DOI: 10.14393/SN-v32-2020-46867 Received: 02 February 2019 |Accepted: 15 January 2020
From planation surface to Holocene climate pulses: the landscape evolution in plateau reliefs
Vinícius Borges Moreira1 Archimedes Perez Filho2
Keywords Abstract Landscape Evolution In the central portion of Brazil, there are extensive and continuous Plateau flat surface plateaus, which are presented in a staggered way, Planation Surface separated by embedded fluvial valleys, among which the Uberlândia- Climate Pulses Uberaba plateau stands out in the region of Triângulo Mineiro - MG. Considering the aforementioned, geomorphological features such as veredas and summit depressions populated by murundus, commonly associated to the drainage network in tabular relief, are considered here as key environments for paleoenvironmental interpretation. To characterize and understand the formation processes of these environments and their evolution in the landscape, morphometric indexes, topographic profiles and evolutionary models of landscape were elaborated, presenting a general panorama and demonstrating the importance of geomorphological elements and landscapes from Paleogene planation surfaces to the Holocene climatic pulses.
1 Institute of Geosciences - UNICAMP. [email protected] 2 Institute of Geosciences - UNICAMP. [email protected]
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INTRODUCTION volcanic sedimentary and/or mafic volcanic. Regarding plateau genesis Martins and Occurring in the central portion of Brazil, Salgado (2017) two preponderant factors are numerous plateau reliefs, characterized by weighted: changes in the base level causing possessing tabular surfaces delimited by the drainage network vertical embedding steep/gradual slope ruptures on its borders, sculpting the residual shape of the plateau which provide them a prominent position in and tectonic processes also being responsible the landscape. Flat surfaces cause the to individualize uplands that posteriorly occurrence of Paleogene, Neogene and evolve into plateaus, with the edges receding Quaternary pediplanation over horizontal or and its flat surface being maintained. sub-horizontal sedimentary layers associated The morphology of these units of relief with basaltic spills and/or concordant indicate processes responsible for the surface hardened sublayers, such as concretions and coverings genesis and geomorphological lateritic crusts. features that occur in this central portion of According to Ab’Sáber (2003), flattened the country, making possible the sedimentary uplands from the central region interpretation and formulation of the local of Brazil, consist in extensive plateaus with landscape evolutionary picture. elevation varying from 600 to 1100 meters Considering the characteristics approximately, naturally covered by Cerrado presented above, the objective of this vegetation. This unity of relief is sectioned by manuscript lies in revising and describing the fluvial valleys occupied by gallery forests, main planation events that occurred in the being characterized, according to the author as region during the post-Cretaceous period, in the “Domain of interior tropical uplands with order to distinguish singular processes Cerrado and gallery forests”. between different topographic levels, thus After discussing with various authors leading to the current distinction of: Soil types, who presented classic definitions regarding lithology, altimetry and surface coverings. plateaus, Martins and Salgado (2017) list Besides, consists as another objective, to some basic attributes to identify and define correlate Holocene climate pulses to the this unity of relief: Sufficient height to establishment of geomorphological features in highlight it in relation to its neighboring area; plateau environments. By means of these minimum extension of 10 hectares; slope interpretations, it is aimed to comprehend rupture between the levels and its part of the evolution from the elements surroundings; surface with a slope of ≤ 6º structuring the local and regional conditioned by layers dip; and emphasizes this relief/landscape. type of relief is primarily modeled on Within this context, the study area is sedimentary rocks, although can occur on low presented as a plateau and its surrounding metamorphism meta-sedimentary rocks, area, located between the municipalities of
