DEGEO - Departamento de Geologia
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/8
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Resultados da Pesquisa
Item Unraveling the origin of the Parnaíba Basin : testing the rift to sag hypothesis using a multi-proxy provenance analysis.(2020) Cerri, Rodrigo Irineu; Warren, Lucas Veríssimo; Varejão, Filipe Giovanini; Marconato, André; Luvizotto, George Luiz; Assine, Mario LuisSyneclises are long-lived sedimentary basins characterized by complex subsidence and erosion histories. The premise that these geotectonic units evolve from initial rifting processes following thermal (or flexural) subsidence is widespread in the geologic sciences and, to this day, remains a controversial issue. Seeking to test this hypothesis, we proceeded a novel multi-proxy provenance study aiming to identify differences (and/or similarities) in the sedimentary signal and source areas of the Jaibaras (rift) and Parnaíba (sag) basins. We conducted a detailed analysis of trace elements geochemistry of detrital rutile grains, macroscopic gravel composition and paleocurrents from the sedimentary deposits of the Aprazível Formation (Ediacaran - Cambrian, top of Jaibaras Basin) and the Ipu Formation (Ordovician, basal unit of Parnaíba Basin). Our data reveal that important changes in source areas occurred between the end of the rifting and the beginning of the sag phase, reinforcing the hypothesis that the evolution of the Jaibaras and Parnaíba basins were not genetically related. Our results demonstrate that conglomerates of the rift sequence are predominantly composed of volcanic, sedimentary, and metamorphic angular to sub-angular clasts, pointing to diverse, nearby source areas. Contrastingly, conglomerates of the initial sag sequence have greater sedimentary maturity, with dominant rounded vein quartz clasts and other minor source contributions, which suggest distant source areas, showing a consistent paleocurrent direction towards NW. Indeed, the detrital rutile trace elements geochemistry demonstrates that the source areas of these two units were distinct, revealing an important decrease in the input of granulite facies and metamafic grains in the sag basin comparing with the rift succession. In conclusion, as well as paleomagnetic and geochronological studies, the provenance methods using a multi-proxy approach proved to be an effective and powerful technique for distinguishing modifications in the sedimentary signal between rift-to-sag sequences.Item Landscape and depositional controls on palaeosols of a distributive fluvial system (Upper Cretaceous, Brazil).(2020) Soares, Marcus Vinícius Theodoro; Basilici, Giorgio; Lorenzoni, Paolo; Colombera, Luca; Mountney, Nigel Philip; Martinelli, Agustin Guillermo; Mesquita, Aquila Ferreira; Marinho, Thiago da Silva; Vásconez García, Richard Guillermo; Marconato, AndréThe stratigraphic record of distributive fluvial systems is commonly characterised by frequent and complex interstratification of palaeosols among channel and overbank deposits. However, current models focus primarily on sedimentation and pay only limited attention to palaeopedogenesis, thereby failing to incorporate important palaeoenvironmental and stratigraphic information. This study proposes a pedosedimentary model for distributive fluvial systems that depicts and accounts for two palaeopedogenetic trends: one downdip, in relation to distality from the fan apex, and one along-strike, in relation to distance from active channel belts. Palaeosols are reported in detail from an Upper Cretaceous succession of the Bauru Basin, southeastern Brazil, through the application of macro-, micromorphological and geochemical studies, combined with facies and architectural-element analyses of sediments. In the downdip palaeopedogenetic trend, the proximal zone of the depositional system is characterised by a dominance of well-drained Inceptisols that develop on amalgamated channel fills; in the medial zone, Inceptisols occur interlayered with overbank deposits containing Entisols and poorly drained Vertisols. The distal zone preserves more mature and poorly drained Inceptisols developed on deposits of overbank and sporadic distal channel fills. These pedotypes show an increase in maturity and hydromorphism, moving away from the apex to the fan toe. This is likely linked to (i) the progressive approach of the topographic surface to the water table, and (ii) the average increase in distance to an active channel belt in distal locations. The along-strike palaeopedogenetic trend culminates in poorly developed palaeosols in floodplain regions that correspond to topographic depressions located between channel belts and which were subject to recurrent floods. Because palaeopedogenesis in the floodplain region is penecontemporaneous to sedimentation, pedotypes show an increase in maturity, bioinduced