O Sistema fluvial distributivo da Formação Guará, Jurássico superior, Gondwana ocidental

Os sistemas fluviais distributivos têm sido um dos temas mais discutidos em sedimentologia nos últimos anos. Foi proposto que estes sistemas constituam a maior parte do registro estratigráfico de sistemas fluviais em bacias continentais, contudo o seu reconhecimento exige estudo na escala de bacia que considerem a distribuição espacial das características sedimentológicas. Esta tese investiga a hipótese de que a Formação Guará constitua um sistema fluvial distributivo de grande porte, depositado entre o Sul do Brasil e o Uruguai, por meio do reconhecimento da extensão total da unidade e da construção de um modelo deposicional quantificado em escala de bacia. Foram levantados 1.071,2 m de perfis colunares em 64 localidades (62 afloramentos e 2 poços) entre os estados do Paraná e Rio Grande do Sul, no Brasil, e no nordeste do Uruguai. A análise de fácies permitiu a expansão da área de ocorrência da Formação Guará, antes restrita ao Rio Grande do Sul e Uruguai, até o estado do Paraná, distinguindo esta unidade das Formações Pirambóia e Botucatu. Por meio da quantificação de parâmetros sedimentológicos, foram reconhecidas variações espaciais no sistema ao longo de uma transecta NNE-SSW, paralela as paleocorrentes fluviais. Parâmetros como tamanho de grão, espessura dos corpos arenosos de canais fluviais, número de storeys por corpo arenoso e tamanho das barras indicam uma redução na profundidade dos canais, competência do fluxo e canalização para jusante, reflexo do aumento da bifurcação dos canais, infiltração e evapotranspiração. Baseado na distribuição espacial de quatro associações de fácies (canais fluviais perenes, canais fluviais efêmeros, depósitos de planície de inundação e depósitos eólicos) foi construído um modelo deposicional dividido em 4 zonas: zona 1, onde dominam os canais fluviais perenes; zona 2, onde canais perenes e efêmeros se intercalam no registro; zona 3, onde a proporção de depósitos intercanais aumenta, representados principalmente por depósitos eólicos; e zona 4, onde os depósitos intercanais são dominados por planícies de inundação. A complexidade estratigráfica da Formação Guará, que não permite o reconhecimento de padrões de empilhamento regionalmente correlacionáveis, é atribuída a flutuações de descarga controladas por variações climáticas de alta frequência. O modelo deposicional demonstra que a Formação Guará registra a deposição de um megaleque fluvial terminal com interação eólica na sua porção distal, um dos maiores sistemas fluviais distributivos já estudados no registro geológico antigo e recente, com pelo menos 1050 km de extensão. A deposição desta unidade constitui o registro da inversão tectônica e 2 reciclagem da Bacia do Paraná durante o Kimmeridgiano-Tithoniano. A criação de espaço de acomodação para a deposição da Formação Guará, bem como sua posterior deformação e erosão são atribuídas à influência tectônica da pluma Paraná-Etendeka no Gondwana ocidental entre o Jurássico Superior e o Cretáceo Inferior.Distributive fluvial systems have been one of the most discussed topics in sedimentology in recent years. It has been proposed that these systems constitute the major part of the stratigraphic record of fluvial systems in continental basins, however, their recognition requires basin-scale studies that consider the spatial distribution of sedimentological characteristics. This thesis investigates the hypothesis that the Guará Formation constitutes a large distributive fluvial system, deposited between Southern Brazil and Uruguay, through the recognition of the total extension of the unit and the construction of a basin-scale quantified depositional model. A total of 1,071.2 m columnar sections were logged in 64 locations (62 outcrops and 2 wells) between the states of Paraná and Rio Grande do Sul, in Brazil, and in the northeast of Uruguay. The facies analysis allowed the expansion of the occurrence area of the Guará Formation, previously restricted to Rio Grande do Sul and Uruguay, to the state of Paraná, distinguishing this unit from the Pirambóia and Botucatu Formations. Through the quantification of sedimentological parameters, spatial trends were recognized along an NNE-SSW transect, parallel to the fluvial paleocurrents. Parameters such as grain size, thickness of the channel bodies, number of storeys per channel body and bar thickness indicate a reduction in the depth of the channels, competence of the flow and channelling downstream, reflecting an increase in bifurcation, infiltration and evapotranspiration. Based on the spatial distribution of four facies associations (perennial fluvial channels, ephemeral fluvial channels, floodplain deposits and aeolian deposits), a depositional model divided into four zones was constructed: zone 1, where the perennial fluvial channels dominate; zone 2, where perennial and ephemeral channels alternation is recorded; zone 3, where the proportion of inter-channel deposits increases, mainly represented by aeolian deposits; and zone 4, where inter-channel deposits are dominated by floodplain deposits. The stratigraphic complexity of the Guará Formation, which does not allow the recognition of regionally correlated stacking patterns, is attributed to discharge fluctuations controlled by high-frequency climatic variations. The depositional model demonstrates that the Guará Formation records the deposition of a terminal fluvial megafan with aeolian interaction in the distal portion, one of the largest distributive fluvial systems ever studied in the ancient and modern geological record, with at least 1050 km extent. The deposition of this unit constitutes the record of the tectonic inversion and recycling of the Paraná Basin during the Kimmeridgian-Tithonian. The accommodation space creation for the Guará Formation deposition, as well this subsequent deformation and erosion are attributed to the tectonic influence of the Paraná-Etendeka plume in Western Gondwana between the Upper Jurassic and the Lower Cretaceous

