access)
Análise integrada dos depósitos de caulim na região do Rio Capim: fácies, estratigrafia, petrografia e isótopos estáveis
(Universidade Federal do Pará, 2006-09-29) SANTOS JÚNIOR, Antonio Emídio de Araújo; ROSSETTI, Dilce de Fátima; http://lattes.cnpq.br/0307721738107549
The kaolin deposits that occur in the Rio Capim area, east of Cametá Sub-Basin, are inserted in the Ipixuna Formation. This unit distinguishs for presenting one of the largest worldwide kaolin concentrations of excellent quality to the cellulose industry. Beyond the economic character, a great volume of academic works focusing these kaolin deposits had led to pedological and geochemical approaches, but without taking into account their sedimentologic aspects, which are important to understand their genesis. Detailed sedimentologic and stratigraphic studies of the Rio Capim kaolin have been increasingly carried out in the last years, which led to the paleoenvironmental interpretations for the Ipixuna Formation, as well as to discuss better the mode of formation of the soft and semi-flint kaolin units that are typical of this unit. These works served to motivate the integration of sedimentologic and stratigraphic data with optical studies combined with hydrogen and oxygen isotope geochemistry in order to discuss the geologic processes involved in the origin and evolution of the soft and semi-flint kaolin units. The sedimentological analysis consisted in a more detailed facies description and stratigraphic analysis of newly open quarries that were not available during previous investigations. The additional exposures led to a better characterization of the lower kaolin unit, known as the “soft kaolin”, which is well stratified, favoring facies analysis. Hence, the soft kaolin unit consists of kaolinitized sandstones and kaolinitized pelites that were formed in tidally influenced fluvial channels (Facies Association A), tidal channel (Facies Association B), tidal flat/mangrove (Facies Association C), and tidal sand bar/tidal sandy flat (Facies Association D). These depositional environments are attributed to a tide-dominated estuarine system. Petrographic studies and scanning electronic microscopy (SEM) of the kaolin deposits in the study area had their composition was strongly modified after sedimentation. The soft kaolin consists of kaolinitized quartz sandstone and either laminated or massive pelites, which are composed by fragments of meta-volcanic lithic and volcanic felsic rocks, as well as metamorphic and granitics rocks. These lithologies were strongly modified during kaolinitization, as revealed by the intense replacement of the framework grains by kaolinite of three types, named herein as Ka, Kb and Kc kaolinites. Ka kaolinite occurs dominantly associated with kaolinitized sandstones, being characterized by pseudohexagonal crystals 10-30 μm in diameter, which are organized as booklets or vermicular forms that reach up to 400 μm in length. Kb kaolinite dominantes in the pelites, and consists of pseudohexagonal crystals 1-3 μm in diameter, occurring as isolated, face-to-face and parallel to pseudo-parallel crystals. Kc kaolinite forms pseudohexagonal to hexagonal crystals of 200 nm in diameter. It occurs dispersed through the soft unit, increasing significantly in abundance in association with paleosols at the top of the unit. The semi-flint kaolin deposits are constituted mainly of reworked grains derived from the underlying soft kaolin unit that are mixed with grains derived from metamorphic and granitic sources. These deposits are dominantly composed of Kc kaolinite that was formed during weathering. The deuterium (δD) and oxygen (δO) isotope analysis of the kaolin deposits from the study area helped to discuss better the evolution of the different types of kaolinites described above. Hence, the soft kaolin deposits display δO values varying between 6.04 ‰ and 19.18 ‰ in the Ka+Kb kaolinites, and between 15.38 ‰ and 24.86 ‰ in the Kc kaolinite. The δD values from this unit vary from – 63.06 ‰ to 79.46 ‰, and from –68.85‰ to -244.35‰ in the Ka+Kb and Kc kaolinites, respectively. The semi-flint kaolin deposits are characterized by δO and δD values ranging from 15.08‰ to 21.77‰, and from -71.31‰ to -87.37‰, respectively. Based on these data and on the isotopic composition of both meteoric and ground waters, it was possible to conclude that the kaolinites had not been formed in balance with modern weathering. These values represent the isotopic composition during the time of formation of the kaolinites, as well as mineralogical contamination of framework grains that are now replaced by kaolinites.
Acesso aberto (Open Access)
Aplicação da cromatografia líquida de alta eficiência na investigação de hidrocarbonetos policíclicos aromáticos em testemunhos sedimentares
(Universidade Federal do Pará, 2013-07-31) EVANGELISTA, Camila do Carmo Pereira; KAWAKAMI, Silvia Keiko; http://lattes.cnpq.br/5306256489815710
Polycyclic aromatic hydrocarbons are organic (PAH) compounds originated from natural or anthropogenic sources and are considered priority substances by environmental agencies because of carcinogenic and mutagenic potentials. Therefore, rapid and low cost analytical methods for these compounds are of significant relevance for environmental purposes. The present study aimed the optimization of an analytical method for PAHs using High Performance Liquid chromatography with a diode array detector (HPLC-DAD) for the application to an estuarine sediment core. For the optimization and evaluation of the method, a sedimentary column measuring 46 cm length was collected at the mouth of the Igarapé Tucunduba (Belém, Pará) and sectioned in 2 cm portions. After dryness, 30 g of each portion were extracted with a mixture of dichloromethane in acetone in ultrasound bath for 40 min. the extracts obtained were centrifuged, purified on silica gel as a clean-up adaptation mainly to retained fine particles, then concentrated using vacuum evaporator and filtered through 0,2 μm nylon membrane before HPLC injection. Samples spiked with 16 PAH analytical standards and procedural blanks were processed on the same way. The parameters assessed showed: (1) good linearity, the calibration curves presented high correlation coefficients ; (2) adequate accuracy: relative standard deviations within acceptable values with 2,1% for acenaphthylene and maximum of 19,7% for fluoranthene; (3) low detection limits between 0,004 to 1,085 ng g-1 which make in situ determinations feasible; (4) adequate recovery for traces with minimum of 40,0% for acenaphthylene and maximum of 103,1% for benzo(k)fluoranthene. The total PAH concentration in the sediment core ranged between 60,77 to 783,3 ng g-1 dry sediment. The optimized method showed advantages over the traditional methods based on soxhlet extrations and clean up adsorption columns in terms of time of analysis and reduced costs with the use of smaller amounts of solvents. The limitation, however, was de coelution of some compounds, which is probably due to the low efficiency of the chromatographic column that was available at the time of the analysis. The method was applicable to estuarine complex samples, rich in silt and clay. Diagnostic ratios using parental PAHs indicated petrogenic sources at 24 - 26 cm and 28 – 30 cm depth; and pirolitics sources at 6 - 8 cm, 10 - 12 cm , and 14 - 16 cm respectively.