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Uberlândia and Uberaba in the Triângulo Serra Geral Formation or Bauru Group, Mineiro region, west of Minas Gerais (MG). showing low occurrence of outcrops over the region. The sandstone grains are rounded and STUDY AREA CHARACTERIZATION opaque, indicating eolian transport and origin, AND LANDSCAPE PHYSICAL its stratification is predominantly plane- ATTRIBUTES parallel changing to crossed (NISHYAMA Lithological aspects 1989). Starting from this stratigraphic level, In order to comprehend the formation the formations are exposed on their own processes of planation surfaces in the erosive scarp from the analyzed plateau or Triângulo Mineiro region, it is primarily superficially outcropping in road cuts, necessary to characterize the regional becoming primarily source material for surface lithology, since each rock formation is coverings. differently affected by the generalized Serra Geral Formation consists of planation imposed by erosive cycles, basaltic rocks with small sandstone lenses depending on the rock hardness degree and alternating with the spills, possesses massive the outcrop elevation level. aspect with containing irregular and According to Batazelli (2003) and subconchoidal fractures, forming layers with Barcelos (1984), the region that forms the diverse thickness over the numerous cycles of study area possesses three abundant rock spills (BARCELOS, 1984). Above this types: Sedimentary (Bauru basin and Cenozoic Formation, the sedimentary rocks from Bauru deposits), metamorphic (Pre-Cambrian group are to be found, grouping up basement – Araxá Group, Bambuí and Adamantina, Uberaba and Marília Formation. Canastra) and magmatic (Serra Geral The sandstones from Bauru Group present Formation and alkaline intrusions from Alto- variable granulometry and composition, Paranaíba uplift). however, they are very friable, thus being Araxá Group is the only unit susceptible to erosive cycle, therefore representing Proterozoic, found around the becoming the basis to the tabular relief in the study area, possessing its main outcrops on region. the East portion of Triângulo Mineiro, From Bauru Group, the uppermost however, it also occur over the canyons dug by member, Marília Formation, is constituted by Araguari river and Uberabinha river in low flat surface covers and scarped edges between course (NISHIYAMA, 1989). Grande, Paranaíba and Araguari rivers. Botucatu Formation consists of According to Barcelos (1983), forming sierra sandstones located above the crystalline tabular reliefs throughout its area of basement from Araxá Group and occurrence over the Triângulo Mineiro oriental below/interspersed the volcanic rocks from portion. Composed by very friable
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conglomeratic sandstones with crossed situ of underlying rocks from Marília stratification, possess significant amount of Formation, altered by the time of exposure, as calcium carbonate in its composition. described by Lima (1996), Feltran Filho (1997) According to Batezelli (2003), the soils among others. In reports of RADAMBRASIL deriving from this rock are very friable, project, pedologists, geologists and originating sandy soils and medium texture, geomorphologists, present distinct hypothesis favoring mechanic erosion and posteriorly on the subject, and are prolonging for many gullies appearance. years the debate over the origin of the covering Covering the tops from part of the material. regional lithology, especially over Uberlâdia- The firstly systematized geological maps Uberada plateau and surroundings, occur the in small scale to all Minas Gerais estate, Cenozoic Covers described by Barcelos (1984) disregard Cenozoic covers in the region of or Dendritic-Lateritic Covers characterized by Triângulo Mineiro, or limit them in small Mamede et al. (1983) as: Planned surfaces occurrence areas. According to Moreira (2017), located in quotas superior to 800 meters, over that was considered a misconception, for this Paleozoic and Mesozoic lithology from Paraná Cenozoic coverings cover all the lithology from Sedimentary Basin. Lateritic hardpans on the Uberlândia-Uberaba plateau, becoming a basis below mottled clays and homogenous relevant element to comprehend the sandy-clay or clay packets about 20 meters occurrence of typical geoforms in plateau tops. thick. The most recent geological mapping of There are important debates in the Triângulo Mineiro region accomplished by literature regarding the origin of Cenozoic CODEMIG (2017) in a more adequate scale to cover material. One current of researchers the region, retake the discussions regarding points to sedimentation evidences and the covering material, denominating them material remobilization over the Tertiary Dendritic-Lateritic coverings, recognizing its covering levels of planation as Mamede et al. vast occurrence over the plateaus in Triângulo (1983), Barcelos (1984), Nishiyama (1989) and Mineiro, corroborating the line of thinking Baccaro (1991) suggesting new from the authors found in this manuscript. On aloestratigraphic unit. Another current Figure 1, the most recent geological map is defends that covers found above Triângulo presented with the Uberlândia-Uberada Mineiro plateau are evidence of alteration in plateau being delimited.
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Figure 1 – Uberlândia-Uberaba plateau and surroudings litoestratigraphic units.
Source: CODEMIG, 2017. Adapted by the authors.