Mixed carbonate-siliciclastic sedimentation in a mesoproterozoic storm-dominated ramp : depositional processes and stromatolite development

Records of shallow-marine ramps with the mixing of carbonate and siliciclastic sediments are common throughout the geological time. All these records have pure carbonate and pure siliciclastic deposits as end members, occurring contemporaneously in distinct depositional regions along the ramp, and transitional hybrid facies between them. The two end member can mix in different scales and can alternate in time due to climatic changes and regressions and transgressions. This work presents a detailed reconstruction of a Mesoproterozoic storm-dominated mixed carbonate-siliciclastic ramp composed of hybrid sediments and whithout the presence of pure siliciclastic or carbonate deposits, a rare example in the geological record. Based on a high resolution logged section (in 1:20 scale) and qualitative thin sections, eleven lithofacies were identified and grouped into three lithofacies associations (offshore, offshore transition and shoreface), which are stacked vertically forming a transgressive–regressive cycle. This faciological distribution indicates a low relief ramp with wide microbial colonization from shallow to relatively deep waters (below storm-wave base level). In offshore low-energy distal areas, microbial mats spread laterally over large distances with little or no interference from currents, while in the offshore transition the morphology of the bioherms is shaped by currents induced by waves. In turn, the high wave energy in the shoreface inhibits the formation of stromatolites, restricting their occurrence to thin layers of microbial carpets or intraclastic lags. The mixing occurs in compositional scale and is relatively homogeneous along the whole logged interval, independent of the shifts in lithofacies or lithofacies associations. This compositional homogeneity is linked to the wide distribution and regularity in the input of siliciclastic sediments during the sedimentary accumulation. Strong currents induced by storms allow the transport and mixing of siliciclastic sediments with carbonate grains generated in the basin during fair-weather periods

Sedimentology of the proximal portion of a large-scale, Upper Jurassic fluvial-aeolian system in Paraná Basin, southwestern Gondwana

Upper Jurassic sedimentary rocks of Guará Formation record the environmental and geotectonic changes of the early break-up stages in the southwestern portion of Gondwana. Newly-described occurrences of this formation allow the expansion of its areal distribution to the central part of the Paraná Basin, Brazil. Four vertical sections are presently described in Paraná State, Brazil. Nineteen lithofacies were grouped in five facies associations, through the classical method of facies analysis. The facies analysis included Guará Formation and the adjacent portions of the underlying Pirambóia Formation and the overlying Botucatu Formation. The depositional system of Pirambóia Formation was wet aeolian fluvial-influenced and is composed by aeolian dunes, aeolian sandsheets/interdunes and ephemeral fluvial deposits facies associations. The Guará Formation is composed of multistorey fluvial facies association constituting a highly amalgamated perennial fluvial system. It is overlaid by the Botucatu Formation, characterized as a dry aeolian system formed by aeolian dune deposits. The stratigraphic units are separated by regional unconformities marked by a shift in facies and depositional systems that reflect climatic changes. The Guará Formation depositional model, established in correlation with southern sections, represents a broad fluvial system with aeolian interaction deposited in a wide basin with more than 800 km in extension. This large depositional paleoenvironment, together with other Upper Jurassic records in southwestern Gondwana, represents the early rift stage of Gondwana break-up

Seasonality effect on the physiological and productive responses of crossbred dairy cows to the equatorial Amazon climate