Acesso aberto (Open Access)
Aporte hídrico e de material particulado em suspensão para a Baía do Marajó: contribuições dos rios Jacaré Grande, Pará e Tocantins
(Universidade Federal do Pará, 2014-03-19) COSTA, Maurício da Silva da; ROLLNIC, Marcelo; http://lattes.cnpq.br/6585442266149471; SOUZA FILHO, Pedro Walfir Martins e; http://lattes.cnpq.br/3282736820907252
The Amazon estuary is influenced by the tide and river discharge systems variations that modify the currents and contribute with inputs of suspended particulate matter (SPM) resulting in morphological changes along the river. The quantification of these parameters provides an understanding of the rates of export and import of materials or volume and its implications in the estuarine geomorphology. The aim of this study is to evaluate the hydrodynamic, volume transport and SPM in different periods in Jacaré Grande, Pará and Tocantins rivers. Speed and current direction, tide, turbidity, volume transport and SPM data were collected over a tide cycle in the dry (2012) and rainy (2013) periods. The Pará river the exported volume in both periods, while the Tocantins river imported during the dry period and the exported in the rainy period. The Jacaré Grande river, influenced by the Amazon river, imported in the rainy season and exported in the dry period. The analysis of the volume transport methods showed a trend of export toward Amazon river and Marajó Bay in the dry season and only toward the Marajó Bay during the rainy season. SPM values were higher in the rainy season and descending from Jacaré Grande river to the Tocantins river in dry and rainy season, respectively. Turbidity followed the same trend of SPM with tide, with maximum values during the flood. SPM transportation methods showed similar values and the same direction. The Jacaré Grande river served as an exporter during the dry period and as an exporter in the dry period, the Para river as an exporter in both periods and the Tocantins river in the dry season as an importer and as an exporter during the rainy season. The system formed by the three rivers showed the same trend of export in both periods, with two exportation routes in the dry season (Amazon river and Marajó Bay), and only one exportation route in the rainy period (Marajó Bay). Annually the system exports between 5 and 7.2 million tons and possibly the Marajó Bay receives 3.7 to 5.8 million tons. The volume transported to the ocean can be much higher. SPM flows, associated with the variability of environmental conditions, molds the estuary, as seen in the mouth of the Tocantins river and Guajará Bay. Thus, it important a continuous monitoring due to the potential boating accidents, oil spills or any contamination in the region that can result in damage the enviroment.
Acesso aberto (Open Access)
Carta de aptidão à urbanização: proposta de ordenamento territorial frente aos processos erosivos na orla marítima das praias do Crispim e de Marudá no município de Marapanim-PA
(Universidade Federal do Pará, 2018-02-07) MELLO, Loury Bastos; SZLAFSZTEIN, Claudio Fabian; lattes.cnpq.br/1348005678649555
Natural disasters have considerably increased considerably in the last decades, and consequently, the number of affected and the volume of damages impacts. Following the increase in population, the cities located in the Coastal Zone of Paraense (ZCP), as well as in the big cities, develop populations of high socioeconomic vulnerability exposed to recurrent natural processes increasingly, such as tides, breakers and erosion. The studies focused on the coastal dynamics with emphasis on socioeconomic aspects in Brazil begin to advance after the approval of Federal Law 7,661 / 88 of the National Coastal Management Plan (PNGC). The ZCP characterized by a regime of macrotidal and estuarine plains, has been the target of natural disasters of great intensity, which are becoming more and more recurrent. In an attempt to provide an improvement in the quality of life of the population living on the Marudá and Crispim coastlines, and to minimize the recurrent damages that affect the seafront of these beaches, this research proposes the development of the suitability chart to urbanization from the mapping of areas with high, medium and low susceptibility, hazard and vulnerability to coastal erosion. Were indicated suitable areas, suitable trough interventions, and areas not suitable to urbanization, and this product will serve as a subsidy to the public policies of management and territorial planning in the ZC of the Marapanim city. The approach consists of: bibliographical compilation and published data; definition of analyzed variables; analysis and acquisition of satellite images; field campaign; classification of variables in units; quantification each unit according to its vulnerability, danger or susceptibility; elaboration of the vectorial spectrum of each variable and its respective units; transformation of these vectors into raster data; multicriteria analysis from GIS environment modeling (AHP); vulnerability mapping; hazard mapping; and integration of the maps obtained and final elaboration of the suitable chart to urbanization through map algebra. Areas of low, medium and high risk and vulnerability were found in Crispim and Marudá, the region most affected by erosion processes, being this area analogous to the region with the highest signs of damage generated in high magnitude events, shoreline and beach profile variation. The areas of greatest vulnerability are determined, mainly by the regions with the highest indexes of exposure to coastal processes and low construction kind. The data obtained in this work are considered extremely useful for adaptations in the region of study, as containment construction to the marine advance, as well as a detailed management of the environments found in the scenario of global climate change. Thus, it will be possible to plan adequately the use, occupation and adaptation of this coastal region, using, above all, the individualities of each area.