Planation Surfaces way (SILVA, 2009). In areas where occur tender lithologies, the surfaces tend to be Planation surfaces can be defined by erosion or fragmented, however in some places, with accumulation surfaces, resulting from specific characteristics such as Uberlândia- structural or paleoclimatic processes, sculpted Uberaba plateau, the surface is continuous during different geological periods/epochs, due to the occurrence of resistant being those short or prolonged duration events paleosurfaces (detritic-lateritic pavement) and (MARQUES NETO, 2014). According to Silva for the low density of the drainage network, (2009), the most elevated level of surfaces which decreases the performance from erosion tends to be older than the ones found in lower processes of surface separation. levels, consequently being younger. According to Salgado (2007), considering The shape and extension of these the large amount of works available related to surfaces can be diverse, depending on tectonic the topic, there is no possibility to comprehend activity, lithology resistance and homogeneity origin of a planation surface at a given that has been under the process. Rocks more location, making use of a unique theoretic resistant to erosion tend to sustain these model, for there are correct and incorrect surfaces for more time and in a contiguous
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points in each one of them. A broader view is in other studies, the model developed by King made necessary to consider such hypothesis of (1959), will be used as a model of reference in surfaces origin to a determined region. this research, in order to understand planation Therefore, juxtaposing several authors and surfaces genesis. their relative chronologies referring to periods After Bauru Group sedimentation in of relief planation, may be the path to achieve Triângulo Mineiro, which dates from superior conclusions on the plateaus of the study area. Cretaceous, in the Paleongene, according to Authors such as De Martone (1943), King (1956), occurred a vast period of King (1956), Barbosa (1959), Ab’Saber (1962), continental proportions with dry/arid climate, Bigarella et al. (1965) and Valadão (1998) and as a result produced planation surfaces proposed relative chronologies to several and leveled several topographies throughout surfaces recognized within the Brazilian the Brazilian and African relief, forming territory, however, the chronology between extensive detritic pavements over the surface these authors differs in terms of period and and providing tabular format to the plateaus structural/sculptural agents. present in the studied region, this event is Silva (2009) presents a comparative known as South American Surface. Posteriorly chart of planation events and chronologies to this event, according to King (1956), (Frame 1), according to the aforementioned another period of erosion occurred, carving authors, recognizing similarities and part of this surface during the Neogene, complement within their works. characterizing the “Velhas” cycle. Comparing every theoretic model on the The “Velhas” cycle, would be responsible topic, it is observed that “South-American” for the incision of fluvial valleys in Minas surface from King (1956) was widely discussed Gerais and São Paulo, carving the plateaus and recognized throughout the national produced by the previous cycle, rarely territory, being cited by several authors as reaching the generalized planation phase as found in the review made by Marques Neto the previous surface. The difference of (2014). Regarding Triângulo Mineiro region, topographic levels in the South American Baccaro (1991), relates the South American surface and the “Velhas” cycle is of surface from King (1956) to the summit levels approximately a 100 meters, possessing as (flat tops that occur between 950 and 1050 main characteristic the drainage channels meters) which have been flattened by branching and ridges for the most recent denudational processes, posteriorly sculpted surface. According to King (1956), this cycle is by the “Velhas” and “Paraguaçu” cycles yet responsible for the origin of extensive providing staggering aspect to the local sandy deposits of Pliocene age in the coastal plateaus. region, denominated Barreiras Formation. Due to the higher correlation presented
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Frame 1 – Events and relative chronologies of planation surfaces.
Source: Silva, 2009. Adapted by the author.