calcification and hydromorphism with distance from the active channels; they pass laterally from Entisols and Inceptisols near active channels, to Vertisols away from active channels. Conversely, following avulsion, abandoned channel belts remain as topographically elevated alluvial ridges located at some distance from the newly active channels and positioned above the water table and this leads to the development of better drained and better developed Inceptisols relative to pedotypes of the floodplain region. Overall, both palaeopedogenetic trends demonstrate the overriding controls of topography, sedimentation rate and parent material on pedogenesis, with only minor climatic influence. This work offers a novel pedosedimentary model for distributive fluvial systems and highlights the palaeoenvironmental significance of palaeosol trends, providing new constraints for the recognition of distributive fluvial systems in the rock record.Item Sedimentology of a distributive fluvial system : the Serra da Galga Formation, a new lithostratigraphic unit (Upper Cretaceous, Bauru Basin, Brazil).(2021) Soares, Marcus Vinícius Theodoro; Basilici, Giorgio; Marinho, Thiago da Silva; Martinelli, Agustin Guillermo; Marconato, André; Mountney, Nigel Philip; Colombera, Luca; Mesquita, Aquila Ferreira; Vasques, Julia Tucker; Abrantes Junior, Francisco Romero; Ribeiro, Luiz Carlos BorgesThe Bauru Basin of SE Brazil is a large (ca. 370,000 km2 ) Upper Cretaceous intracratonic feature, important for its fossil remains and of particular value as a source of regional palaeoclimatic information. Historically, lithostratigraphic reconstructions have been performed mainly for successions of the central and southern parts of the basin, resulting in a lithostratigraphic scheme that is not applicable to the northernmost regions. In particular, the northeastern deposits of the Marília Formation (Serra da Galga and Ponte Alta members) reveal lithological, stratigraphic, and palaeontological differences from southeastern and northwestern counterparts (Echapor~a Member). Nevertheless, these deposits are considered as a single lithostratigraphic formation in the literature. To address this problem, this study demonstrates how the northeastern deposits of the Marília Formation do not show affinity to the rest of the unit. A more suitable lithostratigraphic model is proposed for the northeastern succession as a distinct and independent unit. Lithofacies and palaeopedological analysis, combined with lithostratigraphic mapping of the northeastern deposits, reveal 11 distinct lithofacies and three pedotypes over an area of 450 km2 . Sedimentary facies and pedotypes were assigned to six interbedded architectural elements: (a) type 1 channel fill, (b) type 2 channel fill, (c) type 3 channel fill, (d) interchannels, (e) palaeosols, and (f) calcrete beds. The succession is interpreted as a distributive fluvial system with overall direction of flow to the NNW, and which developed under the influence of a semiarid climate regime. This contrasts with deposits of the southeastern and northwestern Marília Formation, previously suggested to be of fine-grained aeolian affinity with interbedded poorly channelised deposits assigned to an aeolian sand sheet environment. By revising the existing lithostratigraphic scheme for the northeastern deposits, and contrasting them with laterally equivalent strata, this work demonstrates how the previously named Serra da Galga and Ponte Alta members reveal a unique set of lithological, architectural, and genetic signatures that permits to separate them from the Marília Formation. Finally, a new lithostratigraphic classification for the unit is proposed: the Serra da Galga Formation, whose deposition relates to an ancient distributive fluvial system.Item Noasaurid theropod (Abelisauria) femur from the Upper Cretaceous Bauru Group in Triângulo Mineiro (Southeastern Brazil).(2019) Martinelli, Agustin Guillermo; Marinho, Thiago da Silva; Egli, Federico Brisson; Hechenleitner, Esteban Martín; Iori, Fabiano Vidoi; Veiga, Fábio Hiratsuka; Basilici, Giorgio; Soares, Marcus Vinícius Theodoro; Marconato, André; Ribeiro, Luiz Carlos BorgesA new record of noasaurid theropod (Dinosauria, Abelisauria) is here described and compared, including the description of its microstructure. It consists of an almost complete femur of small size (132 mm of preserved length) discovered in 2014 in a new locality at Campina Verde Municipality, Minas Gerais state, Brazil. The new locality is named Fazenda Seis Irm~ aos-Grotas and has also provided thousands of ostracods, few fish remains, and a partial skeleton of an indeterminate baurusuchid mesoeucrocodylian. The bearing-fossil sedimentary sequence is referred to the Adamantina Formation (Bauru Group, Bauru Basin). The femur here presented represents the second putative occurrence of an unusual small-sized noasaurid abelisaur for the Upper Cretaceous Bauru Group.Item Palaeoecological implications of an Upper Cretaceous tetrapod burrow (Bauru Basin; Peirópolis, Minas Gerais, Brazil).