Acesso aberto (Open Access)
O cenozoico superior do centro-oeste da Bacia do Amazonas: paleobotânica do embasamento cretáceo e evolução do Rio Amazonas
(Universidade Federal do Pará, 2018-11-08) BEZERRA, Isaac Salém Alves Azevedo; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
At the end of the Neogene and during the Quaternary, the development of the Amazon River caused significant paleoenvironmental and geomorphological changes that generated current ladscape at Amazonia. Previous models elaborated on a continental scale were based on data obtained from a drill core carried out on the Atlantic continental shelf, distant 200 km of the Amazon River mouth, suggesting the establishment of this drainage with Andean provenance from the Middle to Upper Miocene. In contrast, studies based on outcrops in the western and central portions of the Amazon have indicated younger ages for this ecosystem, from Pliocene to Quaternary. The sedimentological-stratigraphic study of the fluvial terraces of the Amazon River, exposed in the center-west portion of the Amazon Basin, assisted by luminescence geochronology, allowed to sequence the sedimentation events and discuss the paleoenvironmental and paleogeographic since Late Neogene. The studied Neogene- Quaternary deposits overlies Cretaceous rocks whose sedimentological and paleobotanical study revealed the preservation of impressions and counter-impressions of leaves and other macro-plant remains in pelites interpreted as flood plain and abandoned channel deposits of meandering rivers. The first record of angiosperms in this unit with possible affinities to the families Moraceae, Fagaceae, Malvaceae, Sapindaceae and Anarcadiaceae with appearance from Late Cretaceous, and the family Euphorbiaceae with record starting in the Mid- Cretaceous confirm the Cretaceous age for these rocks. The terraces of the Amazon River informally subdivided into lower and upper units are composed of sand, gravel and clay, organized in finning upward cycles representative of channel filling and overbank deposits. The lower unit was interpreted as a record of the proto-Amazonas, with migration to the east and deposition around 2 Ma. During this stage, the alluvial plain was restricted, preferentially following weakness zones coincident with fractures in the Paleozoic and Cretaceous basement. The climatic oscillations during the Quaternary and the increase of the volume of orographic rains in the headwaters region of the fluvial systems, in the eastern flank of the Andean ridge modified the hydrological regime, amplifying the escarpment erosion. The gradual expansion of the alluvial plain formed a large area of 120 km around 1 Ma to 140 ka, recorded by the upper unit deposits. At this stage, the eastern portion of the Amazon Basin topographically higher restricted the Pleistocene sedimentation in minimum accommodation space. The lower unit deposits are correlate in part to the Miocene-Pliocene deposits of the Amazon Basin, while the upper units are correlate with the Pleistocene deposits of the Solimões and Amazon basins. The dynamics of the construction of the Amazon River valley during the end of the Neogene and Quaternary was influenced by neotectonics (106 yr) and climatic oscillations (104-105 yr). The landscape of the central-eastern portion of the Amazon dominated no Pleistoceno by terra firme in elevated areas was governed by the dynamics of expansion and contraction of the alluvial plain. At the end of the Quaternary, the várzea formed by floodplains within the alluvial plain, which used to occupy a wide area, became increasingly restricted by the continuous processes of fluvial incision during the glacial maximum (18 to 22 ka). The continuous lateral migration of the meandering channel to the north led to the confinement of the channel by the fluvial scarps developed in the Cretaceous basement, which culminated in the current landscape in the Center-East of the Amazon. Testing the reliability and accuracy of some Pleistocene and older OSL ages for Amazon River deposits revealed that are much more minimum ages than buried ages for pre- Quaternary deposits.
Acesso aberto (Open Access)
Comportamento de metais pesados e nutrientes nos sedimentos de fundo da Baía do Guajará e Baía do Marajó
(Universidade Federal do Pará, 2010-01-28) HOLANDA, Nielton de Souza; ANGÉLICA, Rômulo Simões; http://lattes.cnpq.br/7501959623721607
Human activities influence the physical and chemical characteristics of water, sediments and organisms in aquatic environments located in industrialized areas and high population density. With the increasing use of estuaries as a reservoir for a large amount of waste, coastal and estuarine ecosystems are gradually being subject to significant impacts. The bottom sediments play an important role in the investigation of these impacts since it has the ability to retain chemical species and inorganic. The objective of this research is to study the geochemical behavior of metals in the bottom sediment of the Bay of Guajará, Guama River and the Bay of Marajo. The two regions were chosen for their opposite characteristics: a Guajará Bay Area (1) under strong anthropogenic influence and Marajó Bay Area (2) considered the reference. We collected 83 points in Area 1 and 60 points in Area 2. Determined chemical concentrations of the following metals: Ba, Cr, Cu, Fe, Pb, Ni, V and Zn, and also the levels of nitrogen, carbon, organic matter, total phosphorus and phosphorus bound to organic compounds. Area 1 shows the average content of nitrogen of 0,08 %, mean levels of carbon and organic matter from 1,51 % and 2,60 %, respectively. The concentration of phosphorus and phosphorus bound to organic compounds 307 mg / kg and 126 mg / kg, respectively. The concentration of metals showed the following values: Ba (529 mg / kg), Cr (91 mg / kg), Cu (17 mg / kg) , Fe (6,82 %), Ni (32 mg / kg), Pb (27mg / kg), V (120 mg / kg) and Zn (69 mg / kg). Area 2 shows the average content of organic matter 1.70 % of carbon and nitrogen 0,98 % and 0,08 % respectively. The concentration of phosphorus and phosphorus bound to organic compounds 193 mg / kg and 7 mg / kg, respectively. The concentration of metals showed the following values: Ba (596 mg / kg), Cr (102 mg / kg), Cu (21 mg / kg) , Fe (8,31 %), Ni (40 mg / kg), Pb (28 mg / kg), V (141 mg / kg) and Zn (85 mg / kg). The carbon and phosphorus (0,98 %, 193 mg / kg), respectively found in area 2 were lower than those found in area 1 (0,51 %, 307 mg / kg) and demonstrate the influence of effluents that are released in the estuary Guajarino. In both areas there is the same downward trend in levels: Fe2O3> Ba> V> Cr> Zn> Ni> Pb> Cu. In area 1 were found higher metal alone while in area 2, with the major averages, the distribution is homogeneous, two areas in the metals has a slight tendency to concentrate where there is a higher content of organic matter.