In accordance with King (1956), in channels that in our interpretation, exhumed relation to denudational events post Neo-Proterozoic rocks found in the river Cretaceous, Ab’Saber (1972) points that past valleys from Uberabinha and Araguari rivers, the end of Group Bauru sedimentation, there nearby Uberlândia-Uberaba plateau. was a drier/semi-arid period, enabling planation processes to occur easily, Planation Surfaces and associated soil types remobilizing materials, demoting the plateau tops and producing lateritic hardpan basis, Among the publications dedicated to nowadays being surfaces corresponding to the identifying the correlations between planation summit levels. During part of the Tertiary the surfaces and associated soil types in the climate became wetter establishing the central plateau, there is concordance current drainage system which carved the concerning the factors of the soil formation in plateaus. these conditions. Motta et al. (2002) and In the Quaternary, the last cycle Barbosa et al. (2009) describe three planation described by King (1956), denominated surfaces in plateaus close to Distrito Federal, “Paraguaçú”, would be responsible for Brazil, concluding that the soil origin material deepening the already established river over the three surfaces are entirely different,
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possessing distinct chemical and mineralogical Uberaba plateau and its surroundings, characteristics. presenting the main soil types in the study Through comparative research area, corroborated by the soil survey from performed in the three regions from central FEAM et al. (2010) and researches plateau, Marques et al. (2004), utilizes Th accomplished by Marques et al. (2004). (thorium) / Zr (zirconium) concentration rates Therefore, in Uberlândia-Uberaba plateau to verify that clay soils in the South American prevail the Red and Red-Yellow Oxisols, clayey erosion surface has common origin from the or very clayey. Gleysols are also common in sediments of Brazil central plateau rocks that wide valleys plains and in depressions, where has been transported to the East to cover the there is a higher humidity concentration. underlying sandstone. The authors conclude that some of the South American surface soils Geomorphological features developed over are amongst the most ancient of Earth and are planation surfaces and the role of Holocene climatic under alteration since the Tertiary. oscillations The presence of hardened ferruginous layers described with several nomenclatures, When proposing the four greater units from is often cited as fundamental for plateau Triângulo Mineiro, Baccaro (1991) describes maintenance, for they can delay erosive the geomorphological units found in: Intensely processes of marginal recoil and difficult water Dissected Relief Area; Medium Dissected infiltration over the top of the plateau. Relief Area; Residual Relief Area and summit According to Motta et al. (2002) the areas with flat, wide and large tops, ferruginous layers are fundamental as soil corresponding to Uberlândia-Uberaba plateau. origin materials, altering the chemical Every unit possess intrinsic geomorphological composition of erosive surfaces when features and are distinguished, according to reworked. the author, by their correspondent planation According to Oliveira et al. (2017), the surfaces. oxisols are the type of soil with the highest Relevant geomorphological features of occurrence in Cerrado biome, and the landscape are cited by Baccaro (1991) as consequently, in the central Brazil plateau fluvial valleys dissection, drainage density, region, being their typologies variable relief ruptures, among other characteristics according to the geomorphic surface analyzed. that are altered according to the Ramos et al. (2006), identified three geomorphological feature analyzed. Among the levels with different types of soil described features the Veredas and concave corresponding to different origin material depressions on summit levels are emphasized nearby Uberlândia-MG city, the data in the landscape, they can be subdivided by presented by the authors coincide with all the relief dissection level. characteristics observed in Uberlândia- In general, Veredas are characterized as
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exudation areas, or, water table emergence in Depression areas constitute in small flat bottom concave valleys, filled by Gleisols stream springs and possess superficial water with high concentration of organic matter. table, which oscillates according to the rainy Buriti (Mauritia flexuosa) is the characteristic and dry periods of the year. As for the vegetal species from this environment, by depressions evolution where murundus can be adapting to constant hydromorphy in the core found Schneider (1996) points geochemical of Vereda, protruding in the landscape shaped processes caused by water accumulation as the in a chain format or scattered along the entire responsible factor that reduced the relief and Vereda (BOAVENTURA, 2007). formed the depressions, theory very similar to The Veredas formation factors are Veredas initial formation phase. Mamede et described by Barbosa (1967), Boaventura al. (1983) proposes another explanation to the (2007), Lima (1996) and Ferreira (2003) occurrence of such depressions, considering among others. All the authors point planation them as residual “bajadas” from antique surfaces and climate oscillation as endorheic drainages, formed during a climate determinant elements to the occurrence of this drier than the current. geomorphological feature in Brazil central The cited depressions frequently occur in region. Moreira and Perez Filho (2017) present flattened plateaus over the central region of a synthesis from the different Veredas the country, as the Veredas, however typologies and the necessary physical restricted to the relief summit level, flattened environmental conditions to its genesis, by the South American Surface, where occur spatializing them according to the Detritic-Lateritic Surfaces over the hardened geomorphological characteristics of