(2019) Martinelli, Agustin Guillermo; Basilici, Giorgio; Fiorelli, Lucas Ernesto; Klock, Carolina; Karfunkel, Joachim; Diniz, Ariela Costa; Soares, Marcus Vinícius Theodoro; Marconato, André; Silva, João Ismael da; Ribeiro, Luiz Carlos Borges; Marinho, Thiago da SilvaWe describe a globally rare example of a tetrapod burrow from the Upper Cretaceous Bauru Group (Bauru Basin) from Peirópolis, Minas Gerais State, Brazil. The sedimentary succession containing the burrow includes a rich vertebrate assemblage comprising fish, podocnemid turtles, mesoeucrocodylians, saurischian dinosaurs, among others. The burrow is composed of an oblique tunnel (~30°), oval in cross-section, with a horizontal and suboval terminal chamber; it is 1.3 m long from the midpoint of its inferred entrance to the midpoint of the bottom of the chamber. It occurs in the upper portion of a sandstone succession, interpreted as a braided channel deposit, and the burrow-fill comprises medium-grained sandstone with mudstone intraclasts derived from fluvial floodplain facies. it is overlain by other fluvial channel deposits. Analyses suggest that the burrow was dug after the filling of the braided channel and during the pedogenesis of its exposed upper surface. Based on burrow morphology and size, the most plausible producer of this burrow is a notosuchian mesoeucrocodylian, such as small to mid-sized notosuchians (e.g., sphagesaurids). The Bauru Group has an extensive fossil record of notosuchians with disparate morphologies, and it is noteworthy that the small-sized notosuchian Labidiosuchus amicum comes from the same unit as the burrow. Moreover, arid to semi-arid conditions have been inferred for fossil-bearing rocks of this unit, and as such the data here presented add to our palaeoecological knowledge of Cretaceous mesoeucrocodylians in Gondwana. Moreover, it constitutes a new Cretaceous record of a tetrapod burrow during a period when such ichnofossils are globally rare.Item Fluvial floodplains prior to greening of the continents : stratigraphic record, geodynamic setting, and modern analogues.(2018) Ielpi, Alessandro; Fralick, Philip; Ventra, Dario; Ghinassi, Massimiliano; Lebeau, Lorraine; Marconato, André; Meek, Robert; Rainbird, RobertFluvial floodplains established prior to the greening of continents have long been overlooked, despite their relevance for landscape reconstructions in deep time. The record of fluvial overbank sedimentation dates back as far as theMesoarchean, and mature assemblages of floodplain landforms had already developed at least by the early Palaeoproterozoic. In this review, a critical assessment of pre-vegetation floodplain processes and deposits is carried out through literature compilation and detailed descriptions of case studies. Pre-vegetation floodplains were variably composed of floodbasins, splay complexes (including crevasse- and distributary-channel fills and related splay lobes) and, in minor proportion, by channel levees. The hydrology of ancient floodbasin environments, mainly inferred from the occurrence or lack of evaporite features, is particularly topical and, once critically tested against other palaeo-environmental indicators, can be related to climate or catchment physiography. Pre-Silurian floodplains preferentially developed in rift basins prone to restricted drainage, where low-gradient axial depressions experienced limited stream power and accumulation of cohesive fines. Since supercontinents prone to host mature intracratonic basins first appeared in the Palaeoproterozoic, a causal relationship is established between the rise of modern-style plate tectonics and fluvial floodplains. By comparison, prevegetation overbank records are sparse in foreland, syn-orogenic, or passive-margin basins, where higher gradients and ocean-ward bypass of cohesive fines would have enhanced reworking by adjacent channels. These features are analogue to modern non-vegetated floodplains, with examples drawn from both arid endorheic drainages (Death Valley, California; Salar de Uyuni, Bolivia), and humid exorheic drainages (coastal plains of southern Iceland). Future developments in pre-Silurian sedimentology will help addressing lingering questions related to, for instance, the biogeomorphology of microbial mats and the morphogenetic variability between floodplains developed in different latitudinal climate belts.Item The ancestors of meandering rivers.