Acesso aberto (Open Access)
Depósitos lacustres rasos da Formação Pedra de Fogo, Permiano da bacia do Parnaíba, Brasil
(Universidade Federal do Pará, 2015-04-15) ARAÚJO, Raphael Neto; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
The Permian Pedra de Fogo Formation, exposed in the east and west borders of Parnaíba Basin, northern Brazil, represent one of the most important terminal Paleozoic sedimentary record of the Western Gondwana. The main lithotypes of this unit are sandstones, shales, carbonate rocks, evaporites. The unit is famous for its large amounts of chert and presence of well-preserved Permian flora. In the last decades of the 20 th century, previous works interpreted the paleoenvironment of the Pedra de Fogo Formation as transitional fluvial-deltaic deposits, storm influenced-shallow neritic (marine) to coastal sabkha plain, lacustrine and fluvial deposits with contribution of marine-aeolian sediments and shallow to restrict sea or epicontinental type. Facies analysis focused principally on outcrops of the base and upper part of this unit, involving approximately 100 m thick of the siliciclastic succession. Eleven sedimentary facies were recognized and grouped into three facies associations (FA), representative of a shallow lacustrine depositional system associated with mudflat and ephemeral rivers. FA1 is interpreted as mudflat deposits, consisting of laminated claystone/siltstone, sandstones/pelites with mud cracks and sandstones with cross-lamination, massive and megaripple beddings. Silicified nodules and molds like popcorn indicate evaporites deposits. Other common features are silica concretions, silicified teppes and silcretes. FA2 represents deposits of nearshore and consists of fine-grained sandstones with even parallel lamination, climbing ripple cross-lamination, massive and megaripple beddings, as well as, laminated mudstone/siltstone. FA3 refers to wadi/inundite deposits, generally organized in fining upward meter-scale cycles, consisting of conglomerates and medium-grained pebbly sandstones with massive bedding and cross-stratification, and claystone/siltstone with even parallel to wavy lamination. Tabular beds are frequent in FA3 while scour-and-fill geometry is rare. The alternation of pelites and fine to medium-grained sandstones with even parallel to wavy lamination are the main framework of the Pedra de Fogo Formation. Bioturbations, shrinkage cracks and different types of siliceous concretions, as well as, teeth of fish, ostracods, bryozoans and scolecodontes are common in the studied succession. Silicified plant remains, preliminarily classified to the genus Psaronius, are found in situ, concentrated near the upper contact with Motuca Formation, considered here as excellent biostratigraphic markers for the upper Pedra de Fogo Formation. Mudflats deposits occur in the basal Pedra de Fogo succession suggesting arid and hot climates for the early Permian. The midlle Permian was predominated semiarid allowing the proliferation of fauna and flora in humid regions adjacent and into the lake margin. The ephemeral fluvial inflow or wadis carried plant remains and terrigenous to the lake generating inundites. Retreat and expansion phases characterized the Pedra de Fogo lake, induced by extreme climatic changes influencing not only the sedimentation pattern as also the fossilization of the best well-preserved Permian fauna and flora. In the late Permian, the climate again became hot and arid due to the complete aggregation of Pangea supercontinent, favoring the deposition of Motuca red beds and establishment of Sambaíba erg, near in the Permian-Triassic boundary.
Acesso aberto (Open Access)
Depósitos pleistocenos da formação Itaubal: paleoambiente e implicações na evolução da planície costeira do Amapá
(Universidade Federal do Pará, 2014-03-28) BEZERRA, Isaac Salém Alves Azevedo; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
In the Late Pleistocene of northern coast of South America, sea level fluctuations, related to climate variations and the sedimentary discharge of the Amazon River, have modified the landscape of this region. Terraces of the Itaubal Formation previously considered as Miocene Barreiras Formation, are part of the Amapá Coastal Plain, which covers the rocks of the Guianas Shield. The geochronological analysis by Optically Stimulated Luminescence / single and multiple aliquote regeneration (OSL/SAR-MAR) provided age around 120.600 (± 12.000) to 58.150 (±6.800) yrs BP and integrated with facies and stratigraphic analysis allowed the identification of coastal deposits and put the Tartarugazliznho Formation in the Upper Pleistocene. These up to 10 m thick, reddish tabular sediments have been divided into two units separated by unconformity. The Lower Unit consists of subtidal plain deposits (FA1), tidally influenced meandering stream deposits (FA2) and tidal plain deposits (FA3), whereas the Upper Unit, containing a higher clay content tham the lower one, is composed of braided stream deposits (FA4). The strata pattern of these units is progadational and takes part in the regressive system tract. The Tartarugazinho Formation onlaps the basement of Guianas Shield, weathered during Miocene-Pliocene and was exposed during the Last Glacial Maximum, about 22.000 – 18.000 yrs BP. Finally fine graided deposits derived from the Amazon River covered the Itaubal Formation and are responsible for the present shape of the northern coastline of South America. For the first time, the Itaubal Formation defines the Pleistocene sedimentary evolution of the Amapá coastal plain and the correlation with similar sediments in Suriname and northeastern Pará expands the discussion about the evolution of the coastal line in Northern South America during Pleistocene.