The objective of this study was to evaluate the seasonal effect of months of the year upon the physiological and productive responses of crossbred dairy cows raised in an Amazonian climate. Twenty lactating cows were evaluated, fed on Brachiaria decumbens pasture, with free access to water and mineral supplementation. Data from climate variables air temperature (AT), relative humidity (RH), rainfall (RA) and temperature and humidity index (THI) were recorded dur ing the months of January to April 2019. The physiological data collected were: respiratory rate (RR, mov/min), heart rate (HR, beats/min), rectal temperature (RT, ºC), udder surface temperature (UST, ºC), body surface temperature (BST, ºC), dorsum surface temperature (DST, ºC), front surface temperature (FST, ºC) and rear shin temperature (RST). Milk production (MP) was also measured. There was a significant difference (P0.05) for BST, and the values for MP and THI were 3.8; 3.8; 4.6; 4.1 kg and 77.7; 79.7; 80.6; 80.1, respectively. It was concluded that there was a seasonal effect of the months of the year evaluated on the respiratory rate of animals, however, it did not change the MP and the THI. The Amazon environment is conducive to causing thermal stress in lactating cows raised on pasture, requiring the use of shading to facilitate the ability of these animals to dissipate heat. Keywords: animal performance; thermal stress; milking; room temperatur

Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear un derstanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5–7 vast areas of the tropics remain understudied.8–11 In the American tropics, Amazonia stands out as the world’s most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepre sented in biodiversity databases.13–15 To worsen this situation, human-induced modifications16,17 may elim inate pieces of the Amazon’s biodiversity puzzle before we can use them to understand how ecological com munities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple or ganism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region’s vulnerability to environmental change. 15%–18% of the most ne glected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lostinfo:eu-repo/semantics/publishedVersio

Mapping density, diversity and species-richness of the Amazon tree flora

Using 2.046 botanically-inventoried tree plots across the largest tropical forest on Earth, we mapped tree species-diversity and tree species-richness at 0.1-degree resolution, and investigated drivers for diversity and richness. Using only location, stratified by forest type, as predictor, our spatial model, to the best of our knowledge, provides the most accurate map of tree diversity in Amazonia to date, explaining approximately 70% of the tree diversity and species-richness. Large soil-forest combinations determine a significant percentage of the variation in tree species-richness and tree alpha-diversity in Amazonian forest-plots. We suggest that the size and fragmentation of these systems drive their large-scale diversity patterns and hence local diversity. A model not using location but cumulative water deficit, tree density, and temperature seasonality explains 47% of the tree species-richness in the terra-firme forest in Amazonia. Over large areas across Amazonia, residuals of this relationship are small and poorly spatially structured, suggesting that much of the residual variation may be local. The Guyana Shield area has consistently negative residuals, showing that this area has lower tree species-richness than expected by our models. We provide extensive plot meta-data, including tree density, tree alpha-diversity and tree species-richness results and gridded maps at 0.1-degree resolution

Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5,6,7 vast areas of the tropics remain understudied.8,9,10,11 In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepresented in biodiversity databases.13,14,15 To worsen this situation, human-induced modifications16,17 may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%–18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost

Unraveling Amazon tree community assembly using Maximum Information Entropy: a quantitative analysis of tropical forest ecology

In a time of rapid global change, the question of what determines patterns in species abundance distribution remains a priority for understanding the complex dynamics of ecosystems. The constrained maximization of information entropy provides a framework for the understanding of such complex systems dynamics by a quantitative analysis of important constraints via predictions using least biased probability distributions. We apply it to over two thousand hectares of Amazonian tree inventories across seven forest types and thirteen functional traits, representing major global axes of plant strategies. Results show that constraints formed by regional relative abundances of genera explain eight times more of local relative abundances than constraints based on directional selection for specific functional traits, although the latter does show clear signals of environmental dependency. These results provide a quantitative insight by inference from large-scale data using cross-disciplinary methods, furthering our understanding of ecological dynamics

Unraveling Amazon tree community assembly using Maximum Information Entropy: a quantitative analysis of tropical forest ecology

In a time of rapid global change, the question of what determines patterns in species abundance distribution remains a priority for understanding the complex dynamics of ecosystems. The constrained maximization of information entropy provides a framework for the understanding of such complex systems dynamics by a quantitative analysis of important constraints via predictions using least biased probability distributions. We apply it to over two thousand hectares of Amazonian tree inventories across seven forest types and thirteen functional traits, representing major global axes of plant strategies. Results show that constraints formed by regional relative abundances of genera explain eight times more of local relative abundances than constraints based on directional selection for specific functional traits, although the latter does show clear signals of environmental dependency. These results provide a quantitative insight by inference from large-scale data using cross-disciplinary methods, furthering our understanding of ecological dynamics