a specific layers, limiting water vertical infiltration. hydromorphic basin. He concluded that Starting from geomorphological Veredas typologies vary according to the interpretations Penteado-Orellana (1980) pattern of the relief, possessing as base proposes evolution scenarios for murundus different planation surfaces. formation, based on Holocene climate Concave depressions found at summits oscillations, being fluvial morphogenesis and are generally characterized by circular or pediment deposits at valley bottoms the elliptic micro-relief occurrence (mounds or protagonists, associated to hot/humid and little hills) with variable size, denominated hot/dry climate episodes. The author proposed murundus, above them, there is a common a model for the river valleys evolution that occurrence of bushes, small trees and termites explain the existence of murundus and (SCHNEIDER, 1996). These depressions are Veredas associated to the drainage network. also known as murundus fields, however As basis, Fairbridge curve (1962) was used as murundus are not exclusive geoforms of this support, signalizing relative positions to the environment, for they occur in other relief sea level to the climate oscillations to South portions. America, and in works carried out in São
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Paulo peripheral depression (PENTEADO, basin contributing to the landscape 1968). characterization, genesis and evolution as pointed out by Himura and Ponçano (1994). MATERIALS AND METHODS In order to perform the morphometric indexes, topographic maps 1:50.000 made To interpret and discuss the theoretical available by IBGE (Brazilian Institute of framework, reconstruction of the Geography and Statistics) were used, having paleoenvironments in plateau reliefs, erosive the purpose of restoring the drainage network cycles will be correlated to: Soil types, of the plateau, surrounding areas and lithology, altimetry, surface coverings and drainage network classification according to geomorphological features, constructing Strahler (1957). Posteriorly, circular samples qualitative relief and landscape models, based with 2km radius were superimposed, on topographic profiles, morphometric indexes uniformly distributed over the analyzed area, and aerial photographs. To complement the as indicated by Rodrigues (2006). data raised, fieldworks were carried out in the To elaborate the evolutional phases from region to recognize the described processes, Uberlândia-Uberada plateau in block elaborate the models and photographic diagrams, the baseline information collected records. during the literature review regarding the The Uberlândia-Uberada plateau rocky substrate and surface coverings was delimitation was carried out from the used, summing to the model proposed by vectorization of flat top summit areas, taking Penteado-Orellana (1980), that through river into consideration the topographic and valleys morphological interpretation, explain geomorphologic aspects, adapting the the origin of murundus and Veredas as methodology from Baccaro (1991). To delimit Holocene forms, Fairbridge curve (1962) and the plateau, its erosive border was used as Penteado (1968) configured the theoretical reference, where occurred abrupt contacts basis of this model. Recent works utilizing between different levels. Locations where this absolute geochronology such as Salgado- limit could not be perceived through Laboriau (1994), Behling (1995), Boaventura topographic maps or SRTM (Shuttle Radar (2007), Storani e Perez Filho (2015) e Dias e Topography Mission) images, the topographic Perez Filho (2015) reaffirmed the chronology elevation of 900 meters prevailed as a and environmental characteristics proposed in reference of the Plateau limits. the model, detailing the importance of Hydrographic and drainage density Holocene climatic oscillations described by analysis were also performed, those are Penteado (1968), being fundamental to important elements in the hydrographic and construct the scenarios proposed. morphometric studies, assisting in correlations The softwares ArcGIS 10.5.1, Corel draw on structural aspects of the hydrographic 2018 and Global Mapper 18 were used to
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produce the profiles and models, aggregating and hydrographic density average values the information gathered over the course of through this technique. the research, in the discussions and presented Drainage density and hydrographic results. density average values (Charts 1 and 2), leave no doubts as to the importance of the Detritic- RESULTS AND DISCUSSIONS Lateritic Cover to maintain the current
hydrologic equilibrium of the plateau in the Morphometric parameters study area. The covers delay erosive processes maintaining the drainage network slightly To analyze the desired environmental branched, so the number of first order variables two morphometric indexes were channels is much lower in relation to the preliminary applied over the drainage network surrounding area analyzed. In this context, of the study area, the figure 2 presents the concretionary sub-layers and local base level, distribution of circular samples over the described by authors such as Baccaro (1991), drainage network of Uberlândia-Uberaba Schneider (1996), Penteado-Orellana (1980), plateau and its surrounding areas, thereby, it among others, has an important role as agents was possible to measure the drainage density that slow down surface erosive processes.
Figure 2 – Sampling of Uberlândia-Uberaba plateau and surrounding areas drainage network.
Source: IBGE, 2006, adapted by the authors.
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Charts 1 and 2 – Hydrographic density and drainage density average values.
Source: Created by the authors.
Referencing on SRTM radar images with elaborated in red and yellow tones, 30 meters spatial resolution (Figure 3), which predominantly possessing a higher altimetry represents Uberlândia-Uberaba plateau was to the West.
Figure 3 – Transects and regional elevation of Uberlândia-Uberaba plateau.
Source: USAF, 2014, adapted by the author.