Acesso aberto (Open Access)
Desenvolvimento da vegetação e morfologia da foz do Amazonas-PA e rio Doce-ES durante o Quaternário tardio
(Universidade Federal do Pará, 2013-11-05) FRANÇA, Marlon Carlos; PESSENDA, Luiz Carlos Ruiz; http://lattes.cnpq.br/0425441943533975; COHEN, Marcelo Cancela Lisboa; http://lattes.cnpq.br/8809787145146228
This work compares the vegetation and morphological changes occurred along the littoral of the Marajó Island, Amazonian littoral, and the coastal plain of the Rio Doce, southeastern Brazil, during the Holocene and late Pleistocene/Holocene, respectively, focused specifically on the response of mangroves to sea-level fluctuations and climate change, which have been identified in several studies along the Brazilian coast. This integrated approach combined radiocarbon dating, description of sedimentary features, pollen data, and organic geochemical indicators (δ13C, δ1₵N and C/N). On coastal plain of the Doce River between ~47,500 and ~29,400 cal yr BP, a deltaic system was developed in response mainly to sea-level fall. The post-glacial sea-level rise caused a marine incursion with invasion of embayed coast and broad valleys, and it favored the evolution of a lagoonal/estuary system with wide tidal mud flats occupied by mangroves between at least ~7400 and ~5100 cal yr BP. Considering the Marajó Island during the early and middle Holocene (~7500 and ~3200 cal yr BP) mangrove area increased over tidal mud flats with accumulation of estuarine/marine organic matter. It was a consequence of the marine incursion caused by post-glacial sea-level rise, further driven by tectonic subsidence. Dry conditions in the Amazon region during this time led to a rise is tidal water salinity and contributed to mangrove expansion. Therefore the effect of relative sea-level (RSL) rise was determinant to the mangrove establishment in the southeastern and northern region. During the late Holocene (~3050 – 1880 cal yr BP) the mangroves in both regions were retracted to a small area, with some areas replaced by freshwater vegetation. This was caused by the increase in river discharge associated to a wet period recorded in the Amazon region, and considering the coastal plain of the Doce River (southeastern Brazil), the mangroves shrank in response to an increase in fluvial sediment input associated to a sea-level fall.
Acesso aberto (Open Access)
Desenvolvimento metodológico e avaliação de contaminação por HPAs em sedimentos da baia de Guajará
(Universidade Federal do Pará, 2014-03-31) SODRÉ, Silvana do Socorro Veloso; CAVALCANTE, Rivelino Martins; http://lattes.cnpq.br/2253127527012522; CORRÊA, José Augusto Martins; http://lattes.cnpq.br/6527800269860568
Polycyclic Aromatic Hydrocarbons (PAHs) are pollutants with toxic effects, harmful to the environment and to human health. They are part of a group of persistent organic pollutants (POPs), which by its characteristics have an impact on the environment and are extensively studied for this reason. They may be present in particulate, dissolved and/or gaseous forms, in different environments such as soil, sediment, air, water, particulate matter in the atmosphere, organisms and food (Kennish, 2007). Natural sources of PAHs include volcanic activity, natural fires, oil oozing and biogenic processes. Anthropogenic PAH pollution may occur by incomplete oil combustion (automotive and industrial), intentional burning of wood and plantations, domestic and/or industrial wastewater, urban water flow, accidental spills of oil and derivatives. Hydrophobic and lipophilic, these substances can be easily adsorbed by sediments, so that this matter is an important reservoir for them. To evaluate the presence of these compounds in the environment, this work used High Performance Liquid Chromatography. The samples used in the development and optimization of the methodology were collected in the Guajará bay (Belém - PA). This work consisted in the development of a methodological procedure (with adaptations and optimizations) to quantify 16 PAHs in 10 points in the Guajará bay in two field campaigns, so that 20 samples were analysed. In the development stage of the analytical method, elution systems, system polarity and eluent flow were tested, among others. In order to validate the method, the following parameters were assessed: fidelity, linearity, detection limit and quantification limit. Diagnostic ratios were calculated to identify the primary sources of PAHs found in the bay. The primary sources of the 16 PAHs studied in the sediments of the bay were identified based on ΣPAHs BMM/ΣPAHsAMM; Phe/Ant; Flt/Pyr; Ant/Σ178; Flt/Σ202; B(a)P/Σ228 and Ind(123cd)pyrene/Σ276. In the first field campaign, the total concentration of light PAHs ranged from 132.3 ng.g-1 to 1704.14 ng.g-1, the ΣPAHs of the heavy ones, from 125.82 ng.g-1 to 1269.71 ng.g-1 and the total ΣPAHs, from 317.84 ng.g-1 to 3117.06 ng.g-1. In the second field campaign, the total concentration of light PAHs ranged from 76.12 ng.g-1 to 1572.80 ng.g-1, the ΣPAHs of the heavy ones, from 213.90 ng.g-1 to 1423.03 ng.g-1, and the total ΣPAHs, from 290.02 ng.g-1 to 2995.82 ng.g-1. Based on these results, the Guajará bay can be classified as moderately impacted. The combustion is the predominant source of PAHs in the sediments of the bay, followed by vegetal biomass combustion and by the contribution of oil and supplies. Most of the points studied in this work, during the two field campaigns, showed concentrations of individual PAHs above the SQGs.