(2016) Almeida, Renato Paes de; Marconato, André; Freitas, Bernardo Tavares; Turra, Bruno BoitoModern alluvial plains, in contrast to their pre-Silurian counterparts, are characterized by the presence of meandering rivers in low-downstream-gradient areas, constituting efficient transport systems that maintain high bottom shear stresses in deep channels, which are made possible by bank stabilization, most commonly provided by vegetation in Earth’s recent history. Here we show, through numerical modeling and field-based description of large-scale exposures in Mesoproterozoic successions, that prevegetation rivers in low-downstream-gradient areas were markedly different from both younger meandering rivers and the common prevegetation sheet-braided rivers, showing deeper braided channels and greater floodplain preservation than the latter. These systems were less frequent and had lower transport efficiency than modern meandering rivers, implying differences in global-scale Earth-surface dynamics, from the weathering of silicate minerals in floodplains to the grain size distribution in all clastic depositional systems.Item Ground penetrating radar investigation of depositional architecture : the São Sebastião and Marizal formations in the Cretaceous Tucano Basin, Northeastern Brazil.(2016) Tamura, Larissa Natsumi; Almeida, Renato Paes de; Taioli, Fabio; Marconato, André; Janikian, LilianeUm fator-chave para o avanço no estudo de depósitos fluviais é a aplicação de métodos geofísicos, e o Radar de Penetração no Solo é um método de especial valor. Embora amplamente aplicado em ambientes de rios ativos, em ambientes fluviais consolidados esse tipo de estudo é mais escasso, em contrapartida há uma grande importância em mais estudos de modelos análogos de hidrocarboneto. Por essa motivação, o presente trabalho aplicou o Radar de Penetração no Solo em afloramentos já estudados estratigraficamente nas Formações São Sebastião e Marizal e comparou ambos os resultados, além de definir se a resolução, a penetração e a frequência da antena foram adequadas na área de estudo. Por meio dos resultados, é possível identificar oito radar fácies diferentes, dos quais seis estão relacionadas a ambientes fluviais, uma a ambiente eólico, e a última a ambiente costeiro. Observou-se que houve compatibilidade entre os refletores encontrados nas seções Radar de Penetração no Solo e as estruturas sedimentares observadas em afloramento, como conjuntos de estratos cruzados preenchidos por estruturas planares ou acanaladas. Nota-se que a resolução do método foi muito eficiente e identificou estruturas decimétricas de até 0,3 m com uma antena de 100 MHz, porém com menor penetração de sinal em comparação com trabalhos de rios ativos. Dessa forma, o Radar de Penetração no Solo mostrou-se de grande potencial para estudos futuros sobre a arquitetura deposicional das unidades investigadas.Item Large barchanoid dunes in the Amazon River and the rock record : implications for interpreting large river systems.(2016) Almeida, Renato Paes de; Galeazzi, Cristiano Padalino; Freitas, Bernardo Tavares; Janikian, Liliane; Ianniruberto, Marco; Marconato, AndréThe interpretation of large river deposits from the rock record is hampered by the scarcity of direct observations of active large river systems. That is particularly true for deep-channel environments, where tens of meters deep flows dominate. These conditions are extremely different from what is found in smaller systems, from which current facies models were derived. MBES and shallow seismic surveys in a selected area of the Upper Amazonas River in Northern Brazil revealed the presence of large compound barchanoid dunes along the channel thalweg. The dunes are characterized by V-shaped, concave-downstream crest lines and convex-up longitudinal profiles, hundreds of meters wide, up to 300 m in wavelength and several meters high. Based on the morphology of compound dunes, expected preserved sedimentary structures are broad, large-scale, low-angle, concave up and downstream cross-strata, passing laterally and downstream to inclined cosets. Examples of such structures from large river deposits in the rock record are described in the Silurian Serra Grande Group and the Cretaceous São Sebastião and Marizal formations in Northeastern Brazil, as well as in Triassic Hawkesburry Sandstone in Southeastern Australia and the Plio–Pleistocene Içá Formation in the western Amazon. All these sedimentary structures are found near channel base surfaces and are somewhat coarser than the overlying fluvial deposits, favoring the interpretation of thalweg depositional settings. The recognition of large barchanoid dunes as bedforms restricted to river thalwegs and probably to large river systems brings the possibility of establishing new criteria for the interpretation of fluvial system scale in the rock record. Sedimentary structures compatible with the morphological characteristics of these bedforms seem to be relatively common in large river deposits, given their initial recognition in five different fluvial successions in Brazil and Australia, potentially enabling substantial improvements in facies models for large rivers.