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Complementing morphometric to the profiles, representing the planation information, three transversal topographic surfaces according to the referenced profiles were produced on different points of bibliography. the plateau starting North of Araguari river, A-B, C-D and E-F transects provide the regional base level, ending at the South of the location of profiles produced to identify plateau. Associated with the profiles, were topographic levels affected by erosive cycles, added bars representing the underlying since the local base level, Araguari river, until lithology throughout the profile to assist in its levels posterior to the plateau. interpretation. Three sub-divisions were added
Figure 4 – A-B, C-D and E-F transversal topographic profiles.
Source: Produced by the authors.
The topographic level represented N(1) generalized planation occurrence caused by acronym in the presented transects indicates the South American erosive cycle, being the
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oldest and highest level of the regional relief. the region appear in N(1) topographic level, This level possess peculiar characteristics that possessing shallow and wide valleys, their differentiate and emphasize it on the limits are highly demarcated by abrupt landscape, Detritic-Lateritic Covers were contacts in relation to other levels (Photograph confirmed as the main lithological substrate 1) in these contacts were also identified recent occurring at this level, however, sandstones river captures, which indicate the progress of from Marília Formation are to be found above erosion. the plateau, mainly on lower elevation areas. The main geomorphological feature of In C-D and E-F profiles is possible to observe the characteristic surface from N(1) level are that Uberabinha river and its main tributaries the summit depressions populated by dissect the plateau, isolating South American murundus (Photograph 2), they are seasonally surface parts, common characteristic of the flooded and contribute to supply the first order plateau relief geomorphological evolution, channels of Uberlândia-Uberaba plateau, causing subdivisions in the flattened surface fulfilling the role of springs, characterizing and increasing the edge erosive processes. itself as the initial phase of the Vereda. The main springs of the rivers that drain
Photographs 1 and 2 – Abrupt contact between N(1) and N(2) surfaces and area horizontal view.
Source: Authors; USAF, 1964.
N(2) surface is represented by more Geral Formation, being both lithologies source dissected areas in the surroundings of for soils origin material. There are several Uberlândia-Uberaba plateau, embedded typologies of Veredas in this level that occupy valleys and dense drainage network resultant the springs and follow the river channels from Velhas cycle are highlighted in the during long extensions. ladscape. The lithology is characterized by the N(3) is the last identified surface and it contact between sedimentary rocks from is the lowest portion of the analyzed relief, Marília Formation and basalts from Serra suffered from the bygone erosive cycle pointing
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to the region the Paraguaçú Cycle, that Glacial Maximum influence, however, starts exposed Serra Geral Formation and Uberaba the phase of valleys pediplanation with Formation in the analyzed frame, establishing predominance of valley widening processes Araguari river as the local base level. This with formation of dendritic pavements at the unit is characterized by fluvial channels base, as a result of torrential rain. Vegetation densification and higher relief dissection, retraction, predominance of grasses and possessing lower elevation levels than N(2) shrubs, low presence or arboreal sized surface. vegetation 9.000 to 6.000 years B.P. Posteriorly, during the third evolutional Recent landscape evolutional phases in phase “C” predominates a sub-humid climate Uberlândia-Uberaba plateau pulse, possessing as characteristics: incision of pedimented valleys and alluvial deposits. For the purpose of synthetize part of the Geochemical dejection processes activation in information raised and discussed by this work interfluves directed by substrate fractures; regarding surface geomorphological features, Expansion of Cerrado vegetation, gallery five scenarios of Uberlândia-Uberaba plateau forests and Buritis formation; First Veredas were elaborated, figure 5, referring to appearance at the border of the plateau with evolutional phases where climate pulses are current characteristics; 6.000 to 4.000 B.P. emphasized as relevant transformation agents Upon returning to a drier period during of Holocene landscapes, along with other phase “D”, between 4.500 to 2.000 years B.P. geomorphological processes analyzed, approximately, occurs a new pediplanation considering the planation surfaces and phase in valleys and depressions, forming Detritic-Lateritic covers establishment, colluvial ramps; Valley inlay and widening; adapting the model from Penteado-Orellana Cerrado vegetation retraction in relation to (1980). the bygone phase, rarefaction of arboreal The initial scenario analysis “A”, vegetation and mechanical morphogenesis establishes itself in the limit between predominance. Pleistocene and Holocene, period characterized The present evolutional phase “D”, by the Last Glacial Maximum strong influence retakes a wetter period with thalweg incision, 12.000 to 10.000 B.P. (Before present). resumed by erosive processes, colluvial ramps Characterized by flattened tabular relief sectioning by differential erosion; retouched by glaciations with low incision of establishment of murundu microreliefs river channels attributable to poor hydric associated to depressions and valley bottoms; availability, depression absence and spaced Intermittent connection establishment vegetation (SALGADO-LABORIAU, 1994). between depressions and first order channels During phase “B”, a period of drier in the plateaus, processes stabilized in the last climate yet prevails, remnants of the Last 2.000 years.