Acesso aberto (Open Access)
Detecção de mudança e sedimentação no estuário do Rio Coreaú
(Universidade Federal do Pará, 2014-09-02) RODRIGUES, Suzan Waleska Pequeno; SOUZA FILHO, Pedro Walfir Martins e; http://lattes.cnpq.br/3282736820907252
The use of new techniques to study the evolution and filling incised valleys has provided, over the years, important results was to understand how the coastal evolution of the Brazilian coastal zone. In this context, this thesis aimed to study the evolution of the estuary Coreaú River, located in the state of Ceará, in different time scales, is "Possible" (months, years), "Engineering" (years, decades) and "Geology" (hundreds, centuries, millennio), proposed by Cowell et al (2003), with the goal to assess whether changes /alterations over the years were significant or not in the estuary. As a result, we obtained the first goal, using remote sensing techniques from image sensor TM, ETM+ and OLI of Landsat 5, 7 and 8 and sensor LISS-3 of satellite ResourceSat-1 from 1985 to 2013, a change minimal in relation to morphological changes along the estuary in the last 28 years (between Possible scales and Engineering), there was an increase in this period of 0.236 km2 (3%) of the area, not bringing significant changes to the estuary. Regarding sedimentation rate, corresponding to the second goal, from the collection of nine witnesses, up to 1m deep and using radionuclídeo 210 Pb along the estuary, we obtained a rate that ranged from 0,33 cm/year 1 cm/year (between scales Geological and Engineering) near the mouth of the estuary, and with a quick sedimentation perceived on the east bank of the river, where there are younger sediments toward the west margin. Regarding the fulfillment, third and final goal from the sampling of testimonials to 18 m depth, using the sampler Rammkernsonden (RKS), profiles and stratigraphic sections that helped understand filling the valley section of the estuary of the Coreaú river were generated and that it is a fluvialmarine estuary, filling the valleys formed in group Barriers in the last 10.000 years before present. These analyzes and results serve as a basis for comparison with other estuaries, either fluvial, fluvio-marine or marine, to better understand what the possible events that dominated sedimentation along the coast of Brazil at diferent scales.
Acesso aberto (Open Access)
Distribuição e registro histórico de metais pesados e assinaturas isotópicas de PB em testemunhos de sedimentos de fundo da Baia do Guajará, Belém-PA
(Universidade Federal do Pará, 2011-08-29) CARVALHO, Jully Hellen dos Santos; CORRÊA, José Augusto Martins; http://lattes.cnpq.br/6527800269860568; LAFON, Jean Michel; http://lattes.cnpq.br/4507815620234645
tuaries constitute the final destination of a significant part of dissolved and particulate materials that are brought by the rivers toward the ocean. These estuaries also act as the final destination for domestic and industrial effluent, which are most of time discarded in natura. A variety of factors and sources together with the complexity of hydrodynamics and physicochemical conditions of this kind of environment makes the study of metals pollution of estuaries a challenge. The analysis of Pb isotopes is a valuable tool to differentiate anthropogenic from geogenic sources, since the lead dispersed in the environment keeps the isotopic characteristics of the source from which it was derived, once the isotopic compositions of Pb are not affected by physical or chemical processes. The hydrographic system of Belem (PA) belongs to the Guajara estuary. In the eastern margin, is located the Belém city. The west margin is an islander set composed 39 islands. About 30 km of natural drainages divide the city, forming channels that drain into, above all, the Guajara Bay which constitutes the main water reservoir receiving pollutants produced by domestic and economic activities of the city. However, the distribution of pollutants released daily in the bay is difficult to be evaluated, due to the hydrodynamic complexity of the estuary. In this context, the purpose of this study was to combine the determination of metal concentrations with Pb isotope signature to establish a historical record and to distinguish the sources of Pb, whether natural or anthropogenic, in sediments on the west edge of Guajará Bay. Samples were collected using a Russian Peat Borer. A set of seven cores of about 50 cm length was collected and subsequently sliced from 10 to 10 cm, totalizing 31 samples. According to the speed of deposition of approximately 0.7 cm/year, previously determined for the sediments of Guajara bay with geochronology 210Pb, cores collected correspond to a historical record of approximately 70 years. The study included grain size study by centrifugation method, mineralogical identification by X-ray diffraction, geochemical analysis to determine the percentage of organic matter and heavy metal contents by ICP-MS spectrometry and isotopic mass spectrometer thermoionization (TIMS). The grain size and mineralogical study of core in bottom sediments from the west edge of the Guajará bay showed a changing of hydrodynamic regime, which became more energetic, throughout the bay over time. This statement was based on the characterization of sediments, which show predominance of silt and sand fraction with a reduction of the sand fraction with the depth and texture that ranged from sandy to sandy-silty. The mineralogical study no showed change in mineralogical composition of the clays, and kaolinite, illite and smectite are claysminerals predominant. Over time the concentrations of metals vary little, however, have detected a slight tendency to decline in more recent times, probably linked to changes in the hydrodynamic regime. Moreover, there is no evidence in the core of a significant a significant increase in metal concentrations (mean 25.3 to 29.1 mg.Kg-1) with the population increase over the last 70 years. These results indicate that the background of Pb in the bay is significantly higher than in rio Guama (18 mg.Kg-1). The isotopic composition of source 206Pb/207Pb geogenic over the cores ranged between 1.186 and 1.199. The average isotopic signature of 1.193 ± 0.0035 was established as the value of the background to the Guajará bay, this value lower than the average value of 1,196 - 1.20 previously determined for the isotope ratio 206Pb/ 207Pb of Pb geogenic in Belém region.The differences in content and isotopic composition of Pb between this study carried out by Saraiva (2007) and Nascimento (2007) on the west edge of the bay, were explained by the difference of the technique used for sampling. This difference indicated that, despite the population growth accelerated during the last decades the contribution of heavy metals by anthropic action is recent, intensifying over the last 7 years.
Acesso aberto (Open Access)
Estratigrafia de dunas costeiras de Salinópolis/PA em associação com variações pluviométricas
(Universidade Federal do Pará, 2010-09-24) LEITE, Wladson da Silva; SOUZA FILHO, Pedro Walfir Martins e; http://lattes.cnpq.br/3282736820907252; ASP NETO, Nils Edvin; http://lattes.cnpq.br/7113886150130994
The present study was carried out at Salinópolis covering the Atalaia and Maçarico beaches (PA/North Brazil) to obtain a morpho-stratigraphic overview of the local coastal dunes and their evolution in Late Holocene, considering also climatic oscillations. Ground Penetrating Radar (GPR), auger coring, granulometric analysis and dating were used. The GPR-system SIR-2000 with a 400MHz antenna was used to reveal dune stratigraphy, including sedimentary facies and reactivation surfaces. At key-points of profiles sediment cores were obtained to proper interpretation of radargrams and sediment samples collection for grain size analysis and optical dating. At the Maçarico beach two main foredune crests were identified and dated at 69 and 80 years B.P. revealing a progradation rate of around 6 meters/year. The Atalaia beach presented a transgressive scenario, including retrogradation of the Holocene beach over older sediment layers, which include a feature interpreted as of Pleistocene age, although optical dating indicates an age of only 58 years B.P. due to actual sun light exposition. There, a parabolic dune was investigated and had revealed a migration rate of around 4 meters/year, where the reflectors indicate annual episodes of migration, possibly corresponding to the seasonal cycles of dryer periods and stronger winds. The general stratigraphy of the area seems to be a good tool for further studies on climate for the region, due to its good correlation with seasonal climatic patterns and long term register.
Acesso aberto (Open Access)
Estudo da qualidade dos sedimentos de fundo do Rio Barcarena-PA
(Universidade Federal do Pará, 2009-08-22) PORTO, Liliane Jucá Lemos da Silva; CORRÊA, José Augusto Martins; http://lattes.cnpq.br/6527800269860568
In estuarine systems, trace metal sources are both natural and anthropogenic. It is often difficult to distinguish between these two sources due to highly variable concentration in the water column. Many studies have shown the usefulness of sediments in understanding the anthropogenic contribution to trace burdens in estuarine systems. Located within a very important industrial region, near Belém city in the Guajará estuary, the Barcarena River receives discharges of urban and industrial runoff. The objective of this study is to study Barcarena River bed sediments to assess the anthropogenic chemical inputs into the river system. Fifteen sampling locations were chosen along the river channel. Bed river sediments samples were collected, and analyzed for their chemical and mineralogical composition. Data revealed that the clay mineral identified was composed mainly of smectite, kaolinite and Illit. The trace elements and heavy metals analysis showed the following average concentrations and standard deviation: Pb (32.54 mg.Kg-1, σ = ± 5.6), Cr (104.33 mg.Kg-1, σ = ± 7.98), Ni (34.27 mg.Kg-1, σ = ± 4.48), Cu (34.71 mg.Kg-1, σ = ± 4.38), V (116.33 mg. kg-1 , σ = ± 42.37), Nb (19.86 mg.Kg-1, σ = ± 3.83), Zr (122.31 mg.Kg-1 σ = ± 21.33). The highest concentration of the studied elements was found near São Francisco urban center, probably due to the presence of a harbor and unloading of solid waste and sewage in the region. Concentrations of trace elements in the sediment were a function a particle size distribution and organic content. The element concentration of Pb, Cr, Cu and Nb in sediments of Barcarena river when compared with sediments of Guajará Bay (Saraiva, 2007), Guamá river (Nascimento, 2007) and bauxite ore (Braga, 2007) show higher values than the two first but lower values than bauxite. The finger print diagrams with heavy metals versus Al suggest the possibility of physical mixing between the bauxite and sediment of the river Barcarena. The elements Pb and Cu had shown concentrations higher than TEL values (Threshold Effect Level), 35 mg.Kg-1 and 35.7 mg.Kg-1 respectively. Therefore, the bottom sediments probably are causing adverse effects to benthic organisms. The elements Cr and Ni, shown concentration values that exceeded the TEL index (Cr = 37.3 mg.Kg-1 and Ni =18 mg.Kg-1) and PEL index, (Cr = 90 mg.Kg-1 and Ni = 36 mg.Kg-1. A value above the PEL index suggests that toxic effects on aquatic biota are frequent. Currently, the introduced metals are deposited near the source area and are mostly associated with the sediment, implying that the river bed sediment acts mainly as a sink, rather than a pool. The accumulated and enriched toxic trace elements can pose a potential pollution of river water and consequently the aquatic biota.
Acesso aberto (Open Access)
Estudo sedimentológico dos paleocanais da região do rio Paracauari, Ilha de Marajó - estado do Pará
(Universidade Federal do Pará, 1981-11-19) BEMERGUY, Ruth Léa; TRUCKENBRODT, Werner Hermann Walter; http://lattes.cnpq.br/5463384509941553
This investigations deals with the paleochannels of the Paracauari river In the northeastern region of Marajó island, based on the photogeological interpretation of maps (scale: 1:20.000) and Sedimentological studies of 13 holes with maximun depth of 50 meters. Morphologically the paleochannels are caracterized by meandering forms and are easily recognized by the vegetation and topographic features. The paleochannels are constituted of texturally mature and well sorted sands. The study of the heavy minerals fractions shows that following species are more importante: tourmaline, staurolite, zircon, andalusite and kianite. These minerals constitute a mature suite whi.ch are not only from the Amazon river system but also from the Tocantins river system. The clay fraction are represented by kaolinite, montmorilionite, illite and chlorite. These mineralogical composition reveals the influente of the more them one climatic change. The possible sources areas for these minerals are: the Andes Mountains; the upper Amazon and the Tocantins basin from this work we conclude that the methods of sedimentological research presented here with the studies of the morphological patterns in the northern and northeastern regions of Marajó Island can be applied to groundwater prospecting.