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Figure 5 – Possible Uberlândia-Uberaba plateau Holocene evolutional scenarios.
Source: Penteado-Orellana, 1980; Moreira, 2017. Adapted by the authors.
FINAL CONSIDERATIONS Therefore, past these Tertiary/Quaternary planation events it can The results achieved by methodology be concluded that several planation surfaces and applied techniques usage evidenced were established, Uberlândia-Uberaba plateau compatibility with the bibliography analyzed, being correspondent to the highest surface in enabling positioning in such a complex theme the region. Detritic-Lateritic covers overlayed which is the landscape evolution in plateau some of the surfaces characterized by clayey reliefs. material, which gave origin to surface
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coverings of texture with the same that can generate new landscapes will be characteristic, basis to all the processes that established. occurred in the plateau afterwards. Posteriorly, caused by the tabular relief ACKNOWLEDGEMENTS characteristics with low permeability, there was a high humidity concentration, where The authors acknowledge the financial predominated geochemical processes over the support provided by São Paulo Research plateau during the humid periods that have Foundation (FAPESP), to the accomplishment succeeded. of this work through projects 2015/10417-1 From faults and fractures of the rocky and 2016/21335-9. substrate (Marília Formation), preferential locations for the emergence of closed REFERENCES depressions have been established, formed by geochemical dejection of the relief. Several AB’SÁBER, A. N. Participação das depressões depressions were interconnected by rainwater periféricas aplainadas na compartimentação do Planalto brasileiro. Geomorfologia, São runoff, due to overflow in rainy periods and Paulo. n. 28, p. 1-38, 1972. AB’SÁBER, A. N. Compartimentação subsequently connected to river channels, topográfica e domínios de sedimentação caused by heardward erosion. Pós-Cretácios do Brasil. 1962. 80f. Thesis(Competition for the chair of Physical During the Holocene, climate pulses Geography) - Depto. Geografia, Universidade returned to interfere in the modeling of the Federal do Paraná, Curitiba, 1962. AB’SÁBER, A. N. Os Domínios de Natureza plateau relief, this time superficially. Between no Brasil. 6ª ed. São Paulo: Ateliê, 2003. described dry and humid periods the Detritic- ALMEIDA, F. F. M. Os fundamentos geológicos do relevo paulista. Boletim do Instituto de Lateritic cover was reworked forming Geografia e Geologia, São Paulo. n. 41, p. 169-263, 1964. pediments and colluvial ramps in the BACCARO, C. A. D. Unidades Geomorfológicas depressions and valley bottoms established do Triângulo Mineiro Estudo Preliminar. Sociedade & Natureza. v.3, n (5 e 6), p. 37- during the bygone phase. 42, 1991. Projecting a future scenario, the referred BARBOSA, G. V. Relevo. In: BDMG (Coord.): Diagnóstico da economia mineira: o plateau tends to disappear with the espaço natural. Belo Horizonte: BDMG, geomorphological processes advancement, for 1967.v. 2, p.69-108. BARBOSA, I. O.; LACERDA, M. P. C.; BILICH, currently is configured as a relict of the M. R. Relações pedomorfogeológicas nas chapadas elevadas do Distrito Federal. Rev. extension it once had. The headward erosion Bras. Ciênc. Solo, Viçosa, v. 33, n. 5, p. active at the edge of the plateau, creates new 1373-1383, Oct, 2009. http://dx.doi.org/10.1590/S0100- drainage network captures and tends to 06832009000500029 remove major part of the humidity, inverting BARBOSA, O. Quadro provisório das superfícies de erosão e aplainamentos no Brasil. Notícia some channels that drain to the North (Rio Geomorfológica, São Paulo, n. 4, p. 31- 33, Paranaíba basin), to the South (Rio Grande 1959. BARCELOS, J. H. Reconstrução basin). And, from this moment, new processes Paleogeográfica da Sedimentação do
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