Acesso aberto (Open Access)
Estudo sedimentológico dos sedimentos Barreiras, Ipixuna e Itapecuru no nordeste do Pará e noroeste do Maranhão
(Universidade Federal do Pará, 1981-06-24) GÓES, Ana Maria; TRUCKENBRODT, Werner Hermann Walter; http://lattes.cnpq.br/5463384509941553
Barreiras, Itapecuru and Ipixuna are exposed in large regions of Pará and Maranhão State. The Barreiras sedimente are divided in conglomeratic, sandy clay and sandy lithofacies. Textural imaturity and abundant mud-s.upported clastics in particular, suggest depositions mainly by debris flows under semiarid conditions. The three lithofacies were probably derived from Precambrian schists of Santa Luzia Formation and preexisting sedimente. The Itapecuru sedimenta consist of crossbedded sandstones, locally with minor conglomerates and mudstones, deposited in fluvial environment, probably tending to a semiarid conditions. The Ipixuna facies consiste of crossbedded kaolinitic sandstones, minor mudstones (lithology A) and laminated mudstonefine sandstone units including thick kaoline layers (lithology B). The fine sandstones are texturally and mineralogically mature. Lacustrine-fluvial origin is proposed for Ipixuna facies. The impoverished heavy-mineral assemblage and thick kaoline-layers suggest humid hot climate that probably prevailed before (during?) the Ipixuna sedimentation. Textural and structural characteristics of the sedimente studied show that there is a olear difference between Barreiras Group and Ipixuna facies and that the latter is correlated with the Itapecuru Formation. Bauxitization of lower Tertiary age affected only the Ipixuna and Itapecuru sedimentary rocks.
Acesso aberto (Open Access)
Estudo tectono-sedimentar da Bacia de Jaibaras, na região entre as cidades de Pacujá e Jaibaras, noroeste do estado do Ceará
(Universidade Federal do Pará, 1996-04-22) QUADROS, Marcos Luiz do Espírito Santo; ABREU, Francisco de Assis Matos de; http://lattes.cnpq.br/9626349043103626
Studies carried out in southwestern portion of the Jaibaras Basin in the area of the 300 km², situated between the Pacujá and Jaibaras towns, northwest region of Ceará State, including geological mapping in 1:25,000 scale, faciologic, petrographic and structural analysis of the Pacujá and Aprazível formations, allowed a better visualization of spatial distribution of these units, as well as the characterization of their depositional environment, structural pattern and, at last to take considerations about the tectono-sedimentary evolution of the Jaibaras Basin. The Pacujá Formation is characterized by a folded and faulted volcanosedimentary sequence without fossils, made of rhythmic interlayers of fine arkosian sandstones to siltistones with pelites, occurring in tabular decimeter thick beds, laterally continuous, showing abrupt base and upward gradation to siltistones. The sandstones could be massive or stratified, showing planar lamination, micro-hummocky cross lamination, climbing wave -ripple cross lamination, locally parting lineation and convolute lamination. On the top of the sandstone beds occur symetrical and assymetrical wavy-ripples. Pelites show planar lamination and mudcracks. Interlayered with Pacujá Formation sediments occur volcanic and subvolcanic rocks (basalts, andesites, dacites and ryolites), at the form sills, dikes and flows, associated with volcaniclastic rocks, included on the Parapuí Suite. The environment of the Pacujá Formation was characterized as lacustrine with volcanism associated, subjected to storm-wave action, proved by the occurrence of microhummocky cross lamination.The rhythmics interlayering of sandstones and pelites characterizes tempestites cycles, usually incomplete. However, marine environment must be assoc iated, but unfortunately the field datas is insufficient to define this environments. In the Jaibaras Basin setting, Pacujá Formation represents the first deposicional pulse that extend from Neoproterozoic era to Cambrian period. This sedimentation occurred in an area wider than Jaibaras Basin out of their present boundaries. The Pacujá Formation shows a complex fold pattern, that resulted from superimposed folding, with geometric shapes similar to type 1 interference pattern - “domes and basins”, and kinks folds. This folding could be related to transpression in ductile -brittle regime, linked to the northest-southwest sinistral strike -slip system in the Eopaleozoic era, that caused a weak inversion of the Jaibaras Basin. The Aprazível Formation comprises a thin sedimentary sequence, faulted and tilted to southeastern on the whole, unconformably covering the Pacujá Formation. It is made of polymitic conglomerates, with clast-supported and matrix -supported framework, massive or stratified, with volcanic, gneiss, granite, rocks calcissilicatic, quartz, amphibolite, rhyolite, marble, mylonite, siltistone and sandstone clasts, varying in size from granules to boulders. The matrix is coarse to very coarse sandy arkosean, locally microconglomeratic. To a lesser proportion, occurs medium to very coarse grained arkosean sandstones, locally stratified, and intercalations of laterally continuos beds of arkosean sandstones and laminated pelites with mudcracks in surfaces of the beds. These sandstones show planar lamination, climbing-ripple cross lamination, and locally trough cross-bedding and convolute lamination. In the surface of sandstone beds, there are, occasionally, symetrical and assymetrical wave-ripples. The depositional environment of the Aprazível Formation was characterized as alluvial fan/plain, dominated by debris-flows and stream-flows, prograding distally over small lacustrine bodies. The tilting of the Aprazível Formation beds to southeastern, is a results from rotation of blocks, due to an extensional axis in the northwest-southeast direction, acting in Ordovician period, that controlled the deposition of Aprazível Formation in the area between Sobral-Pedro II and Café -Ipueiras shear zones. The Aprazível Formation represents the second and last depositional pulse that occurred in the Jaibaras Basin in the Ordovician period, in a more restrict depositional area, controled by Sobral-Pedro II e Café-Ipueiras shear zones. Its deposition occurred in a time interval between the post-Pacujá sequence and Meruoca Suite Granites, and pre-Serra Grande Group sequence of the Parnaiba Basin.